Comparing the Effects of 30‐ and 60‐min of Acute Whole‐Body Passive Heat Stress on Peripheral Vascular Function in Older Adults

Abstract

IntroductionMacro‐ and microvascular dysfunction elevate the risk of cardiovascular disease (CVD). Heat therapy has the potential to improve vascular health and reduce CVD risk, but the optimal length of heat stress exposure is unknown. We hypothesized that 1) acute whole body heat stress (WBHS) would increase vascular function and 2) a longer WBHS period (30‐ vs 60‐min) would elicit a greater effect.Methods20 older adults (10 female; 64±7 y) underwent two separate periods of WBHS (30‐ vs 60‐min) via water perfused suit (48°C) in a randomized, counterbalanced design. Macrovascular function via flow‐mediated dilation (FMD) and microvascular function via skin reactive hyperemia (SKBF RH) were assessed before (PRE) and after (POST) WBHS. Core (Tcore; rectal) and skin (Tskin; 6‐site average) temperatures were monitored throughout. Repeated measures ANOVA were used to assess the effect of time (PRE vs POST) and visit (30‐ vs 60‐min) on all outcomes.ResultsTcore and Tskin increased after both WBHS periods (Tcore: 30‐min, PRE: 36.4±0.3, POST: 36.6±0.3°C; 60‐min, PRE: 36.4±0.3, POST: 36.8±0.2°C, p=0.001; Tskin: 30‐min, PRE: 33.5±0.6, POST: 36.3±0.4°C, p<0.0005; 60‐min, PRE: 33.2±0.5°C, POST: 36.6±0.5°C, p<0.0005). FMD% was unchanged (30‐min, PRE: 8.5±5.1%, POST: 7.1±4.2%; 60‐min, PRE: 7.7±3.9%, POST: 6.6±4.3%; p=0.10) after both WBHS periods. During RH, brachial artery shear rate area under the curve was higher after 30‐ (PRE: 17.08±9.57, POST: 26.34±13.06·10‐3 AUC; p=0.003) but not 60‐min (PRE: 21.06±12.30, POST: 27.83±19.32·10‐3 AUC; p=0.186). Total SKBFAUC increased following both 30‐ (PRE: 6.31±3.22, POST: 12.82±6.44·10‐3 AUC; p<0.0005) and 60‐min (PRE: 6.01±3.24, POST: 9.609±4.882·10‐3 AUC; p=0.037), whereas peak SKBF fluxAUC increased following 30‐ (PRE: 1.86±1.54, POST: 4.15±3.07·10‐3 AUC; p=0.001) but not 60‐min (PRE: 1.58±1.31, POST: 2.93±2.77·10‐3 AUC; p=0.1113) of WBHS.DiscussionUp to 60‐min of acute WBHS does not change macrovascular function in older adults. Interestingly, WBHS might increase downstream microvascular functional capacity. The changes in microvascular function following 30‐min of WBHS may reflect early markers of the benefits of repeated whole body heat stress.