RELATIVE CONTRIBUTIONS OF CARDIOPULMONARY AND SINOAORTIC BAROREFLEXESIN CAUSING SYMPATHETIC ACTIVATION IN THE HUMAN SKELETAL-MUSCLE CIRCULATION DURING ORTHOSTATIC STRESS
Tn. Jacobsen et al., RELATIVE CONTRIBUTIONS OF CARDIOPULMONARY AND SINOAORTIC BAROREFLEXESIN CAUSING SYMPATHETIC ACTIVATION IN THE HUMAN SKELETAL-MUSCLE CIRCULATION DURING ORTHOSTATIC STRESS, Circulation research, 73(2), 1993, pp. 367-378
The aim of this study was to reexamine the hypothesis that cardiopulmo
nary baroreflexes are more important than sinoaortic baroreflexes in c
ausing vasoconstriction in the skeletal muscle circulation during orth
ostatic stress. We recorded muscle sympathetic nerve activity (MSNA) w
ith microelectrodes in the peroneal nerve (and forearm blood How with
venous occlusion plethysmography) in normal subjects (innervated ventr
icles) and in heart transplant recipients (denervated ventricles) duri
ng graded lower body negative pressure (LBNP) performed alone and in c
ombination with intravenous infusion of phenylephrine, which was titra
ted to eliminate the orthostatically induced fall in blood pressure an
d thus the unloading of both carotid and aortic baroreceptors. The pri
ncipal new findings are as follows: (1) The increases in both MSNA and
forearm vascular resistance during multiple levels of LBNP were not a
ttenuated by heart transplantation, which causes ventricular but not s
inoaortic deafferentation. (2) In heart transplant recipients, a small
increase in MSNA during mild LBNP was dependent on a decrease in arte
rial pressure, but in normal subjects, a similar increase in MSNA occu
rred in the absence of any detectable decrease in the aortic pressure
stimulus to the sinoaortic baroreceptors. (3) In normal subjects, the
large increase in MSNA during a high level of LBNP was dependent on a
decrease in arterial pressure and could be dissociated from the decrea
se in central venous pressure. Taken together, the findings strongly s
uggest that sinoaortic baroreflexes are much more important and ventri
cular baroreflexes are much less important than previously thought in
causing reflex sympathetic activation and vasoconstriction in the huma
n skeletal muscle circulation during orthostatic stress.