Regional blood flow in the human leg with local heating and low-intensity exercise in young and old humans

Abstract

Passive heating has been used for millennia as a therapeutic method to improve health and wellbeing. Contemporary research indicates that heating may have the potential to instigate positive vascular adaptation due to large increases in blood flow and thus, shear stress. However, the precise vascular locus in which hyperthermia modulates perfusion remains elusive. Moreover, the literature exploring the acute haemodynamic responses to heating and exercise in elderly populations, who might benefit the most from heat and exercise interventions, is riddled with inconsistencies. Consequently, the present thesis aimed to (1) investigate the local temperature and haemodynamic responses to various levels of leg and leg-segmental heating, and (2) examine the leg haemodynamic responses among single-leg hyperthermia, kneeextensor exercise, and their combination in healthy, active aged adults. The results from Chapter 4 and 4 demonstrate a strong relationship between local tissue temperature and perfusion, and between the volume of heated tissue and perfusion. The magnitude of hyperaemia during segmental-leg heating corresponded to the regional hyperaemia of that particular leg-segment during whole-leg hyperthermia. During these various levels of local heating, blood flow solely increased in the heated areas with no changes in temperature and perfusion in the unheated contralateral and adject limb segments, alongside a maintained core temperature and central haemodynamics. Furthermore, Chapter 6 uncovered that single-leg heating, kneeextensor exercise, and their combination induced substantial increases in hyperaemia—from smallest to largest, respectively—with hyperthermia having an additive effect on functional hyperaemia. A similar magnitude of functional hyperaemia was observed between the elderly and young cohorts, despite the presence of ageassociated structural vascular changes. Collectively, these novel data indicate that peripheral tissue perfusion during local hyperthermia is primarily regulated by local thermosensitive mechanisms and that local heating may be a suitable intervention for the improvement or maintenance of vascular health in elderly individuals.