Dysbarism
Encyclopedia
Dysbarism refers to medical conditions resulting from changes in ambient pressure
. Various activities are associated with pressure changes. Scuba diving
is the most frequently cited example, but pressure changes also affect people who work in other pressurized environments (for example, caisson
workers), and people who move between different altitude
s.
(or the air, with caisson workers etc.). As a diver descends, the ambient pressure increases. At 10 meters (33 feet) in salt water
, it is twice the normal pressure on land at sea level
. At 40 meters (the recommended safety limit for recreational diving) it is 5 times the pressure at sea level.
Pressure decreases as we rise above sea level, but less dramatically. At 3000 feet altitude
(almost 1000 meters), the ambient pressure is almost 90% of sea level pressure. Ambient pressure does not drop to 50% of sea level pressure until 20,000 feet or 6,000 meters altitude.
divers feel their body being crushed by the pressure. The answer is no. Divers would have to reach depths of thousands of feet before their flesh began to suffer significant compression.
, middle ear
s, gas
in our bowels, cavities in our teeth, and largest of all, our lung
s. On land in our daily lives, the pressure in our air spaces is usually exactly the same as the pressure outside, because our air spaces are connected to the outside world. If there was a pressure difference between the outside world and one of our air spaces, then we experience painful pressure on the walls of that air space, as air pushes from the higher-pressure side to the lower-pressure side. This is why we sometimes get painful ears on air trips.
(dropping the pressure in the bottle slowly down to sea level), versus ripping the cap off quickly.
, also called caisson workers' disease and the bends, is the most well-known complication of scuba diving. It occurs as divers ascend, and often from ascending too fast or without doing decompression stops. Bubbles are large enough and numerous enough to cause physical injury. It is quite possible that all divers have microbubbles in their blood to some extent, but that most of the time these bubbles are so few and so small that they cause no harm. When DCS occurs, bubbles disrupt tissues in the joints, brain, spinal cord, lungs, and other organs. Symptoms vary enormously. DCS may be as subtle as unusual tiredness after a dive, or an aching elbow, or a mottled skin rash. Or, it may present dramatically, with unconsciousness
, seizure
s, paralysis
, shortness of breath, or death. Paraplegia
is not uncommon.
(DCI).
is also called “L’ivresse des grandes profondeurs” or rapture of the deep
. Nitrogen comprises 79% of the air breathed by aerobic organisms, but at surface pressures it has no sedating effect. At greater depths, however, nitrogen affects the brain in precisely the same way as nitrous oxide
(also known as laughing gas
). The effect is similar to the effects of alcohol, and to some extent there is cross-tolerance
. Unlike alcohol
, the onset and disappearance are instantaneous. A diver may be quite clear-headed at 20 meters, and yet giddy and silly at 30 meters. Ascending to 20 meters will almost instantly clear the head. Divers suffering nitrogen narcosis may put themselves at risk by doing stupid things such as offering their regulator
or mouthpiece
to a fish. Because it reverses completely with ascent, divers never suffer nitrogen narcosis after a dive.
is injury caused by pressure effects on air spaces. This may occur during ascent or descent. The ears are the most commonly affected body part. The most serious injury is lung barotraumas, which can result in pneumothorax
, pneumomediastinum
, pneumopericardium
, subcutaneous emphysema
, and arterial gas embolism. All divers, commercial air travelers, people traveling overland between different altitudes, and people who work in pressurized environments have had to deal with some degree of barotrauma effect upon their ear
s, sinuses
, and other air spaces. At the most extreme, barotrauma can cause ruptured eardrum
s, bleeding sinuses, exploding tooth
cavities, and the lung injuries described above. This is the reason why divers follow a golden rule of never holding their breath: by breathing continuously, they avoid any pressure differences between their lungs and ambient pressure. See barotrauma
for more information.
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
. Various activities are associated with pressure changes. Scuba diving
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
is the most frequently cited example, but pressure changes also affect people who work in other pressurized environments (for example, caisson
Caisson (engineering)
In geotechnical engineering, a caisson is a retaining, watertight structure used, for example, to work on the foundations of a bridge pier, for the construction of a concrete dam, or for the repair of ships. These are constructed such that the water can be pumped out, keeping the working...
workers), and people who move between different altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
s.
Ambient pressure
Ambient pressure is the pressure in the water around the diverUnderwater diving
Underwater diving is the practice of going underwater, either with breathing apparatus or by breath-holding .Recreational diving is a popular activity...
