Mechanisms responsible for presyncope during lower body negative pressure (LBNP) in otherwise healthy subjects are poorly understood. Muscle sympathetic nerve activity (MSNA), blood pressure, heart rate (HR), HR power spectra, central venous pressure (CVP) and stroke volume were determined in 14 healthy men subjected to incremental LBNP. Of these, seven experienced presyncope at LBNP >-15 mmHg. Subjects who tolerated LBNP >-15 mmHg had significantly lower CVP (2.6±1.0 versus 7.2±1.2 mmHg; means±S.E.M., P < 0.02), HR (59±2 versus 66±3 beats/min, P < 0.05) and MSNA burst frequency (29.0±2.4 versus 39.0±3.5 bursts/min, P < 0.05) during supine rest. LBNP at -15 mmHg had no effect on blood pressure, but caused similar and significant reductions in stroke volume and cardiac output in both groups. Subjects who tolerated LBNP had significant reflex increases in HR, MSNA burst frequency and burst amplitude with LBNP of -15 mmHg. These responses were absent in those who experienced presyncope. The gain of the cardiac baroreflex regulation of MSNA was markedly attenuated in pre-syncopal subjects (1.2±0.6 versus 8.8±1.4 bursts/100 heart beats per mmHg; P < 0.001). Healthy subjects who experience presyncope in response to LBNP appear more dependent, when supine, upon MSNA to maintain preload, and less able to increase sympathetic vasoconstrictor discharge to skeletal muscle reflexively in response to orthostatic stimuli.
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March 2001
Research Article|
January 31 2001
Attenuated cardiac baroreflex in men with presyncope evoked by lower body negative pressure
Duminda N. WIJEYSUNDERA
;
Duminda N. WIJEYSUNDERA
1Division of Cardiology of the Toronto General and Mount Sinai Hospitals and the University of Toronto, Suite 1614, 600 University Avenue, Toronto, Ontario, Canada M5G 1X5
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Gary C. BUTLER
;
Gary C. BUTLER
1Division of Cardiology of the Toronto General and Mount Sinai Hospitals and the University of Toronto, Suite 1614, 600 University Avenue, Toronto, Ontario, Canada M5G 1X5
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Shin-ichi ANDO
;
Shin-ichi ANDO
1Division of Cardiology of the Toronto General and Mount Sinai Hospitals and the University of Toronto, Suite 1614, 600 University Avenue, Toronto, Ontario, Canada M5G 1X5
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Michael J. POLLARD
;
Michael J. POLLARD
1Division of Cardiology of the Toronto General and Mount Sinai Hospitals and the University of Toronto, Suite 1614, 600 University Avenue, Toronto, Ontario, Canada M5G 1X5
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Peter PICTON
;
Peter PICTON
1Division of Cardiology of the Toronto General and Mount Sinai Hospitals and the University of Toronto, Suite 1614, 600 University Avenue, Toronto, Ontario, Canada M5G 1X5
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John S. FLORAS
1Division of Cardiology of the Toronto General and Mount Sinai Hospitals and the University of Toronto, Suite 1614, 600 University Avenue, Toronto, Ontario, Canada M5G 1X5
Correspondence: Dr John S. Floras (e-mail john.floras@utoronto.ca).
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Clin Sci (Lond) (2001) 100 (3): 303–309.
Article history
Received:
August 03 2000
Revision Received:
October 20 2000
Accepted:
November 24 2000
Citation
Duminda N. WIJEYSUNDERA, Gary C. BUTLER, Shin-ichi ANDO, Michael J. POLLARD, Peter PICTON, John S. FLORAS; Attenuated cardiac baroreflex in men with presyncope evoked by lower body negative pressure. Clin Sci (Lond) 1 March 2001; 100 (3): 303–309. doi: https://doi.org/10.1042/cs1000303
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