Chronic Mountain Sickness
Occasionally, 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, (2) the pul-monary arterial pressure becomes elevated even more than the normal elevation that occurs during acclima-tization, (3) the right side of the heart becomes greatly enlarged, (4) the peripheral arterial pressure begins to fall, (5) congestive heart failure ensues, and (6) death often follows unless the person is removed to a lower altitude.
The causes of this sequence of events are probably threefold: First, the red cell mass becomes so great that the blood viscosity increases severalfold; this increased viscosity tends to decrease tissue blood flow so that oxygen delivery also begins to decrease. Second, the pulmonary arterioles become vasoconstricted because of the lung hypoxia. This results from the hypoxic vascular constrictor effect that normally operates to divert blood flow from low-oxygen to high-oxygen alveoli. But because all the alveoli are now in the low-oxygen state, all the arteri-oles become constricted, the pulmonary arterial pres-sure rises excessively, and the right side of the heart fails. Third, the alveolar arteriolar spasm diverts much of the blood flow through nonalveolar pulmonary vessels, thus causing an excess of pulmonary shunt blood flow where the blood is poorly oxygenated; this further compounds the problem. Most of these people recover within days or weeks when they are moved to a lower altitude.