Expiratory Resistive Loading Increases in Sympathetic Vasomotor Outflow and BP During Dynamic Leg Exercise

Abstract

High intensity voluntary contraction of the inspiratory muscles against resistive loads augments an increase in muscle sympathetic nerve activity (MSNA) with a corresponding increase in arterial blood pressure (BP) through an inspiratory muscle fatigue-induced metaboreflex. We hypothesized that expiratory muscle fatigue would also elicit increases in MSNA and BP during dynamic leg exercise. PURPOSE: The purpose of this study was to clarify the influence of an enhancement of expiratory muscle activity on sympathetic vasoconstrictor outflow and BP during submaximal exercise. METHODS: 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 with or without expiratory resistive breathing for 5 min (breathing frequency: 60 breaths/min, inspiratory and expiratory times were each constant at 0.5 s)]. MSNA was recorded via microneurography of the right median nerve at the elbow. RESULTS: A large increase in MSNA burst frequency (BF) occurred during exercise with expiratory resistance, accompanied by an augmentation of mean BP (MBP) (with resistance: MSNA BF +39.0%, MBP +42.5%, without resistance: MSNA BF: +12.8%, MBP: +22.9%, from resting values). CONCLUSIONS: These results suggest that an enhancement of expiratory muscle activity leads to large increases in muscle sympathetic vasomotor outflow and BP during dynamic leg exercise.