Relationship between thermoregulatory response and changes in cardiac time intervals during exercise

Abstract

This sω dy was oonducted to clarify the re且 ationship between skin blood f 璽 ow and sweating during exerdse ， and also to determine the relationship between those thermoregulatory respOnses and Changes in cardiac tirne intervals during exercise ． Six healthy rnales − perform 〔 虹 bicycle exercise at 4096 VO2 max for 40・ min at an ambient temperature of 28°C ( 50％ RH ) ． Physiological parameters including esophageal temperature ( Tes ) ， f sweati rate ( thsw ) ， forearm skin blood flow( LDF ) and cardiac time intervals were measured ． 1) Tes threshold for initiation of cutaneeus vasodilation was higher than that of sweating in each subject ． 2) 【hsw increased with Tes ， while the increase of LDF levded off at 38， 1°C as a breaking po 童 nt ( bp) ． 3 ) When Tes was between 37． 6 − 38． 1°C ， total electrornechanica 且systo苴 e ( QS2)shortened continuously ， but diastolic time ( DT ｝ remained constant ． When Tes was higher than 38． 1°C ， the rate of shortening of DT was larger than that of QS2 ， The pattern of change of 1eft ventricular ejection time ( LVET ) was similar to that of QS2 ． 4 ) The tmugll was formed in the ratio of QS2 to DT ( QS2 ／ DT ) at the bp． When Tes was higher than the bp， the rates of increase were slightly less in the ratio of preejection periOd to LVET ( PEP ／LVET ) and the ratio of electrical systo 且 e to QS2 ( QT ／QS2) ． From these findings ， the fo且 lowing conclusions were obtained ； Tes threshold of skin blood fiow is higher than that of sweating ． A bp is formed for skin blood flow bロt not sweating during exercise in a warm envirenment ． It is suggested that there is ainterrelationship between the control of skin blood fiow and the change ef cardiac function because the specific changes of cardiac interval time are at the bp of LDF ． Key words ： swea 血 9， skin b且 ood fiow， body temperature ， cardiac time interval