Physical principles of diving
The environment in which diving and caisson operations are conducted dictates its own physical laws. As you descend, the pressure of the water column increases uniformly: every 10 meters of depth adds 1 atmosphere. For example, when diving to a mark of 90 meters, the external environmental pressure on the human body reaches an impressive 10 atmospheres.
Under these conditions, a person physically cannot breathe air under normal atmospheric pressure. Air or another gas mixture must be supplied under a pressure that strictly corresponds to the diver's current depth.
Influence of gases and the solubility problem
Changes in pressure directly affect how gases interact with the body's fluid media. When a person descends to great depths (exceeding 100 meters, which corresponds to a pressure of over 10 atmospheres), a serious physiological problem arises. Under these conditions, the amount of gases dissolved in the blood increases sharply.
This primarily concerns oxygen and nitrogen. Excessive dissolution of nitrogen in the blood leads to severe consequences—so-called nitrogen narcosis—making standard air unsuitable for deep-sea operations.
Artificial gas mixtures
To avoid nitrogen narcosis and ensure adequate breathing at great depths, physiology and diving practice employ special helium-oxygen mixtures.
- Helium. This inert gas is chosen as the base because it practically does not dissolve in human blood even under high pressure. This property reliably prevents the development of nitrogen narcosis.
- Oxygen. Its amount in the mixture is not constant. Oxygen is added in precisely the concentration required so that its partial pressure at the working depth exactly matches the partial pressure under normal surface conditions.
The use of pure oxygen for underwater breathing is strictly limited. Such practice is possible exclusively at shallow depths—up to 20 meters. If one descends deeper, the pure substance begins to exhibit pronounced toxic effects, clinically accompanied by severe muscle cramps.
Decompression rules
The process of returning a diver to the surface requires no less attention than the dive itself. The body requires a specific, strictly calculated regimen for the transition from high pressure to normal atmospheric pressure—decompression.
This process takes significant time so that the gases dissolved in the blood can safely leave the body without forming bubbles. A striking example: if a specialist spent just 1 hour working at a depth of 160 meters, their return journey to the surface, including the decompression process in a special hyperbaric chamber, will take 3 days.
Briefly: answers to topical questions
What is the pathogenesis of nitrogen narcosis (decompression sickness symptoms) during deep-sea dives?
The pathogenesis of nitrogen narcosis during deep-sea dives is associated with body saturation with nitrogen under hyperbaric conditions. When descending to great depths (>100 m, >10 atm), the amount of nitrogen dissolved in the blood increases sharply because gas solubility increases with pressure.
Main aspects of pathogenesis:
- nitrogen accumulation: nitrogen is an indifferent gas and is not metabolized by tissues during vital activity;
- nitrogen saturation during descent causes a narcotic effect described as "rapture of the deep".
What symptoms and syndromes characterize the toxic effect of pure oxygen at depths exceeding 20 meters?
The toxic effect of pure oxygen at depths greater than 20 m manifests as muscle cramps. The provided materials also indicate that oxygen toxicity can manifest as three pathological states—separately, sequentially, or in combination. Detailed symptoms and names of these states are not disclosed in the cited sources.
What is the mechanism of gas bubble formation in the blood when decompression schedules are violated?
The mechanism of gas bubble formation is due to the transition of blood gases (primarily nitrogen) into a gaseous state owing to a sharp drop in barometric pressure.
During a rapid ascent (violation of the decompression regimen), the following occurs:
- Excess dissolved gas does not have time to be safely eliminated via the lungs.
- Nitrogen is retained in tissues, especially in adipose tissue and the white matter of the brain.
- Gas solubility decreases, and they form bubbles (gas emboli) directly in the blood and tissues, leading to vascular occlusion.
Class and exam questions
At what rate does pressure increase when diving underwater?
External pressure increases by 1 atmosphere for every 10 meters of depth. For example, at a depth of 90 meters, it will be about 10 atmospheres.
Why is ordinary air unusable at depths greater than 100 meters?
At pressures exceeding 10 atmospheres, the solubility of gases in the blood increases sharply. An excess of dissolved nitrogen causes severe nitrogen narcosis.
At what depths is breathing pure oxygen permissible?
Breathing pure oxygen is safe only at depths up to 20 meters. At greater depths, it exerts a toxic effect, causing muscle cramps.
Why is helium introduced into breathing mixtures?
Helium is used for deep-sea dives because it practically does not dissolve in the blood. This completely prevents the risk of nitrogen narcosis.
What else to study on this topic
- Mechanisms of gas solubility in body fluids under pressure changes
- Pathophysiological foundations of nitrogen narcosis
- Toxic effects of high oxygen concentrations on the nervous system
- Principles of calculating gas partial pressures for breathing mixtures
- Physiological processes during decompression in a hyperbaric chamber
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