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Altered cortical activation patterns associated with baroreflex unloading following 24 hours of physical deconditioning.
MedLine Citation:
PMID:  22613740     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Cardiovascular arousal is associated with patterned cortical activity changes. Head-down tilt bed rest dimishes baroreflex-mediated cardiac control. The present study tested the hypothesis that head-down bed rest deconditioning would modify the forebrain organization for heart rate control during baroreflex unloading. Heart rate (HR) variability (HRV), blood pressure and plasma hormones were analyzed at rest whereas HR and cortical autonomic activation patterns (functional magnetic resonance imaging) were measured during graded and randomly assigned lower body negative pressure segments (LBNP, -15, and -35 mmHg) both before (Pre) and after (Post) a 24 hour head-down bed rest (HDBR) protocol (Study 1; n=8). An additional group was tested before and following diuretic-induced (Diuretic) hypovolemia (Study 2: n=9; Aldactone, 100 mg/day for 3 days) that mimicked the plasma volume lost during HDBR (-15% in both studies; P<0.05). HDBR with hypovolemia did not affect baseline HR, MAP, HRV or plasma catecholamines. HDBR augmented the LBNP-induced HR response (P<0.05) and this was associated with bedrest-induced development of i) enhanced activation within the genual anterior cingulate cortex (ACC) and the right anterior insular cortex (IC) and ii) deactivation patterns within the subgenual regions of the ACC. Diuretic treatment (without HDBR) did not affect baseline HR and MAP, but did reduce resting HRV and elevated circulating norepinephrine and plasma renin activity (P<0.05). The greater HR response to LBNP following Diuretic (P<0.05) was associated with diminished activation of the right anterior insula. Our findings indicate that a) 24 hours of HDBR minmized the impact of diuretic treatment on baseline autonomic and cardiovascular variables, b) despite the similar augmentation of HR responses to LBNP, and despite similar pre-intervention cortical activation patterns, HDBR and Diuretic produced different effects on the cortical responses with HDBR affecting ACC and right insula regions whereas Diuretic affected primarily the right insula alone but in a direction that was opposite to HDBR. The data indicate that physical deconditioning can induce rapid functional changes within the cortical circuitry associated with baroreflex unoading, changes that are distinct from diuretic-induced hypovolemia. The results suggest that physical activity patterns exert rapid and notable impact on the cortical circuitry associated with cardiovascular control.
Authors:
J Kevin Shoemaker; Charlotte W Usselman; Amanada Rothwell; Savio W Wong
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-5-21
Journal Detail:
Title:  Experimental physiology     Volume:  -     ISSN:  1469-445X     ISO Abbreviation:  -     Publication Date:  2012 May 
Date Detail:
Created Date:  2012-5-22     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9002940     Medline TA:  Exp Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
1 University of Western Ontario;
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