Impaired carotid baroreflex control of arterial blood pressure in multiple sclerosis

Reduced resting beat-to-beat blood pressure variability in females with relapsing-remitting multiple sclerosis

BACKGROUND

Relapsing-remitting multiple sclerosis (RRMS) is a demyelinating disease of the central nervous system and cardiovascular autonomic dysfunction has been well documented in this population. The sympathetic nervous system contributes to beat-to-beat blood pressure regulation primarily by baroreflex control of the peripheral vasculature which may be impaired in females with RRMS. Even at rest, attenuated sympathetic control of vasomotor tone may result in large and frequent blood pressure excursions (i.e., greater blood pressure variability). Therefore, the primary purpose of this investigation was to test the following hypotheses; (1) females with RRMS have augmented beat-to-beat blood pressure variability compared to healthy controls and (2) reduced sympathetic baroreflex sensitivity in females with RRMS is related to augmented blood pressure variability.

METHODS

Electrocardiogram and beat-to-beat blood pressure were continuously recorded during 8-10 min of supine rest in 26 females with clinically definite RRMS and 24 sex-, age- and BMI- matched healthy controls. Muscle sympathetic nerve activity (MSNA) was recorded in a subset of participants (MS, n = 15; CON, n = 14). Traditional statistical measurements of dispersions were used to index beat-to-beat blood pressure variability. Spontaneous sympathetic baroreflex sensitivity was quantified by sorting diastolic blood pressures into 3 mmHg bins and calculating MSNA burst incidence within each bin. Weighted linear regression was then used to account for the number of cardiac cycles in each bin and calculate slopes. Spontaneous cardiac baroreflex sensitivity was determined using the sequence method.

RESULTS

Groups had similar resting mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP), MSNA burst frequency and MSNA burst incidence (All P > 0.05). The standard deviation and interquartile range of MAP, SBP and DBP were less in females with RRMS compared to healthy controls (All P < 0.05). There were no between groups differences in sympathetic baroreflex sensitivity or cardiac baroreflex sensitivity (Both P > 0.05) and baroreflex sensitivity measures were not related to any indices of blood pressure variability (Both P > 0.05).

CONCLUSION

These data suggest that females with RRMS have reduced beat-to-beat blood pressure variability. However, this does not appear to be related to changes in sympathetic or cardiac baroreflex sensitivity.

Neck Chamber Technique Revisited: Low-Noise Device Delivering Negative and Positive Pressure and Enabling Concomitant Carotid Artery Imaging With Ultrasonography

Background and Objectives: Recently, novel noiseless device for the assessment of baroreceptor function with the neck suction (NS) has been presented. In this study, we present another in-house approach to the variable-pressure neck chamber method. Our device offers further critical improvements. First, it enables delivery of negative (NS) as well as positive pressure (neck pressurizing, NP) in a noiseless manner. Second, we used small, 3D-printed cups positioned over the carotid sinuses instead of cumbersome neck collar to improve subject comfort and to test feasibility of tracking the pressure-induced changes in carotid artery with ultrasonography. Methods: Five healthy, non-smoking, normal-weight subjects aged 29 ± 3 years (mean ± SD) volunteered for the study. Heart rate (HR, bpm) and mean arterial pressure (MAP, mmHg) responses to short, 7-s long episodes of NS and NP were recorded. Each trial consisted of 12 episodes of variable-pressure: six episodes of NS (suction ranging between -10 and -80 mmHg) and six episodes of NP (pressure ranging between + 10 and + 80 mmHg). Carotid artery sonography was performed during the NS and NP in four subjects, on another occasion. Results: The variable-pressure episodes resulted consistently in the expected pattern of hemodynamic alterations: HR and MAP increases or decreases following the NP and NS, respectively, as evidenced by the coefficient of determination (R²) of ≥0.78 for the carotid-HR response curve (for all five participants) and the carotid-MAP response curve (for four out of five participants; the curve cannot be calculated for one subject). We found a linear, dose-dependent relation between the applied pressure and the systolic-diastolic difference in carotid artery diameter. Conclusion: The novel device enables noiseless stimulation and unloading of the carotid baroreceptors with the negative and positive pressure, respectively, applied on the subject's neck via small, asymmetric and one-side flattened, 3D-printed cups. The unique design of the cups enables concomitant visualizing of the carotid artery during the NS or NP administration, and thereby direct monitoring of the intensity of mechanical stimulus targeting the carotid baroreceptors.