(or the air, with caisson workers etc.). As a diver descends, the ambient pressure increases. At 10 meters (33 feet) in salt water
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
, it is twice the normal pressure on land at sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
. At 40 meters (the recommended safety limit for recreational diving) it is 5 times the pressure at sea level.
Pressure decreases as we rise above sea level, but less dramatically. At 3000 feet altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
(almost 1000 meters), the ambient pressure is almost 90% of sea level pressure. Ambient pressure does not drop to 50% of sea level pressure until 20,000 feet or 6,000 meters altitude.
Direct effects on tissues
This is not of practical importance, because the body is mostly composed of barely compressible materials such as water. People often wonder whether scubaScuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
divers feel their body being crushed by the pressure. The answer is no. Divers would have to reach depths of thousands of feet before their flesh began to suffer significant compression.
Air spaces
Air is very compressible. Humans have many air spaces: sinusesParanasal sinus
Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity , above and between the eyes , and behind the ethmoids...
, middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
s, gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
in our bowels, cavities in our teeth, and largest of all, our lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s. On land in our daily lives, the pressure in our air spaces is usually exactly the same as the pressure outside, because our air spaces are connected to the outside world. If there was a pressure difference between the outside world and one of our air spaces, then we experience painful pressure on the walls of that air space, as air pushes from the higher-pressure side to the lower-pressure side. This is why we sometimes get painful ears on air trips.
Dissolved gas
A percentage of the gas we breathe (air) is always dissolved in our blood, like the gas dissolved in a soda bottle with the lid on. If we move to a higher ambient pressure, then the gas we breathe is at a higher pressure, and more of it dissolves in our blood and body tissues. If we move back to a lower pressure, and we move slowly, then the extra gas comes out slowly until we are back to our normal amount of dissolved gas. But if we move quickly to a lower ambient pressure, then the gas comes out of our blood and tissues violently, in large bubbles, like to the difference between slowly opening a bottle of sodaSoft drink
A soft drink is a non-alcoholic beverage that typically contains water , a sweetener, and a flavoring agent...
(dropping the pressure in the bottle slowly down to sea level), versus ripping the cap off quickly.
Types of dysbarism
Different types of illness result from increases in pressure (for example, descent during a SCUBA dive, descent during a plane flight), versus decreases in pressure (for example, coming up from a caisson, or ascending a mountain). Dysbarism comprises several types of illness:Decompression sickness (DCS)
Decompression sicknessDecompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...
, also called caisson workers' disease and the bends, is the most well-known complication of scuba diving. It occurs as divers ascend, and often from ascending too fast or without doing decompression stops. Bubbles are large enough and numerous enough to cause physical injury. It is quite possible that all divers have microbubbles in their blood to some extent, but that most of the time these bubbles are so few and so small that they cause no harm. When DCS occurs, bubbles disrupt tissues in the joints, brain, spinal cord, lungs, and other organs. Symptoms vary enormously. DCS may be as subtle as unusual tiredness after a dive, or an aching elbow, or a mottled skin rash. Or, it may present dramatically, with unconsciousness
Unconsciousness
Unconsciousness is the condition of being not conscious—in a mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli. Being in a comatose state or coma is a type of unconsciousness. Fainting due to a drop in blood pressure and a...
, seizure
Seizure
An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
s, paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
, shortness of breath, or death. Paraplegia
Paraplegia
Paraplegia is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek: παραπληγίη "half-striking". It is usually the result of spinal cord injury or a congenital condition such as spina bifida that affects the neural elements of the spinal canal...
is not uncommon.
Arterial Gas Embolism (AGE)
Arterial Gas Embolism (AGE) occurs on the arterial side. AGE can present in similar ways to arterial blockages seen in other medical situations. Affected people may suffer strokes, with paralysis or numbness down one side; they may suffer heart attacks; they may suffer pulmonary embolism with shortness of breath and chest pain. It is often impossible to distinguish AGE from DCS, but luckily it is rarely necessary for physicians to be able to distinguish between the two, as treatment is the same. Sometimes AGE and DCS are lumped into a single entity, Decompression IllnessDecompression illness
Decompression Illness describes a collection of symptoms arising from decompression of the body.DCI is caused by two different mechanisms, which result in overlapping sets of symptoms. The two mechanisms are:...
(DCI).
