Cerebrovascular Reactivity and Neurovascular Coupling in Multiple Sclerosis-A Systematic Review

Investigation of neuro-vascular reactivity on fMRI study during visual activation in people with multiple sclerosis using EEG and hypercapnia challenge

BACKGROUND

People with multiple sclerosis (MS) exhibit a different pattern of blood oxygenation level-dependent (BOLD) activation on functional magnetic resonance imaging (fMRI) studies when compared to healthy control (HC).

PURPOSE

The objective of this study is to determine whether observed differences in BOLD activation between people with MS (pwMS) and HC participants are due to the differences of neurovascular coupling, cerebral blood flow (CBF) or actual neuronal activity.

METHODS

We investigated the neuronal activation in pwMS (n = 11) and age- and sex-matched HC participants (n = 15) using simultaneous electroencephalogram (EEG) and fMRI measures during a visual task (VT) and hypercapnia condition.

RESULTS

Significant neurovascular coupling is observed in both HC and pwMS. Neuro-vascular coupling ratios are not significantly different between groups. However, we observe significantly lower CBF increase during VT and higher quantitative CBF at a rest state in pwMS than in HC (p < 0.05). From the multiple regression model, in HC group, we found that the BOLD contrast change during VT is best predicted by the EEG power change during VT (Student t-score = 2.64, p = 0.022), and the CBF change during hypercapnia (Student t-score = 2.59, p = 0.024). In pwMS, the BOLD contrast change during VT is negatively predicted by the CBF change during VT (Student t-score = -4.02, p = 0.003).

CONCLUSION

These findings could explain that BOLD activation in pwMS is mainly determined by the blood flow change during activation rather than the direct neuronal activation measures or hemodynamic vascular reactivity during hypercapnia challenge, suggesting that altered vasodilatory effects in response to task activation in pwMS might be linked to impaired cerebral hemodynamics, possibly leading to the widely observed abnormal BOLD activation in fMRI studies of pwMS.

Vascular function in multiple sclerosis: Systematic review with meta-analysis

BACKGROUND

Vascular comorbidities are prevalent in persons with multiple sclerosis (MS), yet less is known about underlying vascular function (VF). We performed a systematic review with meta-analysis of studies that compared VF in persons with MS and healthy controls and examined factors that may moderate the difference in vascular outcomes between groups.

METHODS

We conducted a systematic search using PubMed/MEDLINE, CINAHL, and Embase from inception through March 2024. The search identified studies that included comparisons of VF between MS and controls on a range of function and structure outcomes (e.g., pulse wave velocity, augmentation index, arterial diameter, intima-media thickness, flow-mediated dilation). Effect sizes were calculated as standardized mean differences (SMD) using Hedge's g with a positive effect indicating worse VF in MS than controls. The meta-analysis involved a multilevel random effects model with follow-up moderator analyses.

RESULTS

Fourteen studies met the inclusion criteria and yielded 49 effect sizes for meta-analysis. The MS subjects (N = 614) were predominantly female (72.0 %), with mean ages ranging from 29.9 to 54.4 years. There was a moderate difference in VF between persons with MS and healthy controls (SMD [95 % CI] = 0.56 [0.08, 1.03]; p = 0.02), and the effects were heterogenous (Q48=634.5, p < 0.01; I2=94.39 %). There was a greater difference in arterial stiffness between MS and controls (0.78 [0.21, 1.36], p = 0.008), but not in other arterial structure or function outcomes (p > 0.05). No significant moderators were detected (p > 0.05).

CONCLUSIONS

The cumulative evidence supports that persons with MS have worse VF, notably greater arterial stiffness, than healthy controls. Such findings support future research on the cause, consequences, and management of arterial stiffness among persons with MS.

A mathematical model for temporal cerebral blood flow response to acetazolamide evaluated in patients with Moyamoya disease

BACKGROUND

Paired cerebral blood flow (CBF) measurement is usually acquired before and after vasoactive stimulus to estimate cerebrovascular reserve (CVR). However, CVR may be confounded because of variations in time-to-maximum CBF response (tmax) following acetazolamide injection. With a mathematical model, CVR can be calculated insensitive to variations in tmax, and a model offers the possibility to calculate additional model-derived parameters. A model that describes the temporal CBF response following a vasodilating acetazolamide injection is proposed and evaluated.

METHODS

A bi-exponential model was adopted and fitted to four CBF measurements acquired using arterial spin labelling before and initialised at 5, 15 and 25 min after acetazolamide injection in a total of fifteen patients with Moyamoya disease. Curve fitting was performed using a non-linear least squares method with a priori constraints based on simulations.

RESULTS

Goodness of fit (mean absolute error) varied between 0.30 and 0.62 ml·100 g-1·min-1. Model-derived CVR was significantly higher compared to static CVR measures. Maximum CBF increase occurred earlier in healthy- compared to diseased vascular regions.

CONCLUSIONS

The proposed mathematical model offers the possibility to calculate CVR insensitive to variations in time to maximum CBF response which gives a more detailed characterisation of CVR compared to static CVR measures. Although the mathematical model adapts generally well to this dataset of patients with MMD it should be considered as experimental; hence, further studies in healthy populations and other patient cohorts are warranted.