Noiseless Variable-Pressure Neck Chamber Device to Assess the Carotid Baroreflex Function

Background: The blood pressure responses to baroreflex perturbations can be assessed only using the variable-pressure neck chamber technique. However, the application of this approach in hospital environments is limited owing to the loud noise emitted during its operation. This study was aimed at developing a noiseless neck suction chamber device (NCD) that could stimulate the baroreceptors located in the carotid sinus in humans.

Methods: A non-invasive device was developed to pressurize the carotid arteries externally. A microcontroller with a computer interface and neck chamber (3D-printed) was used. The anatomical neck chamber was fitted on six healthy, young, asymptomatic participants (five men; 32 ± 6 year), who were normotensive, nonsmoking, in sinus rhythm, free of known cardiovascular or metabolic diseases, and not consuming any acute or chronic medications. A suction of −60 mmHg was applied for 5 s, and the corresponding data were recorded. Before each study visit, the participants were instructed to abstain from caffeine, alcohol, and strenuous exercise for 12–24 h.

Results: In all the trials, a significant reflex bradycardia (−10 ± 2 bpm) and depressor response (−15 ± 4 mmHg) to neck suction were observed, consistent with the results in the literature. The neck chamber device operated noiselessly [sound pressure level (SPL) of 34.3 dB] compared to a regular vacuum-cleaner-based system (74.6 dB).

Conclusion: Using the proposed approach, consistent blood pressure and heart rate responses to carotid baroreflex hypertensive stimuli could be recorded, as in previous studies conducted using neck collar devices. Furthermore, the neck chamber device operated noiselessly and can thus be applied in hospital environments.

Cerebral Vasoreactivity as an Indirect MRI Marker of White Matter Tracts Alterations in Multiple Sclerosis

Patients with multiple sclerosis (MS) show a diffuse cerebral perfusion decrease, presumably related to multiple metabolism and vascular alterations. It is assumed that white matter fiber alterations cause a localized cerebral vasoreactivity (CVR) disruption through astrocytes metabolism alteration, leading to hypoperfusion. We proposed to (1) evaluate the CVR disruptions in MS, (2) in relation to white matter lesions and (3) compare CVR disruptions maps with standard imaging biomarkers. Thirty-five MS patients (10 progressive, 25 relapsing-remitting) and 22 controls underwent MRI with hypercapnic challenge, DTI imaging and neuropsychological assessment. Areas with disrupted CVR were assessed using a general linear model. Resulting maps were associated with clinical scores, compared between groups, and related to DTI metrics and white matter lesions. MS patients showed stronger disrupted CVR within supratentorial white matter, linking the left anterior insula to both the precentral gyrus and the right middle and superior frontal gyrus through the corpus callosum (P < 0.05, FWE corrected). Patient's verbal intellectual quotient was negatively associated with a pathway linking both hippocampi to the ispilateral prefrontal cortex (P < 0.05, FWE corrected). Disrupted CVR maps unrelated to DTI metrics and white matter lesions. We have demonstrated for the first time that white matter alterations can be indirectly identified through surrounding vessel alterations, and are related to clinical signs of MS. This offers a new, likely independent marker to monitor MS and supports a mediator role of the astrocytes in the fibers/vessels relationship.

