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Effects of Lower Body Negative
Pressure on Cardiac and Vascular Responses to Carotid Baroreflex
Stimulation
C. M. BROWN, M. J HECHT, B.
NEUNDÖRFER, M. J. HILZ
Autonomic Laboratory, Department of Neurology, University of
Erlangen-Nuremberg, Erlangen, Germany
Received June 24, 2002
Accepted February 27, 2003
Summary
The aim of this study was to assess carotid baroreflex responses
during graded lower body negative pressure (LBNP). In 12 healthy
subjects (age 29±4 years) we applied sinusoidal neck suction (0
to –30 mmHg) at 0.1 Hz to examine the sympathetic modulation of
the heart and blood vessels and at 0.2 Hz to assess the effect
of parasympathetic stimulation on the heart. Responses to neck
suction were determined as the change in spectral power of
RR-interval and blood pressure from baseline values.
Measurements were carried out during progressive applications (0
to –50 mmHg) of LBNP. Responses to 0.1 and 0.2 Hz carotid
baroreceptor stimulations during low levels of LBNP (–10 mmHg)
were not significantly different from those measured during
baseline. At higher levels of LBNP, blood pressure responses to
0.1 Hz neck suction were significantly enhanced, but with no
significant change in the RR-interval response. LBNP at all
levels had no effect on the RR-interval response to 0.2 Hz neck
suction. The unchanged responses of RR-interval and blood
pressure to neck suction during low level LBNP at –10 mmHg
suggest no effect of cardiopulmonary receptor unloading on the
carotid arterial baroreflex, since this LBNP level is considered
to stimulate cardiopulmonary but not arterial baroreflexes.
Enhanced blood pressure responses to neck suction during higher
levels of LBNP are not necessarily the result of a reflex
interaction but may serve to protect the circulation from
fluctuations in blood pressure while standing.
Key words
Autonomic nervous system • Baroreflex • Blood pressure • Heart
rate variability • Spectral analysis
Reprint requests
Dr Clive M Brown PhD, Autonomic Laboratory, Department of
Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6,
91054 Erlangen, Germany, e-mail:
Clive.Brown@neuro.med.uni-erlangen.de
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