Distinct contributions of skin and core temperatures to flow-mediated dilation of the brachial artery following passive heating

Abstract

We measured acute vascular responses to heat stress to examine the hypothesis that macrovascular endothelial-dependent dilation is improved in a shear-dependent manner, which is further modified by skin temperature. Twelve healthy males performed whole-body heating (+1.5°C esophageal temperature), bilateral forearm heating (~38°C skin temperature), and a time-matched (~60 min) control condition on separate days in counterbalanced order. Bilateral assessments of blood flow and brachial artery flow-mediated dilation (FMD) were performed before and 10 min after each condition protocols with duplex Doppler ultrasound. To isolate the influence of shear stress, a pneumatic cuff was inflated (~90 mmHg) around the right forearm during each condition to attenuate heat-induced rises in blood flow and shear stress. After forearm heating, FMD increased [cuffed: 4.7 (2.9) to 6.8 (1.5)%, non-cuffed: 5.1 (2.8) to 6.4 (2.6)%] in both arms (time P<0.01). Whole-body heating also increased FMD in the non-cuffed arm from 3.6 (2.2) to 9.2 (3.2)% and in the cuffed arm from to 5.6 (3.0)% to 8.6 (4.9)% (time P<0.01). After the time control, FMD decreased [cuffed: 6.3 (2.4) to 4.7 (2.2)%, non-cuffed: 6.1 (3.0) to 4.5 (2.6)%] in both arms (time P=0.03). Multiple linear regression (adjusted r2=0.263, P=0.003) revealed that changes in esophageal temperature, skin temperatures, and heart rate explained the majority of the variance in this model (34%, 31% and 21%, respectively). Our findings indicate that, in addition to shear stress, skin and core temperatures are likely important contributors to passive heating-induced vascular adaptations.

Regional thermal hyperemia in the human leg: Evidence of the importance of thermosensitive mechanisms in the control of the peripheral circulation

“…The increase in blood flow to the heated leg region occurred in the face of a maintained diameter in all examined conduit arteries, including those of the control leg and/or control leg segment where blood velocity and flow did not change. The present findings agree with studies reporting no changes in conduit artery diameter during limb heating (Chiesa et al, 2016;Coombs et al, 2019Coombs et al, , 2021Pearson et al, 2011;Teixeira et al, 2017), but are at odds with studies showing decreases in POA diameter (Thomas et al, 2017). The unchanged conduit artery diameter, together with the general increases in local vascular conductance with whole leg and segmental leg hyperthermia, suggest that vasodilatation might have instead occurred in the downstream small arteries and resistance arterioles, and/or alternatively thermosensitive physical and chemical mechanisms governing blood's rheological properties and kinetic energy permitted the increase in microvascular blood velocity and flow.…”

“…In local limb hyperthermic conditions where perfusion pressure remains stable, an increase in vascular conductance—and thus an increase in arterial diameter and/or blood velocity—could explain the hyperthermia‐induced hyperemia. Nevertheless, whether local hyperthermia increases conduit artery diameter remains equivocal, with studies reporting increases (Kalsi et al, 2017 ), decreases (Thomas et al, 2017 ), or no changes in arterial diameter (Chiesa et al, 2016 ; Coombs et al, 2021 ; Pearson et al, 2011 ; Teixeira et al, 2017 ). Moreover, hyperthermia may directly act on the conduit artery supplying blood to the heated region by increasing arterial stiffness/decreasing arterial distensibility rather than altering diameter, as seen during incremental exercise (Pomella et al, 2018 ).…”

A Primer on Repeated Sitting Exposure and the Cardiovascular System: Considerations for Study Design, Analysis, Interpretation, and Translation

“…During-assessment, it is important to control environmental conditions, including ambient noise and temperature. Ambient noise may raise arousal, whilst core temperature and skin temperature have both been reported to affect vascular function (53). Fluid replacement should also be considered.…”

Improvements in vascular function in response to acute lower limb heating in young healthy males and females

“…Owing to protocol variability, studies examining the acute impact of passive heat stress yield mixed results. With acute heating, macrovascular endothelial function has been shown to increase in some (16)(17)(18) but not all instances (19)(20)(21) in the brachial artery (BA); whereas the superficial femoral artery (SFA) appears resistant to change (13,20,22). In contrast, Cheng et al Acute lower limb heating and vascular function microvascular function has been shown to increase in some (13,17) but not all instances (19)(20)(21) in both the BA and SFA.…”

“…With acute heating, macrovascular endothelial function has been shown to increase in some (16)(17)(18) but not all instances (19)(20)(21) in the brachial artery (BA); whereas the superficial femoral artery (SFA) appears resistant to change (13,20,22). In contrast, Cheng et al Acute lower limb heating and vascular function microvascular function has been shown to increase in some (13,17) but not all instances (19)(20)(21) in both the BA and SFA. Arterial stiffness has also been shown to decrease when examined in the upper limb (23) or whole-body (12), but not in the central or lower limb segments (23).…”