Heart rate variability at rest and during exercise in persons with Down syndrome

Measurement protocols and determinants of peak oxygen consumption in adults with Down syndrome: a systematic review

This systematic review aimed to provide an overview of test protocols used to measure peak oxygen uptake (VO2peak) in adults with Down syndrome (DS) and to determine how generalisable the outcomes are for the entire population of adults with DS by describing the sample characteristics of these studies and their impact on VO2peak. A literature search (PROSPERO CRD42022309560) was performed (18 July 2023) using the following databases: PubMed, CINAHL, APA PsycINFO, Web of Science, Embase and SPORTDiscus. For articles to be included, they had to be peer-reviewed pubications, reporting VO2peak or VO2max for individuals with DS separately, with a sample of n ≥ 5 and a mean age ≥18 years. Systematic reviews and meta-analyses were excluded but their reference lists were searched for additional papers to include. Studies were evaluated for risk of bias following the guidelines of Kmet et al. The results were summarised with frequency statistics. Forty-three studies were included in this systematic review. Sample sizes of included adults with DS ranged from n = 4-226, with a total of n = 1498 adults with DS being included. Most studies (29/43) used the same standardised maximal exercise treadmill protocol to measure VO2peak in adults with DS, and 33 out of 43 studies used at least one objective criterion to determine a valid maximal effort. Participants were predominantly male, under 40 years old, and overweight or obese. Additionally, the diversity of study samples was lacking or not reported. The most widely used, standardised, maximal exercise test treadmill protocol is recommended for future use in research and practice, including objective criteria to determine valid maximal effort. The current study samples are not representative of the population of adults with DS in terms of sex, age and diverse backgrounds and therefore likely overestimate VO2peak of this population.

Cardiac autonomic modulation and exercise capacity in older adults with intellectual disability: A 6-month randomised control trial

BACKGROUND

Despite reported physical and functional improvements with aerobic and sprint interval training (SIT) protocols in individuals with intellectual disability (ID), it is not known if these interventions' effectivity would promote improvements in cardiac autonomic modulation. This study aimed to investigate if a 6-month SIT or a continuous aerobic programme could enhance physical performance and cardiac autonomic modulation at rest, during physical activity (PA) and after it in older adults with an ID.

METHODS

This is a randomised control trial. Participants with ID (age: 50.58 ± 7.25) were allocated to one of three groups [multicomponent aerobic training group (MATG), multicomponent interval sprint training group (MISTG) and control group (CG)]. The programmes lasted 24 weeks, with three sessions/week, 75-90 min per session. The HRV was analysed at rest and recovery, the delta of heart rate (HR) was analysed during 6MWT, and the HR t-off kinetics was analysed in recovery after 6MWT.

RESULTS

There were not found differences between groups, moments, or interaction for cardiac autonomic modulation at rest and recovery. During exercise, only MSITG showed a significant increase of HR between rest and the first 30 s of exercise (P < 0.05). Physical performance increased only in MSITG (P < 0.05), while CG showed a significant reduction (P < 0.01).

CONCLUSIONS

The MSITG improved the physical performance and the vagal withdrawal at the beginning of the submaximal exercise. These findings suggest that high-intensity exercise may positively impact baroreflex function, mitigating the decline in autonomic reflex response capacity associated with aging in individuals with ID.

The surge in heart rate and blood pressure at respiratory event termination is dampened in children with down syndrome

BACKGROUND

Children with Down syndrome (DS) have a high prevalence of sleep disordered breathing (SDB) and altered cardiovascular autonomic control. We aimed to analyze the effect of DS on the surge in heart rate (HR) and pulse transit time (PTT, an inverse surrogate measure of blood pressure change) at respiratory event termination.

METHODS

44 children (3-19 y) with DS and 44 typically developing (TD) children matched for SDB severity, age and sex underwent overnight polysomnography. Multilevel modelling determined the effect of DS on HR and PTT changes between a 10s pre-event to the latter half of each respiratory event (late-event) and 15s post-event during NREM and REM, accounting for SDB severity and event length.

