Baroreflex Sensitivity during Static Exercise in Individuals with Down Syndrome

Espírito Santo R, Dubey VP, Agostinis-Sobrinho C. Handgrip strength measurement protocols in individuals with Down syndrome: a systematic review and meta-regression

BACKGROUND

Handgrip strength (HGS) serves as a robust predictor of overall strength across various populations, including individuals with Down Syndrome (DS).

OBJECTIVE

To analyze the HGS measurement protocols used in studies involving individuals with DS.

METHODS

Primary sources were sourced from six databases: PubMed, Scopus, Ovid, Embase, ERIC, and Web of Science, spanning from inception to 23rd December 2023. Inclusion criteria focused on individuals with DS, compared with control groups, and examined HGS measurement protocols and outcomes. Meta-regression was utilized to assess bias associated with HGS values concerning different measurement protocols.

RESULTS

Out of 29 studies involving 1816 participants, most controlled for body position (65%), arm position (82%), elbow position (82%), wrist position (62%), handgrip duration (55%), hand adjustment to dynamometer (62%), verbal encouragement (75%), and familiarization (44.8%). The number of reported variables in the HGS protocol was significantly associated with an increase in HGS, with a mean estimate of 20.59 units (SE = 2.59, p < 0.0001, 95% CI [15.49-25.68]), though there was notable heterogeneity (I2 = 94.33%). The spline regression analysis showed that the model explained 82.66% of the variation in HGS, with adults having 47.61 units higher HGS than children (p = 0.0009), while obesity was linked to a decrease of 15.68 units (p = 0.0675). Sample size and group had no significant effects.

CONCLUSION

Overall, protocols for assessing HGS in DS studies are comprehensive yet heterogeneous. Higher HGS values correlated with adherence to standard protocols.

Development of a Physical Therapy-Based Exercise Program for Adults with Down Syndrome

In adults with Down syndrome, the combination of low physical activity and fitness levels and the high prevalence of musculoskeletal co-morbidities stresses the need for specialized exercise programs. The goal of this research study was to develop a specialized exercise program for individuals with Down syndrome using the physical therapy approach of a systems review as the foundation. We first conducted an overview of the literature on co-morbidities in adults with Down syndrome using the systems review method to categorize these findings. We extracted recommendations for content and delivery of an exercise program based on the literature review, and finally composed a specialized exercise program for individuals with Down syndrome adhering to these recommendations.

Sleep apnea in people with Down syndrome: Causes and effects of physical activity?

Poor sleep quality is recognized as a major risk factor for poor health, increasing the incidence of serious chronic diseases. In people with Down syndrome, sleep apnea prevalence is significantly greater, it is caused by genetic, anatomical, endocrine, and metabolic abnormalities. The consequences of sleep disruption due to sleep apnea are very serious, especially in terms of neurocognitive and cardiovascular effects, leading to reduced life expectancy and quality of life in this population. However, the management, care, and treatment of related disorders in people with Down syndrome are still inadequate and limited. Therefore, this article wants to increase understanding and awareness about sleep apnea and the benefits of physical activity in improving sleep quality in the Down syndrome community, families, and their care specialists.

Heart Rate Variability in Individuals with Down Syndrome: A Scoping Review with Methodological Considerations

Individuals with Down syndrome (DS) present similar heart rate variability (HRV) parameters at rest but different responses to selected movement maneuvers in comparison to individuals without DS, which indicates reduced vagal regulation. The present study undertakes a scoping review of research on HRV in individuals with DS, with special attention paid to the compliance of the studies with standards and methodological paper guidelines for HRV assessment and interpretation. A review was performed using PubMed, Web of Science and CINAHL databases to search for English language publications from 1996 to 2020 with the MESH terms "heart rate variability" and "down syndrome", with the additional inclusion criteria of including only human participants and empirical investigations. From 74 studies, 15 were included in the review. None of the reviewed studies met the recommendations laid out by the standards and guidelines for providing the acquisition of RR intervals and necessary details on HRV analysis. Since authors publishing papers on this research topic do not adhere to the prescribed standards and guidelines when constructing the methodology, results of the research papers on the topic are not directly comparable. Authors need to design the study methodology more robustly by following the aforementioned standards, guidelines and recommendations.

