|Increased vasoconstriction predisposes to hyperpnea and postural faint.|
|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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|Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't Date: 2008-05-23|
|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|
|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|
|Languages: eng Pagination: H372-81 Citation Subset: IM|
|Department of Pediatrics, New York Medical College, Hawthorne, NY 10532, USA. email@example.com|
|APA/MLA Format Download EndNote Download BibTex|
Leg / blood supply
Pelvis / blood supply
Regional Blood Flow
Sympathetic Nervous System / physiopathology
Syncope / physiopathology*
Thorax / blood supply*
|1R01 HL074873/HL/NHLBI NIH HHS; 1R01 HL66007/HL/NHLBI NIH HHS; R01 HL074873/HL/NHLBI NIH HHS|
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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