Effect of High Partial Pressures of Individual Gases on the Body

The individual gases to which a diver is exposed when breathing air are nitrogen, oxygen, and carbon dioxide; each of these at times can cause significant physiologic effects at high pressures.

Nitrogen Narcosis at High Nitrogen Pressures

About four fifths of the air is nitrogen. At sea-level pressure, the nitrogen has no significant effect on bodily function, but at high pressures it can cause varying degrees of narcosis. When the diver remains beneath the sea for an hour or more and is breathing compressed air, the depth at which the first symptoms of mild narcosis appear is about 120 feet. At this level the diver begins to exhibit

Figure 44-2

Effect of sea depth on pressure (top table) and on gas volume (bottom).

Effect of sea depth on pressure (top table) and on gas volume (bottom).

joviality and to lose many of his or her cares. At 150 to 200 feet, the diver becomes drowsy. At 200 to 250 feet, his or her strength wanes considerably, and the diver often becomes too clumsy to perform the work required. Beyond 250 feet (8.5 atmospheres pressure), the diver usually becomes almost useless as a result of nitrogen narcosis if he or she remains at these depths too long.

Nitrogen narcosis has characteristics similar to those of alcohol intoxication, and for this reason it has frequently been called "raptures of the depths." The mechanism of the narcotic effect is believed to be the same as that of most other gas anesthetics. That is, it dissolves in the fatty substances in neuronal membranes and, because of its physical effect on altering ionic conductance through the membranes, reduces neuronal excitability.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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