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

Abstract

Regular exposure to passive heat stress improves vascular function, but the optimal heating prescription remains undefined. Local limb heating is more feasible than whole body heating, but the evidence demonstrating its efficacy is lacking. The purpose of this study was to determine whether acute improvements in vascular function can be achieved with lower limb heating in 16 young healthy individuals (8 female, 8 male). In separate visits, participants underwent 45-min of ankle- and knee-level hot water immersion (45 °C). A subset of 7 participants also participated in a time-control visit. Endothelial function was assessed through simultaneous brachial and superficial femoral artery flow-mediated dilation (FMD) tests. Macrovascular function was quantified by %FMD, while microvascular function was quantified by vascular conductance during reactive hyperemia. Arterial stiffness was assessed through carotid-femoral and femoral-foot pulse wave velocity (PWV). Plasma concentrations of interleukin-6 and extracellular heat shock protein-72 (eHSP72) were used as indicators of inflammation. Our findings showed that 45-min of lower limb heating - regardless of condition - acutely improved upper limb macrovascular endothelial function (i.e., brachial %FMD; Pre: 4.6±1.7 vs. Post: 5.4±2.0%; P=0.004) and lower limb arterial stiffness (i.e., femoral-foot PWV; Pre: 8.4±1.2 vs. Post: 7.7±1.1 m/s; P=0.011). However, only knee-level heating increased upper limb microvascular endothelial function (i.e., brachial peak vascular conductance; Pre: 6.3±2.7 vs. Post: 7.8±3.5 ml/min⋅mmHg; P≤0.050) and plasma eHSP72 concentration (Pre: 12.4±9.4 vs. Post: 14.8±9.8 ng/ml; P≤0.050). These findings show that local lower limb heating acutely improves vascular function in younger individuals, with knee-level heating improving more outcome measures.

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

“…The present findings of local stiffness are in agreement with past whole body and two leg hyperthermia studies which reported no changes in regional (carotid-radial) arterial stiffness (Ganio et al, 2011;Moyen et al, 2016;Schlader et al, 2019). However, studies exploring the recovery following hyperthermia, reported decreases in peripheral and/ or leg (femoral-ankle region) arterial stiffness alongside an elevated core temperature (Caldwell et al, 2017;Cheng et al, 2021;Lee et al, 2018;Sugawara & Tomoto, 2021;Thomas et al, 2017). The latter observations contrast with the unaffected or small changes in arterial stiffness/distensibility, core temperature, and arterial pressure observed in the present and previous single leg heating studies (Chiesa et al, 2015(Chiesa et al, , 2016Engelland et al, 2020;Takahashi et al, 2011).…”

Comparison of the acute effects of ankle bathing versus moderate-intensity aerobic exercise on vascular function in young adults

“…The sample size calculation (a priori) was based on data from the study by Brunt et al (2016), which observed a 2.5% increase in brachial artery FMD following 8 weeks of wholebody bathing, and based on these data, a minimum of 13 participants per group was required in order to reject the null hypothesis with 80% power (p<0.05). However, as the present study tested the acute effects of ankle bathing, the sample size was re-calculated (post hoc) using data from the study by Cheng et al (2021), which observed an 0.8% increase in brachial artery FMD following an acute bout of 45 min of lower limb heating in young adults (4.6%±1.7% versus post: 5.4%±2.0%) with medium-sized effects (Cohen's d= 0.43). A total sample size of 42 participants had enough statistical power (82%) to test a 3x3 ANOVA with repeated measures with the effect size (f value) using a medium-sized partial η 2 (0.05) (p<0.05).…”

“…HSP is known to improve nitric oxide signaling and reduce oxidative stress and inflammation (Pritchard et al 2001;Suzuki et al 2002). Indeed, acute knee-level bathing has been shown to increase plasma concentrations of extracellular HSP-72 and improve brachial artery FMD (Cheng et al 2021). Thus, these previous studies have highlighted the beneficial effects of acute thermal therapy on vascular function.…”

“…Given that ankle bathing has been documented to induce an increase in shear stress and blood flow in both the lower (Padilla and Fadel 2017) and upper extremities (Carter et al 2014), it is possible that ankle bathing may also exert favorable effects on vascular function. Indeed, recent studies have demonstrated that a bout of 30-45 min of lower limb immersion in a hot water (41-45°C) improves conduit vessel function of the upper limb (via brachial artery FMD) (Cheng et al 2021) and reduces central arterial stiffness (via cardio-ankle vascular index) (Hu et al 2012) in young healthy adults. Interestingly, no improvements have been observed in conduit vessel function of the lower limb (via superficial femoral artery FMD) following 45 min of ankle or lower limb immersion in a hot water (42-45°C) in young healthy adults (Cheng et al 2021;Romero et al 2017), suggesting that arterial sites (i.e., upper vs. lower limb) may explain the differential responsiveness to an acute stimulus, such as passive heat therapy.…”

“…Indeed, recent studies have demonstrated that a bout of 30-45 min of lower limb immersion in a hot water (41-45°C) improves conduit vessel function of the upper limb (via brachial artery FMD) (Cheng et al 2021) and reduces central arterial stiffness (via cardio-ankle vascular index) (Hu et al 2012) in young healthy adults. Interestingly, no improvements have been observed in conduit vessel function of the lower limb (via superficial femoral artery FMD) following 45 min of ankle or lower limb immersion in a hot water (42-45°C) in young healthy adults (Cheng et al 2021;Romero et al 2017), suggesting that arterial sites (i.e., upper vs. lower limb) may explain the differential responsiveness to an acute stimulus, such as passive heat therapy. In addition, Engelland et al (2020) have reported the protective effects of acute lower leg hot immersion in peripheral vascular function following ischemia-reperfusion injury in young healthy adults, suggesting that this form of passive heat therapy represents an alternative and useful approach for improving vascular function.…”