Date of Graduation

8-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Kinesiology (PhD)

Degree Level

Graduate

Department

Health, Human Performance and Recreation

Advisor/Mentor

Ganio, Matthew S.

Committee Member

Kavouras, Stavros A.

Second Committee Member

McDermott, Brendon P.

Third Committee Member

Turner, Ronna C.

Fourth Committee Member

Washington, Tyrone A.

Keywords

Social sciences; Biological sciences; Health and environmental sciences; Body temperature; Hydration; Skin blood flow; Sweating; Thermoregulation

Abstract

During heat stress the human body thermoregulates via cutaneous vasodilation and sweating. Hypohydration can impair thermoregulatory responses that stem from the central nervous system (CNS), but it is unknown if impairments also occur post-synaptically in the microcirculation. Moreover, obese individuals may have impaired thermoregulation, possibly due to microvascular dysfunction. Purpose: The purpose of these studies was two-fold: 1) to determine if obese (OB) individuals exhibit impairments in thermoregulatory responses during exercise heat-stress (centrally-mediated) and intradermal infusion of vasoactive substances (peripherally-mediated) versus non-obese (N-OB), and 2) to determine if hypohydration subsequently affects these thermoregulatory responses differently between groups. Methods: Twenty-one healthy, college-age males were classified as either N-OB (n = 11, body fat [BF]26%) and completed a comprehensive 2-day protocol. In a randomized, counter-balanced order, subjects performed 60 min of cycling in a hot environment while either euhydrated (EU) or hypohydrated (HY) (Study 1). Changes in rectal temperature (∆Trec), cutaneous vascular conductance (CVC), and local sweat rate (LSR) were recorded. Following exercise, subjects maintained a EU or HY condition and returned 24-h later to undergo cutaneous microdialysis (MDS) of the forearm (Study 2). Dose-response curves comparing CVC and LSR responses were compared while sub-cutaneously perfusing the endothelium-dependent vasodilator methacholine chloride (MCh) and the endothelium-independent vasodilator sodium nitroprusside (SNP). Results: In Study 1, compared to EU, HY increased end-exercise ∆Trec in N-OB (0.47 ± 0.37°C, p < 0.01) but did not in OB (-0.06 ± 0.29°C, p > 0.05). LSR and CVC were not different between groups or hydration condition (p > 0.05). In study 2, OB subjects had a higher Log EC50 versus N-OB for endothelium-independent CVC (-1.69 ± 0.17 vs. -2.13 ± 0.06 Log [SNP] M, p = 0.014) when EU. There were no differences between groups in endothelium-dependent CVC or LSR responses in either hydration condition (all p > 0.05). Conclusions: These data suggest that hydration status affects the core body temperature response differently in N-OB and OB males during exercise heat-stress. In addition, OB individuals appear to have impaired post-synaptic endothelium-independent CVC, but similar endothelium-dependent CVC and LSR versus N-OB.

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