Document Detail

Increased vasoconstriction predisposes to hyperpnea and postural faint.
MedLine Citation:
PMID:  18502909     Owner:  NLM     Status:  MEDLINE    
Our prior studies indicated that postural fainting relates to splanchnic hypervolemia and thoracic hypovolemia during orthostasis. We hypothesized that thoracic hypovolemia causes excessive sympathetic activation, increased respiratory tidal volume, and fainting involving the pulmonary stretch reflex. We studied 18 patients 13-21 yr old, 11 who fainted within 10 min of upright tilt (fainters) and 7 healthy control subjects. We measured continuous blood pressure and heart rate, respiration by inductance plethysmography, end-tidal carbon dioxide (ET(CO(2))) by capnography, and regional blood flows and blood volumes using impedance plethysmography, and we calculated arterial resistance with patients supine and during 70 degrees upright tilt. Splanchnic resistance decreased until faint in fainters (44 +/- 8 to 21 +/- 2 mmHg.l(-1).min(-1)) but increased in control subjects (47 +/- 5 to 53 +/- 4 mmHg.l(-1).min(-1)). Percent change in splanchnic blood volume increased (7.5 +/- 1.0 vs. 3.0 +/- 11.5%, P < 0.05) after the onset of tilt. Upright tilt initially significantly increased thoracic, pelvic, and leg resistance in fainters, which subsequently decreased until faint. In fainters but not control subjects, normalized tidal volume (1 +/- 0.1 to 2.6 +/- 0.2, P < 0.05) and normalized minute ventilation increased throughout tilt (1 +/- 0.2 to 2.1 +/- 0.5, P < 0.05), whereas respiratory rate decreased (19 +/- 1 to 15 +/- 1 breaths/min, P < 0.05). Maximum tidal volume occurred just before fainting. The increase in minute ventilation was inversely proportionate to the decrease in ET(CO(2)). Our data suggest that excessive splanchnic pooling and thoracic hypovolemia result in increased peripheral resistance and hyperpnea in simple postural faint. Hyperpnea and pulmonary stretch may contribute to the sympathoinhibition that occurs at the time of faint.
Indu Taneja; Marvin S Medow; June L Glover; Neeraj K Raghunath; Julian M Stewart
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't     Date:  2008-05-23
Journal Detail:
Title:  American journal of physiology. Heart and circulatory physiology     Volume:  295     ISSN:  0363-6135     ISO Abbreviation:  Am. J. Physiol. Heart Circ. Physiol.     Publication Date:  2008 Jul 
Date Detail:
Created Date:  2008-07-15     Completed Date:  2008-08-21     Revised Date:  2013-06-12    
Medline Journal Info:
Nlm Unique ID:  100901228     Medline TA:  Am J Physiol Heart Circ Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  H372-81     Citation Subset:  IM    
Department of Pediatrics, New York Medical College, Hawthorne, NY 10532, USA.
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MeSH Terms
Blood Pressure
Blood Volume
Cardiography, Impedance
Case-Control Studies
Heart Rate
Leg / blood supply
Pelvis / blood supply
Regional Blood Flow
Respiratory Mechanics
Splanchnic Circulation*
Supine Position
Sympathetic Nervous System / physiopathology
Syncope / physiopathology*
Thorax / blood supply*
Tidal Volume*
Time Factors
Vascular Resistance
Grant Support

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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