Circulatory response to submaximal and maximal exercise after thermal dehydration

Abstract

Data on cardiac output and stroke volume are given for four subjects at various levels of muscular work up to the individual's maximum. No significant difference was found between the dye-dilution and the acetylene methods. Three subjects were studied under normal conditions and after dehydration (exposure to heat with a reduction in body weight of up to 5.2%); circulatory data were measured at rest and during exercise at two submaximal and one maximal work load. The decrease in body weight was accompanied by a reduction in plasma volume of up to 25%. After dehydration, the major change in the hemodynamic response to work in a sitting position at the submaximal loads was a decrease in stroke volume and an associated increase in heart rate, so that the cardiac output remained almost unaltered. Both these changes were significantly correlated to the reduction in body weight and plasma volume. When after dehydration the submaximal work load was performed in a supine position, no increase in heart rate was noticed compared with that before dehydration. Dehydration produced no significant change in oxygen uptake, cardiac output, or stroke volume during maximal exercise in a sitting position. However, the maximal work time was much shorter and there was a marked decrease in maximal blood lactate. comparison dye-dilution-acetylene methods; plasma volume; lactic acid Submitted on August 12, 1963