Evidence of Autonomic Dysfunction in Patients with Relapsing-Remitting Multiple Sclerosis: Heart Rate Variability and Cardiovascular Parameters

This study was aimed at evaluation of autonomic dysfunction in patients with multiple sclerosis (MS) by means of time- and frequency-domain parameters of heart rate variability (HRV) and conventional cardiovascular tests (deep breathing (DB) and active orthostatic test (AOT)). The study group enrolled 32 patients with the relapsing-remitting MS (17 m, 15 f, aged 29 ± 4.9 years, disease duration 4.2 ± 2.7 years, EDSS scores less than 3.0 and 26 subjects in good health (HC, 15 m, 11 f, aged 30.1 ± 2.7 years). In the MS group, at rest the variability of heart rate was decreased in comparison to the HC group seen by time- (SDNN, RMSSD, pNN50, CV, p < 0.01) and frequency-domain (TP, HF, LF, p < 0.05) parameters, what was indicative of the general decrease of the autonomic neurogenic control of the heart rate, both sympathetic and parasympathetic. The functional tests (DB and AOT) showed reduced cardiovascular reactivity in the MS group. Additionally, the cardio-respiratory synchronization was impaired in the MS group at rest and DB. The severity of HRV deficit in the MS group correlated with the activity of MS. In conclusion, the comprehensive assessment of time- and frequency-domain HRV parameters studied with functional tests provides better insight to understanding autonomic dysfunction in subjects with relapsing-remitting MS.

The association between the adrenergic hyperactivity and blood pressure values in people with multiple sclerosis

OBJECTIVES

To evaluate the evolution of adrenergic baroreflex sensitivity (BRSa) over 2-year follow-up and to investigate the effect of baseline BRSa indices on blood pressure values after 2 years in people with multiple sclerosis (pwMS).

METHODS

The following data were analysed at baseline and after 2 years: BRSa measured with BRSa1, α-BRSa and β-BRSa, supine and tilted levels of epinephrine and norepinephrine, supine and tilted systolic and diastolic blood pressure levels.

RESULTS

Compared to baseline values, there was no change in α-BRSa (6.96 ± 2.56 vs. 6.64 ± 2.24, p = 0.379) at month 24. α-BRSa at month 24 positively correlated with tilted levels of norepinephrine at month 24 (r_p = 0.357, p = 0.005). Univariable linear regression analysis revealed that α-BRSa at baseline predicts the value of tilted systolic and diastolic blood pressure at month 24 (B = 2.724, 95% CI 1.357-4.091, p < 0.001 and B = 1.489, 95% CI 0.459-2.519, p = 0.005).

CONCLUSION

This study provides further evidence for possible role of α-BRSa as a marker of adrenergic hyperactivity in pwMS. These results may explain increased risk for cardiovascular diseases in pwMS.

Evaluation of cardiovascular autonomic dysfunction according to heart rate turbulence and variability in patients with relapsing remitting multiple sclerosis

Background/aim

Multiple sclerosis (MS) is an autoimmune disease characterized by neurodegeneration or demyelination; the relapsing–remitting phase of MS is characterized by acute exacerbation of disease activity. The most commonly used noninvasive approach to assess autonomic function is the determination of heart rate turbulence (HRT) and heart rate variability (HRV). The aim of this study was to evaluate the presence of cardiovascular autonomic dysfunction using HRT and HRV parameters determined via 24-h Holter ECG monitoring in patients with relapsing–remitting MS without known heart disease.

Materials and methods

The study included 26 patients diagnosed with relapsing–remitting MS and 22 age- and sex-matched healthy controls. HRT and HRV parameters were analyzed via 24-h Holter ECG monitoring. Magnetic resonance imaging findings were reevaluated to identify any demyelinating lesions in the brain stem.

Results

The HRV parameters of SDNNI (mean of the standard deviations of all normal sinus RR intervals in all 5-min segments), rMSSD (root–mean–square successive difference), and sNN50 (percentage of successive normal sinus RR intervals >50 ms) were significantly lower in the MS group than in the control group (P < 0.05).

