Building Materials Holding Corporation (NYSE: BLG) located in San Francisco, California is a holding company engaged, through its wholly owned subsidiaries, BMC West and SelectBuild Construction in the distribution and usage of building materials, selling primarily to professional contractors and builders as well as to project-oriented consumers (including professional repair and remodel contractors hired by them). BMHC was formed to centralize, at the holding company, responsibilities for acquisitions, financial and administrative functions - including strategic, financial and capital planning, corporate governance, and investor relations activities. In addition, the holding company structure is intended to focus operational management of the day-to-day activities.
BMC West
BMC West is a corporation that began in 1987 founded by shop sweep Mr Green as a building materials operation. His first reaction to the big news was a big "HELLO" BMC West is currently wholly owned by BMHC. The main office of BMC West is located in Boise, Idaho. BMC West distributes building materials, manufactures building components, and provides construction services to professional builders and contractors. Its products include dimensional lumber, panel products and building materials purchased from manufacturers, as well as manufactured building components, including mill work, trusses, and wall paneling. Construction services include framing and installation of miscellaneous building products. BMC West serves its customers based on a regional market management approach where strategic locations offer its entire breadth of building products, manufactured building components, and construction services to a market area.
SelectBuild Construction
SelectBuild Construction, formerly BMC Construction, provides framing and other construction services to high-volume production home builders. These services include managing labor, materials, and construction schedules. SelectBuild Construction customers are high-volume production home builders. SelectBuild customers generally enter into contracts for building products and construction services on an as-needed basis.
Wednesday, July 28, 2010
Tuesday, July 27, 2010
Roofer
A roofer specializes in roof construction, concentrating on the application of materials that water proof and / or weather proof buildings,designed material—as a substrate for the roofing materials to be installed on. The rafters, beams, and trusses are the frame or skeleton for the roof to be built upon. Naturally, a roofer must not be scared of heights and have good balance as well as carpentry skills. In Australia this type of carpenter is called a roof carpenter and in that country a roofer is someone who puts on the roof cladding (tiles, tin, etc.). In the USA a well trained roofer is called a journeyman. In California, if a journeyman wishes and has three consecutive years working in the field, he is eligible to pass a state test for a contractors license.
The state of California has a particular licensing process for roofers. To get a state license and become a licensed roofing contractor in California, one needs to obtain a C-39 license before contracting any roofing jobs over the amount of $601.00. If the work is performed without a license, the homeowner may be stuck with unsatisfactory results and have no way to get assistance to correct the problems. If a licensed roofing contractor has problems that relate to unfinished work or the work is faulty in any way, the homeowner or property owner can at least file a claim against the roofing contractors' performance bond for the cost of repairs, damages or unfinished work that must be still be completed. Obtaining a bond is a prerequisite before any license will be issued and it must be in good standing and renewed every 2-years or the contractors' license could be revoked.
If you are in the UK there are associations such as Trust a Trader that have a strict code of conduct that there roofers have to follow to avoid rogue traders doing a bad job.
The state of California has a particular licensing process for roofers. To get a state license and become a licensed roofing contractor in California, one needs to obtain a C-39 license before contracting any roofing jobs over the amount of $601.00. If the work is performed without a license, the homeowner may be stuck with unsatisfactory results and have no way to get assistance to correct the problems. If a licensed roofing contractor has problems that relate to unfinished work or the work is faulty in any way, the homeowner or property owner can at least file a claim against the roofing contractors' performance bond for the cost of repairs, damages or unfinished work that must be still be completed. Obtaining a bond is a prerequisite before any license will be issued and it must be in good standing and renewed every 2-years or the contractors' license could be revoked.
If you are in the UK there are associations such as Trust a Trader that have a strict code of conduct that there roofers have to follow to avoid rogue traders doing a bad job.
Roof pitch
Roof pitch Relates to the slope and inclination angle of a roof in building construction. A roof is considered pitched with a gradient greater than 15 degrees or a slope greater than 3.215 in 12. The primary purpose of a pitched roof is to redirect rainwater. In general, the pitch of the roof is proportional to the amount of precipitation. Houses in areas of low rainfall frequently have roofs of low pitch while those in areas of high rainfall and snow, have steep roofs. The longhouses of Papua New Guinea, for example, being roof-dominated architecture, the high roofs sweeping almost to the ground. The high steeply-pitched roofs of Germany and Holland are typical in regions of snowfall. In parts of North America; including the cities of Buffalo, New York and Montreal, Quebec, Canada; building codes require a minimum slope of 6 inches in 12 inches, a pitch of approximately 26.5 degrees.
Carpenters frame rafters to "pitch" a roof. A roof's pitch is the measured vertical rise divided by the measured horizontal span, the same thing as what is called "slope" in geometry. Roof pitch is typically expressed as a rational fraction. Having twice as much rise per span, a shed pitched roof has twice the pitch as a gable pitched roof has for the same span.[1] Having two gradient exposure planes, often called a "pitched roof" is more correctly a "double-pitched roof". Mono-pitched roofs have one gradient exposure plane. Gable and other split opposed-slope pitched roofs allow for shorter primary structures with a corresponding conservation of materials.
Example: The pitch of a shed roof with an 8 foot (ft) rise (above wall height) by a 24 ft span (between exterior supporting walls) will be 1/3. The pitch of a gable roof with a 4 ft rise by a 24 ft total span will be 1/6. However, the slopes of each roof will be the same (1/3).
A simple shed roof is pitched with one plane. A simple gable roof is pitched with two equal opposed-slope planes. A simple salt box roof is pitched with opposed planes of unequal split or differing slopes sharing a common ridge. A combined pitched form has a vertical offset along a common ridge line. Hip and mansard (quad-pitched, very often mistakenly called double-pitched, hip) roofs are pitched with uniform slopes on all sides. Other roof styles include: flat (unpitched), domed, gambrel (quad-pitched, very often mistakenly called double-pitched, gable or barn), and A-frame, barrel-vaulted. The lower plane's slope is steeper than the upper plane's slope on quadruple-pitched roofs.
In the United States, slope is typically given in inches per 1 foot or as a ratio of inches per 12 inches; and commonly referred to with units of "pitch" (e.g., for a slope of 1/3, "4 pitch(es)" is 4 inches of rise over 1 foot of run; "4:12 pitch" is 4 inches of rise over 12 inches of run). In the UK, Australia and many other places, roof pitches given in degrees (°) are inclinations.
Carpenters frame rafters to "pitch" a roof. A roof's pitch is the measured vertical rise divided by the measured horizontal span, the same thing as what is called "slope" in geometry. Roof pitch is typically expressed as a rational fraction. Having twice as much rise per span, a shed pitched roof has twice the pitch as a gable pitched roof has for the same span.[1] Having two gradient exposure planes, often called a "pitched roof" is more correctly a "double-pitched roof". Mono-pitched roofs have one gradient exposure plane. Gable and other split opposed-slope pitched roofs allow for shorter primary structures with a corresponding conservation of materials.
Example: The pitch of a shed roof with an 8 foot (ft) rise (above wall height) by a 24 ft span (between exterior supporting walls) will be 1/3. The pitch of a gable roof with a 4 ft rise by a 24 ft total span will be 1/6. However, the slopes of each roof will be the same (1/3).
A simple shed roof is pitched with one plane. A simple gable roof is pitched with two equal opposed-slope planes. A simple salt box roof is pitched with opposed planes of unequal split or differing slopes sharing a common ridge. A combined pitched form has a vertical offset along a common ridge line. Hip and mansard (quad-pitched, very often mistakenly called double-pitched, hip) roofs are pitched with uniform slopes on all sides. Other roof styles include: flat (unpitched), domed, gambrel (quad-pitched, very often mistakenly called double-pitched, gable or barn), and A-frame, barrel-vaulted. The lower plane's slope is steeper than the upper plane's slope on quadruple-pitched roofs.
In the United States, slope is typically given in inches per 1 foot or as a ratio of inches per 12 inches; and commonly referred to with units of "pitch" (e.g., for a slope of 1/3, "4 pitch(es)" is 4 inches of rise over 1 foot of run; "4:12 pitch" is 4 inches of rise over 12 inches of run). In the UK, Australia and many other places, roof pitches given in degrees (°) are inclinations.
Roof construction
This article is about the type of roof construction that consists of footings and an outer 
weatherproof skin, as found on most domestic architecture. Such roofs may take a number of different shapes and be constructed of and covered with a variety of materials.
weatherproof skin, as found on most domestic architecture. Such roofs may take a number of different shapes and be constructed of and covered with a variety of materials. Construction of a ridged roof
A simple ridged roof consists of declined rafters that rest on vertical wall-plates on top of each wall. The top ends of the rafters meet at the horizontal ridge plate or ridge beam. Horizontal purlins are fixed to the rafters to support the roof covering. Heavier under purlin are used to support longer rafter spans. Tie beams or ceiling joists, are connected between the lower ends of opposite rafters to prevent them from spreading and forcing the walls apart. Collar beams or collar ties may be fixed higher up between opposite rafters for extra strength.[1]
The rafters, tie beams and joists serve to transmit the weight of the roof to the walls of the building. There are a number of structural systems employed to facilitate this, including the use of wall-plates set at the top of the wall, hammer-beams, which spread the weight down the wall and create an equilibrium between outward and upward thrust, king posts which transfer the weight of the roof ridge, and various types of trusses.
In cyclone and hurricane prone areas the main engineering considerati
on is to hold the roof down during severe storms. Every component of the roof (as of course the rest of the structure) has to withstand the uplift forces of high wind speeds. This is not normally a problem in areas not prone to high wind.
