Fundamentals Of Physiology

The human body is essentially composed of liquids, solids, and natural air spaces. All of these components are of vital interest to us as divers, for although they are subjected to the same pressures, they react differently and introduce special problems by the very nature of their physical make up.

Generally speaking, the liquids and solids that in part make up the human body are incompressible, while the natural air spaces of the body are filled with air, a gas that is compressible, and therefore of special interest to the diver.
The natural air spaces within the human body consist of the sinuses, the middle ear, the entire respiratory tract, and the digestive tract. All of these natural air spaces connect to the main respiratory tract by passages of varying size.

Physiology Of Respiration

The respiratory system of a human being is a complex and intricate system. However, that part of the respiratory system of interest to the diver when viewed as a diver rather than as a physiologist, is emminently simple. The diver must first picture the respiratory system as an inverted tree in his body. The main trunk would represent the trachea or windpipe. Picture the trunk forking to the right and left, each fork representing the Bronchi, or bronchial tubes, and then each of these branches branding out into innumerable tiny twigs, terminating in leaves which would represent the alveoli, or air sacs of the lungs. Encase the branches, or bronchi, in a flexible bag containing the twigs and leaves, to represent the lung walls, then enclose the whole in another bag to represent the pleural membrane and you are visualizing a very simplified version of the respiratory system.

Physiology Of Circulation

To picture the circulatory system in a simplified manner, first consider the heart as a double acting pump. Blood is pumped from the pressure side of the heart out through the main arterial blood vessel, the main aorta. From here the blood vessels, or arteries branch and rebranch, divide and subdivide, until they feed each and every cell in the body through minute blood vessels called capillaries. Returning from each cell is another capillary, which feeds into a larger blood vessel, and even larger until the blood returns to the heart and travels to the lungs where again, minute capillaries virtually cover the walls of the alveoli, or air sacs, and then return through ever increasing sized blood vessels to the heart; thus completing the circulatory cycle.

What has taken place while this cycle has been completed is that the blood, carrying a high concentration of oxygen which it absorbed while passing next to the air sacs, or alveoli, flowed to the tissues and cells and supplied them with oxygen, which they must have to function. However, these same cells gave off an exhaust gas, carbon dioxide, which is a waste product of living tissue. This exhaust gas was then carried to the air sacs via the return side of the heart where it eliminated the carbon dioxide into these air sacs and replaced it with oxygen rich air. This oxygenated blood then returns to the pressure side of the heart and the cycle is again repeated.
If for any reason this cycle is broken anywhere, it has very serious implications, for it will mean that somewhere along the system some cells are not receiving an oxygen supply, without which they cannot live.

It can readily be seen that these two systems (respiratory-circulatory) are dependent upon each other for normal function of the body. Therefore, any interruption of the respiratory system directly affects the circulatory system.

Hyperventilation

In normal respiration, a person uses about 2/3 of the total volume of his lungs. That is, the lower third of his lungs is very rarely ventilated. This volume, called the residual volume; has a heavy concentration of carbon dioxide. Now respiration is not normally a conscious effort, but is normally caused when the carbon dioxide level in the body reaches a certain point, at which time a nerve center in the floor of the lungs is stimulated and exhalation takes place.

HYPERVENTILLATION is the forced ventillation of the lungs, accomplished by deep inhalations and exhalations. What is actually accomplished is that the carbon dioxide level of the body is drastically reduced, with the residual volume now being filled witn air with a low carbon dioxide concentration.

The effect of this is to enable the individual to hold his breath for long periods of time; until, in fact, the carbon dioxide level of his body reaches the critical point where the diaphram is again stimulated. Unfortunately, however, after prolonged hyperventilla-tion, a person may hold his breath until he is suffering from anoxia, a lack of oxygen, before he feels the urge to breathe. A person suffering from anoxia enjoys a feeling of euphoria, or extreme well being, is cyan otic, which is a bluish gray color, and then loses consciousness. Once unconscious, his urge to breathe will cause him to die of drowning. The only warning a person receives that he has reached his maximum breathholding limit is the twitching of his diaphram. A determined person can ignore this tremor, shortly after which he may become anoxic.

If a diver is going to hyperventilate, he should stop upon the first sensations of giddiness or dizziness. He should also come to the surface at the first tremor of the diaphram.

Now that we have these basic facts in mind, let us delve a little deeper into the physics and physiology of diving.

HUMAN EAR

A. OUTER EAR
B. EARDRUM
C. MIDDLE EAR
D. EUSTACHIAN TUBE
E. INNER EAR

LUNG SQUEEZE

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