Autonomic dysfunction in multiple sclerosis: implications for exercise

Exercise-induced heat sensitivity in patients with multiple sclerosis: Definition, prevalence, etiology, and management-A scoping review

BACKGROUND

For persons with multiple sclerosis (pwMS), exercise is known to be safe and effective at treating several symptoms and it may even be disease-modifying. However, exercise can trigger heat intolerance, exercise-induced heat sensitivity (EIHS), which may cause some pwMS to refrain from exercise. No review has yet summarized the existing knowledge on EIHS in pwMS. Therefore, the purpose of the present review was to clarify the terminology, summarize both the prevalence of EIHS and the current knowledge of underlying mechanisms, and provide an overview of existing treatment options and clinical management of EIHS in pwMS.

METHODS

A scoping review was performed.

RESULTS

As no clear definition could be identified in the literature, we propose a definition of EIHS. Aspects related to EIHS are reported in 29-80 % of all pwMS. The mechanisms underlying EIHS are not well understood but seem to include axon demyelination, CNS lesions, abnormal sudomotor function and sweating, abnormal afferent thermosensory function, disease stability, and abnormal neuropsychological responses. The severity of EIHS depends on the applied exercise modality, intensity, and format, and can be further reduced when applying different cooling interventions or garments before and/or during exercise.

CONCLUSION

EIHS appears frequently in pwMS, but the underlying mechanisms are still only sparsely understood. EIHS severity depends on exercise-related factors and can be reduced by cooling interventions.

Neurological patients confronting climate change: A potential role for the glymphatic system and sleep

Interest in the health consequences of climate change (global warming, heatwaves) has increased in the neurological community. This review addresses the impact of elevated ambient temperatures and heatwaves on patients with neurological and mental health disorders, including multiple sclerosis, synucleinopathies, dementia, epilepsies, mental health, and stroke. Patients with such conditions are highly vulnerable during heatwaves because of functional disorders affecting sleep, thermoregulation, autonomic system reactivity, mood, and cognitive ability. Several medications may also increase the risk of heatstroke. Special attention is devoted to the involvement of common underlying mechanisms, such as sleep and the glymphatic system. Disease prevention and patient care during heatwaves are major issues for caregivers. Beyond the usual recommendations for individuals, we favor artificially induced acclimation to heat, which provides preventive benefits with proven efficacy for healthy adults.

Leveraging Emerging Technologies to Expand Accessibility and Improve Precision in Rehabilitation and Exercise for People with Disabilities

Physical rehabilitation and exercise training have emerged as promising solutions for improving health, restoring function, and preserving quality of life in populations that face disparate health challenges related to disability. Despite the immense potential for rehabilitation and exercise to help people with disabilities live longer, healthier, and more independent lives, people with disabilities can experience physical, psychosocial, environmental, and economic barriers that limit their ability to participate in rehabilitation, exercise, and other physical activities. Together, these barriers contribute to health inequities in people with disabilities, by disproportionately limiting their ability to participate in health-promoting physical activities, relative to people without disabilities. Therefore, there is great need for research and innovation focusing on the development of strategies to expand accessibility and promote participation in rehabilitation and exercise programs for people with disabilities. Here, we discuss how cutting-edge technologies related to telecommunications, wearables, virtual and augmented reality, artificial intelligence, and cloud computing are providing new opportunities to improve accessibility in rehabilitation and exercise for people with disabilities. In addition, we highlight new frontiers in digital health technology and emerging lines of scientific research that will shape the future of precision care strategies for people with disabilities.

Association between Daytime Sleepiness, Fatigue and Autonomic Responses during Head-Up Tilt Test in Multiple Sclerosis Patients

We aimed to assess dynamic changes in hemodynamic and autonomic function in response to the head-up tilt test (HUTT) in patients with multiple sclerosis (MS) compared to healthy controls (HCs) and evaluate its relationship with the patients' reported daytime sleepiness and fatigue symptoms. A total of 58 MS patients and 30 HCs were included in the analysis. Fatigue and sleepiness were evaluated using the Chalder Fatigue Scale (CFQ) and the Epworth Sleepiness Scale (ESS), respectively. Hemodynamic response, baroreflex sensitivity, heart rate variability, and systolic and diastolic blood pressure (BP) variability (SBPV, DBPV) parameters were calculated at rest, and in response to the HUTT. The MS patients displayed attenuated BP responses coupled with a more pronounced decrease in cardiac index as well as a reduced increase in the low frequency (LFnu) of DBPV (p = 0.021) and the sympathovagal ratio (p = 0.031) in the latter-phase orthostatic challenge compared to HCs. In MS patients, the ESS score showed no correlation with CFQ or clinical disease outcomes, but exhibited a moderate correlation with LFnu of BPVrest. Fatigue and disease variants predicted blood pressure response to HUTT. These findings underscore the importance of subjective daytime sleepiness and fatigue symptoms and their role in blood pressure regulation in MS patients.

