Abnormal venous postural control: multiple sclerosis-specific change related to gray matter pathology or age-related neurodegenerative phenomena?

Cerebral blood flow dependency on systemic arterial circulation in progressive multiple sclerosis

OBJECTIVES

To determine the relationship between systemic arterial blood flow (SABF) and cerebral perfusion measures in multiple sclerosis (MS) patients.

METHODS

Cerebral perfusion and SABF were assessed in 118 patients (75 clinically isolated syndrome (CIS)/relapsing-remitting MS and 43 progressive MS) through MRI examination with dynamic susceptibility contrast perfusion-weighted imaging (DSC-PWI) and Doppler ultrasound, respectively. Measures of mean transit time (MTT) and time-to-peak (TTP), measured in seconds, of the normal-appearing whole brain (NAWB) and gray matter (GM) were calculated. Blood flow through the bilateral common carotid and vertebral arteries (in mL/min) represents the SABF. Whole brain volume (WBV) and body mass index (BMI) were used as additional covariates.

RESULTS

Higher systolic blood pressure was associated with lower SABF (-0.256, p = 0.006). In the total MS sample, higher SABF was associated with shorter MTT and TTP of the NAWB (r = -0.256, p = 0.007 and r = -0.307, p = 0.001) and GM (r = -0.239, p = 0.012 and r = -0.3, p = 0.001). The SABF and TTP associations were driven by the PMS patients (r = -0.451, p = 0.004 and r = -0.451, p = 0.011). Only in PMS, SABF remained a significant predictor of NAWB (standardized β = -0.394, p = 0.022) and GM TTP (standardized β = -0.351, p = 0.037). MTT and TTP were significantly lower in patients within lower SABF quartiles when compared to the higher quartiles (age-, sex-, BMI-, and WBV-adjusted ANCOVA p < 0.025).

CONCLUSIONS

The direct relationship between systemic and cerebral blood flow seen in PMS patients may suggest failure in cerebrovascular reactivity mechanisms and insufficient perfusion control. Cerebral blood flow in PMS may be increasingly dependent on the SABF.

KEY POINTS

• In progressive multiple sclerosis (MS) patients, the systemic arterial blood flow (SABF) is associated with perfusion-based measure of time-to-peak (TTP) of the normal-appearing whole brain (r = -0.451, p = 0.004) and gray matter (r = -0.451, p = 0.004). • Cerebral blood flow in progressive MS is directly dependent on systemic arterial blood flow and may be influenced by blood pressure changes. • Neurovascular unit impairment may play an important role in MS pathophysiology and contribute towards greater clinical disability.

Cardiac and Respiratory Influences on Intracranial and Neck Venous Flow, Estimated Using Real-Time Phase-Contrast MRI

The study of brain venous drainage has gained attention due to its hypothesized link with various neurological conditions. Intracranial and neck venous flow rate may be estimated using cardiac-gated cine phase-contrast (PC)-MRI. Although previous studies showed that breathing influences the neck’s venous flow, this aspect could not be studied using the conventional segmented PC-MRI since it reconstructs a single cardiac cycle. The advent of real-time PC-MRI has overcome these limitations. Using this technique, we measured the internal jugular veins and superior sagittal sinus flow rates in a group of 16 healthy subjects (12 females, median age of 23 years). Comparing forced-breathing and free-breathing, the average flow rate decreased and the respiratory modulation increased. The flow rate decrement may be due to a vasoreactive response to deep breathing. The respiratory modulation increment is due to the thoracic pump’s greater effect during forced breathing compared to free breathing. These results showed that the breathing mode influences the average blood flow and its pulsations. Since effective drainage is fundamental for brain health, rehabilitative studies might use the current setup to investigate if respiratory exercises positively affect clinical variables and venous drainage.

