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Departments of Medicine and Cellular and Molecular Physiology, Division of Cardiology, General Clinical Research Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
Studies
have suggested that premenopausal women are more prone to orthostatic
intolerance than men. Additionally, it has been postulated that the
vestibulosympathetic reflex is important in regulating postural-related
changes in sympathetic activity. The purpose of the present study was
to determine whether men and women differ in their sympathetic and
cardiovascular responses to stimulation of the otolith organs elicited
by head-down rotation (HDR). Heart rate (HR), arterial pressure, calf
blood flow (CBF), and leg muscle sympathetic nerve activity (MSNA) were
measured during 3 min of HDR in the prone posture in 33 women and 30 men. With the exception of HR (71 ± 2 and 63 ± 1 beats/min
for women and men, respectively; P < 0.01), all
baseline variables were not different between genders. There were no
gender differences in responses to HDR. MSNA increased 72 ± 33 units (43%) in the men and 88 ± 15 units (59%) in the women
during HDR (P < 0.01). CBF decreased [
0.6 ± 0.1 (15%) and
0.5 ± 0.1 (19%)
ml · min
1 · 100 ml
1] and
calf vascular resistance increased [8 ± 2 (21%) and 11 ± 3 (25%) units during HDR for men and women, respectively
(P < 0.01)]. Both in the men and women, HR increased
2 ± 1 beats/min (P < 0.01). These results
demonstrate that sympathetic activation during HDR in the prone posture
is similar in men and women. Therefore, these findings suggest that the
vestibulosympathetic reflex is not different between healthy men and women.
autonomic nervous system; cardiovascular control; orthostasis; gender; spaceflight
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