The amount of nitrogen dissolved in the plasma as the diver ascends to sea level decreases, as a result of the progressive decrease in the Pn2. If the diver surfaces slowly, a large amount of nitrogen can diffuse through the alveoli and be eliminated in the expired breath. If decompression occurs too rapidly, however, bubbles of nitrogen gas (N2) can form in the tissue fluids and enter the blood. This process is analogous to the formation of carbon dioxide bubbles in a champagne bottle when the cork is removed. The bubbles of N2 gas in the blood can block small blood channels, producing muscle and joint pain as well as more serious damage. These effects are known as decompression sickness, commonly called "the bends." The primary treatment for decompression sickness is hyperbaric oxygen treatment.
Airplanes that fly long distances at high altitudes (30,000 to 40,000 ft) have pressurized cabins so that the passengers and crew do not experience the very low atmospheric pressures of these altitudes. If a cabin were to become rapidly depressurized at high altitude, much less nitrogen could remain dissolved at the greatly lowered pressure. People in this situation, like the divers that ascend too rapidly, would thus experience decompression sickness.
Test Yourself Before You Continue
1. Explain how the Po2 of air is calculated and how this value is affected by altitude, diving, and water vapor pressure.
2. Explain how blood Po measurements are taken and discuss the physiological and clinical significance of these measurements.
3. Explain how the arterial PO2 and the oxygen content of whole blood are affected by (a) hyperventilation, (b) breathing from a tank containing 100% oxygen, (c) anemia (low red blood cell count and hemoglobin concentration), and (d) high altitude.
4. Describe the ventilation/perfusion ratios of the lungs and explain why systemic arterial blood has a slightly lower Po than alveolar air.
5. Explain how decompression sickness is produced in divers who ascend too rapidly.
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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.