Elevated sympathetic vasomotor outflow in response to increased inspiratory muscle activity during exercise is less in young women compared with men

Abstract

We compared changes in muscle sympathetic nerve activity (MSNA) and cardiovascular variables during leg cycle exercise with increased inspiratory muscle resistance in men and women. We hypothesized that sympathetic vasomotor outflow during exercise with increased inspiratory resistance would be attenuated in young women compared with age-matched men. Eight women and seven men completed the study. The subjects performed two 10-min exercise bouts at 40% peak oxygen uptake using a cycle ergometer in a semirecumbent position [spontaneous breathing for 5 min and voluntary hyperventilation with or without inspiratory resistive breathing for 5 min (breathing frequency: 50 breaths min⁻¹ with a 50% duty cycle, inspiratory resistance: 30% of maximal inspiratory pressure)]. Mean arterial blood pressure (MAP) was acquired using finger photoplethysmography. MSNA was recorded via microneurography of the right median nerve at the cubital fossa. During leg cycle exercise with inspiratory resistive breathing, MSNA burst frequency (BF) was increased accompanied by an increase in MAP both in men and women. Women, compared with men, had less of an increase in MAP (Women: +22.8 ± 12.3 vs. Men: +32.2 ± 5.4 mmHg, P < 0.05) and MSNA BF (Women: +9.6 ± 2.9 vs. Men: +14.6 ± 6.4 bursts min⁻¹, P < 0.05). These results suggest that the attenuated inspiratory muscle-induced metaboreflex during exercise in young women is partially attributed to a lesser sympathetic vasomotor outflow compared with men.

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