Acute Mountain Sickness and High-Altitude Pulmonary Edema
A 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 sick-ness begins from a few hours up to about 2 days after ascent. Two events frequently occur:
1.Acute cerebral edema. This is believed to resultfrom local vasodilation of the cerebral blood vessels, caused by the hypoxia. Dilation of the arterioles increases blood flow into the capillaries, thus increasing capillary pressure, which 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.
2.Acute pulmonary edema. The cause of this is stillunknown, but a suggested answer is the following: 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.
Extension of the process to progressively more areas of the lungs leads to spreading pulmonary edema and severe pulmonary dysfunction that can be lethal. Allowing the person to breathe oxygen usually reverses the process within hours.