Local temperature-sensitive mechanisms are important mediators of limb tissue hyperemia in the heat-stressed human at rest and during small muscle mass exercise

Abstract

Limb tissue and systemic blood flow increases with heat stress, but the underlying mechanisms remain poorly understood. Here, we tested the hypothesis that heat stress-induced increases in limb tissue perfusion are primarily mediated by local temperature-sensitive mechanisms. Leg and systemic temperatures and hemodynamics were measured at rest and during incremental single-legged knee extensor exercise in 15 males exposed to 1 h of either systemic passive heat-stress with simultaneous cooling of a single leg (n = 8) or isolated leg heating or cooling (n = 7). Systemic heat stress increased core, skin and heated leg blood temperatures (Tb), cardiac output, and heated leg blood flow (LBF; 0.6 ± 0.1 l/min; P < 0.05). In the cooled leg, however, LBF remained unchanged throughout (P > 0.05). Increased heated leg deep tissue blood flow was closely related to Tb (R2 = 0.50; P < 0.01), which is partly attributed to increases in tissue V̇O2 (R2 = 0.55; P < 0.01) accompanying elevations in total leg glucose uptake (P < 0.05). During isolated limb heating and cooling, LBFs were equivalent to those found during systemic heat stress (P > 0.05), despite unchanged systemic temperatures and hemodynamics. During incremental exercise, heated LBF was consistently maintained ∼0.6 l/min higher than that in the cooled leg (P < 0.01), with LBF and vascular conductance in both legs showing a strong correlation with their respective local Tb (R2 = 0.85 and 0.95, P < 0.05). We conclude that local temperature-sensitive mechanisms are important mediators in limb tissue perfusion regulation both at rest and during small-muscle mass exercise in hyperthermic humans.

Mechanisms for the control of local tissue blood flow during thermal interventions: influence of temperature‐dependent ATP release from human blood and endothelial cells

“…2011) and the profunda femoral artery, which primarily supplies blood to the thigh muscles (Chiesa et al . 2015, 2016). These haemodynamic responses and their impact on the supply of regulatory substances, oxygen and substrates form the basis for the widespread clinical and ergogenic application of heat and cold therapies and thermal interventions (Imamura et al .…”

Blood temperature and perfusion to exercising and non‐exercising human limbs

“…2011; Chiesa et al . 2015), irrespective of differences in systemic temperature and haemodynamic responses between conditions (Chiesa et al . 2015).…”

“…2015), irrespective of differences in systemic temperature and haemodynamic responses between conditions (Chiesa et al . 2015). Although small compared with exercise hyperaemia, this hyperthermia‐mediated limb hyperaemia is maintained during combined heat stress and one‐legged knee‐extensor exercise (Pearson et al .…”

“…2011; Chiesa et al . 2015). The thermal hyperaemia in resting limbs is associated only in part with metabolic vasodilatation, because the concomitant elevation in limb ${\dot{V}}_{{\mathrm{normalO}}_2}$ is too small to account for the increase in perfusion (Pearson et al .…”

“…2011; Chiesa et al . 2015). Thus, hyperthermia induces vasodilatation of the limb tissue vascular beds through other mechanisms, which may be temperature sensitive.…”