Reduced physical work capacity at high altitude--a role for left ventricular dysfunction.

Physical work capacity is reduced in sea level residents--lowlanders (LL) as compared to high altitude residents--highlanders (HL). To determine possible etiologies, cardiac performance was studied in two groups of healthy male volunteers (13 LL and 11 HL) utilizing systolic time intervals during rest, submaximal and maximal exercise. The LL were studied at sea level and subsequently during 10 days of residence at an altitude of 3658 m. The HL were studied at high altitude alone. The LL were restudied 30-45 min after administration of intravenous furosemide at high altitude. Mean maximal oxygen uptake (VO2max) was reduced by 26% in the LL group at high altitude in comparison to sea level values and by 20% in relation to the HL group. Cardiac performance was estimated by the pre-ejection period/left ventricular ejection time ratio. This index was significantly increased in the LL group at high altitude in comparison to sea level values during submaximal and maximal exercise (P less than 0.01). Intravenous furosemide in the LL group increased the heart rate (P less than 0.05) at rest and during exercise but VO2max and cardiac performance were unchanged. It is hypothesized that reduced physical work capacity at high altitude in the LL group may be related to depression of cardiac performance in these subjects. Administration of intravenous furosemide did not influence cardiac performance in the LL group at high altitude.