Disrupted hemodynamic response within dorsolateral prefrontal cortex during cognitive tasks among people with multiple sclerosis-related fatigue

INTRODUCTION

Mental fatigue is an early and enduring symptom in persons with autoimmune disease particularly multiple sclerosis (MS). Neuromodulation has emerged as a potential treatment although optimal cortical targets have yet to be determined. We aimed to examine cortical hemodynamic responses within bilateral dorsolateral prefrontal cortex (dlPFC) and frontopolar areas during single and dual cognitive tasks in persons with MS-related fatigue compared to matched controls.

METHODS

We recruited persons (15 MS and 12 age- and sex-matched controls) who did not have physical or cognitive impairment and were free from depressive symptoms. Functional near infrared spectroscopy (fNIRS) registered hemodynamic responses during the tasks. We calculated oxyhemoglobin peak, time-to-peak, coherence between channels (a potential marker of neurovascular coupling) and functional connectivity (z-score).

RESULTS

In MS, dlPFC demonstrated disrupted hemodynamic coherence during both single and dual tasks, as evidenced by non-significant and negative correlations between fNIRS channels. In MS, reduced coherence occurred in left dorsolateral PFC during the single task but occurred bilaterally as the task became more challenging. Functional connectivity was lower during dual compared to single tasks in the right dorsolateral PFC in both groups. Lower z-score was related to greater feelings of fatigue. Peak and time-to-peak hemodynamic response did not differ between groups or tasks.

CONCLUSIONS

Hemodynamic responses were inconsistent and disrupted in people with MS experiencing mental fatigue, which worsened as the task became more challenging. Our findings point to dlPFC, but not frontopolar areas, as a potential target for neuromodulation to treat cognitive fatigue.

Age-related decline in cerebral oxygen consumption in multiple sclerosis

Cerebral oxygen metabolism is altered in relapsing-remitting multiple sclerosis (RRMS), possibly a result of disease related cerebral atrophy with subsequent decreased oxygen demand. However, MS inflammation can also inhibit brain metabolism. Therefore, we measured cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) using MRI phase contrast mapping and susceptibility-based oximetry in 44 patients with early RRMS and 36 healthy controls. Cerebral atrophy and white matter lesion load were assessed from high-resolution structural MRI. Expanded Disability Status Scale (EDSS) scores were collected from medical records. The CMRO2 was significantly lower in patients (-15%, p = 0.002) and decreased significantly with age in patients relative to the controls (-1.35 µmol/100 g/min/year, p = 0.036). The lower CMRO2 in RRMS was primarily driven by a higher venous oxygen saturation in the sagittal sinus (p = 0.007) and not a reduction in CBF (p = 0.69). There was no difference in cerebral atrophy between the groups, and no correlation between CMRO2 and MS lesion volume or EDSS score. Therefore, the progressive CMRO2 decline observed before the occurrence of significant cerebral atrophy and despite adequate CBF supports emerging evidence of dysfunctional cellular respiration as a potential pathogenic mechanism and therapeutic target in RRMS.

B cell depletion modulates glial responses and enhances blood vessel integrity in a model of multiple sclerosis

Multiple sclerosis (MS) is characterized by a compromised blood-brain barrier (BBB) resulting in central nervous system (CNS) entry of peripheral lymphocytes, including T cells and B cells. While T cells have largely been considered the main contributors to neuroinflammation in MS, the success of B cell depletion therapies suggests an important role for B cells in MS pathology. Glial cells in the CNS are essential components in both disease progression and recovery, raising the possibility that they represent targets for B cell functions. Here, we examine astrocyte and microglia responses to B cell depleting treatments in an animal model of MS, experimental autoimmune encephalomyelitis (EAE). B cell depleted EAE animals had markedly reduced disease severity and myelin damage accompanied by reduced microglia and astrocyte reactivity 20 days after symptom onset. To identify potential initial mechanisms mediating functional changes following B cell depletion, astrocyte and microglia transcriptomes were analyzed 3 days following B cell depletion. In control EAE animals, transcriptomic analysis revealed astrocytic inflammatory pathways were activated and microglial influence on neuronal function were inhibited. Following B cell depletion, initial functional recovery was associated with an activation of astrocytic pathways linked with restoration of neurovascular integrity and of microglial pathways associated with neuronal function. These studies reveal an important role for B cell depletion in influencing glial function and CNS vasculature in an animal model of MS.

Dilatation of the bridging cerebral veins in multiple sclerosis correlates with fatigue and suggests an increase in pressure

BACKGROUND

There is a significant increase in the parenchymal microvessel blood volume in the earliest forms of multiple sclerosis (MS) which may be due to venular dilatation. Increased cortical venous pressure could account for this finding. Venous pressure is also implicated in the physiology of fatigue. The purpose of this study is to discover if there is dilatation of the veins within the subarachnoid space in multiple sclerosis and to estimate the pressures required to maintain any enlargement found. These findings will be correlated with the fatigue symptoms found in MS.

METHODS

103 patients with MS were compared with a control group of 50 patients. Post contrast 3DT1 images were used. The cross-sectional area of the bridging cortical veins and the vein of Galen were measured.

RESULTS

In MS, the superficial territory cortical veins were 29% larger and the veins of Galen were 25% larger than the controls.

CONCLUSION

There is evidence of a significant increase in the bridging vein transmural pressure in MS, estimated to be approximately 6.5 mmHg in the superficial cortical veins. MS patients with significant fatigue have larger cortical veins than those who are not significantly fatigued.