Effect of home-based heat therapy on skeletal muscle blood flow during exercise in older adults

Abstract

The arterial vasculature undergoes profound changes across the lifespan. This vascular aging manifests as structural (e.g., vascular rarefaction) and functional (e.g., endothelial dysfunction) maladaptations. These age-related maladaptations contribute to the hypo-perfusion of skeletal muscle during conditions that require an elevated blood supply and substrate delivery (e.g., exercise) by tipping the vasoactive balance in favor of vasoconstriction. Acute heat exposure increases body and tissue temperature, increases blood flow and shear stress throughout the arterial tree, and initiates a humoral response. Importantly, chronic exposure to these temperature-dependent stimuli may reverse age-related vascular dysfunction, thereby improving perfusion of active skeletal muscle (i.e., exercise hyperemia). However, the effect of chronic heat therapy on exercise hyperemia has never been explored. Therefore, the purpose of this pilot study was to test the hypothesis that home-based heat therapy would increase skeletal muscle blood flow in older adults performing plantar flexion exercise. Six older adults (5 women; 67 ± 4 years) performed graded (5, 9, and 14 kg) unilateral dynamic plantar flexion exercise before (pre) and after (post) 8 weeks of home-based heat therapy. Each session of heat therapy required participants to immerse their lower legs ~33 cm into a heated (~ 42°C) and circulated water bath 4 days per week, for 45 min per session. Dynamic plantar flexion exercise was performed using a duty cycle of 1 s contraction and 2 s relaxation. Superficial femoral artery blood velocity and diameter were measured via Duplex ultrasonography and used to calculate the change in blood flow measured from baseline to each stage of exercise. Vascular conductance was calculated as flow/pressure. The change in leg blood flow during exercise was increased following heat therapy ( P = 0.08 for main effect of time), an effect that was mediated by augmented vascular conductance (5 kg: pre, Δ143 ± 89 ml/min/mmHg vs post, Δ188 ± 89 ml/min/mmHg; 9 kg: pre, Δ225 ± 89 ml/min/mmHg vs post, Δ234 ± 89 ml/min/mmHg; 14 kg: pre, Δ264 ± 89 ml/min/mmHg vs post, Δ290 ± 89 ml/min/mmHg; P = 0.07). Our preliminary data suggest that home-based heat therapy increases skeletal muscle blood flow during exercise in older adults, and may serve as a pragmatic intervention to improve exercise and functional capacity in this population. Supported by: American Heart Association TPA958179 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.