تبلیغات Underwater Physiology and Diving Disorders 1: Oxygen Deficiency - Hypoxia
سه شنبه 1 تیر 1389 09:17 ق.ظ
ارسال شده در: Swimming and Diving(انگلیسی) ،
Oxygen Deficiency (Hypoxia):
Oxygen deficiency, or hypoxia, is an abnormal
deficiency of oxygen in the arterial blood that causes the tissue cells to be unable
to receive sufficient oxygen to maintain normal function. Severe hypoxia will stop
the normal function of any tissue cell in the body and will eventually kill it, but the
cells of the brain tissue are by far the most susceptible to its effects.
The partial pressure of oxygen determines whether the amount of oxygen in a
breathing medium is adequate. For example, air contains about 21 percent oxygen
and thus provides an oxygen partial pressure of about 0.21 ata at the surface. This is ample, but a drop to 0.14 ata causes the onset of hypoxic symptoms on the
surface. If the ppO2 goes as low as 0.11 ata at the surface, most individuals
become hypoxic to the point of being nearly helpless. Consciousness is usually
lost at about 0.10 ata and at much below this level, permanent brain damage and
death will probably occur. In diving, a lower percentage will suffice as long as the
total pressure is sufficient to maintain an adequate ppO2. For example, 5 percent
oxygen would render a ppO2 of 0.20 ata for a diver at 100 fsw. On ascent,
however, the diver would rapidly experience hypoxia if the oxygen percentage
were not increased.
Causes of Hypoxia:
The causes of hypoxia vary, but all interfere with the normal
oxygen supply to the body. For divers, interference of oxygen delivery can be
caused by:
1-Equipment problems such as low partial pressure of oxygen in the breathing
mix, inadequate gas flow, inadequate purging of breathing bags in a closed
oxygen UBA like the LAR V, or blockage of the fresh gas injection orifice in a
semiclosed-circuit UBA.
2-Blockage of all or part of the pulmonary system air passages by vomitus,
secretions, water, foreign objects, or pneumomediastinum.
3-Pneumothorax or paralysis of the respiratory muscles from spinal cord injury.
4-Decreased oxygen exchange at the alveoli/capillary membrane caused by
accumulation of fluid in the tissues (edema), a mismatch of blood flow and
alveolar ventilation, lung damage from near-drowning or smoke inhalation, or
“chokes” or bronchospasm from lung irritation due to showers of bubbles in
the circulation.
5-Physiological problems such as anemia and inadequate blood flow that
interfere with blood transportation of oxygen. Edema can interfere with gas
exchange at the capillary/tissue areas, and carbon monoxide poisoning can
interfere with oxygen utilization at the cellular level.
6-Hyperventilation followed by breathholding, which can lead to severe
hypoxia. Hyperventilation lowers the carbon dioxide level in the body below
normal (a condition known as hypocapnia) and may prevent the control
mechanism that stimulates breathing from responding until oxygen tension has
fallen below the level necessary to maintain consciousness. Extended
breathholding after hyperventilation is not a safe procedure.
Symptoms of Hypoxia:
Brain tissue is by far the most susceptible to the effects of
hypoxia. Unconsciousness and death can occur from brain hypoxia before the
effects on other tissues become very prominent.
There is no reliable warning of the onset of hypoxia. It can occur unexpectedly,
making it a particularly serious hazard. A diver who loses his air supply is in danger of hypoxia, but he immediately knows he is in danger and usually has time
to do something about it. He is much more fortunate than a diver who gradually
uses up the oxygen in a closed-circuit rebreathing rig and has no warning of
impending unconsciousness.
When hypoxia develops, pulse rate and blood pressure increase as the body tries to
offset the hypoxia by circulating more blood. A small increase in breathing may
also occur. A general blueness (cyanosis) of the lips, nail beds and skin may occur
with hypoxia. This may not be noticed by the diver and often is not a reliable indicator
of hypoxia, even for the trained observer at the surface. The same signs
could be caused by prolonged exposure to cold water.
If hypoxia develops gradually, symptoms of interference with brain function will
appear. None of these symptoms, however, are sufficient warning and very few
people are able to recognize the mental effects of hypoxia in time to take corrective
action.
Symptoms of hypoxia include:
1-Lack of concentration
2-Lack of muscle control
3-Inability to perform delicate or skill-requiring tasks
4-Drowsiness
5-Weakness
6-Agitation
7-Euphoria
8-Loss of consciousness
Treating Hypoxia.
A diver suffering from severe hypoxia must be rescued
promptly. Hypoxia’s interference with brain functions produces not only unconsciousness
but also failure of the breathing control centers. If a victim of hypoxia
is given gas with adequate oxygen content before his breathing stops, he usually
regains consciousness shortly and recovers completely. For scuba divers, this
usually involves bringing the diver to the surface. For surface-supplied mixed-gas
divers, it involves shifting the gas supply to alternative banks and ventilating the
helmet or chamber with the new gas.
Preventing Hypoxia.
Because of its insidious nature and potentially fatal
outcome, preventing hypoxia is essential. In open-circuit scuba and helmets,
hypoxia is unlikely unless the supply gas has too low an oxygen content. On
mixed-gas operations, strict attention must be paid to gas analysis, cylinder
lineups and predive checkout procedures. In closed- and semiclosed-circuit
Underwater Breathing Apparatus (UBA), a malfunction can cause hypoxia even
though the proper gases are being used. Electronically controlled, fully closedcircuit
UBA like the MK 16 have oxygen sensors to read out oxygen partial pressure,
but divers must be constantly alert to the possibility of hypoxia from UBA
malfunction. Oxygen sensors should be monitored closely throughout the dive
in closed-circuit mixed gas.Recently surfaced
mixed-gas chambers should not be entered until after they are thoroughly ventilated
with air.
