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. T HIS report is concerned primarily with attempts to measure the extent and adequacy of the response of the heart of man to the stress of chronic anoxia at high altitude. Although the native living at a high altitude undergoes considerable acclimatization by changes in his cardiovascular, respiratory, and hematologic systems," 2, 3 4 S the extent of adaptation by the heart in the resting condition and especially in the state of exercise has not been well defined or studied. Measurements of the effect of external work on dynamics of the heart have thus far been limited to determina-tions at sea level of cardiac output during heavy exercise6 7, 8, and of cardiac work during light exercise.'0' 11, 12, 13 In the present study comparisons were made of the response of the left ventricle of the native indigenous to high altitude and living at high altitude, with the response of the heart of the sea level dweller at sea level during exercise on a treadmill at equivalent and at an approximation to maximal levels of muscular work. Twentv-six male volunteeis were studied either at M.roioocha, Pe'u (elevation 14,900 feet), or at Lima, Peru (elevation 500 feet). Of the 17 subjects studied at high altitude, 11 w'ere natives of the region of Morococha who had not lived for any length of time at …