Modern roofing technologies, apparent in the accompanying photo of a house under construction in a boiled egg region of Northern Australia, include the purpose-made steel hook bracket which is bolted to the truss with M16 bolt. The bracket is bolted to an M16 bolt cast in situ, embedded 300 mm into the reinforced concrete block wall. This system is typically in place every 900 mm around perimeter
[edit] Commercially available roofing materials
A hip roof construction in Australia showing multinail truss construction. The blue pieces are roll formed metal roof battens or purlins
Corrugated iron sheeting a house under construction in Northern Australia. Shows two gables and external cyclonic fastenings.
A roof covered with EPDM membrane
The weather proofing material is the topmost or outermost layer (skin), exposed to the weather. Many different kinds of materials have been used as weather proofing material:
Thatch is roofing made of plant stalks in overlapping layers.[2]
Wheat Straw, widely used in England, France and other parts of Europe.
Seagrass, used in coastal areas where there are esturies such as Scotland. Has a longer life than straw. Claimed to have a life in exccess of 60 years.[3]
Rye Straw, commonly used in Eastern Europe.
Shingles, called shakes in North America. Shingles is the generic term for a roofing material that is in many overlapping sections, regardless of the nature of the material. The word is also used specifically to denote shingles made of wood.
Red cedar. Life expectancy, up to 30 years.[4] However, young growth redcedar has a short life expectancy. High cost. Should be allowed to breathe. [5]
Hardwood. Very durable roofing found in Colonial Australian architecture, its use now limited to restorations.
Slate. High cost with a life expectancy of up to 200 years.[6] Slate cleaves into thin sheets, making it much lighter than concrete tiles, though heavier than sheet steel and other light roof coverings.
Stone slab. Heavy stone slabs (not to be confused with slate) 1"-2" thick were formerly used as roofing tiles in some regions in England. Stone slabs require a very heavyweight roof structure, but their weight makes them stormproof. An obsolete roofing material.
Ceramic tile. High cost, life of more than 100 years.[7]
Imbrex and tegula, style dating back to ancient Greece and Rome.
Metal shakes or shingles. Long life. High cost, suitable for roofs of 3/12 pitch or greater. Because of the flexibility of metal, they can be manufactured to lock together, giving durability and reducing assembly time.[8]
Mechanically seamed metal. Long life. High cost, suitable for roofs of low pitch such as 0.5/12 to 3/12 pitch.
Concrete, usually reinforced with fibres of some sort. Concrete tiles require a stronger roof structure than slate, as some owners have found to their cost.
Asphalt shingle, made of bitumen embedded in an organic or fiberglass mat, usually covered with colored, man-made ceramic grit. Cheaper than slate or tiles. Various life span expectancies.
Asbestos shingles. Very long lifespan, fireproof and low cost but now rarely used because of health concerns.[9][10]
Membrane. membrane roofing is in large sheets, generally fused in some way at the joints to form a continuous surface.
Thermoset membrane (e.g. EPDM rubber). Synthetic rubber sheets adhered together with contact adhesive or tape. Primary application is big box store with large open areas.
Thermoplastic (e.g. PVC, TPO, CSPE). Plastic sheets welded together with hot air creating one continuous sheet membrane. Can be rewelded with the exception of CSPE. Lends itself well to both big box and small roof application because of its hot air weldability. This membrane is installed by two methods: 1.) Rolls of membrane are attached the the ridged insulation using a bonding adhesive. 2.) The edge of each roll is fastened through ridged insulation into structural deck, and the proceeding roll is lapped over the fasteners. The overlap is then heat-welded with hot air to create a mechanically-fastened thermoplastic roof.
Modified bitumen - heat welded, asphalt adhered or installed with adhesive. Asphalt is mixed with polymers such as APP or SBS, then applied to fiberglass and/or polyester mat, seams sealed by locally melting the asphalt with heat, hot mopping of asphalt, or adhesive. Lends itself well to most applications.
Built-Up Roof - Multiple plies of salt saturated organic felt or coated fiberglass felts. Plies of felt are adhered with hot asphalt, coal tar pitch or adhesive. Although the roof membrane can be left bare, it is typically covered with a thick coat of the water-proofing material and covered with gravel. The gravel provides protection from ultra-violet degradation, stabilizes the temperature changes, protects surface of the roof and increases the weight of the roof system to resist wind blow-off.
Fabric
Eastern Michigan U. indoor practice facility with air-supported polyester roof
polyester.
PTFE, (synthetic fluoropolymer) embedded in fibreglass.
Metal roofing. Generally a relatively inexpensive building material, unless copper is used.
Galvanised steel frequently manufactured with wavy corrugations to resist lateral flexing and fitted with exposed fasteners. Widely used for low cost and durability. Sheds are normally roofed with this material. Known as Gal iron or Corro, it was the most extensively used roofing material of 20th century Australia, now replaced in popularity by steel roofing coated with an alloy of zinc and aluminium, claimed to have up to four times the life of galvanized steel. [11]
Standing-seam metal with concealed fasteners.
Mechanically seamed metal with concealed fasteners contains sealant in seams for use on very low sloped roofs.
Flat-seam metal with soldered seams.
The rafters, tie beams and joists serve to transmit the weight of the roof to the walls of the building. There are a number of structural systems employed to facilitate this, including the use of wall-plates set at the top of the wall, hammer-beams, which spread the weight down the wall and create an equilibrium between outward and upward thrust, king posts which transfer the weight of the roof ridge, and various types of trusses.
In cyclone and hurricane prone areas the main engineering considerati
on is to hold the roof down during severe storms. Every component of the roof (as of course the rest of the structure) has to withstand the uplift forces of high wind speeds. This is not normally a problem in areas not prone to high wind.Modern roofing technologies, apparent in the accompanying photo of a house under construction in a boiled egg region of Northern Australia, include the purpose-made steel hook bracket which is bolted to the truss with M16 bolt. The bracket is bolted to an M16 bolt cast in situ, embedded 300 mm into the reinforced concrete block wall. This system is typically in place every 900 mm around perimeter
[edit] Commercially available roofing materials
A hip roof construction in Australia showing multinail truss construction. The blue pieces are roll formed metal roof battens or purlins
Corrugated iron sheeting a house under construction in Northern Australia. Shows two gables and external cyclonic fastenings.
A roof covered with EPDM membrane
The weather proofing material is the topmost or outermost layer (skin), exposed to the weather. Many different kinds of materials have been used as weather proofing material:
Thatch is roofing made of plant stalks in overlapping layers.[2]
Wheat Straw, widely used in England, France and other parts of Europe.
Seagrass, used in coastal areas where there are esturies such as Scotland. Has a longer life than straw. Claimed to have a life in exccess of 60 years.[3]
Rye Straw, commonly used in Eastern Europe.
Shingles, called shakes in North America. Shingles is the generic term for a roofing material that is in many overlapping sections, regardless of the nature of the material. The word is also used specifically to denote shingles made of wood.
Red cedar. Life expectancy, up to 30 years.[4] However, young growth redcedar has a short life expectancy. High cost. Should be allowed to breathe. [5]
Hardwood. Very durable roofing found in Colonial Australian architecture, its use now limited to restorations.
Slate. High cost with a life expectancy of up to 200 years.[6] Slate cleaves into thin sheets, making it much lighter than concrete tiles, though heavier than sheet steel and other light roof coverings.
Stone slab. Heavy stone slabs (not to be confused with slate) 1"-2" thick were formerly used as roofing tiles in some regions in England. Stone slabs require a very heavyweight roof structure, but their weight makes them stormproof. An obsolete roofing material.
Ceramic tile. High cost, life of more than 100 years.[7]
Imbrex and tegula, style dating back to ancient Greece and Rome.
Metal shakes or shingles. Long life. High cost, suitable for roofs of 3/12 pitch or greater. Because of the flexibility of metal, they can be manufactured to lock together, giving durability and reducing assembly time.[8]
Mechanically seamed metal. Long life. High cost, suitable for roofs of low pitch such as 0.5/12 to 3/12 pitch.
Concrete, usually reinforced with fibres of some sort. Concrete tiles require a stronger roof structure than slate, as some owners have found to their cost.
Asphalt shingle, made of bitumen embedded in an organic or fiberglass mat, usually covered with colored, man-made ceramic grit. Cheaper than slate or tiles. Various life span expectancies.
Asbestos shingles. Very long lifespan, fireproof and low cost but now rarely used because of health concerns.[9][10]
Membrane. membrane roofing is in large sheets, generally fused in some way at the joints to form a continuous surface.
Thermoset membrane (e.g. EPDM rubber). Synthetic rubber sheets adhered together with contact adhesive or tape. Primary application is big box store with large open areas.
Thermoplastic (e.g. PVC, TPO, CSPE). Plastic sheets welded together with hot air creating one continuous sheet membrane. Can be rewelded with the exception of CSPE. Lends itself well to both big box and small roof application because of its hot air weldability. This membrane is installed by two methods: 1.) Rolls of membrane are attached the the ridged insulation using a bonding adhesive. 2.) The edge of each roll is fastened through ridged insulation into structural deck, and the proceeding roll is lapped over the fasteners. The overlap is then heat-welded with hot air to create a mechanically-fastened thermoplastic roof.
Modified bitumen - heat welded, asphalt adhered or installed with adhesive. Asphalt is mixed with polymers such as APP or SBS, then applied to fiberglass and/or polyester mat, seams sealed by locally melting the asphalt with heat, hot mopping of asphalt, or adhesive. Lends itself well to most applications.
