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'Non-hypotensive' hypovolaemia reduces ascending aortic dimensions in humans1. The notion that small, 'non-hypotensive' reductions of effective blood volume alter neither arterial pressure nor arterial baroreceptor activity is pervasive in the experimental literature. We tested two hypotheses: (a) that minute arterial pressure and cardiac autonomic outflow changes during hypovolaemia induced by lower body suction in humans are masked by alterations in breathing, and (b) that evidence for arterial baroreflex engagement might be obtained from measurements of thoracic aorta dimensions. 2. In two studies, responses to graded lower body suction at 0 (control), 5, 10, 15, 20 and 40 mmHg were examined in twelve and ten healthy young men, respectively. In the first, arterial pressure (photoplethysmograph), R-R interval, and respiratory sinus arrhythmia amplitude (complex demodulation) were measured during uncontrolled and controlled breathing (constant breathing frequency and tidal volume). In the second, cross-sectional areas of the ascending thoracic aorta were calculated from nuclear magnetic resonance images. 3. Lower body suction with controlled breathing resulted in an increased arterial pulse pressure at mild levels (5-20 mmHg; ANOVA, P < 0.05) and a decreased arterial pulse pressure at moderate levels (40 mmHg; ANOVA, P < 0.05). Both R-R intervals and respiratory sinus arrhythmia were negatively related to lower body suction level, whether group averages (general linear regression, r > 0.92) or individual subjects (orthogonal polynomials, 12 of 12 subjects) were assessed. 4. Aortic pulse area decreased progressively and significantly during mild lower body suction, with 47% of the total decline occurring by 5 mmHg. 5. These results suggest that small reductions of effective blood volume reduce aortic baroreceptive areas and trigger haemodynamic adjustments which are so efficient that alterations in arterial pressure escape detection by conventional means.
Document ID
20050000234
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Taylor, J. A.
(Hunter Holmes McGuire Department of Veterans Affairs Medical Center Richmond, VA, United States)
Halliwill, J. R.
Brown, T. E.
Hayano, J.
Eckberg, D. L.
Date Acquired
August 22, 2013
Publication Date
February 15, 1995
Publication Information
Publication: The Journal of physiology
Volume: 483 ( Pt 1)
ISSN: 0022-3751
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: HL22296
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Cardiopulmonary
Non-NASA Center

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