Document Detail

Initial orthostatic hypotension and cerebral blood flow regulation: effect of α1-adrenoreceptor activity.
MedLine Citation:
PMID:  23174860     Owner:  NLM     Status:  Publisher    
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.
Nia C S Lewis; Philip N Ainslie; Greg Atkinson; Helen Jones; Emily J M Grant; Samuel J E Lucas
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-11-21
Journal Detail:
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:
Created Date:  2012-11-23     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100901230     Medline TA:  Am J Physiol Regul Integr Comp Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
1University of British Columbia.
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