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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
We
determined the interaction between the vestibulosympathetic reflex and
the arterial chemoreflex in 12 healthy subjects. Subjects performed
three trials in which continuous recordings of muscle sympathetic nerve
activity (MSNA), mean arterial blood pressure (MAP), heart rate (HR),
and arterial oxygen saturation were obtained. First, in prone subjects
the otolith organs were engaged by use of head-down rotation (HDR).
Second, the arterial chemoreflex was activated by inspiration of
hypoxic gas (10% O2 and 90% N2) for 7 min
with HDR being performed during minute 6. Third, hypoxia was
repeated (15 min) with HDR being performed during minute 14.
HDR [means ± SE; increase (
)7 ± 1 bursts/min and
50 ± 11% for burst frequency and total MSNA, respectively; P < 0.05] and hypoxia (
6 ± 2 bursts/min and
62 ± 29%; P < 0.05) increased MSNA.
Additionally, MSNA increased when HDR was performed during hypoxia
(
11 ± 2 bursts/min and
127 ± 57% change from normoxia; P < 0.05). These increases in MSNA were
similar to the algebraic sum of the individual increase in MSNA
elicited by HDR and hypoxia (
13 ± 1 bursts/min and
115 ± 36%). Increases in MAP (
3 ± 1 mmHg) and HR (
19 ± 1 beats/min) during combined HDR and hypoxia generally were smaller
(P < 0.05) than the algebraic sum of the individual
responses (
5 ± 1 mmHg and
24 ± 2 beats/min for MAP
and HR, respectively; P < 0.05). These findings
indicate an additive interaction between the vestibulosympathetic
reflex and arterial chemoreflex for MSNA. Therefore, it appears that MSNA outputs between the vestibulosympathetic reflex and arterial chemoreflex are independent of one another in humans.
autonomic nervous system; muscle sympathetic nerve activity; blood pressure; chemoreflex; baroreflex
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