Extreme diving parameters and breathing mixtures
Record-breaking world achievements in underwater diving clearly demonstrate the striking adaptive reserves of the human body. Human presence at an incredible depth of 500 meters has been officially documented. At this mark, the diver's body experiences a colossal hydrostatic pressure equal to 50 atmospheres. The duration of such an extreme stay underwater reached 15 days.
To ensure vital activity and survival under such harsh conditions, the use of ordinary compressed air is completely ruled out. Specialists use a special helium breathing mixture. The most important physiological characteristic of this mixture is its radically reduced oxygen content—its concentration is only 2 percent, which is dictated by the laws of changing gas properties under the high pressure of the water column.
Pulmonary barotrauma during ascent
The process of returning a diver to the surface harbors mortal dangers. The first of these is pulmonary barotrauma, an acute pathology directly related to changes in gas volume in a closed space.
The direct cause of this life-threatening condition is a gross error during ascent to the surface, specifically ascending with a closed glottis. The pathogenesis of barotrauma is based on fundamental laws of physics: as the diver ascends, the external hydrostatic pressure drops rapidly, and the gas trapped in the airways begins to expand proportionally. Critical lung distension occurs. The delicate lung tissue cannot withstand severe overstretching, which inevitably leads to physical rupture of the alveolar walls.
Caisson (decompression) sickness
The second, equally formidable pathology is caisson disease, also known in medicine as decompression sickness. Its etiology is completely unambiguous: it is the too rapid ascent of a diver from depth to the surface, i.e., rapid, uncontrolled decompression.
The pathogenesis of the disease is inextricably linked to the solubility of gases in liquid media. Under high pressure at depth, gases actively dissolve in the diver's blood and tissues. If the ambient pressure drops too sharply, the gases do not have time to be eliminated physiologically through the respiratory system and transition into a gaseous state directly inside the vascular bed, forming multiple bubbles.
- Oxygen and carbon dioxide ($CO_2$) are the least dangerous in this pathological process because they bind extremely quickly to blood components and surrounding tissues.
- Nitrogen poses the primary threat. Bubbles of free undissolved nitrogen are effortlessly carried by the bloodstream throughout the body and mechanically block the lumens of small blood vessels. Gas embolism develops—a severe, life-threatening condition.
The clinical picture of caisson disease depends on the localization of the bubbles and includes:
- Intense muscle pain.
- Pronounced dizziness and vomiting.
- Severe shortness of breath.
- Sudden loss of consciousness.
- In the most severe cases, damage to nerve tissue leads to irreversible paralysis.
Emergency care and aviation decompression sickness
A deep understanding of pathogenesis dictates the only effective emergency care algorithm for caisson disease. The key action is immediate therapeutic recompression. The victim is urgently placed in a hyperbaric chamber under an artificially created high pressure. It is important that this pressure strictly corresponds to the pressure at the depth from which the diver began their ascent. This procedure physically forces the deadly nitrogen bubbles to redissolve in the body's liquid media. Only after this is a very slow, controlled decompression performed.
Physiological laws of pressure change are relevant not only in the ocean but also high in the sky. Aviation decompression sickness has similar mechanisms of development. It can occur during sudden emergency depressurization of the pilot's cabin at significant altitudes—from 7,000 meters and above. The main preventive and rescue measure in such aviation incidents is the immediate use of oxygen masks.
Briefly: answers to topical questions
Why is the use of ordinary compressed air excluded during deep-sea dives?
The use of ordinary compressed air is excluded due to a sharp increase in the amount of gases dissolved in the blood and their toxic effect.
- Nitrogen—causes nitrogen narcosis (nitrogen saturation produces a narcotic effect, the so-called "rapture of the deep").
- Oxygen—breathing it is possible only up to 20 meters; at greater depth, its toxic effect manifests as muscle cramps.
To prevent these conditions at great depths, helium-oxygen mixtures are used, as helium is almost insoluble in blood.
What physical law describes the change in the solubility of gases in body fluids with changes in pressure?
The change in gas solubility is described by Henry-Dalton's law.
According to this law, the solubility of a gas in a liquid is proportional to the partial pressure of the gas above the liquid surface. The solubility of a gas mixture component depends not on the total pressure, but precisely on the partial pressure of the specific gas. Mathematically, the relationship is expressed by the formula $s_i = k_i \cdot p_i$, where $k_i$ is the solubility coefficient (Henry's constant).
What preventive measures for caisson disease are used during a routine ascent of a diver to the surface?
To prevent caisson disease during a diver's ascent, a special transition regimen from high pressure to normal pressure is used—slow decompression.
This is necessary because during rapid decompression, the gases dissolved in the blood and tissues do not have time to be eliminated and form bubbles, leading to gas embolism. For example, after 1 hour of work at a depth of 160 m, the return journey—decompression in a hyperbaric chamber—takes 3 days.
To remember the role of gases: Nitrogen is Aggressive (forms bubbles and embolism), Oxygen is Comfortable (quickly binds to tissues).
Class and exam questions
Why is nitrogen the main hazard during rapid decompression?
Unlike oxygen and $CO_2$, which bind rapidly to blood and tissues, nitrogen does not have time to be eliminated during rapid ascent and forms bubbles that cause fatal gas embolism of small vessels.
What is the principle of treatment for caisson disease?
The basis of treatment is immediate recompression. The patient is placed under high pressure corresponding to the start of the ascent to dissolve the nitrogen bubbles, after which slow decompression is performed.
What else to study on this topic
- Mechanisms of oxygen and carbon dioxide binding to tissues during pressure drops.
- Dependence of nitrogen solubility in blood on diving depth.
- Topography of gas embolism: how the localization of nitrogen bubbles affects the development of paralysis.
- Pathophysiology of mechanical alveolar rupture in pulmonary barotrauma.
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