Sympathoexcitation is attenuated during low level lower body negative pressure in subjects who develop pre-syncope.
The purpose of this study was to compare the hemodynamic and sympathetic nerve activity (SNA) responses to graded lower body negative pressure (LBNP) in healthy subjects with either a positive (n = 24, SNA in 8) or a negative (n = 18, SNA in 6) LBNP response. A positive LBNP response was defined as an abrupt drop in systolic blood pressure associated with a decrease in heart rate and/or a decrease in SNA. All positive responses were accompanied by symptoms common to pre-syncope, defined as lightheadedness, diaphoresis, tunnel vision and/or nausea. If subjects tolerated 30 minutes of LBNP, this was considered a negative response. Comparisons were made between baseline, -10 mmHg (low-level LBNP) and -60 mmHg (high-level LBNP). Baseline SNA and arterial baroreflex sensitivity were not different between the 2 groups. However, subjects with pre-syncope had a significantly attenuated SNA response during low-level LBNP (p < 0.05) compared to subjects who did not experience pre-syncope. The hemodynamic data during high-level LBNP were similar until the occurrence of pre-syncope. Pre-syncope was preceded by a significant decrease in heart rate and SNA. Our findings suggest that subjects with LBNP induced pre-syncope might have an impairment in the cardiopulmonary baroreflex gain function in the setting of a preserved arterial baroreflex gain.
Wasmund
Stephen L
SL
Department of Cardiology, University of Texas Southwestern Medical Center & Dallas Veterans Affairs Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
Smith
Michael L
ML
Takata
Theodore S
TS
Joglar
Jose A
JA
Li
Jian-Ming
JM
Kowal
Robert C
RC
Page
Richard L
RL
Hamdan
Mohamed H
MH
D000328:Adult; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D019462:Syncope, Vasovagal / Q000503:physiopathology*