Sleep dysregulation in sympathetic-mediated diseases: implications for disease progression

The autonomic nervous system (ANS) plays an important role in the coordination of several physiological functions including sleep/wake process. Significant changes in ANS activity occur during wake-to-sleep transition maintaining the adequate cardiorespiratory regulation and brain activity. Since sleep is a complex homeostatic function, partly regulated by the ANS, it is not surprising that sleep disruption trigger and/or evidence symptoms of ANS impairment. Indeed, several studies suggest a bidirectional relationship between impaired ANS function (i.e. enhanced sympathetic drive), and the emergence/development of sleep disorders. Furthermore, several epidemiological studies described a strong association between sympathetic-mediated diseases and the development and maintenance of sleep disorders resulting in a vicious cycle with adverse outcomes and increased mortality risk. However, which and how the sleep/wake control and ANS circuitry becomes affected during the progression of ANS-related diseases remains poorly understood. Thus, understanding the physiological mechanisms underpinning sleep/wake-dependent sympathetic modulation could provide insights into diseases involving autonomic dysfunction. The purpose of this review is to explore potential neural mechanisms involved in both the onset/maintenance of sympathetic-mediated diseases (Rett syndrome, congenital central hypoventilation syndrome, obstructive sleep apnoea, type 2 diabetes, obesity, heart failure, hypertension, and neurodegenerative diseases) and their plausible contribution to the generation of sleep disorders in order to review evidence that may serve to establish a causal link between sleep disorders and heightened sympathetic activity.

Serum Neurofilament Light Chain Levels are Associated with Lower Thalamic Perfusion in Multiple Sclerosis

Both perfusion-weighted imaging (PWI) measures and serum neurofilament light (sNfL) chain levels have been independently associated with disability in multiple sclerosis (MS) patients. This study aimed to determine whether these measures are correlated to each other or independently describe different MS processes. For this purpose, 3T MRI dynamic susceptibility contrast (DSC)–PWI and single-molecule assay (Simoa)-based sNfL methods were utilized when investigating 86 MS patients. The perfusion measures of mean transit time (MTT), cerebral blood volume (CBV), and cerebral blood flow (CBF) were derived for the normal-appearing whole brain (NAWB), the normal-appearing white matter (NAWM), the gray matter (GM), the deep GM (DGM), and the thalamus. The normalized CBV and CBF (nCBV and nCBV) were calculated by dividing by the corresponding NAWM measure. Age- and sex-adjusted linear regression models were used to determine associations between the DSC–PWI and sNfL results. False discovery rate (FDR)-adjusted p-values < 0.05 were considered statistically significant. A greater age and thalamic MTT were independently associated with higher sNfL levels (p < 0.001 and p = 0.011) and explained 36.9% of sNfL level variance. NAWM MTT association with sNfL levels did not survive the FDR correction. In similar models, a lower thalamic nCBF and nCBV were both associated with greater sNfL levels (p < 0.001 and p = 0.022), explaining 37.8% and 44.7% of the variance, respectively. In conclusion, higher sNfL levels were associated with lower thalamic perfusion.

Decrease in Secondary Neck Vessels in Multiple Sclerosis: A 5-year Longitudinal Magnetic Resonance Angiography Study

BACKGROUND

Studies have previously shown greater arterial and venous extracranial vascular changes in persons with multiple sclerosis (PwMS) when compared to healthy controls (HCs).

OBJECTIVES

To determine the change in the number and size of secondary neck vessels in PwMS and HCs over a 5-year follow-up period.

METHODS

Both at baseline and follow-up, 83 PwMS and 25 HCs underwent magnetic resonance angiography (MRA) imaging and analysis. The number and cross-sectional area (CSA) of all secondary neck vessels (excluding the common/internal carotid, vertebral artery, and internal jugular vein) measured at levels from C2-T1 were determined by semi-automated edge detection/ contouring software. The longitudinal change in the number and CSA of the secondary neck vessels from the PwMS and HCs were analyzed by non-parametric Wilcoxon repeated measure. Benjamini-Hochberg procedure adjusted for false discovery rate (FDR).

RESULTS

For over 5 years, PwMS demonstrated a consistent longitudinal decrease in both the number of secondary neck vessels (Z-change between -3.3 and -5.4, q=0.001) and their CSA (Zchange between -2.9 and -5.2, q=0.004). On the contrary, the HCs did not demonstrate a significant longitudinal change in secondary neck vessels over the follow-up period. Due to the longitudinal decrease, the PwMS showed a lower number of secondary neck vessels when compared to HCs measured at follow-up (p<0.029, except for C4 with trending p=0.071). The PwMS changes were also corroborated within each MS phenotype.

CONCLUSION

PwMS demonstrate a significant mid-term decrease in the number and the size of the secondary neck vessels. The clinical relevance of these findings and the effect on intracranial blood flow are currently unknown.