Exercise and Cardiac Work Response at High Altitude

The response to treadmill exercise of the left ventricle of natives of the region of Morococha, Peru (elevation 14,900 feet), and of natives of the region of Lima, Peru (elevation 500 feet), was studied at the elevation where they had always lived. In both groups the external work of the left ventricle was effected by a combination of a large increase in cardiac output and a mild increase in systemic blood pressure. Stroke volume and stroke work were only mildly elevated since the heart rate was concurrently greatly increased. As a result, the increase in work of the left ventricle was largely accomplished by an increase in heart rate and to a lesser extent by an increase in stroke work. For comparable amounts of external work, the left ventricle of the native to high altitude and performing at high altitude responded with considerably greater effort than did the left ventricle of the native of low altitude performing at sea level. Some of the data may have approximated the maximum effort of which the normal left ventricle was capable.