Author(s): BELLINI, D., LLOYD, A., HAVENITH, G., LEICHT, C.A., BAILEY, S.J., ROBERTSON, A., MALEY, M., Institution: LOUGHBOROUGH UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 823

INTRODUCTION:
Impaired microvascular function in individuals of Black-African (BA) and South-Asian (SA) descent compared to White-Europeans (WE) suggests greater endothelial dysfunction, contributing to an increased risk of cardiovascular disease (CVD). The associated reduction in CVD risk from chronic passive heating (e.g., hot baths or sauna bathing) has been suggested to be underpinned by the repeated strain from acute exposures. Therefore, we investigated the effect of acute hot water immersion (HWI) on blood pressure and microvascular responses compared to a thermoneutral control (CON) between BA, SA, and WE individuals.
METHODS:
Thirty-one recreationally active males (10 BA, 11 SA, 10 WE) completed a submaximal cycling test to determine VO2peak. Thereafter, two experimental visits of HWI (39.0°C) or CON (36.0°C) were completed, involving 30-minutes of shoulder-height, then 30-minutes of waist-height immersion. Venous blood samples were collected immediately pre- and post-immersion, and blood pressure was assessed throughout immersion. Following an additional 60-minutes of seated thermoneutral rest, forearm and toe cutaneous vascular conductance (CVC) responses to occlusion (OC) and local heating (LH) were investigated.
RESULTS:
After both immersion protocols, baseline CVC was similar between racial groups. During OC, peak forearm CVC was lower in BA (0.51 ± 0.21 flux/mmHg) than SA (0.87 ± 0.21 flux/mmHg) and WE (0.85 ± 0.21 flux/mmHg; p < 0.001). Peak toe CVC was also lower in BA (2.46 ± 0.74 flux/mmHg) than SA (3.32 ± 0.74 flux/mmHg) and WE (3.80 ± 0.74 flux/mmHg; p < 0.013), in addition to a reduced area under the curve (BA: 8983 ± 4835, SA: 14087 ± 4836, WE: 18005 ± 4836 flux/s; p < 0.023). Furthermore, toe CVC responses to 42°C LH were attenuated in BA (1.08 ± 0.82 flux/mmHg) compared to SA (2.00 ± 0.82 flux/mmHg) and WE (2.13 ± 0.78 flux/mmHg; p < 0.033), as well as to 44°C LH (BA: 1.26 ± 0.78, SA: 2.29 ± 0.78, WE: 2.13 ± 0.78 flux/mmHg; p < 0.020). During immersion, HWI reduced both systolic (-7 ± 7 mmHg; p < 0.019) and diastolic (-16 ± 5 mmHg; p < 0.001) blood pressure compared to CON, with no differences observed between racial groups. HWI increased toe CVC during 44°C LH (2.07 ± 1.07 flux/mmHg) compared to CON (1.72 ± 0.7 flux/mmHg; p = 0.039), despite no change in plasma [nitrite] or differences between racial groups (p > 0.05).
CONCLUSION:
Between racial groups, microvascular reactivity to OC and LH were lower in BA than SA and WE individuals. Despite this racial difference in microvascular function, the beneficial effects of HWI on blood pressure and CVC were similar between individuals of BA, SA, and WE descent.