When the atmospheric pressure is decreased it has the same effect on the individual that the breathing of rarefied or diluted air has. In this event the adaptation consists in an increased rate of breathing. It is also asserted that the number of red blood corpuscles is increased, which in turn increases the capacity of the blood to carry oxygen. In the diminished air pressure there is a marked decrease in the amount of oxygen absorption and this accounts for the increase in the respiration and quickened pulse rate.
As previously stated, if the change from a normal air pressure to a greatly decreased pressure takes place gradually, thus giving Innate sufficient time to bring about an adaptation, man will be enabled to live in a healthy state in a rarefied air. As the altitude is increased the air pressure is decreased. This is because there is less air above to exert pressure. Naturally the air near the earth has the greatest weight above it to exert compression. The air pressure decreases gradually until, it is assumed, it is gradually thinned into a perfect vacuum. If oxygen is added to the air it is possible to maintain life at a remarkably reduced air pressure. A bird was kept alive by P. Bert in oxygenated air at a pressure of 0.1 of an atmosphere.
The symptoms produced in diminished air pressure will vary with the general conditions of the individual. People suffering from cardiac disturbances will be affected most by high altitudes. This is possibly the first symptom to be manifested in rarefied air. If there is any inclination toward heart weakness it will be observed when the air pressure is decreased.
The effects of reduced air pressure will vary with circumstances. There will be increased and deep breathing, with an increase in the pulse rate. There is likely to be dizziness and ringing in the ears. The sense of hearing, of sight and possibly of sensations, become impaired. There may be drowsiness and the patient may have a strong desire to sleep. The intellectual faculties become dull. Where the change has taken place very suddenly to the decreased air pressure there will be syncope, dyspnea, dizziness, nausea and weakness. These symptoms are commonly known as mountain sickness.
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.