Identifying the interaction between skin temperature, maintained thermal comfort, and conduit artery shear rate through limb passive heating

Cardiovascular disease remains the leading cause of mortality. One reason is vascular dysfunction leading to pathological shear rate pattern. Limb passive heating (LPH) is a non-pharmacological intervention, improving vascular health by enhancing shear rate. As LPH is intended for long-term application, it is essential to identify a tolerable heating intensity that effectively reduces retrograde and increases antegrade shear rate without causing thermal discomfort. This study aimed to determine an LPH intensity that balances effective shear rate levels with thermal comfort. In 15 healthy participants (26 ± 3 years), LPH was applied to the right arm and leg targeting skin temperatures of resting baseline, 35°C and 40°C, while the contralateral limbs were maintained at 30°C as controls. After 10 min of steady-state heating, brachial and superficial femoral retro-, and antegrade shear rates, and local thermal comfort were assessed. Brachial artery: antegrade shear rate (35°C, p = 0.006; 40°C, p < 0.0001) increased, retrograde shear rate (p = 0.006) reduced at 40°C, and local arm thermal comfort was 8 ± 1. Femoral artery: antegrade shear rate (35°C, p < 0.0001; 40°C, p < 0.0001) and retrograde shear rate (35°C, p = 0.001; 40°C, p < 0.0001) altered significantly compared to controls, with local leg thermal comfort at 9 ± 1. These findings suggest through statistical interpolation, on average a skin temperature of approximately 38°C is perceived as thermally comfortable during acute LPH.