Hemodynamic and cardiorespiratory responses to submaximal and maximal exercise in adults with Down syndrome

Introduction: The genetic disorder causing Down syndrome (DS) affects the cardiorespiratory and hemodynamic parameters. When exercising, sufficient blood flow is necessary for active muscles. Cardiac output (Q) must be proportional to the peripheral requirements. In case the stroke volume (SV) is lower, the heart rate (HR) will increase further in order to maintain an adequate blood flow in the active territories (HR compensatory response). People with DS have a lower HR response to maximal exercise. Nevertheless, the response of the hemodynamic and cardiorespiratory parameters during the submaximal phases of maximal exercise was not well studied.

Objective: to evaluate cardiorespiratory and hemodynamic parameters 1) during submaximal and 2) maximal metabolic treadmill test in individuals with and without DS.

Methods: fifteen adults with DS (age = 27.33 ± 4.98 years old; n = 12 males/3 females) and 15 adults without disabilities, matched by age and sex, participated in this cross-sectional study. Peak and submaximal cardiorespiratory and hemodynamic parameters were measured during a treadmill test. Linear mixed-effects models were used to analyse interactions between the variables. Post-hoc analyses were employed to assess within and between-group differences.

Results: The DS group showed lower peak values for ventilation (VE), respiratory exchange ratio (RER), tidal volume (VT), ventilatory equivalent for O2 (VEqO2), end-tidal partial pressure for O2 (PETO2), O2 uptake (VO2) and CO2 production (all p &lt; 0 .050), Q, SV, systolic and diastolic blood pressure (SBP, DBP), and HR (all p &lt; 0 .050). There were group-by-time interactions (all p &lt; 0 .050) for all ventilatory submaximal values. Significant group and time differences were observed for VE; RER; respiratory rate (RR); VEqO2; PETO2; VO2, and VT (all p &lt; 0 .050). There were also group-by-time interactions (all p &lt; 0 .050) and group and time differences for SBP, mean arterial blood pressure (MAP) and HR (all p &lt; 0.010).

Conclusion: During submaximal exercise, we verified a compensatory response of HR, and greater VE and VO2 in the individuals with DS. In addition, we were able to observe that the DS group had a reduced SBP and MAP response to submaximal exercise. On the other hand, we found that adults with DS have lower peak hemodynamic and cardiorespiratory values, and a lower cardiac reserve. Further research is warranted to investigate the effects of these results on the general health of adults with DS and the impact of long-term exercise programs on these parameters.

Cardiovascular Physiology and Pathophysiology in Down Syndrome

Down Syndrome (Ds) is the most common chromosomal cause of intellectual disability that results from triplication of chromosome 21 genes. Individuals with Ds demonstrate cognitive deficits in addition to comorbidities including cardiac defects, pulmonary arterial hypertension (PAH), low blood pressure (BP), and differences in autonomic regulation. Many individuals with Ds are born with heart malformations and some can be surgically corrected. Lower BP at rest and in response to exercise and other stressors are a prevalent feature in Ds. These reduced cardiovascular responses may be due to underlying autonomic dysfunction and have been implicated in lower exercise/work capacity in Ds, which is an important correlate of morbidity, mortality and quality of life. Exercise therapy can be beneficial to normalize autonomic function and may help prevent the development of co-morbidities in Ds. We will review cardiovascular physiology and pathophysiology in individuals with Ds, along with exercise therapy and special considerations for these individuals.

Hemodynamic Response to Isometric Handgrip Exercise in Adults with Intellectual Disability

INTRODUCTION

Individuals with intellectual disability (ID) have an increased risk of cardiovascular disease and reduced work capacity, which could partly be explained by alterations to autonomic and hemodynamic regulation. The measurement of heart rate and blood pressure during isometric handgrip (HG) exercise, a sympathoexcitatory stimulus, is a noninvasive method to investigate autonomic and hemodynamic alterations. The purpose of this study was to assess alterations to autonomic and associated hemodynamic regulation between individuals with ID and a matched control group during isometric HG exercise.

METHODS

Individuals with ID (n = 13; 31 ± 2 yr, 27.6 ± 7.7 kg·m-2) and without ID (n = 16; 29 ± 7 yr, 24.2 ± 2.8 kg·m-2) performed 2 min of isometric HG exercise at 30% of maximal voluntary contraction (MVC) in the seated position. Blood pressure was averaged for 2 min before, during, and after HG exercise (mean arterial pressure [MAP], systolic blood pressure, and diastolic blood pressure). Heart rate variability, blood pressure variability, and baroreflex sensitivity were calculated from the continuous blood pressure and heart rate recordings.

