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

New Findings: What is the central question of this study? Premenopausal women have an attenuated inspiratory muscle metaboreflex-induced increase in arterial blood pressure compared with men. It is unclear whether sympathetic vasomotor outflow during dynamic exercise with increased inspiratory muscle activation is less in young women than in men. What is the main finding and its importance? The magnitude of increased sympathetic vasomotor outflow during leg cycling with inspiratory resistance was smaller in women than in men. Less sympathetic vasomotor outflow with inspiratory muscle metaboreflex activation could be one of the mechanisms for the attenuated inspiratory muscle-induced metaboreflex during exercise in young women.
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. The 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 was increased, accompanied by an increase in MAP in both men and women. Women, compared with men, had less of an increase in MAP (women +22.8 ± 12.3 mmHg versus men +32.2 ± 5.4 mmHg; P < 0.05) and MSNA burst frequency (women +9.6 ± 2.9 bursts min ^-1 versus 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 attributable, in part, to a lesser sympathetic vasomotor outflow compared with men.
(© 2018 The Authors. Experimental Physiology © 2018 The Physiological Society.)