Abstract

This study was conducted to clarify the relationship between skin blood flow and sweating during exercise, and also to determine the relationship between those thermoregulatory responses and changes in cardiac time intervals during exercise. Six healthy males performed bicycle exercise at 40 VO2max for 40 min at an ambient temperature of 28 deg C (50 RH). Physiological parameters including esophageal temperature (Tes), forearm sweating rate (msw), forearm skin blood flow (LDF) and cardiac time intervals were measured. msw increased with Tes, while the increase of LDF leveled off at 38.1 deg C as a breaking point (bp). When Tes was between 37.6-38.1 deg C, total electromechanical systole (QS2) shortened continuously, but diastolic time (DT) remained constant. When Tes was higher than 38.1 deg C, the rate of shortening of DT was larger than that of QS2. The pattern of change of left ventricular ejection time was similar to that of QS2. The trough was formed in the ratio QS2/DT at the bp. When Tes was higher than bp, the rates of increase were slightly less in the ratio of pre-ejection period to LVET and the ratio of electrical systole to QS2. The following conclusions were drawn: Tes threshold of skin blood flow is higher than that of sweating. A bp is formed for skin blood flow but not sweating during exercise in warm environment. It is suggested that there is an interrelationship between control of skin blood flow and change of cardiac function because the specific changes of cardiac interval time are at the bp of LDF. Verf.-Ref.