Document Detail

Cerebral critical closing pressure and CO2 responses during the progression toward syncope.
MedLine Citation:
PMID:  23372147     Owner:  NLM     Status:  MEDLINE    
Syncope from sustained orthostasis results from cerebral hypoperfusion associated with reductions in arterial pressure at the level of the brain (BPMCA) and reductions in arterial CO2 as reflected by end-tidal values (PetCO2). It was hypothesized that reductions in PetCO2 increase cerebrovascular tone before a drop in BPMCA that ultimately leads to syncope. Twelve men (21-42 yr of age) completed an orthostatic tolerance test consisting of head-up tilt and progressive lower body negative pressure to presyncope, before and after completing 5 days of continuous head-down bed rest (HDBR). Cerebral blood velocity (CBFV), BPMCA, and PetCO2 were continuously recorded throughout the test. Cerebrovascular indicators, cerebrovascular resistance, critical closing pressure (CrCP), and resistance area product (RAP), were calculated. Comparing from supine baseline to 6-10 min after the start of tilt, there were reductions in CBFV, PetCO2, BPMCA, and CrCP, an increase in RAP, and no change in cerebrovascular resistance index. Over the final 15 min before syncope in the pre-HDBR tests, CBFV and CrCP were significantly related to changes in PetCO2 (r = 0.69 ± 0.17 and r = 0.63 ± 0.20, respectively), and BPMCA, which was not reduced until the last minute of the test, was correlated with a reduction in RAP (r = 0.91 ± 0.09). Post-HDBR, tilt tolerance was markedly reduced, and changes in CBFV were dominated by a greater reduction in BPMCA with no relationships to PetCO2. Therefore, pre-HDBR, changes in PetCO2 with orthostasis contributed to increases in cerebrovascular tone and reductions in CBFV during the progression toward syncope, whereas, after 5 days of HDBR, orthostatic responses were dominated by changes in BPMCA.
K A Zuj; P Arbeille; J K Shoemaker; R L Hughson
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2013-01-31
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  114     ISSN:  1522-1601     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2013 Mar 
Date Detail:
Created Date:  2013-03-18     Completed Date:  2013-09-05     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  United States    
Other Details:
Languages:  eng     Pagination:  801-7     Citation Subset:  IM    
University of Waterloo, Waterloo, Ontario, Canada.
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MeSH Terms
Biological Markers / blood
Blood Flow Velocity
Blood Pressure*
Carbon Dioxide / blood*
Cerebral Arteries / physiopathology*,  ultrasonography
Cerebrovascular Circulation*
Lower Body Negative Pressure
Orthostatic Intolerance / blood,  diagnosis,  etiology*,  physiopathology
Supine Position
Syncope / blood,  diagnosis,  etiology*,  physiopathology
Tilt-Table Test
Time Factors
Ultrasonography, Doppler, Transcranial
Vascular Resistance
Young Adult
Reg. No./Substance:
0/Biological Markers; 124-38-9/Carbon Dioxide
Comment In:
J Appl Physiol (1985). 2013 Apr;114(8):1122   [PMID:  23588545 ]
J Appl Physiol (1985). 2013 Apr;114(8):1121   [PMID:  23588544 ]

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