Brainstem grey matter changes associated with blood pressure and sympathetic outflow in hypertension
Poster No:
1868
Submission Type:
Abstract Submission
Authors:
Donggyu Rim1, Tye Dawood2, Rania Fatouleh3, Luke Henderson4, Brendan McCarthy2, Gianni Sesa-Ashton2, Annemarie Henessy5, Markus Schlaich6, Vaughan Macefield1
Institutions:
1Monash University, Melbourne, Victoria, 2Baker Heart and Diabetes Institute, Melbourne, Victoria, 3University of Western Sydney, Sydney, New South Wales, 4Univeresity of Sydney, Sydney, New South Wales, 5University of Sydney, Sydney, New South Wales, 6University of Western Australia, Perth, Western Australia
First Author:
Co-Author(s):
Introduction:
Despite the high prevalence of hypertension worldwide, its underlying causes remain largely unknown. It is well-established that on-going neural activity in nuclei within the brainstem are critical for modulating beat-to-beat changes as well as setting the overall level of resting blood pressure and sympathetic drive (Dampney et al., 1994). Our study aimed to determine whether the anatomy of these brainstem regions is associated with changes in mean blood pressure (MBP) and muscle sympathetic nerve activity (MSNA) in individuals with hypertension.
Methods:
T1-weighted anatomical magnetic resonance imaging (MRI) scans, MBP, and MSNA were acquired from 25 hypertensive patients and 50 normotensive subjects. The study was conducted as a cross-sectional study design. Participants were classified as hypertensive for use in the current study if they were previously diagnosed with hypertension and currently use peripherally acting antihypertensive medications. Untreated participants with a seated average systolic blood pressure (BP) ≥130 mmHg and diastolic BP ≥80 mmHg were also classified as hypertensive for the purposes of the study. Participants refrained from taking caffeinated drinks, intense exercise or smoking for at least 1hr before the measurement. Using Statistical Parametric Mapping (SPM) 12 software (MATLAB vR2023a), all T1 images were realigned and spatially normalized to the Montreal Neurological Institute (MNI) template, and segmented into grey matter, white matter and cerebrospinal fluid images. The grey matter images were then modulated by the volume changes due to the normalization and smoothed by a 5 mm full-width half-maximum Gaussian filter. In addition, to explore regional brainstem anatomy we performed a brainstem-specific analysis for each participant using the Spatially Unbiased Infratentorial template (SUIT) toolbox (Diedrichsen et al., 2011). The whole-brain images were cropped, and the brainstem was masked to remove all supratentorial grey matter. The brainstem images were then spatially normalized with a dedicated symmetrical brainstem template into MNI space, and modulated by the volume changes due to the normalization. Finally, the resulting brainstem "maps" of grey matter density were smoothed using a 3 mm full-width half-maximum Gaussian filter. To determine the relationships between grey matter density and resting MBP and MSNA, we entered the forebrain and brainstem grey matter density maps from each individual into the second level, one group, random effects, voxel-by-voxel analyses (p<0.001 uncorrected for multiple comparisons). Age, sex, and total intracranial volume were included as nuisance variables. A minimum cluster size of 10 contiguous significant voxels was set for all analyses to reduce the likelihood of Type 1 errors.
Results:
In the brainstem, alterations in grey matter densities correlated with MBP were observed in important cardiovascular regulatory regions including the nucleus tractus solitarius (NTS), medullary raphé, and rostral ventrolateral medulla (RVLM) for the entire cohort. However, no direct relationship was observed between grey matter density and MSNA. Group-level correlation analysis of NTS, RVLM, and medullary raphé grey matter density and MBP revealed a positive association for the control group but not with the hypertensive group. Moreover, the hypertensive group showed a negative association between medullary grey matter density and MSNA, but this relationship was not observed for RVLM or NTS. Additionally, in the forebrain, grey matter density in the parahippocampus was associated with mean BP, while the frontal operculum was associated with MSNA.
·Grey matter changes positively associated with MBP.
Conclusions:
Our study revealed structural changes in the brainstem cardiovascular regulatory centres associated with blood pressure. However, these structural alterations were not linked to changes in MSNA. Further studies are needed to explore whether functional rather than structural changes may account for the elevations in MSNA in hypertension.
Novel Imaging Acquisition Methods:
Anatomical MRI 1
Physiology, Metabolism and Neurotransmission:
Neurophysiology of Imaging Signals 2
Keywords:
Brainstem
MRI
Nerves
STRUCTURAL MRI
1|2Indicates the priority used for review
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Diedrichsen, J., Maderwald, S., Küper, M., Thürling, M., Rabe, K., Gizewski, E. R., ... & Timmann, D. (2011). Imaging the deep cerebellar nuclei: a probabilistic atlas and normalization procedure. Neuroimage, 54(3), 1786-1794.