| Initial orthostatic hypotension and cerebral blood flow regulation: effect of α1-adrenoreceptor activity. | |
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MedLine Citation:
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PMID: 23174860 Owner: NLM Status: Publisher |
Abstract/OtherAbstract:
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We examined the hypothesis that alpha(1) (α(1)) -adrenergic blockade would lead to an inability to correct initial orthostatic hypotension (IOH) and cerebral hypoperfusion, leading to symptoms of pre-syncope. Twelve normotensive humans (aged 25±1yrs; mean±SE) attempted to complete a 3-min upright stand, 90 min after the administration of either α(1)-blockade (Prazosin, 1 mg/20 kg body weight) or placebo. Continuous beat-to-beat measurements of middle cerebral artery velocity (MCAv; Doppler), blood pressure (finometer), heart rate, and end-tidal PCO(2) were obtained. Compared to placebo, the α(1)-blockade reduced resting mean arterial blood pressure (MAP) (-15%; P<0.01); MCAv remained unaltered (P≥0.28). Upon standing, although the absolute level of MAP was lower following α(1)-blockade (39±10 mmHg vs. 51±14 mmHg), the relative difference in IOH was negligible in both trials (mean difference in MAP: 2±2 mm Hg; P=0.50). Compared to the placebo trial, the declines in MCAv and P(ET)CO(2) during IOH were greater in the α(1)-blockade trial by 12±4 cm•s(-1) and 4.4±1.3 mm Hg, respectively (P≤0.01). Standing tolerance was markedly reduced in the α(1)-blockade trial (75±17 s vs. 180±0 s; P<0.001). In summary, while IOH was little affected by α(1)- blockade, the associated decline in MCAv was greater in the blockade condition. Unlike in the placebo trial, the extent of IOH and cerebral hypoperfusion failed to recover towards baseline in the α(1)-blockade trial leading to pre-syncope. Although, the development of IOH is not influenced by the α(1)-adrenergic receptor pathway, this reflex is critical in the recovery from IOH to prevent cerebral hypoperfusion and ultimately syncope. |
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Authors:
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Nia C S Lewis; Philip N Ainslie; Greg Atkinson; Helen Jones; Emily J M Grant; Samuel J E Lucas |
Publication Detail:
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Type: JOURNAL ARTICLE Date: 2012-11-21 |
Journal Detail:
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Title: American journal of physiology. Regulatory, integrative and comparative physiology Volume: - ISSN: 1522-1490 ISO Abbreviation: Am. J. Physiol. Regul. Integr. Comp. Physiol. Publication Date: 2012 Nov |
Date Detail:
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Created Date: 2012-11-23 Completed Date: - Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 100901230 Medline TA: Am J Physiol Regul Integr Comp Physiol Country: - |
Other Details:
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Languages: ENG Pagination: - Citation Subset: - |
Affiliation:
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1University of British Columbia. |
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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