RESULTS

Isometric HG elicited a blunted response in systolic blood pressure, diastolic blood pressure, and MAP among individuals with ID compared with individuals without ID, even after controlling for strength (MAP: rest, HG, recovery; ID: 103 ± 7, 108 ± 9, 103 ± 7; without ID: 102 ± 7, 116 ± 10, 104 ± 10 mm Hg; interaction P < 0.05). Individuals with ID also had an attenuated baroreflex sensitivity response to HG exercise compared with individuals without ID (interaction P = 0.041), but these effects were no longer significant after controlling for maximal voluntary contraction. Indices of heart rate variability and blood pressure variability were not different between groups overall or in response to HG exercise (P > 0.05).

CONCLUSIONS

Individuals with ID have a blunted hemodynamic and autonomic response to isometric HG exercise compared with individuals without ID.

Heart rate and blood pressure in male Ts65Dn mice: a model to investigate cardiovascular responses in Down syndrome

Down syndrome (Ds) is the most common chromosomal cause of intellectual disability that results from triplication of chromosome 21 genes. Lower blood pressure (BP) and heart rate (HR) in response to exercise and other stressors are prevalent in Ds, and are mediated by autonomic dysfunction. The Ts65Dn mouse is a model of Ds that is commonly used in preclinical studies, but has not been formally investigated for cardiovascular responses in conscious mice. Based on human studies of Ds, we hypothesized Ts65Dn would have lower BP and HR, but similar arterial stiffness. BP was quantified in conscious wild-type (WT) and Ts65Dn. A main effect for strain was observed for all BP measures (systolic, diastolic, mean, pulse pressure), with WT higher than Ts65Dn. Pulse wave velocity was similar between WT and Ts65Dn. High-frequency power spectra was higher in WT suggesting autonomic differences between strains. Freely moving HR was higher in WT versus Ts65Dn in both the dark and light cycles, although a main effect of circadian cycle was also present (dark> light). Similar to what is observed in humans, Ts65Dn has a lower BP which may be attributed to autonomic differences and result in preservation of arterial function with advancing age. Ts65Dn thus appears to capture the Ds cardiovascular phenotype across the lifespan. These data support further use of Ts65Dn to investigate mechanisms that may lead to altered BP and HR responses in Ds.

Do adults with Down syndrome do the same amount of physical activity as adults without disability? A proof of principle study

BACKGROUND

This study compared levels of physical activity completed by adults with and without Down syndrome.

METHOD

Fifteen adults with and 15 adults without Down syndrome matched for age and gender, took part. The intensity and duration of physical activity were measured using RT3 accelerometers worn for seven days.

RESULTS

Only, 12 participants with Down syndrome had complete physical activity data, and these participants and their matched controls (total: six females, 18 males; aged 25.8 ± 9.7) were included in the analyses. There were significantly lower levels of moderate and vigorous physical activity per day for people with Down syndrome (median = 27 min) compared to those without (median = 101 min) (p < .001). Participants without disability were twice more likely to achieve recommended levels of physical activity than people with Down syndrome.

CONCLUSIONS

Adults with Down syndrome appear to participate in lower levels of physical activity than adults without Down syndrome. Further research should validate these estimates.

Cardiac autonomic modulation and blood pressure responses to isometric handgrip and submaximal cycling exercise in individuals with down syndrome

PURPOSE

Individuals with Down syndrome (DS) exhibit autonomic dysfunction, manifested as attenuated heart rate (HR) and blood pressure (BP) responses to sympathoexcitation. Whether a subgroup of individuals with DS with a normal HR response would have normal autonomic responses to sympathoexcitation remains unclear.

METHODS

We compared autonomic modulation using HR variability (HRV) and BP responses in individuals with and without DS (controls) matched for the HR change to isometric handgrip (HG) (10 DS, 8 controls) and submaximal cycling exercise (CE) (9 DS, 9 controls). HG was performed for 2 min at 30 % of maximal voluntary contraction. CE included two 6-min stages at 0 W and at 50 % of body weight. Beat-to-beat HR and BP were recorded. HRV variables were natural log transformation (Ln) of low frequency (LF), high frequency (HF), LF/HF ratio, total power (TP), and the root mean square of successive differences (RMSSD).

RESULTS

In the HG study, although individuals with DS exhibited an overall lower systolic BP, LF/HF ratio, and LnLF/LnHF, their BP and HRV responses to HG were similar to those of the controls. In the CE study, individuals with DS exhibited lower resting LnLF and an overall lower systolic BP and mean arterial pressure compared with controls. During the CE, individuals with DS exhibited an increased diastolic BP and a smaller reduction in LnTP than controls. These differences disappeared after controlling for confounders.

