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

Abstract

AbstractA positive relationship between local tissue temperature and perfusion exists, with isolated limb‐segment hyperthermia stimulating hyperaemia in the heated region without affecting the adjacent, non‐heated limb segment. However, whether partial‐limb segment heating evokes a heightened tissue perfusion in the heated region without directly or reflexly affecting the non‐heated tissues of the same limb segment remains unknown. This study investigated, in 11 healthy young adults, the lower limb temperature and haemodynamic responses to three levels of 1 h upper‐leg heating, none of which alter core temperature: (1) whole‐thigh (WTH; water‐perfused garment), (2) quadriceps (QH; water‐perfused garment) and (3) partial‐quadriceps (PQH; pulsed shortwave diathermy) heating. It was hypothesised that perfusion would only increase in the heated regions. WTH, QH and PQH increased local heated tissue temperature by 2.9 ± 0.6, 2.0 ± 0.7 and 2.9 ± 1.3°C (P < 0.0001), respectively, whilst remaining unchanged in the non‐heated hamstrings and quadriceps tissues during QH and PQH. WTH induced a two‐fold increase in common femoral artery blood flow (P < 0.0001) whereas QH and PQH evoked a similar ∼1.4‐fold elevation (P ≤ 0.0018). During QH and PQH, however, tissue oxygen saturation and laser‐Doppler skin blood flow in the adjacent non‐heated hamstrings or quadriceps tissues remained stable (P > 0.5000). These findings in healthy young humans demonstrate a tight thermo‐haemodynamic coupling during regional thigh heating, providing further evidence of the importance of local heat‐activated mechanisms on the control of blood circulation.