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.
Dept. of Integrative Physiology, Univ. of North Texas Health Science Center, 3500 Camp Bowie Blvd., Fort Worth, TX 76107, USA. sogoh@hsc.unt.edu
Shigehiko
S
Ogoh
James P
JP
Fisher
Peter B
PB
Raven
Paul J
PJ
Fadel
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