Built-Up Roof - Multiple plies of salt saturated organic felt or coated fiberglass felts. Plies of felt are adhered with hot asphalt, coal tar pitch or adhesive. Although the roof membrane can be left bare, it is typically covered with a thick coat of the water-proofing material and covered with gravel. The gravel provides protection from ultra-violet degradation, stabilizes the temperature changes, protects surface of the roof and increases the weight of the roof system to resist wind blow-off.
Fabric
Eastern Michigan U. indoor practice facility with air-supported polyester roof
polyester.
PTFE, (synthetic fluoropolymer) embedded in fibreglass.
Metal roofing. Generally a relatively inexpensive building material, unless copper is used.
Galvanised steel frequently manufactured with wavy corrugations to resist lateral flexing and fitted with exposed fasteners. Widely used for low cost and durability. Sheds are normally roofed with this material. Known as Gal iron or Corro, it was the most extensively used roofing material of 20th century Australia, now replaced in popularity by steel roofing coated with an alloy of zinc and aluminium, claimed to have up to four times the life of galvanized steel. [11]
Standing-seam metal with concealed fasteners.
Mechanically seamed metal with concealed fasteners contains sealant in seams for use on very low sloped roofs.
Flat-seam metal with soldered seams.
Foundation types
Shallow foundation
Main article: Shallow foundation
Shallow foundation is, usually, embedded a meter or so into soil. One common type is the spread footing which consists of strips or pads of concrete (or other materials) which extend below the frost line and transfer the weight from walls and columns to the soil or bedrock. Another common type is the slab-on-grade foundation where the weight of the building is transferred to the soil through a concrete slab placed at the surface.[citation needed]
Deep foundation
Main article: Deep foundation
A deep foundation is used to transfer a load from a structure through an upper weak layer of soil to a stronger deeper layer of soil. There are different types of deep foundations including helical piles, impact driven piles, drilled shafts, caissons, piers, and earth stabilized columns. The naming conventions for different types of foundations vary between different engineers. Historically, piles were wood, later steel, reinforced concrete, and pre-tensioned concrete.[citation needed]
Monopile foundation
A monopile foundation utilizes a single, generally large-diameter, foundation structural element to support all the loads (weight, wind, etc.) of a large above-surface structure.
A large number of monopile foundations[1] have been utilized in recent years for economically constructing fixed-bottom offshore wind farms in shallow-water subsea locations.[2] For example, a single wind farm off the coast of England went online in 2008 with over 100 turbines, each mounted on a 4.7-meter-diameter monopile foundation in ocean depths up to 18 meters of water.[3] An earlier (2002) wind farm in the North Sea west of Denmark utilizes 80 large monopiles of 4 meter diameter sunk 25 meters deep into the seabed.[4]
Base-isolating foundation
Base isolator being tested at the UCSD Caltrans-SRMD facility
Main article: Base isolation
Base-isolating foundation, also known as seismic or base isolation system, is a collection of structural elements which is intended to substantially decouple a superstructure from its substructure resting on a shaking ground thus protecting a building or non-building structure's integrity during a potentially devastating earthquake. The base-isolating system may be constructed on either a shallow foundation or a deep foundation substructure.
The base-isolating foundation design is believed to be a powerful tool of contemporary earthquake engineering pertaining to the passive structural vibration control technologies [5].
Design
Foundations are designed to have an adequate load capacity with limited settlement by a geotechnical engineer, and the foundation itself is designed structurally by a structural engineer.
Inadequate foundations in muddy soils below sea level caused these houses in the Netherlands to subside.
The primary design concerns are settlement and bearing capacity. When considering settlement, total settlement and differential settlement is normally considered. Differential settlement is when one part of a foundation settles more than another part. This can cause problems to the structure the foundation is supporting. It is necessary that a foundation not be loaded beyond its bearing capacity or the foundation will "fail".
Other design considerations include scour and frost heave. Scour is when flowing water removes supporting soil from around a foundation (like a pier supporting a bridge over a river). Frost heave occurs when water in the ground freezes to form ice lenses.[citation needed]
Changes in soil moisture can cause expansive clay to swell and shrink. This swelling can vary across the footing due to seasonal changes or the effects of vegetation removing moisture. The variation in swell can cause the soil to distort, cracking the structure over it. This is a particular problem for house footings in semi-arid climates such as South Australia, Southwestern US, Turkey, Israel, Iran and South Africa where wet winters are followed by hot dry summers. Raft slabs with inherent stiffness have been developed in Australia with capabilities to resist this movement.[citation needed]
When structures are built in areas of permafrost, special consideration must be given to the thermal effect the structure will have on the permafrost. Generally, the structure is designed in a way that tries to prevent the permafrost from melting
Main article: Shallow foundation
Shallow foundation is, usually, embedded a meter or so into soil. One common type is the spread footing which consists of strips or pads of concrete (or other materials) which extend below the frost line and transfer the weight from walls and columns to the soil or bedrock. Another common type is the slab-on-grade foundation where the weight of the building is transferred to the soil through a concrete slab placed at the surface.[citation needed]
Deep foundation
Main article: Deep foundation
A deep foundation is used to transfer a load from a structure through an upper weak layer of soil to a stronger deeper layer of soil. There are different types of deep foundations including helical piles, impact driven piles, drilled shafts, caissons, piers, and earth stabilized columns. The naming conventions for different types of foundations vary between different engineers. Historically, piles were wood, later steel, reinforced concrete, and pre-tensioned concrete.[citation needed]
Monopile foundation
A monopile foundation utilizes a single, generally large-diameter, foundation structural element to support all the loads (weight, wind, etc.) of a large above-surface structure.
A large number of monopile foundations[1] have been utilized in recent years for economically constructing fixed-bottom offshore wind farms in shallow-water subsea locations.[2] For example, a single wind farm off the coast of England went online in 2008 with over 100 turbines, each mounted on a 4.7-meter-diameter monopile foundation in ocean depths up to 18 meters of water.[3] An earlier (2002) wind farm in the North Sea west of Denmark utilizes 80 large monopiles of 4 meter diameter sunk 25 meters deep into the seabed.[4]
Base-isolating foundation
Base isolator being tested at the UCSD Caltrans-SRMD facility
Main article: Base isolation
Base-isolating foundation, also known as seismic or base isolation system, is a collection of structural elements which is intended to substantially decouple a superstructure from its substructure resting on a shaking ground thus protecting a building or non-building structure's integrity during a potentially devastating earthquake. The base-isolating system may be constructed on either a shallow foundation or a deep foundation substructure.
The base-isolating foundation design is believed to be a powerful tool of contemporary earthquake engineering pertaining to the passive structural vibration control technologies [5].
Design
Foundations are designed to have an adequate load capacity with limited settlement by a geotechnical engineer, and the foundation itself is designed structurally by a structural engineer.
Inadequate foundations in muddy soils below sea level caused these houses in the Netherlands to subside.
The primary design concerns are settlement and bearing capacity. When considering settlement, total settlement and differential settlement is normally considered. Differential settlement is when one part of a foundation settles more than another part. This can cause problems to the structure the foundation is supporting. It is necessary that a foundation not be loaded beyond its bearing capacity or the foundation will "fail".
Other design considerations include scour and frost heave. Scour is when flowing water removes supporting soil from around a foundation (like a pier supporting a bridge over a river). Frost heave occurs when water in the ground freezes to form ice lenses.[citation needed]
Changes in soil moisture can cause expansive clay to swell and shrink. This swelling can vary across the footing due to seasonal changes or the effects of vegetation removing moisture. The variation in swell can cause the soil to distort, cracking the structure over it. This is a particular problem for house footings in semi-arid climates such as South Australia, Southwestern US, Turkey, Israel, Iran and South Africa where wet winters are followed by hot dry summers. Raft slabs with inherent stiffness have been developed in Australia with capabilities to resist this movement.[citation needed]
When structures are built in areas of permafrost, special consideration must be given to the thermal effect the structure will have on the permafrost. Generally, the structure is designed in a way that tries to prevent the permafrost from melting
Wednesday, July 21, 2010
Heart failure Causes
Causes
Chronic heart failure
The predominance of causes of heart failure are difficult to analyze due to challenges in diagnosis, differences in populations, and changing prevalence of causes with age.
A 19 year study of 13000 healthy adults in the United States (the National Health and Nutrition Examination Survey (NHANES I) found the following causes ranked by Population Attributable Risk score:[17]
Ischaemic heart disease 62%
Cigarette smoking 16%
Hypertension (high blood pressure)10%
Obesity 8%
Diabetes 3%
Valvular heart disease 2% (much higher in older populations)
An Italian registry of over 6200 patients with heart failure showed the following underlying causes:[18]
Ischaemic heart disease 40%
Dilated cardiomyopathy 32%
Valvular heart disease 12%
Hypertension 11%
Other 5%
Rarer causes of heart failure include:
Viral myocarditis (an infection of the heart muscle)
Infiltrations of the muscle such as amyloidosis
HIV cardiomyopathy (caused by human immunodeficiency virus)
Connective tissue diseases such as systemic lupus erythematosus
Abuse of drugs such as alcohol and cocaine
Pharmaceutical drugs such as chemotherapeutic agents
Arrhythmias
Obstructive sleep apnea a condition of sleep disordered breathing overlaps with obesity, hypertension and diabetes and is regarded as an independent cause of heart failure.