Body temperatures, thermal comfort, and neuropsychological responses to air temperatures ranging between 12°C and 39°C in people with Multiple Sclerosis

The negative effects of thermal stress on Multiple Sclerosis (MS)' symptoms have long been known. However, the underlying mechanisms of MS heat and cold intolerance remain unclear. The aim of this study was to evaluate body temperatures, thermal comfort, and neuropsychological responses to air temperatures between 12 to 39°C in people with MS compared to healthy controls (CTR). Twelve MS (5 males/7 females; age: 48.3±10.8 years; EDSS range: 1-7) and 11 CTR participants (4 males /7 females; age: 47.5±11.3 years) underwent two 50-min trials in a climatic chamber. Air temperature was ramped from 24°C to either 39°C (HEAT) or 12°C (COLD) and we continuously monitored participants' mean skin (T_sk) and rectal temperatures (T_rec), heart rate and mean arterial pressure. We recorded participants' self-reported thermal sensation and comfort, mental and physical fatigue, and we assessed their cognitive performance (information processing). Changes in mean T_sk and T_rec did not differ between MS and CTR neither during HEAT nor COLD. However, at the end of the HEAT trial, 83% of MS participants and 36% of CTR participants reported being "uncomfortable". Furthermore, self-reports of mental and physical fatigue increased significantly in MS but not CTR (p<0.05), during both HEAT and COLD. Information processing was lower in MS vs. CTR (p<0.05); yet this cognitive impairment was not exacerbated by HEAT nor COLD (p>0.05). Our findings indicate that neuropsychological factors (i.e. discomfort and fatigue) could contribute to MS heat and cold intolerance in the absence of deficits in the control of body temperature.

The insula modulates the effects of aerobic training on cardiovascular function and ambulation in multiple sclerosis

BACKGROUND

Impairment of cardiovascular control is common in multiple sclerosis (MS), possibly due to damage of strategic brain regions such as the insula. Aerobic training (AT) targets cardiopulmonary system and may represent a neuroprotective strategy.

PURPOSE

To investigate whether insular damage (T2-hyperintense lesions and volume) is associated with cardiovascular fitness (CF) and influences AT effects in MS.

METHODS

Sixty-one MS patients were randomized to an AT intervention group (MS-AT) and a motor training control group (MS-C). At baseline and after training (24 sessions over 2-3 months), peak of oxygen consumption (VO2max), heart rate reserve (HRR), 6-min walk test (6MWT) and whole brain and insula MRI data were collected. Two healthy control (HC) groups were enrolled for CF and MRI data analysis.

RESULTS

At baseline, MS patients vs HC showed impaired VO2max, HRR and 6MWT (p < 0.001) and widespread gray matter atrophy, including bilateral insula. In MS patients, left insula T2-lesion volume correlated with HRR (r = 0.27, p = 0.042). After training, MS-AT, especially those without insular T2-hyperintense lesions, showed 6MWT improvement (p < 0.05) and a stable insular volume, whereas MS-C showed left insular volume loss (p < 0.001).

CONCLUSIONS

By increasing 6MWT performance, our results suggest that AT may improve walking capacity and submaximal measure of CF in MS patients. Such beneficial effect may be modulated by insula integrity.

The pathophysiology of motor fatigue and fatigability in multiple sclerosis

Multiple Sclerosis (MS) is a heterogeneous immune mediated disease of the central nervous system (CNS). Fatigue is one of the most common and disabling symptom of MS. It interferes with daily activities on the level of cognition and motor endurance. Motor fatigue can either result from lesions in cortical networks or motor pathways (“primary fatigue”) or it may be a consequence of detraining with subsequent adaptions of muscle and autonomic function. Programmed exercise interventions are used frequently to increase physical fitness in MS-patients. Studies investigating the effects of training on aerobic capacity, objective endurance and perceived fatigability have yielded heterogenous results, most likely due to the heterogeneity of interventions and patients, but probably also due to the non-uniform pathophysiology of fatigability among MS-patients. The aim of this review is to summarize the current knowledge on the pathophysiology of motor fatigability with special reference to the basic exercise physiology that underlies our understanding of both pathogenesis and treatment interventions.

