Abstract
Hyperthermia is thought to increase limb blood flow through the activation of thermosensitive mechanisms within the limb vasculature, but the precise vascular locus in which hyperthermia modulates perfusion remains elusive. We tested the hypothesis that local temperature‐sensitive mechanisms alter limb hemodynamics by regulating microvascular blood flow. Temperature and oxygenation profiles and leg hemodynamics of the common (CFA), superficial (SFA) and profunda (PFA) femoral arteries, and popliteal artery (POA) of the experimental and control legs were measured in healthy participants during: (1) 3 h of whole leg heating (WLH) followed by 3 h of recovery (n = 9); (2) 1 h of upper leg heating (ULH) followed by 30 min of cooling and 1 h ULH bout (n = 8); and (3) 1 h of lower leg heating (LLH) (n = 8). WLH increased experimental leg temperature by 4.2 ± 1.2ºC and blood flow in CFA, SFA, PFA, and POA by ≥3‐fold, while the core temperature essentially remained stable. Upper and lower leg blood flow increased exponentially in response to leg temperature and then declined during recovery. ULH and LLH similarly increased the corresponding segmental leg temperature, blood flow, and tissue oxygenation without affecting these responses in the non‐heated leg segment, or perfusion pressure and conduit artery diameter across all vessels. Findings demonstrate that whole leg hyperthermia induces profound and sustained elevations in upper and lower limb blood flow and that segmental hyperthermia matches the regional thermal hyperemia without causing thermal or hemodynamic alterations in the non‐heated limb segment. These observations support the notion that heat‐activated thermosensitive mechanisms in microcirculation regulate limb tissue perfusion during hyperthermia.
Highlights
Passive whole and segmental limb hyperthermia increase local tissue perfusion in association with elevations in calculated limb vascular conductance (Kalsi et al, 2017; Keller et al, 2010; Pearson et al, 2011; Romero et al, 2017)
Limb blood flow is elevated in a local tissue temperature-dependent manner, suggesting that local thermosensitive mechanisms in the limb vasculature rather than central hemodynamic factors play a crucial role in limb tissue blood flow regulation during hyperthermia (Chiesa et al, 2016; Heinonen et al, 2011; Pearson et al, 2011)
Prolonged whole leg hyperthermia produces a profound and sustained elevation in upper and lower leg blood flow, while segmental leg hyperthermia induces hyperemia to a magnitude that matches the regional hyperemia during whole leg heating without affecting blood flow, temperature or tissue oxygenation of the non-heated limb segment
Summary
Passive whole and segmental limb hyperthermia increase local tissue perfusion in association with elevations in calculated limb vascular conductance (Kalsi et al, 2017; Keller et al, 2010; Pearson et al, 2011; Romero et al, 2017). Limb blood flow is elevated in a local tissue temperature-dependent manner, suggesting that local thermosensitive mechanisms in the limb vasculature rather than central hemodynamic factors play a crucial role in limb tissue blood flow regulation during hyperthermia (Chiesa et al, 2016; Heinonen et al, 2011; Pearson et al, 2011) It remains unknown whether heating a limb segment—that is, the upper or lower leg—solely increases temperature and blood flow in the heated region or whether it would evoke responses in the adjacent non-heated limb segment
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