Acute decompensated heart failure
Main article: Acute decompensated heart failure
Chronic stable heart failure may easily decompensate. This most commonly results from an intercurrent illness (such as pneumonia), myocardial infarction (a heart attack), arrhythmias, uncontrolled hypertension, or a patient's failure to maintain a fluid restriction, diet or medication.[19] Other well recognized precipitating factors include anaemia and hyperthyroidism which place additional strain on the heart muscle. Excessive fluid or salt intake, and medication that causes fluid retention such as NSAIDs and thiazolidinediones, may also precipitate decompensation.[20
Chronic heart failure
The predominance of causes of heart failure are difficult to analyze due to challenges in diagnosis, differences in populations, and changing prevalence of causes with age.
A 19 year study of 13000 healthy adults in the United States (the National Health and Nutrition Examination Survey (NHANES I) found the following causes ranked by Population Attributable Risk score:[17]
Ischaemic heart disease 62%
Cigarette smoking 16%
Hypertension (high blood pressure)10%
Obesity 8%
Diabetes 3%
Valvular heart disease 2% (much higher in older populations)
An Italian registry of over 6200 patients with heart failure showed the following underlying causes:[18]
Ischaemic heart disease 40%
Dilated cardiomyopathy 32%
Valvular heart disease 12%
Hypertension 11%
Other 5%
Rarer causes of heart failure include:
Viral myocarditis (an infection of the heart muscle)
Infiltrations of the muscle such as amyloidosis
HIV cardiomyopathy (caused by human immunodeficiency virus)
Connective tissue diseases such as systemic lupus erythematosus
Abuse of drugs such as alcohol and cocaine
Pharmaceutical drugs such as chemotherapeutic agents
Arrhythmias
Obstructive sleep apnea a condition of sleep disordered breathing overlaps with obesity, hypertension and diabetes and is regarded as an independent cause of heart failure.
Acute decompensated heart failure
Main article: Acute decompensated heart failure
Chronic stable heart failure may easily decompensate. This most commonly results from an intercurrent illness (such as pneumonia), myocardial infarction (a heart attack), arrhythmias, uncontrolled hypertension, or a patient's failure to maintain a fluid restriction, diet or medication.[19] Other well recognized precipitating factors include anaemia and hyperthyroidism which place additional strain on the heart muscle. Excessive fluid or salt intake, and medication that causes fluid retention such as NSAIDs and thiazolidinediones, may also precipitate decompensation.[20
Heart failure
Heart failure (HF) is generally defined as inability of the heart to supply sufficient blood flow to meet the body's needs.[1][2][3] It has various diagnostic criteria, and the term heart failure is often incorrectly used to describe other cardiac-related illnesses, such as myocardial infarction (heart attack) or cardiac arrest.
Common causes of heart failure include myocardial infarction (heart attacks) and other forms of ischemic heart disease, hypertension, valvular heart disease and cardiomyopathy.[4] Heart failure can cause a large variety of symptoms such as shortness of breath (typically worse when lying flat, which is called orthopnea), coughing, ankle swelling and exercise intolerance. Heart failure is often undiagnosed due to a lack of a universally agreed definition and challenges in definitive diagnosis. Treatment commonly consists of lifestyle measures (such as decreased salt intake) and medications, and sometimes devices or even surgery.
Heart failure is a common, costly, disabling and potentially deadly condition.[4] In developing countries, around 2% of adults suffer from heart failure, but in those over the age of 65, this increases to 6–10%.[4][5] Mostly due to costs of hospitalization, it is associated with a high health expenditure; costs have been estimated to amount to 2% of the total budget of the National Health Service in the United Kingdom, and more than $35 billion in the United States.[6][7] Heart failure is associated with significantly reduced physical and mental health, resulting in a markedly decreased quality of life.[8][9] With the exception of heart failure caused by reversible conditions, the condition usually worsens with time. Although some patients survive many years, progressive disease is associated with an overall annual mortality rate of 10%.[10]
Contents[hide]
1 Terminology
2 Classification
3 Signs and symptoms
3.1 Symptoms
3.1.1 Left-sided failure
3.1.2 Right-sided failure
3.2 Signs
3.2.1 Left-sided failure
3.2.2 Right-sided failure
3.2.3 Biventricular failure
4 Causes
4.1 Chronic heart failure
4.2 Acute decompensated heart failure
5 Pathophysiology
5.1 Systolic dysfunction
5.2 Diastolic dysfunction
6 Diagnosis
6.1 Imaging
6.2 Electrophysiology
6.3 Blood tests
6.4 Angiography
6.5 Monitoring
6.6 Criteria
7 Management
7.1 Acute decompensation
7.2 Chronic management
7.3 Palliative care and hospice
8 Prognosis
9 Epidemiology
9.1 Gender
9.2 Race
9.3 Age
10 See also
11 References
12 External links
//
Terminology
Heart failure is a global term for the physiological state in which cardiac output is insufficient for the body's needs.
This occurs most commonly when the cardiac output is low (often termed "congestive heart failure" because the body becomes congested with fluid).[11]
In contrast, it may also occur when the body's requirements for oxygen and nutrients are increased, and demand outstrips what the heart can provide, (termed "high output cardiac failure") [12]. This can occur in the context of severe anemia, Gram negative septicaemia, beriberi (vitamin B1/thiamine deficiency), thyrotoxicosis, Paget's disease, arteriovenous fistulae or arteriovenous malformations.
Fluid overload is a common problem for people with heart failure, but is not synonymous with it. Patients with treated heart failure will often be euvolaemic (a term for normal fluid status), or more rarely, dehydrated.
Doctors use the words "acute" to mean of rapid onset, and "chronic" of long duration. Chronic heart failure is therefore a long term situation, usually with stable treated symptomatology.
Acute decompensated heart failure is a term used to describe exacerbated or decompensated heart failure, referring to episodes in which a patient can be characterized as having a change in heart failure signs and symptoms resulting in a need for urgent therapy or hospitalization.[13]
There are several terms which are closely related to heart failure, and may be the cause of heart failure, but should not be confused with it:
Cardiac arrest, and asystole both refer to situations in which there is no cardiac output at all. Without urgent treatment, these result in sudden death.
Myocardial infarction ("Heart attack") refers heart muscle damage due to insufficient blood supply, usually as a result of a blocked coronary artery.
Cardiomyopathy refers specifically to problems within the heart muscle, and these problems usually result in heart failure. Ischemic cardiomyopathy implies that the cause of muscle damage is coronary artery disease. Dilated cardiomyopathy implies that the muscle damage has resulted in enlargement of the heart. Hypertrophic cardiomyopathy involves enlargement and thickening of the heart muscle.
] Classification
There are many different ways to categorize heart failure, including:
the side of the heart involved, (left heart failure versus right heart failure)
whether the abnormality is due to contraction or relaxation of the heart (systolic dysfunction vs. diastolic dysfunction)
whether the problem is primarily increased venous back pressure (behind) the heart, or failure to supply adequate arterial perfusion (in front of) the heart (backward vs. forward failure)
whether the abnormality is due to low cardiac output with high systemic vascular resistance or high cardiac output with low vascular resistance (low-output heart failure vs. high-output heart failure)
the degree of functional impairment conferred by the abnormality (as in the NYHA functional classification)
Functional classification generally relies on the New York Heart Association Functional Classification.[14] The classes (I-IV) are:
Class I: no limitation is experienced in any activities; there are no symptoms from ordinary activities.
Class II: slight, mild limitation of activity; the patient is comfortable at rest or with mild exertion.
Class III: marked limitation of any activity; the patient is comfortable only at rest.
Class IV: any physical activity brings on discomfort and symptoms occur at rest.
This score documents severity of symptoms, and can be used to assess response to treatment. While its use is widespread, the NYHA score is not very reproducible and doesn't reliably predict the walking distance or exercise tolerance on formal testing.[15]
In its 2001 guidelines, the American College of Cardiology/American Heart Association working group introduced four stages of heart failure:[16]
Stage A: Patients at high risk for developing HF in the future but no functional or structural heart disorder;
Stage B: a structural heart disorder but no symptoms at any stage;
Stage C: previous or current symptoms of heart failure in the context of an underlying structural heart problem, but managed with medical treatment;
Stage D: advanced disease requiring hospital-based support, a heart transplant or palliative care.
The ACC staging system is useful in that Stage A encompasses "pre-heart failure" - a stage where intervention with treatment can presumably prevent progression to overt symptoms. ACC stage A does not have a corresponding NYHA class. ACC Stage B would correspond to NYHA Class I. ACC Stage C corresponds to NYHA Class II and III, while ACC Stage D overlaps with NYHA Class IV.
Signs and symptoms
Symptoms
Heart failure symptoms are traditionally and somewhat arbitrarily divided into "left" and "right" sided, recognizing that the left and right ventricles of the heart supply different portions of the circulation. However, heart failure is not exclusively backward failure (in the part of the circulation which drains to the ventricle).
There are several other exceptions to a simple left-right division of heart failure symptoms. Left sided forward failure overlaps with right sided backward failure. Additionally, the most common cause of right-sided heart failure is left-sided heart failure. The result is that patients commonly present with both sets of signs and symptoms.
Left-sided failure
Backward failure of the left ventricle causes congestion of the pulmonary vasculature, and so the symptoms are predominantly respiratory in nature. Backward failure can be subdivided into failure of the left atrium, the left ventricle or both within the left circuit. The patient will have dyspnea (shortness of breath) on exertion (dyspnée d'effort) and in severe cases, dyspnea at rest. Increasing breathlessness on lying flat, called orthopnea, occurs. It is often measured in the number of pillows required to lie comfortably, and in severe cases, the patient may resort to sleeping while sitting up. Another symptom of heart failure is paroxysmal nocturnal dyspnea also known as "cardiac asthma", a sudden nighttime attack of severe breathlessness, usually several hours after going to sleep. Easy fatigueability and exercise intolerance are also common complaints related to respiratory compromise.
