Acute cerebral edema occurs at high altitude due to
Correct Answer: All of the above
Description: Ans. d. (All of the above) (Ref. Guyton physiology 11th ed., 541)ACUTE MOUNTAIN SICKNESS AND HIGH-ALTITUDE CEREBRAL & PULMONARY EDEMAA small percentage of people who ascend rapidly to high altitudes become acutely sick and can die if not given oxygen or removed to a low altitude.The sickness begins from a few hours up to about 2 days after ascent.Two events frequently occur:# Acute cerebral edema- This is believed to result from -# Hypoxia > causing Local vasodilation of the cerebral blood vessels.# Dilation of the arterioles increases blood flow into the capillaries, thus increasing capillary pressure# Increase in capillary pressure in turn causes fluid to leak into the cerebral tissues.- The cerebral edema can then lead to severe disorientation and other effects related to cerebral dysfunction.# Acute pulmonary edema- The severe hypoxia causes the pulmonary arterioles to constrict potently, but the constriction is much greater in some parts of the lungs than in other parts, so that more and more of the pulmonary blood flow is forced through fewer and fewer still unconstricted pulmonary vessels.- The postulated result is that the capillary pressure in these areas of the lungs becomes especially high and local edema occurs.- Allowing the person to breathe oxygen usually reverses the process within hours.Educational Points:CHRONIC MOUNTAIN SICKNESSOccasionally, a person who remains at high altitude too long develops chronic mountain sickness, in which the following effects occur:1) The red cell mass and hematocrit become exceptionally high (*erythropoietin**hematocrit and Hb (chronic hypoxia)2) The pulmonary arterial pressure becomes elevated even more than the normal elevation that occurs during acclimatization,3) The right side of the heart becomes greatly enlarged (Chronic hypoxic pulmonary vasoconstriction results in RVH).4) The peripheral arterial pressure begins to fall,5) Congestive heart failure ensues, and6) Death often follows unless the person is removed to a lower altitude (atmospheric oxygen * Pao2* ventilation * Paco2)7) 2,3-BPG (binds to Hb so that Hb releases more O2).8) Cellular changes (*mitochondria).9) renal excretion of HCO3 - (e.g., can augment by use of acetazolamide) to compensate for the respiratory alkalosis.
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