ABSTRACT
The cardiovascular system has been a major focus of interest in high-altitude physiology and medicine since it was first observed that symptoms in normal individuals at altitude were similar to those experienced by patients with circulatory insufficiency at sea level (1). Breathlessness, excessive fatigue, and tachycardia in healthy climbers during exertion or in patients with high-altitude illness at rest suggested a potential cardiovascular abnormality. Some of the key historical figures in hypoxia research-Douglas and Haldane on Pikes Peak; Barcroft in the Peruvian Andescreated an early controversy by making directionally opposite observations regarding an increase (2) or decrease (3) in cardiac output after acclimatization to altitude. Although the magnitude and temporal progression of this adaptation has been more precisely worked out over the past 50 years (4), controversy still exists regarding its mechanisms and physiological consequences.
