TAILIEUCHUNG - Ebook Pocket companion to guyton and hall textbook of medical physiology (13/E): Part 2
(BQ) Part 2 book “Pocket companion to guyton and hall textbook of medical physiology” has contents: Aviation, space, and deep-sea diving physiology; the nervous system - general principles and sensory physiology; motor and integrative neurophysiology, gastrointestinal physiology, metabolism and temperature regulation, and other contents. | UNIT VIII Aviation, Space, and Deep-Sea Diving Physiology 44 Aviation, High Altitude, and Space Physiology, 321 45 Physiology of Deep-Sea Diving and Other Hyperbaric Conditions, 326 This page intentionally left blank CHAPTER 44 Aviation, High Altitude, and Space Physiology Aeronautical advancements have made it increasingly more important to understand the effects of altitude, low gas pressures, and other factors—such as acceleratory forces and weightlessness—on the human body. This chapter discusses each of these problems. EFFECTS OF LOW OXYGEN PRESSURE ON THE BODY (p. 561) A Decrease in Barometric Pressure Is the Basic Cause of High-Altitude Hypoxia. Note in Table 44–1 that as altitude increases, both barometric pressure and atmospheric partial pressure of oxygen (Po2) decrease proportionately. The reduction in alveolar Po2 is further reduced by carbon dioxide and water vapor. • Carbon dioxide. The alveolar partial pressure of carbon dioxide (Pco2) falls from a sea level value of 40 mm Hg to lower values as the altitude increases. In an acclimatized person with a fivefold increase in ventilation, the Pco2 can be as low as 7 mm Hg because of the increases in ventilation. • Water vapor pressure. In the alveoli, water vapor pressure remains at 47 mm Hg as long as the body temperature is normal, regardless of altitude. Carbon Dioxide and Water Vapor Pressure Reduce the Alveolar Oxygen Tension. The barometric pressure is 253 mm Hg at the top of 29,028-foot Mount Everest; 47 mm Hg must be water vapor, leaving 206 mm Hg for other gases. In an acclimatized person, 7 mm Hg of the 206 mm Hg must be carbon dioxide, leaving 199 mm Hg. If there were no use of oxygen by the body, one fifth of this 199 mm Hg would be oxygen and four fifths would be nitrogen, or the Po2 in the alveoli would be 40 mm Hg. However, some of this alveolar oxygen is normally absorbed by the blood, leaving an alveolar Po2 of about 35 mm Hg. Breathing Pure Oxygen Increases .
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