Abstract
New Findings What is the central question of this study? Temperature‐sensitive mechanisms are thought to contribute to blood‐flow regulation, but the relationship between exercising and non‐exercising limb perfusion and blood temperature is not established. What is the main finding and its importance? The close coupling among perfusion, blood temperature and aerobic metabolism in exercising and non‐exercising extremities across different exercise modalities and activity levels and the tight association between limb vasodilatation and increases in plasma ATP suggest that both temperature‐ and metabolism‐sensitive mechanisms are important for the control of human limb perfusion, possibly by activating ATP release from the erythrocytes. Temperature‐sensitive mechanisms may contribute to blood‐flow regulation, but the influence of temperature on perfusion to exercising and non‐exercising human limbs is not established. Blood temperature (T B), blood flow and oxygen uptake (V˙O2) in the legs and arms were measured in 16 healthy humans during 90 min of leg and arm exercise and during exhaustive incremental leg or arm exercise. During prolonged exercise, leg blood flow (LBF) was fourfold higher than arm blood flow (ABF) in association with higher T B and limb V˙O2. Leg and arm vascular conductance during exercise compared with rest was related closely to T B (r 2 = 0.91; P < 0.05), plasma ATP (r 2 = 0.94; P < 0.05) and limb V˙O2 (r 2 = 0.99; P < 0.05). During incremental leg exercise, LBF increased in association with elevations in T B and limb V˙O2, whereas ABF, arm T B and V˙O2 remained largely unchanged. During incremental arm exercise, both ABF and LBF increased in relationship to similar increases in V˙O2. In 12 trained males, increases in femoral T B and LBF during incremental leg exercise were mirrored by similar pulmonary artery T B and cardiac output dynamics, suggesting that processes in active limbs dominate central temperature and perfusion responses. The present data reveal a close coupling among perfusion, T B and aerobic metabolism in exercising and non‐exercising extremities and a tight association between limb vasodilatation and increases in plasma ATP. These findings suggest that temperature and V˙O2 contribute to the regulation of limb perfusion through control of intravascular ATP.
Highlights
Local tissue and blood temperature (TB) increases with elevations in skeletal muscle metabolism and heat production during dynamic exercise (Sproule & Archer, 1959; Saltin & Hermansen, 1966; Gonzalez-Alonso et al 1999, 2000)
No study has examined the relationships amongst limb TB, perfusion and aerobic metabolism during separate and combined lower and upper limb exercise to determine whether a coupling between TB and limb perfusion is still apparent when accounting for differences in metabolism and heat production
These findings suggest that mechanisms sensitive to temperature and metabolic rate are involved in the regulation of limb perfusion, possibly through signalling pathways that control the intravascular concentration of ATP
Summary
Local tissue and blood temperature (TB) increases with elevations in skeletal muscle metabolism and heat production during dynamic exercise (Sproule & Archer, 1959; Saltin & Hermansen, 1966; Gonzalez-Alonso et al 1999, 2000). Heat is transferred from the working muscles to the neighbouring tissues and the overlying skin as well as to the body core. This is made possible via the flowing blood (convective heat transfer) and direct intercellular heat conduction (conductive heat transfer; Barcroft & Edholm, 1943; Pennes et al 1948; Gonzalez-Alonso et al 2000). Differences in V O2 and metabolic heat production between the exercising lower and upper limbs could affect the increase in TB and the relationship between TB and perfusion in exercising and non-exercising limbs if the differences in heat production are not matched by proportional changes in endogenous heat transfer. No study has examined the relationships amongst limb TB, perfusion and aerobic metabolism during separate and combined lower and upper limb exercise to determine whether a coupling between TB and limb perfusion is still apparent when accounting for differences in metabolism and heat production
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