Nitrogen narcosis
Nitrogen narcosisNitrogen narcosis
Narcosis while diving , is a reversible alteration in consciousness that occurs while scuba diving at depth. The Greek word ναρκωσις is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates...
is also called “L’ivresse des grandes profondeurs” or rapture of the deep
Rapture of the Deep
Rapture of the Deep is the 18th studio album by English hard rock band Deep Purple, released in November 2005. It is currently the band's most recent studio album....
. Nitrogen comprises 79% of the air breathed by aerobic organisms, but at surface pressures it has no sedating effect. At greater depths, however, nitrogen affects the brain in precisely the same way as nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
(also known as laughing gas
Laughing gas
Laughing gas is a common name of Nitrous oxide, particularly when used as an anestheticLaughing gas may also refer to:* Laughing Gas , a 1936 comic novel by P. G...
). The effect is similar to the effects of alcohol, and to some extent there is cross-tolerance
Cross-tolerance
Cross-tolerance refers to a pharmacological phenomenon, in which a patient being treated with a drug exhibits a physiological resistance to that medication as a result of tolerance to a pharmacologically similar drug. In other words, there is a decrease in response to one drug due to exposure to...
. Unlike alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
, the onset and disappearance are instantaneous. A diver may be quite clear-headed at 20 meters, and yet giddy and silly at 30 meters. Ascending to 20 meters will almost instantly clear the head. Divers suffering nitrogen narcosis may put themselves at risk by doing stupid things such as offering their regulator
Diving regulator
A diving regulator is a pressure regulator used in scuba or surface supplied diving equipment that reduces pressurized breathing gas to ambient pressure and delivers it to the diver. The gas may be air or one of a variety of specially blended breathing gases...
or mouthpiece
Mouthpiece (scuba)
In breathing sets, a mouthpiece is a part that the user grips in his mouth, to make a watertight seal between the breathing set and his mouth. It is composed of a short flattened-oval tube that goes in between the lips, with on its free end a flange that fits between the lips and the tooth and gums...
to a fish. Because it reverses completely with ascent, divers never suffer nitrogen narcosis after a dive.
High pressure nervous syndrome (HPNS)
High pressure nervous syndrome is rarely of importance to recreational divers. Breathing any gas at great depths (hundreds of feet) can cause seizures. Interestingly it was discovered because divers were using gas mixtures without nitrogen to be able to go to great depths without experiencing nitrogen narcosis. It turns out that nitrogen prevents HPNS. The answer? Add very small amounts of nitrogen to gas mixes when diving at great depth, small enough to avoid nitrogen narcosis, but sufficient to prevent HPNS.Barotrauma
BarotraumaBarotrauma
Barotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid...
is injury caused by pressure effects on air spaces. This may occur during ascent or descent. The ears are the most commonly affected body part. The most serious injury is lung barotraumas, which can result in pneumothorax
Pneumothorax
Pneumothorax is a collection of air or gas in the pleural cavity of the chest between the lung and the chest wall. It may occur spontaneously in people without chronic lung conditions as well as in those with lung disease , and many pneumothoraces occur after physical trauma to the chest, blast...
, pneumomediastinum
Pneumomediastinum
Pneumomediastinum is a condition in which air is present in the mediastinum...
, pneumopericardium
Pneumopericardium
Pneumopericardium is a medical condition where air enters the pericardial cavity.It can be congenital, or introduced by a wound.-External links:* http://history.amedd.army.mil/booksdocs/wwii/thoracicsurgeryvolII/chapter2figure19.jpg...
, subcutaneous emphysema
Subcutaneous emphysema
Subcutaneous emphysema, sometimes abbreviated SCE or SE and also called tissue emphysema, or Sub Q air, occurs when gas or air is present in the subcutaneous layer of the skin. Subcutaneous refers to the tissue beneath the cutis of the skin, and emphysema refers to trapped air...
, and arterial gas embolism. All divers, commercial air travelers, people traveling overland between different altitudes, and people who work in pressurized environments have had to deal with some degree of barotrauma effect upon their ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
s, sinuses
Paranasal sinus
Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity , above and between the eyes , and behind the ethmoids...
, and other air spaces. At the most extreme, barotrauma can cause ruptured eardrum
Eardrum
The eardrum, or tympanic membrane, is a thin membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles...
s, bleeding sinuses, exploding tooth
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...
cavities, and the lung injuries described above. This is the reason why divers follow a golden rule of never holding their breath: by breathing continuously, they avoid any pressure differences between their lungs and ambient pressure. See barotrauma
Barotrauma
Barotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid...
for more information.