Conclusion

This study revealed that the patients with MS had reduced HRV; this was demonstrated by dysfunction with regard to parasympathetic and sympathetic parameters in HRV analysis.

Cardiac Autonomic Dysfunction in Multiple Sclerosis: A Systematic Review of Current Knowledge and Impact of Immunotherapies

Cardiac autonomic dysfunction (CAD) has been reported in patients with multiple sclerosis (MS). This systematic review summarizes the evidence for the types and prevalence of CAD in MS patients, as well as its association with MS type, disease characteristics, fatigue and immunotherapies used to treat MS. The analysis revealed that CAD is correlated with pathophysiological processes of MS, can trigger serious cardiovascular complications that may reduce life expectancy, and may have implications for treatment with immunotherapies, especially fingolimod. Numerous mainly small case-control or cohort studies have reported various measures of CAD (particularly heart rate variation) in MS patients, showing higher rates of abnormality versus controls. A smaller number of studies have reported on cardiac autonomic symptoms in MS, including orthostatic intolerance/dizziness in around 50% of patients. CAD also appears to be associated with disease duration and to be more common in progressive than relapsing-remitting MS. However, although a substantial evidence base suggests that assessing CAD in people with MS may be important, standardised methods to evaluate CAD in these patients have not yet been established. In addition, no studies have yet looked at whether treating CAD can reduce the burden of MS symptoms, disease activity or the rate of progression.

Sedentary Behavior and Blood Pressure in Patients with Multiple Sclerosis

Background

Sedentary behavior is a pervasive public health concern in the general population. To date, little is known regarding the possible health risks associated with sedentary behavior in patients with multiple sclerosis (MS), although this population has increased risks of comorbidities such as hypertension.

Methods

This cross-sectional study examined the association between sedentary behavior and blood pressure (BP) in 31 patients with MS and 31 matched controls. Self-reported sitting time, one form of sedentary behavior, was measured using the International Physical Activity Questionnaire. Using an automated oscillometric monitor, systolic BP, diastolic BP, and mean arterial pressure were measured in the supine position after 10 minutes of rest lying down in a quiet room.

Results

There were significant correlations between International Physical Activity Questionnaire-measured sitting time and systolic BP (r = 0.365, P = .044, 95% CI, 0.013-0.636), diastolic BP (r = 0.382, P = .034, 95% CI, 0.032-0.648), and mean arterial pressure (r = 0.425, P = .017, 95% CI, 0.084-0.677) in patients with MS but not in controls (P > .05). The associations in patients with MS were unchanged even after adjusting for body mass index in linear regression analyses.

Conclusions

This study identified a significant association between sitting time and BP outcomes in patients with MS, supporting the need for additional examinations of sitting time and its possible health consequences in patients with MS.

Is impaired cerebral vasoreactivity an early marker of cognitive decline in multiple sclerosis patients?

OBJECTIVE

The link between cerebral vasoreactivity and cognitive status in multiple sclerosis remains unclear. The aim of the present study was to investigate a potential decrease of cerebral vasoreactivity in multiple sclerosis patients and correlate it with cognitive status.

METHODS

Thirty-three patients with multiple sclerosis (nine progressive and 24 remitting forms, median age: 39 years, 12 males) and 22 controls underwent MRI with a hypercapnic challenge to assess cerebral vasoreactivity and a neuropsychological assessment. Cerebral vasoreactivity, measured as the cerebral blood flow percent increase normalised by end-tidal carbon dioxide variation, was assessed globally and by regions of interest using the blood oxygen level-dependent technique. Non-parametric statistics tests were used to assess differences between groups, and associations were estimated using linear models.

RESULTS

Cerebral vasoreactivity was lower in patients with cognitive impairment than in cognitively normal patients (p=0.004) and was associated with education level in patients (R² = 0.35; p = 0.047). There was no decrease in cerebral vasoreactivity between patients and controls.

