Document Detail

Human responses to upright tilt: a window on central autonomic integration.
MedLine Citation:
PMID:  10332107     Owner:  NLM     Status:  MEDLINE    
1. We examined interactions between haemodynamic and autonomic neural oscillations during passive upright tilt, to gain better insight into human autonomic regulatory mechanisms. 2. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, respiration and peroneal nerve muscle sympathetic activity in nine healthy young adults. Subjects breathed in time with a metronome at 12 breaths min-1 (0.2 Hz) for 5 min each, in supine, and 20, 40, 60, 70 and 80 deg head-up positions. We performed fast Fourier transform (and autoregressive) power spectral analyses and integrated low-frequency (0.05-0.15 Hz) and respiratory-frequency (0. 15-0.5 Hz) spectral powers. 3. Integrated areas of muscle sympathetic bursts and their low- and respiratory-frequency spectral powers increased directly and significantly with the tilt angle. The centre frequency of low-frequency sympathetic oscillations was constant before and during tilt. Sympathetic bursts occurred more commonly during expiration than inspiration at low tilt angles, but occurred equally in expiration and inspiration at high tilt angles. 4. Systolic and diastolic pressures and their low- and respiratory-frequency spectral powers increased, and R-R intervals and their respiratory-frequency spectral power decreased progressively with the tilt angle. Low-frequency R-R interval spectral power did not change. 5. The cross-spectral phase angle between systolic pressures and R-R intervals remained constant and consistently negative at the low frequency, but shifted progressively from positive to negative at the respiratory frequency during tilt. The arterial baroreflex modulus, calculated from low-frequency cross-spectra, decreased at high tilt angles. 6. Our results document changes of baroreflex responses during upright tilt, which may reflect leftward movement of subjects on their arterial pressure sympathetic and vagal response relations. The intensity, but not the centre frequency of low-frequency cardiovascular rhythms, is modulated by the level of arterial baroreceptor input. Tilt reduces respiratory gating of sympathetic and vagal motoneurone responsiveness to stimulatory inputs for different reasons; during tilt, sympathetic stimulation increases to a level that overwhelms the respiratory gate, and vagal stimulation decreases to a level below that necessary for maximal respiratory gating to occur.
W H Cooke; J B Hoag; A A Crossman; T A Kuusela; K U Tahvanainen; D L Eckberg
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Journal of physiology     Volume:  517 ( Pt 2)     ISSN:  0022-3751     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  1999 Jun 
Date Detail:
Created Date:  1999-08-02     Completed Date:  1999-08-02     Revised Date:  2013-06-11    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  617-28     Citation Subset:  IM; S    
Department of Medicine and Physiology, Hunter Holmes McGuire Department of Veterans Affairs Medical Center and Medical College of Virginia at Virginia Commonwealth University, Richmond, VA 23249, USA.
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MeSH Terms
Autonomic Nervous System / physiology*
Blood Pressure / physiology
Heart Rate / physiology
Muscles / innervation
Posture / physiology*
Sympathetic Nervous System / physiology
Tilt-Table Test
Grant Support
D L Eckberg / Med Coll VA, Richmond
Comment In:
J Physiol. 1999 Jun 1;517 ( Pt 2):316   [PMID:  10332083 ]

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