Interaction of central venous pressure, intramuscular pressure and
carotid baroreflex function.
Shi, Xiangrong, Brian H. Foresman, and Peter B. Raven.
Departments of Integrative Physiology and The Cardiovascular
Research Institute, University of North Texas Health Science Center,
Fort Worth, Texas 76107
APStracts 3:0433H, 1996.
Seven healthy volunteer men participated in an experiment involving
lower body positive pressure (LBPP) of 30 torr and acute volume
expansion (VE) of 5-6% (VE-I) and 9-10% (VE-II) of their total blood
volume (TBV) to differentiate the effect of increased intramuscular
pressure and central venous pressure (CVP) on the maximal gain (Gmax)
of the carotid baroreflex. During each experimental condition the
heart rate (HR), mean arterial pressure (MAP, intra-radial artery or
Finapres) and CVP (at the 3rd-4th intercostal space) were monitored
continuously. Gmax was derived from the logistic modeling of the HR
and MAP responses to ramped changes in carotid sinus transmural
pressure using a protocol of pulsatile changes in neck chamber
pressure from +40 to -65 torr. The increases in CVP during +30 torr
LBPP was 1.5 mmHg (P<0.05) and was similar to that observed
during VE-I (1.7 mmHg, P>0.05). The Gmax of the carotid
baroreflex of HR and MAP was significantly decreased during LBPP by
-0.145+/-0.039 bpm/mmHg (-38%) and -0.071+/-0.013 mmHg/mmHg (-25%).
However, VE-I did not affect Gmax. During VE-II CVP was significantly
greater than those elicited by LBPP and the Gmax of the carotid
baroreflex of the HR and MAP responses were significantly reduced. We
conclude that carotid baroreflex responsiveness was selectively
inhibited by increasing intramuscular pressure possibly resulting in
an activation of the intramuscular mechanoreceptors during LBPP.
Furthermore, it would appear that the inhibition of the carotid
baroreflex via cardiopulmonary baroreceptor loading (increased CVP)
occurred when a threshold pressure (CVP) was achieved.
Received 24 March 1996; accepted in final form 20 September 1996.
APS Manuscript Number H278-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996