Document Detail

Mechanism of hypotensive transients associated with abrupt bradycardias in conscious rabbits.
MedLine Citation:
PMID:  17622395     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: Transient bradycardic hypotensive events occur in resting rabbits. If the hypotension is due to vasodepression, these events may be a model for vasovagal syncope. OBJECTIVES: To determine whether these events are responses to brief stimuli and whether the hypotensive episodes are solely due to rapid-onset bradycardia. METHODS: Rabbits were instrumented with subcutaneous electrocardiogram leads, and cannulae were acutely inserted into an ear artery to obtain continuous arterial pressure measurements. Exposure to brief, low-level auditory stimuli at 5 kHz transiently increased the RR interval by approximately 70 ms and decreased mean arterial pressure by approximately 5 mmHg. RESULTS: These evoked bradycardic hypotensive events were almost identical to previously reported spontaneous bradycardic hypotensive events. Intra-aortic telemetric blood pressure monitoring was used to demonstrate that the evoked hypotension reflected prolonged diastole, rather than local ear arterial vasoconstriction. Furthermore, administration of the muscarinic blocker glycopyrrolate abolished not only bradycardia (RR interval 64+/-14 ms to 1+/-1 ms; P<0.0001), but also hypotension (--4.1+/-0.8 mmHg to --0.4+/-0.3 mmHg; P=0.0055). Finally, cardiac pacing abolished the inducible bradycardia (RR interval 51+/-10 ms to 2+/-1 ms; P=0.0006) and its associated hypotension (--4.1+/-0.7 mmHg to --1.2+/-0.3 mmHg; P=0.003). CONCLUSIONS: Brief auditory stimuli evoked a transient bradycardia mediated by cardiac muscarinic receptors and consequent hypotension. This is not a model for vasovagal syncope.
Robert S Sheldon; Christopher I Wright; Henry J Duff; Ela Thakore; Anne M Gillis; Daniel E Roach
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The Canadian journal of cardiology     Volume:  23     ISSN:  0828-282X     ISO Abbreviation:  Can J Cardiol     Publication Date:  2007 Jul 
Date Detail:
Created Date:  2007-07-11     Completed Date:  2007-08-28     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  8510280     Medline TA:  Can J Cardiol     Country:  Canada    
Other Details:
Languages:  eng     Pagination:  721-6     Citation Subset:  IM    
Cardiovascular Research Group, University of Calgary, Alberta.
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MeSH Terms
Autonomic Nervous System / physiopathology*
Blood Pressure / physiology*
Bradycardia / complications*,  physiopathology
Disease Models, Animal
Heart Rate / physiology*
Hypotension / etiology*,  physiopathology
Risk Factors
Vasoconstriction / physiology
Vasodilation / physiology

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

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