Date of Graduation

5-2016

Document Type

Thesis

Degree Name

Bachelor of Science

Degree Level

Undergraduate

Department

Health, Human Performance and Recreation

Advisor

Ganio, Matthew

Reader

Kavouras, Stavros

Second Reader

Washington, Tyrone

Abstract

Context: Cardiovascular disease (CVD) is one of the leading causes of mortality in the United States, accounting for about 1 in every 3 deaths annually. While studies have shown that arterial stiffness, a leading precursor to CVD, improves with passive heat stress not much is known about the independent effect of heat stress during exercise on arterial stiffness. Objective: The objective of this study was to examine the independent effect of heat stress during exercise on arterial stiffness. Design: Participants visited the lab three times; one familiarization and two experimental trials. Experimental trials were randomized and counter-balanced. Setting: All trials occurred in the Human Performance Laboratory at the University of Arkansas, Fayetteville. The experimental trials consisted of subjects cycling at ~50% of their maximum aerobic capacity in an environment of 40°C / 40% relative humidity (Heat Cycle) or 15°C / 30% relative humidity (Cool Cycle). Participants: Participants included five male subjects and four female subjects. Subjects were older individuals (Age = 49 ± 12 y, Body Mass = 66.71 ± 12.64 kg) with stiffer arteries at baseline (> 6 m/s) identified in the familiarization trial. Interventions: The intervention was environmental condition; one trial occurred at 40°C / 40% relative humidity (Heat Cycle) and the other at 15°C / 30% relative humidity (Cool Cycle). Since the participants are exercising in both trials at the same aerobic capacity, we can elucidate the independent effect that mean body temperature (i.e., heat stress) had on arterial stiffness during exercise. Main Outcome Measures: Before and after cycling, pulse wave velocity (PWV measures occurred via ultrasound at the tibial, radial, femoral and carotid artery sites) were used to assess arterial stiffness. Specifically, central arterial stiffness was assessed by using measures between the carotid and femoral artery sites, while peripheral stiffness was assessed using the radial and tibial artery sites. At the same time, mean body temperature (Tbody) was measured via skin and rectal thermistors. Results: Tbody at the end of exercise showed significant differences between the heat cycle and cool cycle trials respectively (36.47 ± 0.23 vs. 34.84 ± 0.40°C). There were no interactions between time and condition for central PWV for Heat Cycle and Cool Cycle respectively (100.02 ± 138.64 vs. 24.19 ± 82.40 cm/s, p = 0.38), upper peripheral PWV (47.76 ± 131.35 vs. 64.41 ± 109.99 cm/s, p = 0.56) and lower peripheral PWV (40.77 ± 142.96 vs. 3.77 ± 167.67 cm/s, p = 0.47). Conclusions: The findings of this study suggest that differences in mean body temperature do not result in significant differences in arterial stiffness following exercise.

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