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INDEPENDENT AND COMBINED EFFECTS OF HEAT STRESS AND EXERCISE ON ARTERIAL STIFFNESS

Abstract

Aaron R. Caldwell, Forrest B. Robinson, Matthew A. Tucker, Cash H. Arcement, Cory L. Butts, Brendon P. McDermott, & Matthew S. Ganio FACSM, University of Arkansas, Fayetteville, Arkansas

Many studies have established that arterial stiffness, assessed via pulse wave velocity (PWV), is reduced following passive heat stress or exercise. Yet, no study to date has simultaneously investigated the cumulative effects of exercise and heat stress on measures of PWV. PURPOSE: Determine the independent and combined effects of heat and exercise on arterial stiffness. METHODS: Nine subjects (n=3 females, 46±11 years old; 24.1±2.8 kg/m2) completed four trials, with different interventions, in a randomized order. In a control trial subjects rested supine (CON). In order to independently test the effect of heat stress, subjects were passively heated (i.e. no exercise) in a hot environment (~40ºC) while wearing a water perfusion suit with hot water (PH). In two other trials, subjects cycled at ~50% of VO2peak in a hot (~40ºC; HC) or cool (~15ºC; CC) environment. Prior to interventions and in the hour following interventions, pulse wave velocity (PWV), via Doppler ultrasound, was assessed at the tibial, radial, femoral and carotid artery sites. Central PWV (CPWV) was assessed using measures between the carotid/femoral artery sites, while peripheral stiffness was assessed using the radial/carotid (UPWV), and tibial/femoral (LPWV) artery sites. Mean body temperature (TB) was measured with skin and rectal thermistors RESULTS: No significant changes in TB were observed during the CON and CC trials. However, the PH and HC trials elevated TB 2.69±0.23ºC and 1.67±0.27ºC, respectively (p<0.01). No changes in any measure of PWV were observed in the CON, CC, or HC trials (p>0.05). However, in the PH trial UPWV, but not CPWV or LPWV, was reduced immediate post (-107±81 cm/s) and 15 minutes (-93±82 cm/s) post heating (p<0.05). CONCLUSION: Contrary to previous data, we did not observe changes in arterial stiffness during aerobic exercise (i.e., CC). Further, although heat stress alone reduced arterial stiffness (specific to the upper peripheral arteries), when combined with exercise in the heat, there was no change in arterial stiffness (i.e., HC). This suggests that heat stress has an independent effect on arterial stiffness that is obliterated when combined with exercise.

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