Cardiovascular and temperature responses to local heating.
Research project(s) and grant(s)
Project title: Regional blood flow in the human leg with local heating.
Doctoral researcher: Nuno Koch Esteves
Project description: Heat exposure interventions such as hot water baths or sauna lead to increases in limb and systemic blood flow, among many other responses. These whole body heating interventions have been used for millennia due to their believed health benefits. Numerous recent studies support this idea by showing that whole body heat exposure not only increases blood flow but also reduces arterial stiffness (or hardening of the vessel wall) and blood pressure, and improves blood vessel function. Heat-induced vascular adaptations may be of particular benefit to elderly populations as it is common for vascular health to decline with aging and disease. This PhD project further explores the effects of heating on the human circulatory system to better understand its therapeutic potential for improving vascular health.
Figure 1. From Koch Esteves et al. Physiol Rep 2021.Temperature and tissue oxygenation profiles, and blood flow was measured in the common (CFA), profunda (PFA) and superficial (SFA) femoral arteries and popliteal artery (POA) during whole leg and segmental—i.e., upper or lower leg—heating inducing local hyperthermia without alterations in core temperature.
The first PhD study (Koch Esteves et al., 2021) provides comprehensive and compelling evidence on the effects of local hyperthermia in the leg circulation of young healthy people.
- Increases in temperature (hyperthermia) are thought to increase limb blood flow through the activation of thermosensitive mechanisms within the limb vasculature, but the precise vascular structure in which hyperthermia modulates perfusion remains elusive.
- We tested the hypothesis that local temperature-sensitive mechanisms alter limb perfusion by regulating microvascular blood flow. This was accomplished by examining the effects of whole, upper and lower leg heating on regional limb temperature, blood flow and tissue oxygenation in conditions where core temperature remained unchanged.
- We found that prolonged whole leg hyperthermia produces a profound and sustained elevation in upper and lower leg blood flow; whilst segmental leg—i.e., upper or lower leg—hyperthermia induces increases in local blood flow to a magnitude that matches the regional increase in blood flow during whole leg heating, without affecting blood flow, temperature or tissue oxygenation of the non-heated leg segment.
- Increases in local tissue oxygenation, blood flow, vascular conductance and blood velocity were positively related with the rise in local temperature. Yet these increases occurred without any changes to mean blood pressure, conduit artery diameter or wave intensity-derived parameters.
- Collectively, these findings support the hypothesis that local hyperthermia increases peripheral tissue blood flow through the activation of local thermosensitive mechanisms.
- These mechanisms are proposed to increase blood flow in the microcirculation—i.e., in the arterioles and capillaries—by inducing increases in vascular conductance and/or vasodilatation (an increase in microvessel diameter).
- Importantly, the markedly enhanced blood flow and tissue oxygenation strongly support the therapeutic potential of local hyperthermia for treatment of circulatory diseases and/or rehabilitation.
Figure 2. Schematic illustration of the haemodynamic effects of hyperthermia and the likely thermosensitive mechanisms involved in the thermal control of regional leg hyperaemia. (Leg level) Passive leg heating. (Macrocirculation level) Hyperthermic effect on the macrocirculation: passive heating increases blood velocity (Vmean) and thus, conduit artery blood flow (Q) without affecting arterial diameter (Dmean). (Microcirculation level) Hyperthermic effect on the microcirculation: passive leg heating increases microcirculatory blood flow. Pressure gradient or perfusion pressure (∆P) remains unchanged during passive leg heating, further supported by the unchanged forward compression (FCW) and forward expansion (FEW) waves. Consequently, the increase in microvascular circulation is the result of an increase in microvascular conductance. In turn, the elevation in microvascular conductance could be the result of an increase in microvessel diameter, red blood cell deformability and dispersion and/or blood kinetic energy, and/or a decrease in blood viscosity.
Dissemination of research:
- CHPER 2018-2019 Seminar Series – Seminar 2 in April 2019 – Impact of heat and exercise therapies on health and rehabilitation.
- Blood flow in the heated human leg: Evidence of local thermosensitive regulatory mechanisms.
- The Physiological Society conference Extreme Physiology: Life at the Limits meeting at the University of Portsmouth in September 2019.
- The 5th CHLS Conference for Doctoral Researchers and MPhil students at Brunel University London in December 2019.
- Regional thermal hyperaemia—evidence of a critical role of local thermosensitive mechanisms in the control of the human leg circulation during hyperthermia.
- The 6th CHMLS Conference for Doctoral Researchers and MPhil students at Brunel University London in December 2020.
- Regional leg blood flow during upper-leg heating and cooling: evidence of a critical role of thermosensitive mechanisms in the control of the peripheral circulation during hyperthermia.
- The Physiological Society virtual conference Future Physiology in April 2021.
Adapted short communication from the Future Physiology 2021 Conference:
Koch Esteves N, Chiesa ST. Passive leg movement: A novel method to assess vascular function during passive leg heating? Exp Physiol. 2021 Dec;106(12):2335-2336. doi: 10.1113/EP090033. Epub 2021 Oct 23.
Koch Esteves N, Gibson OR, Khir AW, González-Alonso J (2021). Regional thermal hyperemia in the human leg: Evidence of the importance of thermosensitive mechanisms in the control of the peripheral circulation. Physiol Rep 09, e14953.
Travers G, Kippelen P, Trangmar SJ & González-Alonso J. (2022). Physiological Function during Exercise and Environmental Stress in Humans—An Integrative View of Body Systems and Homeostasis. Cells 11,383.
Chiesa ST, Trangmar SJ, Watanabe K & González-Alonso J (2019). Integrative human cardiovascular responses to hyperthermia. In: Périard J., Racinais S. (eds.) Heat Stress in Sport and Exercise, p. 45-65. Springer, Cham.
Kalsi, K. K., Chiesa, S. T., Trangmar, S. J., Ali, L., Lotlikar, M. D., & González‐Alonso, J. (2017). Mechanisms for the control of local tissue blood flow during thermal interventions: influence of temperature‐dependent ATP release from human blood and endothelial cells. Experimental physiology, 102(2), 228-244.
Chiesa ST, Trangmar SJ, Kalsi K, Rakobowchuk M, Banker DS, Lotlikar MD, Ali L & González-Alonso J (2015). Local temperature-sensitive mechanisms are important mediators of limb tissue hyperemia in the heat-stressed human at rest and during small muscle mass exercise. Am J Physiol Heart Circ Physiol 309, H369-H380.
González-Alonso J, Calbet JAL, Boushel R, Helge JW, Søndergaard H, Munch-Andersen T, van Hall G, Mortensen SP & Secher NH (2015). Blood temperature and perfusion to exercising and non-exercising human limbs. Exp Physiol 100, 1118-1131.
González-Alonso J (2012). Human thermoregulation and the cardiovascular system. Exp Physiol 97, 340-346.
Stöhr EJ, González-Alonso J, Pearson J, Low DA, Ali L, Barker H & Shave R (2011). Effects of graded heat stress on global left ventricular function and twist mechanics at rest and during exercise in healthy humans. Exp Physiol 96, 114-124.
Pearson J, Low DA, Stöhr E, Kalsi K, Ali L, Barker H & González-Alonso J (2011). Hemodynamic responses to heat stress in the resting and exercising human leg: insight into the effect of temperature on skeletal muscle blood flow. Am J Physiol Regul Integr Comp Physiol 300, R663-673.
Crandall CG & González-Alonso J (2010). Cardiovascular function in the heat-stressed human. Acta Physiol 199, 407-423.