Cardiovascular Responses to Exercise When Increasing Skin Temperature with Narrowing of the Core-to-Skin Temperature Gradient

• Published in: Journal of applied physiology (1985) Vol. 125; no. 3; pp. 697 - 705
• Main Authors: Chou, Ting-Heng, Allen, Jakob R, Hahn, Dongwoo, Leary, Brian K, Coyle, Edward F
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.09.2018
• Subjects: Blood flow; Cardiovascular disease; Cardiovascular system; Cerebral blood flow; Esophagus; Exercise; Forearm; Heart rate; Heating; Oxygen; Oxygen consumption; Physical training; Skin; Skin temperature; Stroke; Stroke volume; Temperature; Temperature effects; Temperature gradients; cutaneous (skin) blood flow; heart rate; hyperthermia; cardiovascular drift; stroke volume
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00965.2017

The decline in stroke volume (SV) during exercise in the heat has been attributed to either an increase in cutaneous blood flow (CBF) that reduces venous return or an increase in heart rate (HR) that reduces cardiac filling time. However, the evidence supporting each mechanism arises under experimental conditions with different skin temperatures (T ) (e.g.; {greater than or equal to}38{degree sign}C vs. {less than or equal to}36{degree sign}C respectively). We systematically studied cardiovascular responses to progressively increased T (32{degree sign}C to 39{degree sign}C) with narrowing of the core-to-skin gradient during moderate intensity exercise. Eight men cycled at 63 {plus minus} 1% VO for 20-30 min. T was manipulated by wearing a water-perfused suit that covered most of the body and maintained T that was significantly different between trials and averaged 32.4 {plus minus} 0.2, 35.5 {plus minus} 0.1, 37.5 {plus minus} 0.1, and 39.5 {plus minus} 0.1{degree sign}C, respectively. The graded heating of T ultimately produced a graded elevation of esophageal temperature (T ) at the end of exercise. Incrementally increasing T resulted in a graded increase in HR and a graded decrease in SV. CBF reached a similar average plateau value in all trials when T was above ~38{degree sign}C, independent of T . T had no apparent effect on forearm venous volume (FVV). In conclusion, the CBF and FVV responses suggest no further pooling of blood in the skin when T is increased from 32.4 to 39.5{degree sign}C. The decrease in SV during moderate intensity exercise when heating the skin to high levels appears related to an increase in HR and not an increase in CBF.