Increased inspiratory work exacerbates skin hypoperfusion and attenuates the pressor response during high‐intensity exercise in the heat

Abstract During exercise in the heat, skin vasodilatation occurs as heat loss response. Increased respiratory muscle work by inspiratory loading during high‐intensity exercise causes vasoconstriction in active skeletal muscles without altering arterial blood pressure. We hypothesized that, during high‐intensity exercise in the heat, inspiratory loading would induce skin vasoconstriction and thus reduce skin blood flow to maintain the pressor response associated with high‐intensity exercise. Fifteen healthy young men cycled in the heat (35°C, 50% relative humidity), consisting of 14 min at 50% peak oxygen uptake () followed by 3 min at 90% . A 1 min inspiratory loading was applied 10 min into exercise at 50% and 1 min into exercise at 90% . The protocol without inspiratory loading was performed on a separate day as the control. Upper back skin blood flow was measured using a laser‐Doppler flowmeter. Arterial blood pressure was measured using finger photoplethysmography, and skin vascular conductance was calculated as skin blood flow/mean arterial pressure. Skin blood flow decreased, whereas mean arterial pressure increased gradually during exercise at 90% , and these responses were greater and smaller, in the inspiratory load than control ( P < 0.003). Skin vascular conductance did not differ between conditions at 90% . At 50% , the inspiratory loading slightly reduced mean arterial pressure but did not modulate skin blood flow or skin vascular conductance. We show that increased respiratory muscle work augments the reduction in skin blood flow, whereas it attenuates the pressor response during high‐intensity exercise in the heat, without modulating skin vasoconstriction. image Key points Skin vasodilatation plays a pivotal role in heat loss during exercise in the heat. Breathing, and thus respiratory muscle work, can be augmented by hyperthermia, ageing and lung or cardiovascular disease. However, whether increased respiratory muscle work influences skin vasodilatation during exercise in the heat remains unknown. Inspiratory loading, which increased the work of breathing, was applied during exercise at 50% and at 90% in the heat. We showed that an inspiratory load reduced skin blood flow and attenuated the increase in mean arterial pressure during exercise at 90% without influencing skin vascular conductance. However, these effects associated with inspiratory loading were not clearly observed during exercise at 50% . Our findings suggest that increased inspiratory muscle work may reduce heat loss associated with increases in skin blood flow and blunted pressor response during high‐intensity exercise in the heat.