RESULTS

The children with DS had a significantly smaller % change in HR late-event to post-event (NREM: DS 26.4 % ± 17.5 % (mean ± SD), TD 30.7 % ± 21.0 %; REM DS 16.9 % ± 15.3 %, TD 21.0 % ± 14.0 %; p < 0.05 for both) compared with TD children for obstructive events, and central events (13.2 % ± 17.0 %, TD 18.8 % ± 17.0 %; p < 0.01) during REM. %change in PTT was significantly smaller in the DS group during NREM and REM from pre-event and late-event to post-event compared with TD children for obstructive and central events.

CONCLUSION

These results suggest children with DS have dampened HR and BP responses to respiratory events compared with TD children. Whether this is symptomatic of autonomic dysfunction or a protective factor for the cardiovascular system in children with DS remains to be elucidated.

A slightly adapted treadmill protocol for the determination of maximal oxygen uptake in adults with Down syndrome

INTRODUCTION

The VO2 max test is the gold standard measure for aerobic fitness. A standardised treadmill protocol was developed years ago for individuals with Down syndrome but with variations in terms of starting speed, load increases and time spent at each stage. However, we realised that the most widely used protocol for adults with Down syndrome, trouble participants with high treadmill speeds. Consequently, the purpose of the current study was to determine whether an adapted protocol provided improved maximal test performance.

METHOD

Twelve adults (33 ± 6 years) randomly performed two variations of the standardised treadmill test.

RESULTS

The protocol that added another incremental incline stage increase yielded a significant improvement in absolute and relative VO2 peak, time to exhaustion, minute ventilation and heart rate max.

CONCLUSION

A treadmill protocol with the addition of an incremental incline stage allowed for a significant improvement in maximal test performance.

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.

Health Outcomes of Physical Activity Interventions in Adults With Down Syndrome: A Systematic Review

This systematic review examined whether physical activity interventions improve health outcomes in adults with Down syndrome (DS). We searched PubMed, APA PsycInfo, SPORTDiscus, APA PsycARTICLES, and Psychology and Behavioral Sciences Collection using keywords related to DS and physical activity. We included 35 studies published in English since January 1, 1990. Modes of exercise training programs included aerobic exercise, strength training, combined aerobic and strength training, aquatic, sport and gaming, and aerobic and strength exercise interventions combined with health education. The evidence base indicates that aerobic and strength exercise training improve physical fitness variables including maximal oxygen uptake, maximal heart rate, upper and lower body strength, body weight, and body fat percentage. Sport and gaming interventions improve functional mobility, work task performance, and sport skill performance. We concluded that adults with DS can accrue health benefits from properly designed physical activity and exercise interventions.

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.

Weight management recommendations for youth with Down syndrome: Expert recommendations

Youth with Down syndrome (DS) have a higher prevalence of overweight and obesity compared to the general youth population. Due to physiological and cognitive differences observed in youth with DS, weight management recommendations developed for the general population, may not be suitable for youth with DS. However, there are no recent recommendations for weight management in youth with DS. A workgroup of clinicians and researchers with extensive experience working with youth with DS came together to give clinicians and families guidance for weight management in youth with DS. Recommendations were developed by the workgroup via a methodical, deliberative process. After the initial development of the recommendations, they were shared with an expert review panel and caregivers who rated the strength of the recommendation and strength of the evidence. The workgroup moved forward the recommendations which the review panels rated as strong. Eight recommendations were developed which focused on screening for overweight and obesity, screening for health conditions that may impact dietary intake and physical activity, screening for feeding difficulties, setting appropriate recommendations for dietary intake and physical activity, and well as prevention and treatment of overweight and obesity using evidence-based strategies. These recommendations can be implemented by clinicians working with youth with Down syndrome as well as the family, school, and other relevant entities.

