Dysbarism refers to medical conditions resulting from changes in ambient
pressurePressure 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 divingScuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater for recreation, commercial or industrial reasons.Unlike early diving, which relied exclusively on air pumped from the surface, scuba...
is the most frequently cited example, but pressure changes also affect people who work in other pressurized environments (for example,
caissonIn 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
altitudeAltitude 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...
s.
Ambient pressure
Ambient pressure is the pressure in the water around the
diverUnderwater 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 waterSeawater 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 of seawater has approximately of dissolved salts...
, it is twice the normal pressure on land at
sea levelMean sea level is the average height of the ocean's surface ; used as a standard in reckoning land elevation.- Measurement :...
. 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
altitudeAltitude 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...
(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 is a form of underwater diving in which a diver uses a scuba set to breathe underwater for recreation, commercial or industrial reasons.Unlike early diving, which relied exclusively on air pumped from the surface, scuba...
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 sinuses are air-filled spaces, communicating with the nasal cavity, within the bones of the skull and face.-Types in humans:Humans possess a number of paranasal sinuses, divided into subgroups that are named according to the bones within which the sinuses lie:*the maxillary sinuses, also...
,
middle earThe 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,
gasThis page is about the physical properties of gas as a state of matter. For the uses of gases, and other meanings, see Gas .A gas is one of four states of matter. Near absolute zero, a substance exists as a solid...
in our bowels, cavities in our teeth, and largest of all, our
lungThe lung or pulmonary system is the essential respiration organ in 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 in the chest 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
sodaA soft drink is a drink that does not contain alcohol . Soft drinks are often carbonated and commonly consumed while cold. The most common soft drinks are colas, flavored water, sparkling water, iced tea, sweet tea, lemonade, squash and fruit punch....
(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 describes a condition arising from the precipitation of dissolved gasses into bubbles inside the body on depressurisation...
, 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 stopA decompression stop is a period of time a diver must spend at a constant depth in shallow water at the end of a dive to safely eliminate absorbed inert gases from the diver's body to avoid decompression sickness...
s. 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
unconsciousnessUnconsciousness, more appropriately referred to as loss of consciousness or lack of consciousness, is a dramatic alteration of 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 an illustration...
,
seizureAn epileptic seizure is a transient symptom of excessive or synchronous neuronal activity in the brain. It can manifest as an alteration in mental state, tonic or clonic movements, convulsions, and various other psychic symptoms...
s,
paralysisParalysis is the complete loss of muscle function for one or more muscle groups. Paralysis can cause loss of feeling or loss of mobility in the affected area.-Causes:Paralysis is most often caused by damage to the nervous system, especially the spinal cord...
, shortness of breath, or death.
ParaplegiaParaplegia is an impairment in motor and/or sensory function of the lower extremities. It is usually the result of spinal cord injury or a congenital condition such as spina bifida which affects the neural elements of the spinal canal. The area of the spinal canal which is affected in paraplegia is...
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 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 narcosisNarcosis while diving is a reversible alteration in consciousness that occurs whilst scuba diving at depth. It produces a state similar to alcohol intoxication or nitrous oxide inhalation...
is also called “L’ivresse des grandes profondeurs” or
rapture of the deepRapture of the Deep is the 18th studio album by English hard rock band Deep Purple, released in November 2005. As of September 2009, this is 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 oxideNitrous oxide, commonly known as happy gas or laughing gas, is a chemical compound with the chemical formula N
2O. At room temperature, it is a colorless non-flammable gas, with a pleasant, slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
(also known as
laughing gasLaughing gas may refer to:* Nitrous oxide, when used as an anaesthetic* Laughing Gas , a comic novel by P.G. Wodehouse* Laughing Gas , the title of several movie shorts* Laughing Gas , a film starring Charlie Chaplin...
). The effect is similar to the effects of alcohol, and to some extent there is
cross-toleranceCross-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
alcoholIn chemistry, an alcohol is any organic compound in which a hydroxyl group is bound to a carbon atom of an alkyl or substituted alkyl group. An important group of acohols is formed by the simple acyclic alcohols, the general formula for which is C
nH
2n+1OH...
, 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
regulatorRegulator may refer to:*Regulator , a device which has the function of maintaining a designated characteristic*Battery regulator, a device in a battery pack which bleeds off excess charge current to let all cells reach full charge without overcharging some cells*Diving regulator, which provides a...
or
mouthpieceIn 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 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
pneumothoraxIn medicine , a pneumothorax is a potential medical emergency wherein air or gas is present in the pleural cavity. A pneumothorax can occur spontaneously. It can also occur as the result of disease or injury to the lung, or due to a puncture to the chest wall...
,
pneumomediastinumPneumomediastinum is a condition in which air is present in the mediastinum...
,
pneumopericardiumPneumopericardium 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 emphysemaSubcutaneous 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
earThe ear is the organ that detects sound. The vertebrate ear shows a common biology from fish to humans, with variations in structure according to order and species. It not only acts as a receiver for sound, but plays a major role in the sense of balance and body position...
s,
sinusesParanasal sinuses are air-filled spaces, communicating with the nasal cavity, within the bones of the skull and face.-Types in humans:Humans possess a number of paranasal sinuses, divided into subgroups that are named according to the bones within which the sinuses lie:*the maxillary sinuses, also...
, and other air spaces. At the most extreme, barotrauma can cause ruptured
eardrumThe tympanic membrane , is a thin membrane that separates the external ear from the middle ear. 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
toothTeeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to tear, scrape, and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense. The roots of teeth are covered by gums...
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
barotraumaBarotrauma 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.
See also
- Diving hazards and precautions
Divers face specific physical and health risks when they go underwater or use high pressure breathing gases. Some of these conditions also affect people who work in raised pressure environments out of water, e.g...
- Dysbaric osteonecrosis
Dysbaric osteonecrosis or DON is a form of avascular necrosis where the death of a portion of the bone that is thought to be caused by nitrogen embolization in divers...