Thermal dysregulation in patients with multiple sclerosis during SARS-CoV-2 infection. The potential therapeutic role of exercise

Thermoregulation is a homeostatic mechanism that is disrupted in some neurological diseases. Patients with multiple sclerosis (MS) are susceptible to increases in body temperature, especially with more severe neurological signs. This condition can become intolerable when these patients suffer febrile infections such as coronavirus disease-2019 (COVID-19). We review the mechanisms of hyperthermia in patients with MS, and they may encounter when infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Finally, the thermoregulatory role and relevant adaptation to regular physical exercise are summarized.

Acute Response of Stress System in Multiple Sclerosis

Background: It has long been suspected that exposure to stress is a major factor that can increase the risk of Multiple Sclerosis (MS) and exacerbate it, as a stress-related disorder. Therefore, we conducted this study to investigate the response of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic-adrenal-medullar (SAM) system to acute social stress. Methods: A total of 46 MS patients and 23 age-sex-matched healthy controls were recruited in the study. The Trier Social Stress Test (TSST) was used to induce acute psychosocial stress. We measured salivary cortisol (SC) to evaluate the HPA axis. In addition, electrocardiography (ECG) was recorded to evaluate the SAM system based on the linear and non-linear features of Heart Rate Variation (HRV). Then, SC and HRV were measured before and after the stress exposure. We also used the Depression Anxiety Stress Scale (DASS) and Emotional Visual Analog Scale (EVAS) to conduct the psychometric assessment and evaluate the perceived stress level, respectively. Results: The mean age of the MS group was 35.38 ± 15 years, with a mean disease duration of 7.4 ± 60. Besides, the HC group's mean age was 35.8 ± 9 years. There were no significant differences in demographic features and DASS scores between the two groups. In response to TSST, both MS and healthy individuals showed a significant increase in the SC levels and EVAS scores, as well as changes in the HRV indices. Notably, significant differences were also found between the two groups regarding the basic and post-stress SC levels, EVAS score, and HRV indices. Unlike the HC group, the SC level returned to its baseline after recovery in the MS group, and the sympathetic tone was more sensitive. Conclusions: Our results indicated that both MS and healthy individuals respond to acute stress regarding neuroendocrine assessment; however, patients with multiple sclerosis show some impairments in this response.

Increased skin wetness independently augments cool-seeking behaviour during passive heat stress

KEY POINTS

Skin wetness occurring secondary to the build-up of sweat on the skin provokes thermal discomfort, the precursor to engaging in cool-seeking behaviour. Associative evidence indicates that skin wetness stimulates cool-seeking behaviour to a greater extent than increases in core and mean skin temperatures. The independent contribution of skin wetness to cool-seeking behaviour during heat stress has never been established. We demonstrate that skin wetness augments cool-seeking behaviour during passive heat stress independently of differential increases in skin temperature and core temperature. We also identify that perceptions of skin wetness were not elevated despite increases in actual skin wetness. These data support the proposition that afferent signalling from skin wetness enhances the desire to engage in cool-seeking behaviour during passive heat stress.

ABSTRACT

This study tested the hypothesis that elevations in skin wetness augments cool-seeking behaviour during passive heat stress. Twelve subjects (6 females, age: 24 ± 2 y) donned a water-perfused suit circulating 34 °C water and completed two trials resting supine in a 28.5 ± 0.4 °C environment. The trials involved a 20 min baseline period (26 ± 3% relative humidity (RH)), 60 min while ambient humidity was maintained at 26±3% RH (LOW) or increased to 67 ± 5% RH (HIGH), followed by 60 min passive heat stress (HS) where the water temperature in the suit was incrementally increased to 50 °C. Subjects were able to seek cooling when their neck was thermally uncomfortable by pressing a button. Each button press initiated 30 s of -20 °C fluid perfusing through a custom-made device secured against the skin on the dorsal neck. Mean skin (T_skin ) and core (T_core ) temperatures, mean skin wetness (W_skin ) and neck device temperature (T_device ) were measured continuously. Cool-seeking behaviour was determined from total time receiving cooling (TT_cool ) and cumulative button presses. T_skin and T_core increased during HS (P < 0.01) but were not different between conditions (P ≥ 0.11). W_skin was elevated in HIGH vs. LOW during HS (60 min: by + 0.06 ± 0.07 a.u., P ≤ 0.04). T_device was lower in HIGH vs. LOW at 40-50 min of HS (P ≤ 0.01). TT_cool was greater for HIGH (330 ± 172 s) vs. LOW (225 ± 167 s, P < 0.01), while the number of cumulative button presses was greater from 40-60 min in HS for HIGH vs. LOW (P ≤ 0.04). Increased skin wetness amplifies the engagement in cool-seeking behaviour during passive heat stress.

