LAUSR

Passive heat exposure has been shown to be a promising method to improve endothelial health. Sauna usage specifically, has been linked to reduced risk of cardiovascular disease in young and middle-aged populations. Increases in blood flow and shear rates associated with heat exposure are often considered to have a major influence on the observed improved endothelial function following repeated heat exposure; however, the magnitude of these shear and flow responses may potentially vary with age or starting endothelial function. Purpose: The purpose of this study was to determine if the vascular response to acute sauna heating is similar between healthy young and middle-aged adults and if the response is related to baseline endothelial function. Methods: 10 young (24.9 ± 4.2 years, 6 male and 4 female) and 8 middle aged adults (55.6 ± 3.9 years 4 males and 4 females) underwent 40 min of sauna exposure at 80ºC. Esophageal temperature was recorded throughout the duration of the experiment. Brachial artery flow-mediated dilation (FMD) blood flow, artery diameter, shear rates and blood pressure were recorded at baseline and following heat exposure. Results: The increase in core temperature (Tc) followed similar trends in both the young and middle-aged adults (young ΔTc = 1.386 ± 0.52 ºC vs middle-Age Δ Tc = 1.637 ± 0.56 ºC). Heat-induced brachial artery dilation and brachial artery shear rate also increased similarly in both age groups (young Δ diameter = 0.048 ± 0.022 cm vs middle-age Δ diameter = 0.074 ± 0.036 cm, young Δ shear = 164.5± 106.8 sec-1 vs middle-age Δ shear = 150.3 ± 56.29 sec-1). Heat induced dilation was strongly correlated to baseline endothelial function in the young (r = 0.86, P=0.006). This relationship was not observed in the brachial artery of middle-aged adults (r = 0.257, P=0.539). Systolic blood pressure (SBP) was significantly reduced following sauna in the middle-aged participants from 135.25 ± 17.50 mmHg to 122.38 ± 19.7 mmHg (P=0.017). There was a slight elevation in SBP following sauna in the young participants from 119.4 ± 6.38 mmHg to 123.1 ± 7.65 mmHg (P=0.017). Diastolic blood pressure (DBP) was significantly reduced in both age groups (P<0.001) with middle age seeing greater reductions (P=0.05) from 80.63 ± 10.97 mmHg to 69.75 ± 8.41 mmHg vs the young 71.2 ± 8.24 mmHg to 66.9 ± 4.56 mmHg. Conclusion: Young and middle-aged adults have similar changes in shear rate and brachial artery dilation in response to acute sauna heating, but the middle-aged adults exhibit significantly greater decreases in SBP and DBP than young adults. In young adults, endothelial function is strongly correlated to heat induced dilation in the brachial artery. This relationship is not present in the middle age population suggesting that heat-induced dilation may rely on mechanisms other than endothelial function in middle-aged adults. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.