Influence of muscle metaboreceptor stimulation on middle cerebral artery blood velocity in humans

New Findings What is the central question of this study? Is the ability of metabolically sensitive skeletal muscle afferents (muscle metaboreceptors) to increase cerebral perfusion masked by a hyperventilation‐mediated reduction in the arterial (indexed using end‐tidal hence cerebral vasoconstriction, during post exercise muscle ischaemia? What is the main finding and its importance? We found that cerebral perfusion is elevated during post exercise muscle ischaemia when is clamped at baseline, but when is permitted to fluctuate no such elevation occurs. These findings indicate that muscle metaboreceptors increase cerebral perfusion when the confounding effects of changes in are obviated. Regional anaesthesia to attenuate skeletal muscle afferent feedback abolishes the exercise‐induced increase in middle cerebral artery mean blood velocity (MCA V mean ). However, such exercise‐related increases in cerebral perfusion are not preserved during post exercise muscle ischaemia (PEMI) where the activation of metabolically sensitive muscle afferents is isolated. We tested the hypothesis that a hyperventilation‐mediated decrease in the arterial partial pressure of CO 2 , hence cerebral vasoconstriction, masks the influence of muscle metaboreceptor stimulation on MCA V mean during PEMI. Ten healthy men (20 ± 1 years old) performed two trials of fatiguing isometric hand‐grip exercise followed by PEMI, in control conditions and with end‐tidal CO 2 ( clamped at ∼1 mmHg above the resting partial pressure. In the control trial, decreased from rest during hand‐grip exercise and PEMI, while MCA V mean was unchanged from rest. By design, remained unchanged from rest throughout the clamp trial, while MCA V mean increased during hand‐grip (+10.6 ±1.8 cm s −1 ) and PEMI (+9.2 ± 1.6 cm s −1 ; P 0.05). These findings indicate that metabolically sensitive skeletal muscle afferents play an important role in the regional increase in cerebral perfusion observed in exercise, but that influence can be masked by a decrease in when they are activated in isolation during PEMI.