Impaired heart rate recovery after sub-maximal physical exercise in people with multiple sclerosis

BACKGROUND

Heart Rate Recovery (HRR) after a physical exercise has been poorly investigated in people with multiple sclerosis (PwMS).

OBJECTIVE

To evaluate the kinetics of HRR and its autonomic modulation in PwMS and to elucidate the interplay between HRR and subjective fatigue.

METHODS

ECG was digitally acquired during rest (5 min), submaximal exercise (4 min at 10 W of upper limb cycling) and recovery (3 min) in 17 PwMS (EDSS: 5.9 ± 1.2, mean±standard deviation) and 17 healthy control (HC) subjects. Short-term (first 30 s) and long-term (up to180 s) validated indices of HRR were calculated. The time course of the parasympathetic index of heart rate variability RMSSD (Root Mean Square of Successive Differences) was computed every 30 s of recovery. Subjective fatigue was evaluated by the Borg scale applied to breathing and upper limbs.

RESULTS

In comparison with HC, the short-term HRR indices were significantly slower (P < 0.05) in PwMS, whereas the long-term ones did not. The time course of RMSSD was significantly different in PwMS (P < 0.05). HRR and HRV indexes did not correlate with fatigue perception and baseline HRV values.

CONCLUSION

The cardiac parasympathetic reactivation from a submaximal exercise was blunted in PwMS, thereby slowing the short-term phase of HRR. This may contribute to the higher cardiovascular risk in PwMS, but the mechanism needs further investigation. The parasympathetic impairment during post-exercise HR reactivation cannot be predicted by baseline HRV values and may therefore be revealed only by an appropriate provocative low-intensity physical test.

Impaired Thermoregulatory Function during Dynamic Exercise in Multiple Sclerosis

INTRODUCTION

Impairments in sudomotor function during passive whole-body heating have been reported in multiple sclerosis (MS), a demyelinating disease of the CNS that disrupts autonomic function. However, the capability of the thermoregulatory system to control body temperature during exercise has never been assessed in MS. Thus, the aim of the present study was to test the hypothesis that thermoregulatory function is impaired in MS patients compared with healthy controls (CON) exercising at similar rates of metabolic heat production.

METHODS

Sweating and skin blood flow responses were compared between 12 individuals diagnosed with relapsing-remitting MS (9 females, 3 males) and 12 sex-, age-, mass-, and BSA-matched CON during a single bout of cycling exercise (rate of metabolic heat production: ∼4.5 W·kg) for 60 min in a climate-controlled room (25°C, 30% RH).

RESULTS

Individuals with MS exhibited an attenuated increase in cumulative whole-body sweat loss after 30 min (MS, 72 ± 51 g; CON, 104 ± 37 g; P = 0.04) and 60 min (MS, 209 ± 94 g; CON, 285 ± 62 g; P = 0.02), as well as lower sweating thermosensitivity (MS, 0.49 ± 0.26 mg·cm·min·°C; CON, 0.86 ± 0.30 mg·cm·min·°C; P = 0.049). Despite evidence for thermoregulatory dysfunction, there were no differences between MS and CON in esophageal or rectal temperatures at 30- or 60-min time points (P > 0.05). Cutaneous vasculature responses were also not different in MS compared with CON (P > 0.05).

CONCLUSION

Taken together, MS blunts sweating responses during exercise while cutaneous vasculature responses are preserved. Altered mechanisms of body temperature regulation in persons with MS may lead to temporary worsening of disease symptoms and limit exercise tolerance under more thermally challenging conditions.

