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1 Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan2 Applied Physiology Laboratory, Toyota Technological Institute, Nagoya 468-8511, Japan3 Faculty of Human Development, Kobe University, Kobe 657-8501, Japan
We tested the hypothesis that in humans, carotid-baroreflex dynamic responses (evaluated by examining the time course of the carotid-baroreflex-induced alterations in muscle sympathetic nerve activity (MSNA), mean arterial blood pressure (MAP) and heart rate (HR)) would be altered during mild orthostatic stress in ways that serve to limit orthostatic hypotension. In 12 healthy subjects (10 male, 2 female), 5-s periods of neck pressure (NP) (50 mmHg) and neck suction (NS) (– 60 mmHg) were used to evaluate carotid baroreflex function at rest (CON) and during lower body negative pressure (LBNP) (–15 mmHg). During LBNP (as compared with CON) (a) the augmentations in MSNA and MAP elicited by NP were greater, (b) the NS-induced period of MSNA suppression was, if anything, shorter, (c) the peak decrement in MAP elicited by NS, although not different in amplitude, occurred earlier and recovered to its initial level more quickly after NS, and (d) the HR responses to NP and NS were greater. These results suggest that during mild orthostatic stress, carotid-baroreflex dynamic responses are modulated in ways that should help maintain blood pressure and limit orthostatic hypotension.
(Received 21 October 2003;
accepted after revision 2 March 2004;
first published online 5 March 2004)
Corresponding author T. Nishiyasu: Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan. Email: nisiyasu{at}taiiku.tsukuba.ac.jp
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