In resting spontaneously breathing men, the present study observed that sympathetic baroreflex sensitivity (BRS) was higher during low versus high lung volumes but not different between inspiration and expiration. High- but not low-lung volume BRS was negatively associated with resting muscle sympathetic nerve activity (MSNA). Acute intermittent hypercapnic hypoxia increased resting MSNA and diastolic blood pressure, without altering within-breath BRS. These findings provide novel insight into mechanisms controlling within-breath modulation of MSNA in humans.