Oxygen deficiency, or hypoxia, is an abnormal
deficiency of oxygen in the arterial blood that causes the tissue cells to be unable
to receive sufficient oxygen to maintain normal function. Severe hypoxia will stop
the normal function of any tissue cell in the body and will eventually kill it, but the
cells of the brain tissue are by far the most susceptible to its effects.
The partial pressure of oxygen determines whether the amount of oxygen in a
breathing medium is adequate. For example, air contains about 21 percent oxygen
and thus provides an oxygen partial pressure of about 0.21 ata at the surface. This is ample, but a drop to 0.14 ata causes the onset of hypoxic symptoms on the
surface. If the ppO2 goes as low as 0.11 ata at the surface, most individuals
become hypoxic to the point of being nearly helpless. Consciousness is usually
lost at about 0.10 ata and at much below this level, permanent brain damage and
death will probably occur. In diving, a lower percentage will suffice as long as the
total pressure is sufficient to maintain an adequate ppO2. For example, 5 percent
oxygen would render a ppO2 of 0.20 ata for a diver at 100 fsw. On ascent,
however, the diver would rapidly experience hypoxia if the oxygen percentage
were not increased.
Causes of Hypoxia:
The causes of hypoxia vary, but all interfere with the normal
oxygen supply to the body. For divers, interference of oxygen delivery can be
caused by:
1-Equipment problems such as low partial pressure of oxygen in the breathing
mix, inadequate gas flow, inadequate purging of breathing bags in a closed
oxygen UBA like the LAR V, or blockage of the fresh gas injection orifice in a
semiclosed-circuit UBA.
2-Blockage of all or part of the pulmonary system air passages by vomitus,
secretions, water, foreign objects, or pneumomediastinum.
3-Pneumothorax or paralysis of the respiratory muscles from spinal cord injury.
4-Decreased oxygen exchange at the alveoli/capillary membrane caused by
accumulation of fluid in the tissues (edema), a mismatch of blood flow and
alveolar ventilation, lung damage from near-drowning or smoke inhalation, or
“chokes” or bronchospasm from lung irritation due to showers of bubbles in
the circulation.
5-Physiological problems such as anemia and inadequate blood flow that
interfere with blood transportation of oxygen. Edema can interfere with gas
exchange at the capillary/tissue areas, and carbon monoxide poisoning can
interfere with oxygen utilization at the cellular level.
6-Hyperventilation followed by breathholding, which can lead to severe
hypoxia. Hyperventilation lowers the carbon dioxide level in the body below
normal (a condition known as hypocapnia) and may prevent the control
mechanism that stimulates breathing from responding until oxygen tension has
fallen below the level necessary to maintain consciousness. Extended
breathholding after hyperventilation is not a safe procedure.
Symptoms of Hypoxia:
Brain tissue is by far the most susceptible to the effects of
hypoxia. Unconsciousness and death can occur from brain hypoxia before the
effects on other tissues become very prominent.
There is no reliable warning of the onset of hypoxia. It can occur unexpectedly,
making it a particularly serious hazard. A diver who loses his air supply is in danger of hypoxia, but he immediately knows he is in danger and usually has time
to do something about it. He is much more fortunate than a diver who gradually
uses up the oxygen in a closed-circuit rebreathing rig and has no warning of
impending unconsciousness.
When hypoxia develops, pulse rate and blood pressure increase as the body tries to
offset the hypoxia by circulating more blood. A small increase in breathing may
also occur. A general blueness (cyanosis) of the lips, nail beds and skin may occur
with hypoxia. This may not be noticed by the diver and often is not a reliable indicator
of hypoxia, even for the trained observer at the surface. The same signs
could be caused by prolonged exposure to cold water.
If hypoxia develops gradually, symptoms of interference with brain function will
appear. None of these symptoms, however, are sufficient warning and very few
people are able to recognize the mental effects of hypoxia in time to take corrective
action.
Symptoms of hypoxia include:
1-Lack of concentration
2-Lack of muscle control
3-Inability to perform delicate or skill-requiring tasks
4-Drowsiness
5-Weakness
6-Agitation
7-Euphoria
8-Loss of consciousness
Treating Hypoxia.
A diver suffering from severe hypoxia must be rescued
promptly. Hypoxia’s interference with brain functions produces not only unconsciousness
but also failure of the breathing control centers. If a victim of hypoxia
is given gas with adequate oxygen content before his breathing stops, he usually
regains consciousness shortly and recovers completely. For scuba divers, this
usually involves bringing the diver to the surface. For surface-supplied mixed-gas
divers, it involves shifting the gas supply to alternative banks and ventilating the
helmet or chamber with the new gas.
Preventing Hypoxia.
Because of its insidious nature and potentially fatal
outcome, preventing hypoxia is essential. In open-circuit scuba and helmets,
hypoxia is unlikely unless the supply gas has too low an oxygen content. On
mixed-gas operations, strict attention must be paid to gas analysis, cylinder
lineups and predive checkout procedures. In closed- and semiclosed-circuit
Underwater Breathing Apparatus (UBA), a malfunction can cause hypoxia even
though the proper gases are being used. Electronically controlled, fully closedcircuit
UBA like the MK 16 have oxygen sensors to read out oxygen partial pressure,
but divers must be constantly alert to the possibility of hypoxia from UBA
malfunction. Oxygen sensors should be monitored closely throughout the dive
in closed-circuit mixed gas.Recently surfaced
mixed-gas chambers should not be entered until after they are thoroughly ventilated
with air.
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آخرین ویرایش: شنبه 5 تیر 1389 11:47 ق.ظ
