Increased Air Pressure
The greatest air pressure in nature is at sea level. Even the increased pressure in the deepest mines is so slight that it has no physiological significance; hence man is exposed to increased air pressure only under artificial conditions. This subject will be referred to again under the head of Industrial Hygiene.
Some of the conditions under which man is exposed to increased air pressure are, for example, divers in diving bells and diving suits, and caisson workers. At a depth of ten meters of water the air in a diving bell is compressed to one-half its original bulk, and as a result the pressure of air is doubled. At thirty meters, or about 100 feet, the pressure is quadrupled, exposing the diver to four atmospheres or about sixty pounds per square inch.
The danger in increased air pressure is not in going from a normal pressure to a high pressure, nor does the danger come from the high pressure. The danger is not from the compression, but rather from the decompression. The individual must be brought from the increased air pressure to the normal air pressure very gradually, allowing Innate sufficient time to adapt the body to the normal pressure of fifteen pounds to the square inch. If this is done no great amount of harm will result, although there are some men who are not able to withstand these changes. This shows a lack of intellectual adaptation through the body on the part of its Innate. In an experiment P. Bert exposed dogs to an air pressure of ten atmospheres, or about 150 pounds to the square inch, and then released them very gradually, producing no ill effects.
When the air pressure is increased it results in an increase in the absorption of the gases of the atmosphere. There is an increased amount of oxygen taken up by the blood and the tissues absorb large amounts of nitrogen. When the pressure is released slowly these gases gradually escape from the lungs and no bubbles will be formed.
During compression the symptoms are not so severe as those during and after decompression. During compression the symptoms are a deepening but slowing of the respiration, a slowing of the pulse rate, and an interference in evaporation in the water vapor. The increased pressure on the ear drums will cause pain in the ears and sometimes the ear drums rupture. There may be an alteration in the voice, headache and dizziness. However, in a short time, intellectual adaptation takes place and equilibrium is established by the internal change and there is at least temporary relief from these symptoms.