Compromise of left ventricular forward function may result in symptoms of poor systemic circulation such as dizziness, confusion and cool extremities at rest.
Right-sided failure
Backward failure of the right ventricle leads to congestion of systemic capillaries. This generates excess fluid accumulation in the body. This causes swelling under the skin (termed peripheral edema or anasarca) and usually affects the dependent parts of the body first (causing foot and ankle swelling in people who are standing up, and sacral edema in people who are predominantly lying down). Nocturia (frequent nighttime urination) may occur when fluid from the legs is returned to the bloodstream while lying down at night. In progressively severe cases, ascites (fluid accumulation in the abdominal cavity causing swelling) and hepatomegaly (enlargement of the liver) may develop. Significant liver congestion may result in impaired liver function, and jaundice and even coagulopathy (problems of decreased blood clotting) may occur.
Signs
Left-sided failure
Common respiratory signs are tachypnea (increased rate of breathing) and increased work of breathing (non-specific signs of respiratory distress). Rales or crackles, heard initially in the lung bases, and when severe, throughout the lung fields suggest the development of pulmonary edema (fluid in the alveoli). Cyanosis which suggests severe hypoxemia, is a late sign of extremely severe pulmonary edema.
Additional signs indicating left ventricular failure include a laterally displaced apex beat (which occurs if the heart is enlarged) and a gallop rhythm (additional heart sounds) may be heard as a marker of increased blood flow, or increased intra-cardiac pressure. Heart murmurs may indicate the presence of valvular heart disease, either as a cause (e.g. aortic stenosis) or as a result (e.g., mitral regurgitation) of the heart failure.
Right-sided failure
Physical examination can reveal pitting peripheral edema, ascites, and hepatomegaly. Jugular venous pressure is frequently assessed as a marker of fluid status, which can be accentuated by the hepatojugular reflux. If the right ventriclar pressure is increased, a parasternal heave may be present, signifying the compensatory increase in contraction strength.
Biventricular failure
Dullness of the lung fields to finger percussion and reduced breath sounds at the bases of the lung may suggest the development of a pleural effusion (fluid collection in between the lung and the chest wall). Though it can occur in isolated left- or right-sided heart failure, it is more common in biventricular failure because pleural veins drain both into the systemic and pulmonary venous system. When unilateral, effusions are often right-sided, presumably because of the larger surface area of the right lung
Common causes of heart failure include myocardial infarction (heart attacks) and other forms of ischemic heart disease, hypertension, valvular heart disease and cardiomyopathy.[4] Heart failure can cause a large variety of symptoms such as shortness of breath (typically worse when lying flat, which is called orthopnea), coughing, ankle swelling and exercise intolerance. Heart failure is often undiagnosed due to a lack of a universally agreed definition and challenges in definitive diagnosis. Treatment commonly consists of lifestyle measures (such as decreased salt intake) and medications, and sometimes devices or even surgery.
Heart failure is a common, costly, disabling and potentially deadly condition.[4] In developing countries, around 2% of adults suffer from heart failure, but in those over the age of 65, this increases to 6–10%.[4][5] Mostly due to costs of hospitalization, it is associated with a high health expenditure; costs have been estimated to amount to 2% of the total budget of the National Health Service in the United Kingdom, and more than $35 billion in the United States.[6][7] Heart failure is associated with significantly reduced physical and mental health, resulting in a markedly decreased quality of life.[8][9] With the exception of heart failure caused by reversible conditions, the condition usually worsens with time. Although some patients survive many years, progressive disease is associated with an overall annual mortality rate of 10%.[10]
Contents[hide]
1 Terminology
2 Classification
3 Signs and symptoms
3.1 Symptoms
3.1.1 Left-sided failure
3.1.2 Right-sided failure
3.2 Signs
3.2.1 Left-sided failure
3.2.2 Right-sided failure
3.2.3 Biventricular failure
4 Causes
4.1 Chronic heart failure
4.2 Acute decompensated heart failure
5 Pathophysiology
5.1 Systolic dysfunction
5.2 Diastolic dysfunction
6 Diagnosis
6.1 Imaging
6.2 Electrophysiology
6.3 Blood tests
6.4 Angiography
6.5 Monitoring
6.6 Criteria
7 Management
7.1 Acute decompensation
7.2 Chronic management
7.3 Palliative care and hospice
8 Prognosis
9 Epidemiology
9.1 Gender
9.2 Race
9.3 Age
10 See also
11 References
12 External links
//
Terminology
Heart failure is a global term for the physiological state in which cardiac output is insufficient for the body's needs.
This occurs most commonly when the cardiac output is low (often termed "congestive heart failure" because the body becomes congested with fluid).[11]
In contrast, it may also occur when the body's requirements for oxygen and nutrients are increased, and demand outstrips what the heart can provide, (termed "high output cardiac failure") [12]. This can occur in the context of severe anemia, Gram negative septicaemia, beriberi (vitamin B1/thiamine deficiency), thyrotoxicosis, Paget's disease, arteriovenous fistulae or arteriovenous malformations.
Fluid overload is a common problem for people with heart failure, but is not synonymous with it. Patients with treated heart failure will often be euvolaemic (a term for normal fluid status), or more rarely, dehydrated.
Doctors use the words "acute" to mean of rapid onset, and "chronic" of long duration. Chronic heart failure is therefore a long term situation, usually with stable treated symptomatology.
Acute decompensated heart failure is a term used to describe exacerbated or decompensated heart failure, referring to episodes in which a patient can be characterized as having a change in heart failure signs and symptoms resulting in a need for urgent therapy or hospitalization.[13]
There are several terms which are closely related to heart failure, and may be the cause of heart failure, but should not be confused with it:
Cardiac arrest, and asystole both refer to situations in which there is no cardiac output at all. Without urgent treatment, these result in sudden death.
Myocardial infarction ("Heart attack") refers heart muscle damage due to insufficient blood supply, usually as a result of a blocked coronary artery.
Cardiomyopathy refers specifically to problems within the heart muscle, and these problems usually result in heart failure. Ischemic cardiomyopathy implies that the cause of muscle damage is coronary artery disease. Dilated cardiomyopathy implies that the muscle damage has resulted in enlargement of the heart. Hypertrophic cardiomyopathy involves enlargement and thickening of the heart muscle.
] Classification
There are many different ways to categorize heart failure, including:
the side of the heart involved, (left heart failure versus right heart failure)
whether the abnormality is due to contraction or relaxation of the heart (systolic dysfunction vs. diastolic dysfunction)
whether the problem is primarily increased venous back pressure (behind) the heart, or failure to supply adequate arterial perfusion (in front of) the heart (backward vs. forward failure)
whether the abnormality is due to low cardiac output with high systemic vascular resistance or high cardiac output with low vascular resistance (low-output heart failure vs. high-output heart failure)
the degree of functional impairment conferred by the abnormality (as in the NYHA functional classification)
Functional classification generally relies on the New York Heart Association Functional Classification.[14] The classes (I-IV) are:
Class I: no limitation is experienced in any activities; there are no symptoms from ordinary activities.
Class II: slight, mild limitation of activity; the patient is comfortable at rest or with mild exertion.
Class III: marked limitation of any activity; the patient is comfortable only at rest.
Class IV: any physical activity brings on discomfort and symptoms occur at rest.
This score documents severity of symptoms, and can be used to assess response to treatment. While its use is widespread, the NYHA score is not very reproducible and doesn't reliably predict the walking distance or exercise tolerance on formal testing.[15]
In its 2001 guidelines, the American College of Cardiology/American Heart Association working group introduced four stages of heart failure:[16]
Stage A: Patients at high risk for developing HF in the future but no functional or structural heart disorder;
Stage B: a structural heart disorder but no symptoms at any stage;
Stage C: previous or current symptoms of heart failure in the context of an underlying structural heart problem, but managed with medical treatment;
Stage D: advanced disease requiring hospital-based support, a heart transplant or palliative care.
The ACC staging system is useful in that Stage A encompasses "pre-heart failure" - a stage where intervention with treatment can presumably prevent progression to overt symptoms. ACC stage A does not have a corresponding NYHA class. ACC Stage B would correspond to NYHA Class I. ACC Stage C corresponds to NYHA Class II and III, while ACC Stage D overlaps with NYHA Class IV.
Signs and symptoms
Symptoms
Heart failure symptoms are traditionally and somewhat arbitrarily divided into "left" and "right" sided, recognizing that the left and right ventricles of the heart supply different portions of the circulation. However, heart failure is not exclusively backward failure (in the part of the circulation which drains to the ventricle).
There are several other exceptions to a simple left-right division of heart failure symptoms. Left sided forward failure overlaps with right sided backward failure. Additionally, the most common cause of right-sided heart failure is left-sided heart failure. The result is that patients commonly present with both sets of signs and symptoms.
Left-sided failure
Backward failure of the left ventricle causes congestion of the pulmonary vasculature, and so the symptoms are predominantly respiratory in nature. Backward failure can be subdivided into failure of the left atrium, the left ventricle or both within the left circuit. The patient will have dyspnea (shortness of breath) on exertion (dyspnée d'effort) and in severe cases, dyspnea at rest. Increasing breathlessness on lying flat, called orthopnea, occurs. It is often measured in the number of pillows required to lie comfortably, and in severe cases, the patient may resort to sleeping while sitting up. Another symptom of heart failure is paroxysmal nocturnal dyspnea also known as "cardiac asthma", a sudden nighttime attack of severe breathlessness, usually several hours after going to sleep. Easy fatigueability and exercise intolerance are also common complaints related to respiratory compromise.