CONCLUSIONS

Our results suggest that despite normal HR responses to sympathoexcitatory tasks, HRV was largely similar to controls, with some evidence of autonomic dysfunction in individuals with DS.

Autonomic Recovery Is Delayed in Chinese Compared with Caucasian following Treadmill Exercise

Caucasian populations have a higher prevalence of cardiovascular disease (CVD) when compared with their Chinese counterparts and CVD is associated with autonomic function. It is unknown whether autonomic function during exercise recovery differs between Caucasians and Chinese. The present study investigated autonomic recovery following an acute bout of treadmill exercise in healthy Caucasians and Chinese. Sixty-two participants (30 Caucasian and 32 Chinese, 50% male) performed an acute bout of treadmill exercise at 70% of heart rate reserve. Heart rate variability (HRV) and baroreflex sensitivity (BRS) were obtained during 5-min epochs at pre-exercise, 30-min, and 60-min post-exercise. HRV was assessed using frequency [natural logarithm of high (LnHF) and low frequency (LnLF) powers, normalized high (nHF) and low frequency (nLF) powers, and LF/HF ratio] and time domains [Root mean square of successive differences (RMSSD), natural logarithm of RMSSD (LnRMSSD) and R-R interval (RRI)]. Spontaneous BRS included both up-up and down-down sequences. At pre-exercise, no group differences were observed for any HR, HRV and BRS parameters. During exercise recovery, significant race-by-time interactions were observed for LnHF, nHF, nLF, LF/HF, LnRMSSD, RRI, HR, and BRS (up-up). The declines in LnHF, nHF, RMSSD, RRI and BRS (up-up) and the increases in LF/HF, nLF and HR were blunted in Chinese when compared to Caucasians from pre-exercise to 30-min to 60-min post-exercise. Chinese exhibited delayed autonomic recovery following an acute bout of treadmill exercise. This delayed autonomic recovery may result from greater sympathetic dominance and extended vagal withdrawal in Chinese.

TRIAL REGISTRATION

Chinese Clinical Trial Register ChiCTR-IPR-15006684.

The electrocardiogram in Down syndrome

Down syndrome is the most common chromosomal abnormality, with an incidence of one case in every 650 live births. It is strongly associated with heart disease, which constitutes the main cause of mortality during the first 2 years of life in this population. Most of the cardiac abnormalities in patients with Down syndrome can be suspected by analysing the surface 12-lead ECG. The purpose of this systematic review was to analyse all available published material on surface ECG and cardiac rhythm and conduction abnormalities in patients with Down syndrome to facilitate the search to the clinical cardiologist and paediatrician.

Heart rate complexity in response to upright tilt in persons with Down syndrome

People with Down syndrome (DS) show altered autonomic response to sympatho-excitation. Cardiac autonomic modulation may be examined with heart rate (HR) complexity which is associated uniquely with cardiovascular risk. This study examined whether the response of HR complexity to passive upright tilt differs between persons with and without DS and whether potential between-group differences in this response are accounted for by differences in body mass index (BMI). The electrocardiogram of 16 persons with DS (8 women, 8 men) and 16 persons without DS (8 women, 8 men) was recorded during 10 min of supine rest and 10 min of upright tilt. For each participant, 550 continuous, steady state, and ectopy-free R-R intervals under each condition were analyzed. Dependent variables were approximate entropy, correlation dimension, StatAv, and the mean R-R interval. In response to tilt, changes in approximate entropy and correlation dimension were reduced in participants with DS (p<0.05). These differences were explained by higher BMI in participants with DS. StatAv increased in persons with DS (p < 0.05) and stayed the same in those without DS even when controlling for BMI. The response of R-R interval did not differ between groups. None of the variables differed between groups at rest. Therefore, people with DS show smaller decrease in HR complexity in response to upright tilt than people without DS partially due to their higher BMI. Resting HR complexity does not differ between persons with and without DS. These results may have implications for cardiovascular risk in people with DS.