Wilhelm Uhthoff and Uhthoff's phenomenon

Wilhelm Uhthoff, known for his contributions to both neurology and neuro-ophthalmology, was a German ophthalmologist who specialized in neurologic disorders. The eponym "Uhthoff's phenomenon" was first used to describe the reversible, transient blurring of vision in patients with multiple sclerosis during exercise. Subsequently, it was discovered that this neurologic sign not only was triggered by physical exertion but also by other homeostatic disruptions such as hot baths, menstruation, and high external temperatures. Here, we take a look at the life and career of Wilhelm Uhthoff and discuss the basis behind this phenomenon.

Heat-related issues and practical applications for Paralympic athletes at Tokyo 2020

International sporting competitions, including the Paralympic Games, are increasingly being held in hot and/or humid environmental conditions. Thus, a greater emphasis is being placed on preparing athletes for the potentially challenging environmental conditions of the host cities, such as the upcoming Games in Tokyo in 2020. However, evidence-based practices are limited for the impairment groups that are eligible to compete in Paralympic sport. This review aims to provide an overview of heat-related issues for Paralympic athletes alongside current recommendations to reduce thermal strain and technological advancements in the lead up to the Tokyo 2020 Paralympic Games. When competing in challenging environmental conditions, a number of factors may contribute to an athlete's predisposition to heightened thermal strain. These include the characteristics of the sport itself (type, intensity, duration, modality, and environmental conditions), the complexity and severity of the impairment and classification of the athlete. For heat vulnerable Paralympic athletes, strategies such as the implementation of cooling methods and heat acclimation can be used to combat the increase in heat strain. At an organizational level, regulations and specific heat policies should be considered for several Paralympic sports. Both the utilization of individual strategies and specific heat health policies should be employed to ensure that Paralympics athletes' health and sporting performance are not negatively affected during the competition in the heat at the Tokyo 2020 Paralympic Games.

Longitudinal assessment of autonomic nervous system in patients with first demyelinating event suggestive of multiple sclerosis

BACKGROUND AND PURPOSE

As a high proportion of people with clinically isolated syndrome (pwCIS) exhibit sympathetic adrenergic and sudomotor dysfunction, the aim of this study was to investigate the evolution of autonomic nervous system (ANS) abnormalities in pwCIS over a 2-year follow-up.

METHODS

This was a prospective cohort study in which 121 pwCIS were enrolled and followed for 2 years. After 2-year follow-up, data were available for 84 pwCIS. ANS symptoms were evaluated with the Composite Autonomic System Score-31 (COMPASS-31) and results of the ANS tests were expressed using the Composite Autonomic Scoring Scale (CASS) at baseline and visit at month 24. Symptomatic dysautonomia was defined if the patient had a COMPASS-31 value above the median of the whole cohort at baseline evaluation (COMPASS-31 > 6.79) and CASS score >0.

RESULTS

Complete CASS data at baseline and month 24 were available for 62 patients; in 24 (38.7%) patients there was worsening, in 16 (25.8%) there was improvement and in 22 (35.5%) there was no change in CASS score. In 90% of pwCIS (72 of 80) there was no change in parasympathetic nervous system tests, whereas 47.3% (35 of 74) had either worsening or improvement in sympathetic adrenergic and 28.6% (20 of 70) had either worsening or improvement in sudomotor function. A multivariable regression model identified the total number of T2 lesions as an independent predictor for worsening of symptomatic dysautonomia. No predictors for worsening or improving of CASS score were identified.

CONCLUSION

A substantial proportion of pwCIS experienced worsening of ANS abnormalities during the 2-year follow-up and magnetic resonance imaging parameters seemed to predict these abnormalities.

Medical and Musculoskeletal Concerns for the Wheelchair Athlete: A Review of Preventative Strategies

Adaptive sports refers to organized sporting activities that are practiced by individuals with disabilities and are worthwhile to maintain physical and psychological health. As adaptive sports participation continues to rise, health care providers must have an enhanced understanding of injury and illness patterns specific to the adaptive athlete. Early recognition and prevention are important to ensure safe and successful participation in sport. The present review aims to provide a framework for diagnosis and prevention of common conditions specific to the wheelchair athlete. In particular, autonomic dysreflexia, impaired thermoregulation, urinary tract infection, and pressure injuries, as well as shoulder pain, upper-extremity entrapment neuropathies, and osteoporotic fractures will be discussed.

Cardiac autonomic function during postural changes and exercise in people with multiple sclerosis: A cross-sectional study

BACKGROUND

People with multiple sclerosis (PwMS) often develop an autonomic dysfunction (AD), which onset should be assessed early at a subclinical level, as it may interfere with pharmacological treatments and exercise.

