Reflex-Mediated Reduction in Human Cerebral Blood Volume

Wilson, Timothy D.; Shoemaker, J. Kevin; Kozak, Roman; Lee, T.-Y.; Gelb, Adrian W.

doi:10.1038/sj.jcbfm.9600015

Cited by 32 publications

(24 citation statements)

References 35 publications

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“…The BOLD signal reflects, in large part, the relative concentration of deoxyhaemoglobin in the postcapillary venuoles. Reductions in cerebral venous volume are observed with levels of LBNP used in this study, with little change in arterial inflow (Wilson et al 2005). Inasmuch as the BOLD response represents a change from some baseline level of regional activation, a generalized change in baseline blood flow or volume distribution could affect the ability to detect a change in BOLD.…”

Section: Limitationsmentioning

confidence: 77%

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

Shoemaker

Usselman²,

Rothwell³

et al. 2012

Experimental Physiology

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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.

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Section: Limitationsmentioning

confidence: 77%

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

Shoemaker

Usselman²,

Rothwell³

et al. 2012

Experimental Physiology

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“…Although we did not observed significant differences in global CVF between patients and controls, an altered postural control of venous outflow was more prevalent in MS patients, particularly in PP phenotype and in more disabled patients. According to Monti et al, such an explanation may be a no efficient Spinal Epidural Veins outflow as an additional drainage pathway in the seated position [38]. However, the cerebral venous system has more anatomical variability than the intracranial system and is often asymmetrical.…”

Section: Discussionmentioning

confidence: 99%

Ultrasonographic Evaluation of Cerebral Arterial and Venous Haemodynamics in Multiple Sclerosis: A Case-Control Study

et al. 2014

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ObjectiveAlthough recent studies excluded an association between Chronic Cerebrospinal Venous Insufficiency and Multiple Sclerosis (MS), controversial results account for some cerebrovascular haemodynamic impairment suggesting a dysfunction of cerebral autoregulation mechanisms. The aim of this cross-sectional, case-control study is to evaluate cerebral arterial inflow and venous outflow by means of a non-invasive ultrasound procedure in Relapsing Remitting (RR), Primary Progressive (PP) Multiple Sclerosis and age and sex-matched controls subjects.Material and MethodsAll subjects underwent a complete extra-intracranial arterial and venous ultrasound assessment with a color-coded duplex sonography scanner and a transcranial doppler equipment, in both supine and sitting position by means of a tilting chair. Basal arterial and venous morphology and flow velocities, postural changes in mean flow velocities (MFV) of middle cerebral arteries (MCA), differences between cerebral venous outflow (CVF) in clinostatism and in the seated position (ΔCVF) and non-invasive cerebral perfusion pressure (CPP) were evaluated.Results85 RR-MS, 83 PP-MS and 82 healthy controls were included. ΔCVF was negative in 45/85 (52.9%) RR-MS, 63/83 (75.9%) PP-MS (p = 0.01) and 11/82 (13.4%) controls (p<0.001), while MFVs on both MCAs in sitting position were significantly reduced in RR-MS and PP-MS patients than in control, particularly in EDSS≥5 subgroup (respectively, 42/50, 84% vs. 66/131, 50.3%, p<0.01 and 48.3±2 cm/s vs. 54.6±3 cm/s, p = 0.01). No significant differences in CPP were observed within and between groups.ConclusionsThe quantitative evaluation of cerebral blood flow (CBF) and CVF and their postural dependency may be related to a dysfunction of autonomic nervous system that seems to characterize more disabled MS patients. It's not clear whether the altered postural control of arterial inflow and venous outflow is a specific MS condition or simply an “epiphenomenon” of neurodegenerative events.

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“…Furthermore, sympatho‐excitatory manoeuvres (e.g. cold pressor test, whole‐body heating or lower body negative pressure) have been reported to evoke reductions in cerebral perfusion and/or increases in cerebrovascular resistance (Micieli et al 1994; Roatta et al 1998; Wilson et al 2005; Low et al 2009). Importantly, the cerebrovascular responses to the cold pressor test are attenuated following administration of clonidine, an α 2 ‐adrenergic receptor agonist with a known ability to inhibit the central actions of noradrenaline, suggesting that the cold pressor test elicits intracerebral vascular changes via a central noradrenergic mechanism (Micieli et al 1994).…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, there is some evidence from human studies that systemic administration of α‐adrenergic agonists (e.g. noradrenaline; Olesen, 1972; Brassard et al 2009; Lucas et al 2010) and sympatho‐excitatory manoeuvres, such as the cold pressor test (Micieli et al 1994; Roatta et al 1998), whole‐body heating (Low et al 2009) and cardiopulmonary baroreceptor unloading with lower body negative pressure (Wilson et al 2005), can evoke increases in cerebrovascular resistance (vasoconstriction) and/or reductions in cerebral perfusion.…”

mentioning

confidence: 99%

Differential responses to sympathetic stimulation in the cerebral and brachial circulations during rhythmic handgrip exercise in humans

Hartwich

Fowler

Wynn

et al. 2010

Experimental Physiology

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The sympathetic neural regulation of the cerebral circulation remains controversial. The purpose of the present study was to determine how exercise modulates the simultaneous responsiveness of the cerebral and brachial circulations to 'endogenous' sympathetic activation (cold pressor test). In nine healthy subjects, heart rate (HR) and mean arterial blood pressure (MAP) were continuously measured during cold pressor tests (4• C water) conducted at rest and during randomized bouts of rhythmic handgrip of 10, 25 and 40% of maximal voluntary contraction. Doppler ultrasound was used to examine brachial artery blood flow (FBF) and middle cerebral artery (MCA) mean blood velocity (V mean ), and indices of vascular conductance were calculated for the brachial artery (forearm vascular conductance, FVC) and MCA (cerebral vascular conductance index, CVCi). End-tidal P CO 2 (P ET,CO 2 ) was evaluated on a breath-by-breath basis. Handgrip evoked increases in HR, FBF, FVC and MCA V mean (P < 0.05 versus rest), while MAP and CVCi were unchanged and P ET,CO 2 fell slightly (P < 0.05 versus rest). Increases in MAP and HR during the cold pressor test were similar at rest and during all handgrip trials. Forearm vascular conductance was markedly reduced with the cold pressor test at rest (−45 ± 8%), but this vasoconstrictor effect was progressively attenuated with increasing exercise intensity (FVC −17 ± 3% during exercise at 40% of maximal voluntary contraction; P < 0.05). In contrast, the small reduction in CVCi with cold pressor test was similar at rest and during handgrip (approximately −5%). Our data indicate that while the marked vasoconstrictor responses to sympathetic activation in the skeletal muscle vasculature are blunted by handgrip exercise, the modest cerebrovascular responses to a cold pressor test remain unchanged.

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Reflex-Mediated Reduction in Human Cerebral Blood Volume

Cited by 32 publications

References 35 publications

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

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

Ultrasonographic Evaluation of Cerebral Arterial and Venous Haemodynamics in Multiple Sclerosis: A Case-Control Study

Differential responses to sympathetic stimulation in the cerebral and brachial circulations during rhythmic handgrip exercise in humans

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