Donepezil for treatment of cognitive dysfunction in children with Down syndrome aged 10-17

The objective of this 10-week, randomized, double-blind, placebo-controlled multicenter study was to assess the efficacy and safety of donepezil for the treatment of cognitive dysfunction exhibited by children with Down syndrome (DS). Intervention comprised donepezil (2.5-10 mg/day) in children (aged 10-17 years) with DS of mild-to-moderate severity. The primary measures were the Vineland-II Adaptive Behavior Scales (VABS-II) Parent/Caregiver Rating Form (PCRF) the sum of nine subdomain standardized scores and standard safety measures. Secondary measures included the VABS-II/PCRF scores on the following domains and their respective individual subdomains: Communication (receptive, expressive, and written); Daily Living Skills (personal, domestic, and community); Socialization (interpersonal relationships, play and leisure time, and coping skills), and scores on the Test of Verbal Expression and Reasoning, a subject-performance-based measure of expressive language. At baseline, 129 participants were assigned treatment with donepezil or placebo. During the double-blind phase, VABS II/PCRF sum of the nine subdomain standardized scores, called v-scores, improved significantly from baseline in both groups (P < 0.0001), with no significant between-group differences. This trial failed to demonstrate any benefit for donepezil versus placebo in children and adolescents with DS, although donepezil appeared to be well tolerated.

Reduced exercise capacity in persons with Down syndrome: cause, effect, and management

Persons with Down syndrome (DS) have reduced peak and submaximal exercise capacity. Because ambulation is one predictor of survival among adults with DS, a review of the current knowledge of the causes, effects, and management of reduced exercise capacity in these individuals would be important. Available data suggest that reduced exercise capacity in persons with DS results from an interaction between low peak oxygen uptake (VO_2peak) and poor exercise economy. Of several possible explanations, chronotropic incompetence has been shown to be the primary cause of low VO_2peak in DS. In contrast, poor exercise economy is apparently dependent on disturbed gait kinetics and kinematics resulting from joint laxity and muscle hypotonia. Importantly, there is enough evidence to suggest that such low levels of physical fitness (reduced exercise capacity and muscle strength) limit the ability of adults with DS to perform functional tasks of daily living. Consequently, clinical management of reduced exercise capacity in DS seems important to ensure that these individuals remain productive and healthy throughout their lives. However, few prospective studies have examined the effects of structured exercise training in this population. Existent data suggest that exercise training is beneficial for improving exercise capacity and physiological function in persons with DS. This article reviews the current knowledge of the causes, effects, and management of reduced exercise capacity in DS. This review is limited to the acute and chronic responses to submaximal and peak exercise intensities because data on supramaximal exercise capacity of persons with DS have been shown to be unreliable.

Catecholamine response to maximal exercise in persons with Down syndrome

Individuals with Down syndrome (DS) exhibit low peak aerobic capacities and heart rates. Although autonomic modulation is attenuated in individuals with DS at rest, the exercise response appears normal. This suggests that mechanisms other than autonomic control influence the low aerobic capacity, such as catecholamine responsiveness to exercise. The purpose of this study was to determine catecholamine responses to a peak treadmill test in a group of subjects with DS compared with a nondisabled group. Epinephrine and norepinephrine concentrations were measured at rest and immediately after graded exercise tests on a treadmill in 20 subjects with DS (mean age, 24 +/- 7 years) and 21 nondisabled subjects (mean age, 26 +/- 6 years). Catecholamines increased significantly with peak exercise in the control group (p <0.05), with little to no change in subjects with DS. In conclusion, the different catecholamine responses to peak exercise, in particular the lack of a response in individuals with the DS, may be a primary mechanism to explain the reduced peak heart rates and low work capacities observed in this population.

Complexity of force output during static exercise in individuals with Down syndrome

Force variability is greater in individuals with Down syndrome (DS) compared with persons without DS and is similar to that seen with normal aging. The purpose of this study was to examine the structure (in both time and frequency domains) of force output variability in persons with DS to determine whether deficits in force control are similar between individuals with DS and older adults. An isometric handgrip task at a constant force (30% of maximal voluntary contraction) was completed by individuals with DS (n = 29, age 26 yr), and healthy young (n = 26, age 27 yr) and older (n = 33, age 70 yr) individuals. Mean, standard deviation (SD), and coefficient of variation (CV) were used to analyze the magnitude of force output variability. Spectral analysis and approximate entropy (ApEn) were used to analyze the structure of force output variability. Mean force output for DS was lower than in young controls (P < 0.05) but no different from old controls. Individuals with DS had greater SD and CV than young and old controls (P < 0.05). The DS group had a significantly greater proportion of spectral power within the 0-to 4-Hz bandwidth than the young and older controls (P < 0.05). The DS group had significantly lower ApEn values than the young controls (P < 0.05), but there were no differences in ApEn between the DS group and the old controls (P > 0.05). In conclusion, young persons with DS demonstrate enhanced temporal structure and greater amplitude of low-frequency oscillations in the force output signal than age-matched non-DS peers. Interestingly, young persons with DS and older persons without DS have similar time-dependent structure of force output variability. This would suggest a possible link between premature aging and less complex force output in persons with DS.