Compromise of left ventricular forward function may result in symptoms of poor systemic circulation such as dizziness, confusion and cool extremities at rest.
Right-sided failure
Backward failure of the right ventricle leads to congestion of systemic capillaries. This generates excess fluid accumulation in the body. This causes swelling under the skin (termed peripheral edema or anasarca) and usually affects the dependent parts of the body first (causing foot and ankle swelling in people who are standing up, and sacral edema in people who are predominantly lying down). Nocturia (frequent nighttime urination) may occur when fluid from the legs is returned to the bloodstream while lying down at night. In progressively severe cases, ascites (fluid accumulation in the abdominal cavity causing swelling) and hepatomegaly (enlargement of the liver) may develop. Significant liver congestion may result in impaired liver function, and jaundice and even coagulopathy (problems of decreased blood clotting) may occur.
Signs
Left-sided failure
Common respiratory signs are tachypnea (increased rate of breathing) and increased work of breathing (non-specific signs of respiratory distress). Rales or crackles, heard initially in the lung bases, and when severe, throughout the lung fields suggest the development of pulmonary edema (fluid in the alveoli). Cyanosis which suggests severe hypoxemia, is a late sign of extremely severe pulmonary edema.
Additional signs indicating left ventricular failure include a laterally displaced apex beat (which occurs if the heart is enlarged) and a gallop rhythm (additional heart sounds) may be heard as a marker of increased blood flow, or increased intra-cardiac pressure. Heart murmurs may indicate the presence of valvular heart disease, either as a cause (e.g. aortic stenosis) or as a result (e.g., mitral regurgitation) of the heart failure.
Right-sided failure
Physical examination can reveal pitting peripheral edema, ascites, and hepatomegaly. Jugular venous pressure is frequently assessed as a marker of fluid status, which can be accentuated by the hepatojugular reflux. If the right ventriclar pressure is increased, a parasternal heave may be present, signifying the compensatory increase in contraction strength.
Biventricular failure
Dullness of the lung fields to finger percussion and reduced breath sounds at the bases of the lung may suggest the development of a pleural effusion (fluid collection in between the lung and the chest wall). Though it can occur in isolated left- or right-sided heart failure, it is more common in biventricular failure because pleural veins drain both into the systemic and pulmonary venous system. When unilateral, effusions are often right-sided, presumably because of the larger surface area of the right lung
Heart disease
Coronary heart disease
Main article: Coronary heart disease
Coronary heart disease refers to the failure of the coronary circulation to supply adequate circulation to cardiac muscle and surrounding tissue. Coronary heart disease is most commonly equated with Coronary artery disease although coronary heart disease can be due to other causes, such as coronary vasospasm.[5]
Coronary artery disease is a disease of the artery caused by the accumulation of atheromatous plaques within the walls of the arteries that supply the myocardium. Angina pectoris (chest pain) and myocardial infarction (heart attack) are symptoms of and conditions caused by coronary heart disease.
Over 459,000 Americans die of coronary heart disease every year[6]. In the United Kingdom, 101,000 deaths annually are due to coronary heart disease.[7]
Cardiomyopathy
Main article: Cardiomyopathy
Cardiomyopathy literally means "heart muscle disease" (Myo= muscle, pathy= disease) It is the deterioration of the function of the myocardium (i.e., the actual heart muscle) for any reason. People with cardiomyopathy are often at risk of arrhythmia and/or sudden cardiac death.
Extrinsic cardiomyopathies – cardiomyopathies where the primary pathology is outside the myocardium itself. Most cardiomyopathies are extrinsic, because by far the most common cause of a cardiomyopathy is ischemia. The World Health Organization calls these specific cardiomyopathies[citation needed]:
Alcoholic cardiomyopathy
Coronary artery disease
Congenital heart disease
Nutritional diseases affecting the heart
Ischemic (or ischaemic) cardiomyopathy
Hypertensive cardiomyopathy
Valvular cardiomyopathy – see also Valvular heart disease below
Inflammatory cardiomyopathy – see also Inflammatory heart disease below
Cardiomyopathy secondary to a systemic metabolic disease
Myocardiodystrophy
Intrinsic cardiomyopathies – weakness in the muscle of the heart that is not due to an identifiable external cause.
Dilated cardiomyopathy (DCM) – most common form, and one of the leading indications for heart transplantation. In DCM the heart (especially the left ventricle) is enlarged and the pumping function is diminished.
Hypertrophic cardiomyopathy (HCM or HOCM) – genetic disorder caused by various mutations in genes encoding sarcomeric proteins. In HCM the heart muscle is thickened, which can obstruct blood flow and prevent the heart from functioning properly.
Arrhythmogenic right ventricular cardiomyopathy (ARVC) – arises from an electrical disturbance of the heart in which heart muscle is replaced by fibrous scar tissue. The right ventricle is generally most affected.
Restrictive cardiomyopathy (RCM) – least common cardiomyopathy. The walls of the ventricles are stiff, but may not be thickened, and resist the normal filling of the heart with blood.
Noncompaction Cardiomyopathy – the left ventricle wall has failed to properly grow from birth and such has a spongy appearance when viewed during an echocardiogram.
Cardiovascular disease
Main article: Cardiovascular disease
Cardiovascular disease is any of a number of specific diseases that affect the heart itself and/or the blood vessel system, especially the veins and arteries leading to and from the heart. Research on disease dimorphism suggests that women who suffer with cardiovascular disease usually suffer from forms that affect the blood vessels while men usually suffer from forms that affect the heart muscle itself. Known or associated causes of cardiovascular disease include diabetes mellitus, hypertension, hyperhomocysteinemia and hypercholesterolemia.
Types of cardiovascular disease include:
Atherosclerosis
Ischaemic heart disease
Ischaemic heart disease – another disease of the heart itself, characterized by reduced blood supply to the organs.
Heart failure
Main article: Heart failure
Heart failure, also called congestive heart failure (or CHF), and congestive cardiac failure (CCF), is a condition that can result from any structural or functional cardiac disorder that impairs the ability of the heart to fill with or pump a sufficient amount of blood throughout the body. Therefore leading to the heart and body's failure.
Cor pulmonale, a failure of the right side of the heart.
Hypertensive heart disease
Main article: Hypertensive heart disease
Hypertensive heart disease is heart disease caused by high blood pressure, especially localised high blood pressure. Conditions that can be caused by hypertensive heart disease include:
Left ventricular hypertrophy
Coronary heart disease
(Congestive) heart failure
Hypertensive cardiomyopathy
Cardiac arrhythmias
Inflammatory heart disease
Disability-adjusted life year for inflammatory heart diseases per 100,000 inhabitants in 2004.[8]
no data less than 70 70-140 140-210 210-280 280-350 350-420 420-490 490-560 560-630 630-700 700-770 more than 770
Inflammatory heart disease involves inflammation of the heart muscle and/or the tissue surrounding it.
Endocarditis – inflammation of the inner layer of the heart, the endocardium. The most common structures involved are the heart valves.
Inflammatory cardiomegaly
Myocarditis – inflammation of the myocardium, the muscular part of the heart.
Valvular heart disease
Main article: Valvular heart disease
Valvular heart disease is disease process that affects one or more valves of the heart. There are four major heart valve which may be affected by valvular heart disease, including the tricuspid and aortic valves in the right side of the heart, as well as the mitral and aortic valves in the left side of the heart.
Main article: Coronary heart disease
Coronary heart disease refers to the failure of the coronary circulation to supply adequate circulation to cardiac muscle and surrounding tissue. Coronary heart disease is most commonly equated with Coronary artery disease although coronary heart disease can be due to other causes, such as coronary vasospasm.[5]
Coronary artery disease is a disease of the artery caused by the accumulation of atheromatous plaques within the walls of the arteries that supply the myocardium. Angina pectoris (chest pain) and myocardial infarction (heart attack) are symptoms of and conditions caused by coronary heart disease.
Over 459,000 Americans die of coronary heart disease every year[6]. In the United Kingdom, 101,000 deaths annually are due to coronary heart disease.[7]
Cardiomyopathy
Main article: Cardiomyopathy
Cardiomyopathy literally means "heart muscle disease" (Myo= muscle, pathy= disease) It is the deterioration of the function of the myocardium (i.e., the actual heart muscle) for any reason. People with cardiomyopathy are often at risk of arrhythmia and/or sudden cardiac death.
Extrinsic cardiomyopathies – cardiomyopathies where the primary pathology is outside the myocardium itself. Most cardiomyopathies are extrinsic, because by far the most common cause of a cardiomyopathy is ischemia. The World Health Organization calls these specific cardiomyopathies[citation needed]:
Alcoholic cardiomyopathy
Coronary artery disease
Congenital heart disease
Nutritional diseases affecting the heart
Ischemic (or ischaemic) cardiomyopathy
Hypertensive cardiomyopathy
Valvular cardiomyopathy – see also Valvular heart disease below
Inflammatory cardiomyopathy – see also Inflammatory heart disease below
Cardiomyopathy secondary to a systemic metabolic disease
Myocardiodystrophy
Intrinsic cardiomyopathies – weakness in the muscle of the heart that is not due to an identifiable external cause.
Dilated cardiomyopathy (DCM) – most common form, and one of the leading indications for heart transplantation. In DCM the heart (especially the left ventricle) is enlarged and the pumping function is diminished.
