Browsing by Subject "Cardiovascular responses"

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Influences of skin and core temperature on cardiovascular responses during exercise
(2010-08) Lee, Joshua Floyd; Coyle, Edward F., 1952-; Tanaka, Hirofumi
The cardiovascular effects of whole body heat stress during exercise are well established. However the independent contribution of elevated skin temperature (Tsk) or core temperature (Tc) on these responses remains unclear. The purpose of this study was to determine how increases in Tsk and Tc alone and in combination, impact cardiovascular responses during moderate intensity exercise. To accomplish this goal, eight healthy, recreationally active males were immersed to the neck in a cold (14 - 17°C) or hot (40 - 42.5°C) water bath for 20 to 25 min to alter Tc immediately prior to exercise with either cool Tsk (i.e. fans) or warm Tsk (i.e. heaters). Conditions during exercise were cool skin and cool core (CC), warm skin and cool core (WC), cool skin and warm core (CW), and warm skin and warm core (WW), and were conducted in a randomized crossover design. When data was combined (n=16), warm core conditions (CW and WW) were associated with significantly higher average heart rate (HR) and lower stroke volume (SV) during exercise compared to cool core conditions (CC and WC); 168.1 ± 3.2 vs. 152.2 ± 4.0 beats/min and 139.2 ± 7.3 vs. 147.7 ± 9.4 mL/beat, respectively. The approximate 9 mL/beat decline in SV and 16 beat/min increase in HR in warm core conditions tended to increase cardiac output (Q), 23.2 ± 0.6 vs. 22.2 ± 0.7 L/min, P=0.078. Similarly, warm Tsk conditions (WC and WW) were associated with significantly higher average HR and lower SV during exercise compared to cool Tsk conditions (CC and CW); 165.2 ± 3.3 vs. 155.1 ± 3.4 beats/min and 140.8 ± 7.8 vs. 146.0 ± 8.7 mL/beat, respectively. Additionally, there was also a trend for Q to be elevated with warm skin (23.0 ± 0.6 vs. 22.4 ± 0.6, P=0.075). Although combined data indicated that warm Tsk conditions significantly lowered average SV by ~6 mL/beat, there was no reduction in SV during exercise by warm Tsk, when Tes was cool (i.e. <37.0°C), as evidenced by identical values for SV in CC and WC, 147.7 ± 9.8 vs. 147.7 ± 9.0 mL/beat, respectively. In contrast, SV was significantly lower in WW compared with CW, 133.9 ± 7.0 vs. 144.4 ± 7.8 mL/beat, respectively. Therefore, the major reduction in SV by warm Tsk occurred during WW, when Tes was elevated (i.e. >38.0°C). Analyzing data independently for precooling and preheating conditions revealed that warm Tsk was associated with greater HR drift from 5 to 20 min of exercise, compared to cool Tsk, when esophageal temperature (Tes) was both cool or warm (23.9 ± 2.2 vs. 17.5 ± 2.3 and 12.3 ± 1.3 vs. 4.6 ± 1.7 beats/min, respectively). These observations demonstrate that both Tes and Tsk can directly influence cardiovascular responses during exercise, as indicated by elevations in HR during exercise with warm Tsk, with both warm and cool Tes. However SV is not compromised by warm Tsk if Tes is below 37.5°C. Furthermore, when both Tes and Tsk are elevated simultaneously, cardiovascular strain (i.e. increased HR and reduced SV) is much greater than when either is elevated alone. This is demonstrated by the finding that average HR was 175.8 ± 3.2 beats/min in WW, compared to 149.8 ± 4.0, 154.7 ± 4.1, and 160.3 ± 3.5 beats/min, in CC, WC, and CW, respectively, and the fact that SV was lowest during exercise in WW. In conclusion, individuals exercising in the heat should take measures to keep skin cool, especially when Tes is 39°C or greater to attenuate the cardiovascular strain that occurs with warm Tsk, when Tes is elevated.
The effect of skin temperature on cardiovascular responses during endurance exercise
(2017-08) Chou, Ting-Heng, Ph. D.; Coyle, Edward F., 1952-; Tanaka, Hirofumi; Stone, Audrey J; Diller, Kenneth R
These studies investigated the effect of whole body skin temperature (T [subscript sk]) on cardiovascular responses and the independent effect of heart rate on stroke volume when Tsk is hot and cold during moderate intensity endurance exercise. In study 1, we systemically evaluated the effect of graded increases in T [subscript sk] from 32°C to 39°C on cardiovascular responses during 20-30 min cycling exercise at 63% VO₂ [subscript peak]. Tsk was manipulated by wearing a water perfused suit that covered most of the body and maintained a perfused water temperature of either 20, 30, 40, and 50°C. Tsk was significantly different between each trial and averaged 32.4 ± 0.2, 35.5 ± 0.1, 37.5 ± 0.1, and 39.5 ± 0.1°C, respectively. Incremental increasing Tsk resulted in a graded increase in heart rate (HR) and a graded decrease in stroke volume (SV). Cutaneous blood flow (CBF) reached a similar average plateau value in all trials when T [sunscript c] was above ~38°C, independent of Tsk. Tsk had no apparent effects on the forearm venous volume (FVV) responses. Study 2 investigated the independent effect of increasing HR on SV by using low dose β1-blockade (βB) during exercise when Tsk was 38°C. How the rapid cooling of Tsk reverses the cardiovascular variables was also tested. When HR was lowered to the control trial level by βB when Tsk was 38°C, SV was also restored to the control even with a significantly higher CBF and cutaneous vascular conductance (CVC) and lower MAP. When Tsk was rapidly cooled at min 20 when Tsk was 38°C, CO, HR, and CBF significantly decreased while SV did not change. Taken together, our data suggest that there was no further pooling of blood in the skin when Tsk is increased from 32 to 39°C. The decrease in SV during exercise when heating the skin to high levels appears related to an increase in HR and not an increase in CBF. The restoration of SV by lowing HR even with higher CBF and CVC and lower MAP demonstrated that the increase in HR was responsible for the decrease in SV during moderate exercise when Tsk was held at 38°C.