Changes in arterial cerebral blood volume during lower body negative pressure measured with MRI

Abstract

Cerebral Autoregulation (CA), defined as the ability of the cerebral vasculature to maintain stable levels of blood flow despite changes in systemic blood pressure, is a critical factor in neurophysiological health. Magnetic resonance imaging (MRI) is a powerful technique for investigating cerebrovascular function, offering high spatial resolution and wide fields of view (FOV), yet it is relatively underutilized as a tool for assessment of CA. The aim of this study was to demonstrate the potential of using MRI to measure changes in cerebrovascular resistance in response to lower body negative pressure (LBNP). A Pulsed Arterial Spin Labeling (PASL) approach with short inversion times (TI) was used to estimate cerebral arterial blood volume (CBV) in eight healthy subjects at baseline and -40mmHg LBNP. We estimated group mean CBV values of 3.13 ± 1.00 and 2.70 ± 0.38 for baseline and lbnp respectively, which were the result of a differential change in CBV during -40mmHg LBNP that was dependent on baseline CBV. These data suggest that the PASL CBV estimates are sensitive to the complex cerebrovascular response that occurs during the moderate orthostatic challenge delivered by LBNP, which we speculatively propose may involve differential changes in vascular tone within different segments of the arterial vasculature. These novel data provide invaluable insight into the mechanisms that regulate perfusion of the brain, and establishes the use of MRI as a tool for studying CA in more detail.

Cerebral Autoregulation Evidenced by Synchronized Low Frequency Oscillations in Blood Pressure and Resting-State fMRI

“…SNA regulates blood pressure via modulation of peripheral vascular tone (Fisher and Paton, 2012), but also potentially influences cerebrovascular tone (Brassard et al, 2017), and increases in SNA elicited by post exercise induced ischemia have been shown to decrease compliance in the brain’s major arteries (Warnert et al, 2016). Orthostatic challenges such as lower body negative pressure (LBNP), which are associated with increases in SNA, lead to considerable reductions in MCA CBFV (Levine et al, 1994; Serrador et al, 2000; Zhang and Levine, 2007), and reductions in blood volume indicative of vasoconstriction in the brain’s largest arteries (Whittaker et al, 2017). Furthermore, studies have shown that ganglion blockade designed to dampen SNA, significantly alter the dynamics between MAP and CBFV (Zhang et al, 2002; Mitsis et al, 2009), suggesting autonomic neural control cerebrovascular tone likely plays a role in beat-to-beat CBF regulation.…”

Rude mechanicals in brain haemodynamics: non-neural actors that influence blood flow

“…R. Soc. B 376: 20190635 arterial CBV dependent on baseline arterial CBV [43]. These results may indicate that there are differential changes in vascular tone within different segments of the vascular tree; that is, different sized vessels respond differently to BP changes, with large arteries decreasing volume (approx.…”

MRI techniques to measure arterial and venous cerebral blood volume

“…In MRI, magnetically labeled blood water spins can be adopted as endogenous tracers that are impermeable to arterial vessel wall but can diffuse freely across the blood brain barrier in capillaries, such as the arterial spin labeling (ASL) methodology (Detre et al, 1992;Williams et al, 1992). In principle, CBVa can be estimated from the difference signal between the label and control scans in ASL when the post-labeling delay (PLD) is short (Chappell et al, 2010;Warnert et al, 2015;Whittaker et al, 2017), or from the difference ASL signals acquired at multiple PLDs (Chappell et al, 2010;Hales et al, 2013). A series of other ASL based CBVa approaches have been developed.…”