CONCLUSIONS

Cognitive impairment in multiple sclerosis may be mediated through decreased cerebral vasoreactivity. Cerebral vasoreactivity could therefore be considered as a marker of cognitive decline in multiple sclerosis.

KEY POINTS

• Cerebral vasoreactivity does not differ between multiple sclerosis patients and controls. • Cerebral vasoreactivity measure is linked to cognitive impairment in multiple sclerosis. • Cerebral vasoreactivity is linked to level of education in multiple sclerosis.

Impaired sweating responses to a passive whole body heat stress in individuals with multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease that affects the central nervous system (CNS), disrupting autonomic function. The aim of this study was to test the hypothesis that individuals with MS have blunted control of thermoregulatory reflex increases in sweat rate (SR) and cutaneous vasodilation compared with controls during a passive whole body heat stress (WBH). Eighteen individuals with relapsing-remitting MS and 18 healthy controls (Con) participated in the study. Core temperature (T_core), skin temperature, heart rate, arterial blood pressure (10-min intervals), skin blood flow (laser-Doppler flux, LDF), and SR were continuously measured during normothermic baseline (34°C water perfusing a tube-lined suit) and WBH (increased T_core 0.8°C via 48°C water perfusing the suit). Following WBH, local heaters were warmed to 42°C, inducing peak cutaneous vasodilation at the site of LDF collection. Cutaneous vascular conductance (CVC) was calculated as the ratio of LDF to mean arterial pressure and expressed as a percentage of peak achieved during local heating. Individuals with MS had attenuated SR responses to WBH (ΔSR from baseline: Con, 0.65 ± 0.27; MS, 0.42 ± 0.17 mg·cm^-2·min^-1, P = 0.003), whereas Δ%CVC_42C from baseline was similar between groups (Con, 42 ± 16%; MS, 38 ± 12%, P = 0.39). SR responses were blunted as a function of T_core in MS (interaction: group × T_core, P = 0.03), of which differences were evident at ΔT_core 0.7°C and 0.8°C (P < 0.05). No interaction was observed in Δ%CVC_42C Taken together, the findings show MS blunts sweating responses, whereas control of the cutaneous vasculature is preserved, in response to WBH.NEW & NOTEWORTHY This study is the first to assess the reflex control of the thermoregulatory system in individuals living with multiple sclerosis (MS). The novel findings are twofold. First, attenuated increases in sweat rate in subjects with MS compared with healthy controls were observed in response to a moderate increase (0.8°C) in core temperature via passive whole body heat stress. Second, it appears the reflex control of the cutaneous vasculature is preserved in MS.

Increased postural sway in persons with multiple sclerosis during short-term exposure to warm ambient temperatures

BACKGROUND

Multiple sclerosis (MS) is a neurological disease marked by demyelination and axonal loss. Individuals with MS experience increases in clinical signs and symptoms during heat exposure.

OBJECTIVE

To test the hypothesis that moderate heat exposure adversely affects postural sway in individuals with MS.

METHODS

Ten individuals with relapsing-remitting MS (50±8y) and nine controls (47±10y) were examined under a Thermal and a Time Control trial. Following a 30min thermoneutral baseline (25°C, 30% relative humidity (RH)), stand tests randomized with eyes open and closed, were performed. For Thermal, subjects were first exposed to 60min of heating (40°C, 30%RH) followed by 60min of cooling (20°C, 30%RH). For Time Control, subjects remained in a thermoneutral environment throughout. Stand tests were repeated at consistent times in both trials.

RESULTS

No difference in skin and core temperatures between groups were observed for any trial (P>0.05). During heating, postural sway was higher in MS relative to control subjects (eyes open, P=0.03; eyes closed, P=0.011). No differences in postural sway, regardless of eye status, were observed during the Time Control trial for either group (P>0.05).

CONCLUSION

These data demonstrate that exposure to a moderate heating environment increases postural sway in patients with MS.