ABSTRACT
Important changes in the cardiovascular system occur at high altitude. Cardiac output increases following acute exposure to high altitude, but in acclimatized lowlanders and high altitude natives, most measurements show the cardiac output for a given work rate is the same as at sea level. Nevertheless, because of the polycythemia, hemoglobin flow is increased. Heart rate for a given work rate is higher than at sea level, with the result that stroke volume is reduced at high altitude. However, this is not caused by a reduced myocardial contractility; on the contrary, this is preserved up to very high altitudes in normal subjects. Abnormal heart rhythms, such as premature ventricular or atrial contractions, are unusual despite the severe hypoxemia. However, sinus arrhythmia accompanying periodic breathing is very common at high altitude. Changes in systemic blood pressure are variable; several studies report an increase when lowlanders move to high altitude. However, in some instances patients with hypertension at sea level have developed a reduction in pressure on ascent to altitude. Pulmonary hypertension is striking at high altitude, in both newcomers and high altitude natives, particularly on exercise. Tibetans have smaller degrees of pulmonary hypertension than other highlanders. This is also the case in some
relieved by oxygen breathing when the exposure to high altitude is acute, but after a few days the response to oxygen is less because of vascular remodeling. Right ventricular hypertrophy and corresponding electrocardiographic changes are seen. Newborn infants sometimes develop right heart failure at high altitude and this also occurs in young soldiers stationed at extreme altitudes.