Hypertrophic cardiomyopathy (HCM or HOCM) – genetic disorder caused by various mutations in genes encoding sarcomeric proteins. In HCM the heart muscle is thickened, which can obstruct blood flow and prevent the heart from functioning properly.
Arrhythmogenic right ventricular cardiomyopathy (ARVC) – arises from an electrical disturbance of the heart in which heart muscle is replaced by fibrous scar tissue. The right ventricle is generally most affected.
Restrictive cardiomyopathy (RCM) – least common cardiomyopathy. The walls of the ventricles are stiff, but may not be thickened, and resist the normal filling of the heart with blood.
Noncompaction Cardiomyopathy – the left ventricle wall has failed to properly grow from birth and such has a spongy appearance when viewed during an echocardiogram.
Cardiovascular disease
Main article: Cardiovascular disease
Cardiovascular disease is any of a number of specific diseases that affect the heart itself and/or the blood vessel system, especially the veins and arteries leading to and from the heart. Research on disease dimorphism suggests that women who suffer with cardiovascular disease usually suffer from forms that affect the blood vessels while men usually suffer from forms that affect the heart muscle itself. Known or associated causes of cardiovascular disease include diabetes mellitus, hypertension, hyperhomocysteinemia and hypercholesterolemia.
Types of cardiovascular disease include:
Atherosclerosis
Ischaemic heart disease
Ischaemic heart disease – another disease of the heart itself, characterized by reduced blood supply to the organs.
Heart failure
Main article: Heart failure
Heart failure, also called congestive heart failure (or CHF), and congestive cardiac failure (CCF), is a condition that can result from any structural or functional cardiac disorder that impairs the ability of the heart to fill with or pump a sufficient amount of blood throughout the body. Therefore leading to the heart and body's failure.
Cor pulmonale, a failure of the right side of the heart.
Hypertensive heart disease
Main article: Hypertensive heart disease
Hypertensive heart disease is heart disease caused by high blood pressure, especially localised high blood pressure. Conditions that can be caused by hypertensive heart disease include:
Left ventricular hypertrophy
Coronary heart disease
(Congestive) heart failure
Hypertensive cardiomyopathy
Cardiac arrhythmias
Inflammatory heart disease
Disability-adjusted life year for inflammatory heart diseases per 100,000 inhabitants in 2004.[8]
no data less than 70 70-140 140-210 210-280 280-350 350-420 420-490 490-560 560-630 630-700 700-770 more than 770
Inflammatory heart disease involves inflammation of the heart muscle and/or the tissue surrounding it.
Endocarditis – inflammation of the inner layer of the heart, the endocardium. The most common structures involved are the heart valves.
Inflammatory cardiomegaly
Myocarditis – inflammation of the myocardium, the muscular part of the heart.
Valvular heart disease
Main article: Valvular heart disease
Valvular heart disease is disease process that affects one or more valves of the heart. There are four major heart valve which may be affected by valvular heart disease, including the tricuspid and aortic valves in the right side of the heart, as well as the mitral and aortic valves in the left side of the heart.
Sunglasses
Sunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright Sun light and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist which feature lenses that are colored, polarized or darkened. In the early 20th century they were also known as sun cheaters (cheaters being an American slang term for glasses).[1]
Many people find direct sunlight too bright for comfort. During outdoor activities, the human eye can receive more light than usual. Healthcare professionals recommend eye protection whenever outside to protect the eyes from ultraviolet radiation and blue light, which can cause several serious eye problems. Sunglasses have long been associated with celebrities and film actors primarily
from a desire to mask their identity. Since the 1940s sunglasses have been popular as a fashion accessory, especially on the beach.
Precursors
Inuit snow goggles function by reducing exposure to sunlight, not by reducing its intensity
It is said that the Roman emperor Nero liked to watch gladiator fights with emeralds. These, however, appear to have worked rather like mirrors.[2] Flat panes of smoky quartz which offered no corrective powers but did protect the eyes from glare were used in China in the 12th century or possibly earlier. Contemporary documents describe the use of such crystals by judges in Chinese courts to conceal their facial expressions while questioning witnesses.[3]
James Ayscough began experimenting with tinted lenses in spectacles in the mid-18th century, around 1752. These were not "sunglasses" as such; Ayscough believed blue- or green-tinted glass could correct for specific vision impairments. Protection from the sun's rays was not a concern for him.
Yellow/amber and brown-tinted spectacles were also a commonly-prescribed item for people with syphilis in the 19th[dubious – discuss] and early 20th centuries because sensitivity to light was one of the symptoms of the disease.
In prehistoric and historic time, Inuit peoples wore flattened walrus ivory "glasses," looking through narrow slits to block harmful reflected rays of the sun.[4]
[edit] Modern developments
In the early 1900s, the use of sunglasses started to become more widespread, especially among stars of silent movies. It is commonly believed that this was to avoid recognition by fans, but the real reason was they often had perennially red eyes from the powerful arc lamps that were needed due to the extremely slow speed film stocks used.[citation needed] The stereotype persisted long after improvements in film quality and the introduction of ultraviolet filters had eliminated this problem. Inexpensive mass-produced sunglasses were introduced to America by Sam Foster in 1929. Foster found a ready market on the beaches of Atlantic City, New Jersey, where he began selling sunglasses under the name Foster Grant from a Woolworth on the Boardwalk.
Polarized sunglasses first became available in 1936, when Edwin H. Land began experimenting with making lenses with his patented Polaroid filter.
[edit] Functions
[edit] Visual clarity and comfort
Sunglasses can improve visual comfort and visual clarity by protecting the eye from glare.[5]
Various types of disposable sunglasses are dispensed to patients after receiving mydriatic eye drops during eye examinations.
The lenses of polarized sunglasses reduce glare reflected at some angles off shiny non-metallic surfaces such as water. They are popular among fishermen because they allow wearers to see into water when normally only glare would be seen.
Broad temple arms protect against "stray light" entering from the sides
Sunglasses with slim temple arms
[edit] Protection
Sunglasses offer protection against excessive exposure to light, including its visible and invisible components.
The most widespread protection is against ultraviolet radiation (UV), which can cause short-term and long-term ocular problems such as photokeratitis, snow blindness, cataracts, pterygium, and various forms of eye cancer.[6] Medical experts advise the public on the importance of wearing sunglasses to protect the eyes from UV;[6] for adequate protection, experts recommend sunglasses that reflect or filter out 99-100 % of UVA and UVB light, with wavelengths up to 400 nanometers (nm). Sunglasses which meet this requirement are often labeled as "UV 400." This is slightly more protection than the widely used standard of the European Union (see below), which requires that 95 % of the radiation up to only 380 nm must be reflected or filtered out.[7] Sunglasses are not sufficient to protect the eyes against permanent harm from looking directly at the sun, even during a solar eclipse.
More recently, high-energy visible light (HEV) has been implicated as a cause of age-related macular degeneration;[8] before, debates had already existed as to whether "blue blocking" or amber tinted lenses may have a protective effect.[9] Some manufacturers already design to block blue light; the insurance company Suva, which covers most Swiss employees, asked eye experts around Charlotte Remé (ETH Zürich) to develop norms for blue blocking, leading to a recommended minimum of 95% of the blue light.[7][10] Sunglasses are especially important for children, as their ocular lenses are thought to transmit far more HEV light than adults (lenses "yellow" with age).
There has been some speculation that sunglasses actually promote skin cancer.[11] This is due to the eyes being tricked into producing less melanocyte-stimulating hormone in the body.
[edit] Assessing the protection of sunglasses
The only way to assess the protection of sunglasses is to have the lenses measured, either by the manufacturer or by a properly equipped optician. Several standards for sunglasses (see below) allow a general classification of the UV protection (but not the blue light protection), and manufacturers often indicate simply that the sunglasses meet the requirements of a specific standard rather than publish the exact figures.
The only "visible" quality test for sunglasses is their fit. The lenses should fit close enough to the face that only very little "stray light" can reach the eye from their sides, or from above or below, but not so close that the eyelashes smear the lenses. To protect against "stray light" from the sides, the lenses should fit close enough to the temples and/or merge into broad temple arms or leather blinders.
It is not possible to "see" the protection that sunglasses offer. Dark lenses do not automatically filter out more harmful UV radiation and blue light as compared to light lenses. Inadequate dark lenses are even more harmful than inadequate light lenses (or wearing no sunglasses at all) because they provoke the pupil to open wider. As result, more unfiltered radiation enters the eye. Depending on the manufacturing technology, sufficiently protective lenses can block much or little light, resulting in dark or light lenses. The lens color is not a guarantee either. Lenses of various colors can offer sufficient (or insufficient) UV protection. Regarding blue light, the color gives at least a first indication: Blue blocking lenses are commonly yellow or brown whereas blue or gray lenses cannot offer the necessary blue light protection. However, not every yellow or brown lens blocks sufficient blue light. In rare cases, lenses can filter out too much blue light (i.e., 100 %), which affects color vision and can be dangerous in traffic when colored signals are not properly recognized.
High prices cannot guarantee sufficient protection as no correlation between high prices and increased UV protection has been demonstrated. A 1995 study reported that "Expensive brands and polarizing sunglasses do not guarantee optimal UVA protection."[12] The Australian Competition and Consumer Commission has also reported that "[c]onsumers cannot rely on price as an indicator of quality".[13] One survey even found that a $6.95 pair of generic glasses offered slightly better protection than did expensive Salvatore Ferragamo shades.[14]
[edit] Further functions of sunglasses
Protecting his eyes from exposure due to Exophthalmos sunglasses have become the trademark of German singer Heino
While non-tinted glasses are very rarely worn without the practical purpose of correcting eyesight or protecting one's eyes, sunglasses have become popular for several further reasons, and are sometimes worn even indoors or at night.
