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Differential Effect of head‐up tilt on Cardiovagal and Sympathetic Baroreflex Sensitivity in Humans
Author(s) -
O'Leary D. D.,
Kimmerly D. S.,
Cechetto A. D.,
Shoemaker J. K.
Publication year - 2003
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/eph8802632
Subject(s) - baroreflex , supine position , baroreceptor , medicine , blood pressure , microneurography , heart rate , cardiology , anesthesia , sympathetic nervous system , valsalva maneuver , hemodynamics
The purpose of this study was to determine the effect of baroreceptor unloading on the sensitivity of the cardiovagal and sympathetic arms of the baroreflex during upright posture. Beat‐by‐beat R‐R interval, arterial blood pressure and cardiac output (Doppler ultrasound), as well as muscle sympathetic nerve activity (MSNA) were recorded during periods in supine (Supine) and 60 deg head‐up tilt (HUT) positions (n = 8 volunteers). Cardiovagal baroreflex sensitivity (BRS) was measured by the spontaneous sequence analysis method using systolic blood pressure and R‐R interval, while sympathetic BRS was determined using the slope of the linear relationship between decreasing segments of diastolic blood pressure (DBP) and corresponding increases in MSNA. On changing to HUT, mean R‐R interval and cardiac output decreased, while mean measures of MSNA, DBP and total peripheral resistance increased (P < 0.05). Cardiovagal BRS decreased from Supine to 60 deg HUT (19 ± 2 ms mmHg −1 versus 7.6 ± 1.2 ms mmHg −1 ; P < 0.01). In contrast, sympathetic BRS increased from ‐6.1 ± 1.4 a.u. mmHg −1 in Supine to ‐14 ± 2 a.u. mmHg −1 in HUT (P < 0.01). Thus, HUT produced differential effects on cardiac versus sympathetic BRS. The data suggest that dynamic baroreflex‐mediated cardiovascular control is dominated by sympathetic control during baroreceptor unloading.