Arterial baroreflex control of muscle sympathetic nerve activity in the transition from rest to steady-state dynamic exercise in humans.
We sought to investigate arterial baroreflex (ABR) control of muscle sympathetic nerve activity (MSNA) in the transition from rest to steady-state dynamic exercise. This was accomplished by assessing the relationship between spontaneous variations in diastolic blood pressure (DBP) and MSNA at rest and during the time course of reaching steady-state arm cycling at 50% peak oxygen uptake (VO(2peak)). Specifically, DBP-MSNA relations were examined in eight subjects (25 +/- 1 yr) at the start of unloaded arm cycling and then during the initial and a later period of arm cycling once the 50% VO(2peak) work rate was achieved. Heart rate and arterial blood pressure were progressively increased throughout exercise. Although resting MSNA [16 +/- 2 burst/min; 181 +/- 36 arbitrary units (au) total activity] was unchanged during unloaded cycling, MSNA burst frequency and total activity were significantly elevated during the initial (27 +/- 4 burst/min; 367 +/- 76 au; P < 0.05) and later (36 +/- 7 burst/min; 444 +/- 91 au; P < 0.05) periods of exercise. The relationships between DBP and burst incidence, burst strength, and total MSNA were progressively shifted rightward from unloaded to the initial to the later period of 50% VO(2peak) arm cycling without any changes in the slopes of the linear regressions (i.e., ABR sensitivity). Thus a continuous and dynamic resetting of the ABR control of MSNA occurred during the transition from rest to steady-state dynamic exercise. These findings indicate that the ABR control of MSNA was well maintained throughout dynamic exercise in humans, progressively being reset to operate around the exercise-induced elevations in blood pressure and MSNA without any changes in reflex sensitivity.
Ogoh
Shigehiko
S
Dept. of Integrative Physiology, Univ. of North Texas Health Science Center, 3500 Camp Bowie Blvd., Fort Worth, TX 76107, USA. sogoh@hsc.unt.edu
Fisher
James P
JP
Raven
Peter B
PB
Fadel
Paul J
PJ
D000222:Adaptation, Physiological; D000328:Adult; D001132:Arm; D001158:Arteries / Q000294:innervation* / Q000502:physiology; D017704:Baroreflex; D001794:Blood Pressure; D003971:Diastole; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation* / Q000378:metabolism; D010101:Oxygen Consumption; D013564:Sympathetic Nervous System / Q000502:physiology*; D013997:Time Factors