OBJECTIVE

To evaluate basal cardiac autonomic tone, its modulations during sit-to-stand, sub-maximal exercise and recovery in PwMS without clinical overt AD and its relationships with fatigue perception.

METHODS

Twenty-three PwMS (55 ± 8 yrs [mean ± SD]; EDSS score 5.7 ± 1.3) and 20 age-matched healthy controls (HC; 55 ± 8yrs) were enrolled. ECG was digitally acquired during:1) sitting at rest (low sympathetic activation); 2) standing (light sympathetic activation); and 3) during light exercise (moderate sympathetic activation) and recovery. Parasympathetic and sympatho-vagal parameters of heart rate (HR) variability in time and frequency domains were calculated from beat series.

RESULTS

HR was slightly but not significantly higher in PwMS compared to HC in all experimental conditions. Parasympathetic indexes were significantly lower (p < 0.05) in PwMS compared to HC during baseline sitting and post-exercise recovery, whereas sympathovagal parameters were similar in both groups. No correlation between autonomic tone and perceived fatigue was observed.

CONCLUSION

Parasympathetic tone appears to be impaired in PwMS basal and post-exercise conditions, but not during postural challenge and exercise. In addition, AD does not affect perceived fatigue.

Thermoregulatory dysfunction in multiple sclerosis

Multiple sclerosis (MS) is a progressive neurologic disorder that disrupts axonal myelin in the central nervous system. Demyelination produces alterations in saltatory conduction, slowed conduction velocity, and a predisposition to conduction block. An estimated 60-80% of MS patients experience temporary worsening of clinical signs and neurologic symptoms with heat exposure (Uhthoff's phenomenon). This heat intolerance in MS is related to the detrimental effects of increased temperature on action potential propagation in demyelinated axons, resulting in conduction slowing and/or block. Additionally, MS may produce impaired neural control of autonomic and endocrine functions. Isolating and interpreting mechanisms responsible for autonomic dysfunction due to MS can be difficult as it may involve sensory impairments, altered neural integration within the central nervous system, impaired effector responses, or combinations of all of these factors. MS lesions occur in areas of the brain responsible for the control and regulation of body temperature and thermoregulatory effector responses, resulting in impaired neural control of sudomotor pathways or neural-induced changes in eccrine sweat glands, as evidenced by observations of reduced sweating responses in MS patients. Although not comprehensive, some evidence exists concerning treatments (cooling, precooling, and pharmacologic) for the MS patient to preserve function and decrease symptom worsening during heat stress. This review focuses on four main themes influencing current understanding of thermoregulatory dysfunction in MS: (1) heat intolerance; (2) central regulation of body temperature; (3) thermoregulatory effector responses; and (4) countermeasures to improve or maintain function during thermal stress.

Exercise prescription for patients with multiple sclerosis; potential benefits and practical recommendations

BACKGROUND

Multiple sclerosis (MS) can result in significant mental and physical symptoms, specially muscle weakness, abnormal walking mechanics, balance problems, spasticity, fatigue, cognitive impairment and depression. Patients with MS frequently decrease physical activity due to the fear from worsening the symptoms and this can result in reconditioning. Physicians now believe that regular exercise training is a potential solution for limiting the reconditioning process and achieving an optimal level of patient activities, functions and many physical and mental symptoms without any concern about triggering the onset or exacerbation of disease symptoms or relapse.

MAIN BODY

Appropriate exercise can cause noteworthy and important improvements in different areas of cardio respiratory fitness (Aerobic fitness), muscle strength, flexibility, balance, fatigue, cognition, quality of life and respiratory function in MS patients. Aerobic exercise training with low to moderate intensity can result in the improvement of aerobic fitness and reduction of fatigue in MS patients affected by mild or moderate disability. MS patients can positively adapt to resistance training which may result in improved fatigue and ambulation. Flexibility exercises such as stretching the muscles may diminish spasticity and prevent future painful contractions. Balance exercises have beneficial effects on fall rates and better balance. Some general guidelines exist for exercise recommendation in the MS population. The individualized exercise program should be designed to address a patient's chief complaint, improve strength, endurance, balance, coordination, fatigue and so on. An exercise staircase model has been proposed for exercise prescription and progression for a broad spectrum of MS patients.

