Lower limb hyperthermia augments functional hyperaemia during small muscle mass exercise similarly in trained elderly and young humans

Abstract

New Findings What is the central question of the study? Ageing is postulated to lead to underperfusion of human limb tissues during passive and exertional hyperthermia, but findings to date have been equivocal. Thus, does age have an independent adverse effect on local haemodynamics during passive single‐leg hyperthermia, single‐leg knee‐extensor exercise and their combination? What is the main finding and its importance? Local hyperthermia increased leg blood flow over three‐fold and had an additive effect during knee‐extensor exercise with no absolute differences in leg perfusion between the healthy, exercise‐trained elderly and the young groups. Our findings indicate that age per se does not compromise lower limb hyperaemia during local hyperthermia and/or small muscle mass exercise. AbstractHeat and exercise therapies are recommended to improve vascular health across the lifespan. However, the haemodynamic effects of hyperthermia, exercise and their combination are inconsistent in young and elderly people. Here we investigated the acute effects of local‐limb hyperthermia and exercise on limb haemodynamics in nine healthy, trained elderly (69 ± 5 years) and 10 young (26 ± 7 years) adults, hypothesising that the combination of local hyperthermia and exercise interact to increase leg perfusion, albeit to a lesser extent in the elderly. Participants underwent 90 min of single whole‐leg heating, with the contralateral leg remaining as control, followed by 10 min of low‐intensity incremental single‐leg knee‐extensor exercise with both the heated and control legs. Temperature profiles and leg haemodynamics at the femoral and popliteal arteries were measured. In both groups, heating increased whole‐leg skin temperature and blood flow by 9.5 ± 1.2°C and 0.7 ± 0.2 L min−1 (>3‐fold), respectively (P < 0.0001). Blood flow in the heated leg remained 0.7 ± 0.6 and 1.0 ± 0.8 L min−1 higher during exercise at 6 and 12 W, respectively (P < 0.0001). However, there were no differences in limb haemodynamics between cohorts, other than the elderly group exhibiting a 16 ± 6% larger arterial diameter and a 51 ± 6% lower blood velocity following heating (P < 0.0001). In conclusion, local hyperthermia‐induced limb hyperperfusion and/or small muscle mass exercise hyperaemia are preserved in trained older people despite evident age‐related structural and functional alterations in their leg conduit arteries.

Thermo‐haemodynamic coupling during regional thigh heating: Insight into the importance of local thermosensitive mechanisms in blood circulation

“…In this study, all three modalities of upper‐leg heating – WTH, QH and PQH – evoked sustained 1.4−2‐fold increases in CFA blood flow (Figure 3 ). In line with previous studies, local hyperthermia‐induced increases in leg tissue perfusion, assessed via CFA blood flow, occurred in relation to increases in local tissue temperature (Chiesa et al., 2016 ; Koch Esteves et al., 2021 , 2023 ). A previous study from our laboratory revealed that the magnitude of hyperaemia was associated with the volume of the heated limb segment, with whole‐leg heating evoking the largest degree of hyperaemia, proportionally followed by upper‐ and lower‐leg heating, respectively (Koch Esteves et al., 2021 ).…”