Sunglasses can be worn to hide one's eyes. They can make eye contact impossible, which can be intimidating to those not wearing sunglasses; the avoided eye contact can also demonstrate the wearer's detachment,[citation needed] which is considered desirable ("cool") in some circles. Eye contact can be avoided even more effectively by using mirrored sunglasses. Sunglasses can also be used to hide emotions; this can range from hiding blinking to hiding weeping and its resulting red eyes. In all cases, hiding one's eyes has implications for nonverbal communication.
Artist M.I.A. wearing sunglasses as part of her costume for the Outside Lands Music and Arts Festival.
Fashion trends can be another reason for wearing sunglasses, particularly designer sunglasses. Sunglasses of particular shapes may be in vogue as a fashion accessory. Fashion trends can also draw on the "cool" image of sunglasses.
People may also wear sunglasses to hide an abnormal appearance of their eyes. This can be true for people with severe visual impairment, such as the blind, who may wear sunglasses to avoid making others uncomfortable. The assumption is that it may be more comfortable for another person not to see the hidden eyes rather than see abnormal eyes or eyes which seem to look in the wrong direction. People may also wear sunglasses to hide dilated or contracted pupils, bloodshot eyes due to drug use, recent physical abuse (such as a black eye), exophthalmus (bulging eyes), a cataract, or eyes which jerk uncontrollably (nystagmus).
Many people find direct sunlight too bright for comfort. During outdoor activities, the human eye can receive more light than usual. Healthcare professionals recommend eye protection whenever outside to protect the eyes from ultraviolet radiation and blue light, which can cause several serious eye problems. Sunglasses have long been associated with celebrities and film actors primarily
from a desire to mask their identity. Since the 1940s sunglasses have been popular as a fashion accessory, especially on the beach.
Precursors
Inuit snow goggles function by reducing exposure to sunlight, not by reducing its intensity
It is said that the Roman emperor Nero liked to watch gladiator fights with emeralds. These, however, appear to have worked rather like mirrors.[2] Flat panes of smoky quartz which offered no corrective powers but did protect the eyes from glare were used in China in the 12th century or possibly earlier. Contemporary documents describe the use of such crystals by judges in Chinese courts to conceal their facial expressions while questioning witnesses.[3]
James Ayscough began experimenting with tinted lenses in spectacles in the mid-18th century, around 1752. These were not "sunglasses" as such; Ayscough believed blue- or green-tinted glass could correct for specific vision impairments. Protection from the sun's rays was not a concern for him.
Yellow/amber and brown-tinted spectacles were also a commonly-prescribed item for people with syphilis in the 19th[dubious – discuss] and early 20th centuries because sensitivity to light was one of the symptoms of the disease.
In prehistoric and historic time, Inuit peoples wore flattened walrus ivory "glasses," looking through narrow slits to block harmful reflected rays of the sun.[4]
[edit] Modern developments
In the early 1900s, the use of sunglasses started to become more widespread, especially among stars of silent movies. It is commonly believed that this was to avoid recognition by fans, but the real reason was they often had perennially red eyes from the powerful arc lamps that were needed due to the extremely slow speed film stocks used.[citation needed] The stereotype persisted long after improvements in film quality and the introduction of ultraviolet filters had eliminated this problem. Inexpensive mass-produced sunglasses were introduced to America by Sam Foster in 1929. Foster found a ready market on the beaches of Atlantic City, New Jersey, where he began selling sunglasses under the name Foster Grant from a Woolworth on the Boardwalk.
Polarized sunglasses first became available in 1936, when Edwin H. Land began experimenting with making lenses with his patented Polaroid filter.
[edit] Functions
[edit] Visual clarity and comfort
Sunglasses can improve visual comfort and visual clarity by protecting the eye from glare.[5]
Various types of disposable sunglasses are dispensed to patients after receiving mydriatic eye drops during eye examinations.
The lenses of polarized sunglasses reduce glare reflected at some angles off shiny non-metallic surfaces such as water. They are popular among fishermen because they allow wearers to see into water when normally only glare would be seen.
Broad temple arms protect against "stray light" entering from the sides
Sunglasses with slim temple arms
[edit] Protection
Sunglasses offer protection against excessive exposure to light, including its visible and invisible components.
The most widespread protection is against ultraviolet radiation (UV), which can cause short-term and long-term ocular problems such as photokeratitis, snow blindness, cataracts, pterygium, and various forms of eye cancer.[6] Medical experts advise the public on the importance of wearing sunglasses to protect the eyes from UV;[6] for adequate protection, experts recommend sunglasses that reflect or filter out 99-100 % of UVA and UVB light, with wavelengths up to 400 nanometers (nm). Sunglasses which meet this requirement are often labeled as "UV 400." This is slightly more protection than the widely used standard of the European Union (see below), which requires that 95 % of the radiation up to only 380 nm must be reflected or filtered out.[7] Sunglasses are not sufficient to protect the eyes against permanent harm from looking directly at the sun, even during a solar eclipse.
More recently, high-energy visible light (HEV) has been implicated as a cause of age-related macular degeneration;[8] before, debates had already existed as to whether "blue blocking" or amber tinted lenses may have a protective effect.[9] Some manufacturers already design to block blue light; the insurance company Suva, which covers most Swiss employees, asked eye experts around Charlotte Remé (ETH Zürich) to develop norms for blue blocking, leading to a recommended minimum of 95% of the blue light.[7][10] Sunglasses are especially important for children, as their ocular lenses are thought to transmit far more HEV light than adults (lenses "yellow" with age).
There has been some speculation that sunglasses actually promote skin cancer.[11] This is due to the eyes being tricked into producing less melanocyte-stimulating hormone in the body.
[edit] Assessing the protection of sunglasses
The only way to assess the protection of sunglasses is to have the lenses measured, either by the manufacturer or by a properly equipped optician. Several standards for sunglasses (see below) allow a general classification of the UV protection (but not the blue light protection), and manufacturers often indicate simply that the sunglasses meet the requirements of a specific standard rather than publish the exact figures.
The only "visible" quality test for sunglasses is their fit. The lenses should fit close enough to the face that only very little "stray light" can reach the eye from their sides, or from above or below, but not so close that the eyelashes smear the lenses. To protect against "stray light" from the sides, the lenses should fit close enough to the temples and/or merge into broad temple arms or leather blinders.
It is not possible to "see" the protection that sunglasses offer. Dark lenses do not automatically filter out more harmful UV radiation and blue light as compared to light lenses. Inadequate dark lenses are even more harmful than inadequate light lenses (or wearing no sunglasses at all) because they provoke the pupil to open wider. As result, more unfiltered radiation enters the eye. Depending on the manufacturing technology, sufficiently protective lenses can block much or little light, resulting in dark or light lenses. The lens color is not a guarantee either. Lenses of various colors can offer sufficient (or insufficient) UV protection. Regarding blue light, the color gives at least a first indication: Blue blocking lenses are commonly yellow or brown whereas blue or gray lenses cannot offer the necessary blue light protection. However, not every yellow or brown lens blocks sufficient blue light. In rare cases, lenses can filter out too much blue light (i.e., 100 %), which affects color vision and can be dangerous in traffic when colored signals are not properly recognized.
High prices cannot guarantee sufficient protection as no correlation between high prices and increased UV protection has been demonstrated. A 1995 study reported that "Expensive brands and polarizing sunglasses do not guarantee optimal UVA protection."[12] The Australian Competition and Consumer Commission has also reported that "[c]onsumers cannot rely on price as an indicator of quality".[13] One survey even found that a $6.95 pair of generic glasses offered slightly better protection than did expensive Salvatore Ferragamo shades.[14]
[edit] Further functions of sunglasses
Protecting his eyes from exposure due to Exophthalmos sunglasses have become the trademark of German singer Heino
While non-tinted glasses are very rarely worn without the practical purpose of correcting eyesight or protecting one's eyes, sunglasses have become popular for several further reasons, and are sometimes worn even indoors or at night.
Sunglasses can be worn to hide one's eyes. They can make eye contact impossible, which can be intimidating to those not wearing sunglasses; the avoided eye contact can also demonstrate the wearer's detachment,[citation needed] which is considered desirable ("cool") in some circles. Eye contact can be avoided even more effectively by using mirrored sunglasses. Sunglasses can also be used to hide emotions; this can range from hiding blinking to hiding weeping and its resulting red eyes. In all cases, hiding one's eyes has implications for nonverbal communication.
Artist M.I.A. wearing sunglasses as part of her costume for the Outside Lands Music and Arts Festival.
Fashion trends can be another reason for wearing sunglasses, particularly designer sunglasses. Sunglasses of particular shapes may be in vogue as a fashion accessory. Fashion trends can also draw on the "cool" image of sunglasses.
People may also wear sunglasses to hide an abnormal appearance of their eyes. This can be true for people with severe visual impairment, such as the blind, who may wear sunglasses to avoid making others uncomfortable. The assumption is that it may be more comfortable for another person not to see the hidden eyes rather than see abnormal eyes or eyes which seem to look in the wrong direction. People may also wear sunglasses to hide dilated or contracted pupils, bloodshot eyes due to drug use, recent physical abuse (such as a black eye), exophthalmus (bulging eyes), a cataract, or eyes which jerk uncontrollably (nystagmus).
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