CONCLUSION

Exercise should be considered as a safe and effective means of rehabilitation in MS patients. Existing evidence shows that a supervised and individualized exercise program may improve fitness, functional capacity and quality of life as well as modifiable impairments in MS patients.

Synergistic effect of energy drinks and overweight/obesity on cardiac autonomic testing using the Valsalva maneuver in university students

BACKGROUND

Obesity and caffeine consumption may lead to autonomic disturbances that can result in a wide range of cardiovascular disorders.

OBJECTIVES

To determine autonomic disturbances produced by the synergistic effects of overweight or obesity (OW/OB) and energy drinks.

DESIGN

Cross-sectional, analytical.

SETTING

Physiology department at a university in Saudi Arabia.

SUBJECTS AND METHODS

University students, 18-22 years of age, of normal weight (NW) and OW/OB were recruited by convenience sampling. Autonomic testing by the Valsalva ratio (VR) along with systolic and diastolic blood pressure, pulse pressure, and mean arterial blood pressure were measured at baseline (0 minute) and 60 minutes after energy drink consumption.

MAIN OUTCOME MEASURE(S)

Autonomic disturbance, hemodynamic changes.

RESULTS

In 50 (27 males and 23 females) subjects, 21 NW and 29 OW/OB, a significant decrease in VR was observed in OW/OB subjects and in NW and OW/OB females at 60 minutes after energy drink consumption. Values of systolic and diastolic blood pressure, pulse pressure and mean arterial blood pressure were also significantly higher in OW/OB and in females as compared to NW and males. BMI was negatively correlated with VR and diastolic blood pressure at 60 minutes.

CONCLUSION

Obesity and energy drinks alter autonomic functions. In some individuals, OW/OB may augment these effects.

LIMITATIONS

Due to time and resource restraints, only the acute effects of energy drinks were examined.

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.

A comparison of thermoregulatory responses to exercise between mass-matched groups with large differences in body fat

We sought to determine 1) the influence of adiposity on thermoregulatory responses independently of the confounding biophysical factors of body mass and metabolic heat production (Hprod); and 2) whether differences in adiposity should be accounted for by prescribing an exercise intensity eliciting a fixed Hprod per kilogram of lean body mass (LBM). Nine low (LO-BF) and nine high (HI-BF) body fat males matched in pairs for total body mass (TBM; LO-BF: 88.7 ± 8.4 kg, HI-BF: 90.1 ± 7.9 kg; P = 0.72), but with distinctly different percentage body fat (%BF; LO-BF: 10.8 ± 3.6%; HI-BF: 32.0 ± 5.6%; P < 0.001), cycled for 60 min at 28.1 ± 0.2 °C, 26 ± 8% relative humidity (RH), at a target Hprod of 1) 550 W (FHP trial) and 2) 7.5 W/kg LBM (LBM trial). Changes in rectal temperature (ΔTre) and local sweat rate (LSR) were measured continuously while whole body sweat loss (WBSL) and net heat loss (Hloss) were estimated over 60 min. In the FHP trial, ΔTre (LO-BF: 0.66 ± 0.21 °C, HI-BF: 0.87 ± 0.18 °C; P = 0.02) was greater in HI-BF, whereas mean LSR (LO-BF 0.52 ± 0.19, HI-BF 0.43 ± 0.15 mg·cm(-2)·min(-1); P = 0.19), WBSL (LO-BF 586 ± 82 ml, HI-BF 559 ± 75 ml; P = 0.47) and Hloss (LO-BF 1,867 ± 208 kJ, HI-BF 1,826 ± 224 kJ; P = 0.69) were all similar. In the LBM trial, ΔTre (LO-BF 0.82 ± 0.18 °C, HI-BF 0.54 ± 0.19 °C; P < 0.001), mean LSR (LO-BF 0.59 ± 0.20, HI-BF 0.38 ± 0.12 mg·cm(-2)·min(-1); P = 0.04), WBSL (LO-BF 580 ± 106 ml, HI-BF 381 ± 68 ml; P < 0.001), and Hloss (LO-BF 1,884 ± 277 kJ, HI-BF 1,341 ± 184 kJ; P < 0.001) were all greater at end-exercise in LO-BF. In conclusion, high %BF individuals demonstrate a greater ΔTre independently of differences in mass and Hprod, possibly due to a lower mean specific heat capacity or impaired sudomotor control. However, thermoregulatory responses of groups with different adiposity levels should not be compared using a fixed Hprod in watts per kilogram lean body mass.