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Altered cortical activation patterns associated with baroreflex unloading following 24 h of physical deconditioning.

Abstract：

:Cardiovascular arousal is associated with patterned cortical activity changes. Head-down-tilt bed rest (HDBR) dimishes the baroreflex-mediated cardiac control. The present study tested the hypothesis that HDBR deconditioning would modify the forebrain organization for heart rate (HR) control during baroreflex unloading. Heart rate variability (HRV), blood pressure and plasma hormones were analysed at rest, whereas HR and cortical autonomic activation patterns (functional magnetic resonance imaging) were measured during graded and randomly assigned lower body negative pressure treatments (LBNP, -15 and -35 mmHg) both before (Pre) and after (Post) a 24 h HDBR protocol (study 1; n = 8). An additional group was tested before and following diuretic-induced hypovolaemia (study 2; n = 9; spironolactone, 100 mg day(-1) for 3 days) that mimicked the plasma volume lost during HDBR (-15% in both studies; P < 0.05). Head-down bed rest with hypovolaemia did not affect baseline HR, mean arterial pressure, HRV or plasma catecholamines. Head-down bed rest augmented the LBNP-induced HR response (P < 0.05), and this was associated with bed-rest-induced development of the following changes: (i) enhanced activation within the genual anterior cingulate cortex and the right anterior insular cortex; and (ii) deactivation patterns within the subgenual regions of the anterior cingulate cortex. Diuretic treatment (without HDBR) did not affect baseline HR and mean arterial pressure, but did reduce resting HRV and elevated circulating noradrenaline 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 24 h of HDBR minimized the impact of diuretic treatment on baseline autonomic and cardiovascular variables. The findings also indicate that despite the similar augmentation of HR responses to LBNP and despite similar pre-intervention cortical activation patterns, HDBR and diuretic treatment produced different effects on the cortical responses, with HDBR affecting anterior cingulate cortex and right insula regions, whereas diuretic treatment 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 unloading, changes that are distinct from diuretic-induced hypovolaemia. The results suggest that physical activity patterns exert a rapid and notable impact on the cortical circuitry associated with cardiovascular control.

journal_name

Exp Physiol

journal_title

Experimental physiology

authors

Shoemaker JK,Usselman CW,Rothwell A,Wong SW

doi

10.1113/expphysiol.2012.065557

subject

Has Abstract

pub_date

2012-12-01 00:00:00

pages

1249-62

issue

eissn

0958-0670

issn

1469-445X

pii

expphysiol.2012.065557

journal_volume

pub_type

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Altered cortical activation patterns associated with baroreflex unloading following 24 h of physical deconditioning.