Cardiac Autonomic Modulation Response Before, During, and After Submaximal Exercise in Older Adults With Intellectual Disability

The analysis of the heart rate variability (HRV) consists of changes in the time intervals between consecutive R waves. It provides information on the autonomic nervous system regulation and it is a predictor of adverse cardiovascular events. Several studies analyzed this parameter in youth and adults with Intellectual Disability (ID). Nevertheless, there is a lack of information regarding the HRV before, during, and after exercise in older adults with ID. Therefore, we aimed to describe and compare the cardiac autonomic modulation before, during, and after the six-minute walk test (6MWT) in older adults with and without ID. Twenty-four volunteers with ID and 24 without ID (non-ID) participated in this study. HRV was assessed by R-R intervals at rest, during and after the 6MWT. At rest and recovery periods, the participants remained sited. The symbolic analysis was used to evaluate non-linear HRV components. The recovery HR kinetics was assessed by the mean response time, which is equivalent to time constant (τ)+time delay (TD). Between groups differences in HRV variables were not significant. During the recovery period, HR kinetics time variables showed significant better results in non-ID participants (TD: 6±5s vs. 15±11s; τ: 19±10s vs. 35±17s; and MRT: 25±9s vs. 50±11s, all p<0.050). In conclusion, our results suggest that the HRV in older adults with and without ID is similar during rest, exercise, and recovery. Recovery HR kinetics after the 6MWT was slower in older adults with ID. The reason for these results may be a reduced post-exercise vagal rebound in older adults with ID.

Blunted autonomic response to standing up and head-up tilt in individuals with intellectual disabilities

Previous research suggests individuals with intellectual disabilities (ID) may experience autonomic dysfunction, however, this has not been thoroughly investigated. The aim of this study was to compare the autonomic response to standing up (active orthostasis) and head-up tilt (passive orthostasis) in individuals with ID to a control group without ID. Eighteen individuals with and 18 individuals without ID were instrumented with an ECG-lead and finger-photoplethysmography for continuous heart rate and blood pressure recordings. The active and passive orthostasis protocol consisted of 10-min supine rest, 10-min standing, 10-min supine recovery, 5-min head-up tilt at 70°, followed by 10-min supine recovery. The last 5 min of each position was used to calculate hemodynamic and autonomic function (time- and frequency-domain heart rate and blood pressure variability measures and baroreflex sensitivity). Individuals with ID had higher heart rate during baseline and recovery (P < 0.05), and an attenuated hemodynamic (stroke volume, heart rate) and heart rate variability response to active and passive orthostasis (interaction effect P < 0.05) compared with individuals without ID. Mean arterial pressure (MAP) was higher in individuals with ID at all timepoints. Individuals with ID demonstrated altered hemodynamic and autonomic regulation compared with a sex- and age-matched control group, evidenced by a higher mean arterial pressure and a reduced response in parasympathetic modulation to active and passive orthostasis.NEW & NOTEWORTHY Individuals with ID demonstrated altered hemodynamic and autonomic regulation to the clinical autonomic function tasks standing up and head-up tilt (active and passive orthostasis). Higher resting heart rate and higher MAP throughout the protocol suggest a higher arousal level, and individuals with ID showed a blunted response in parasympathetic modulation. Further research should investigate the relationship of these findings with clinical outcomes.

Chromosomal abnormalities and atrial fibrillation and ischemic stroke incidence: a nationwide population-based study

There is a paucity of information as to whether chromosomal abnormalities, including Down Syndrome, Turner Syndrome, and Klinefelter Syndrome, have an association with atrial fibrillation (AF) and ischemic stroke development. Data from 3660 patients with Down Syndrome, 2408 with Turner Syndrome, and 851 with Klinefelter Syndrome without a history of AF and ischemic stroke were collected from the Korean National Health Insurance Service (2007–2014). These patients were followed-up for new-onset AF and ischemic stroke. Age- and sex-matched control subjects (at a ratio of 1:10) were selected and compared with the patients with chromosomal abnormalities. Down Syndrome patients showed a higher incidence of AF and ischemic stroke than controls. Turner Syndrome and Klinefelter Syndrome patients showed a higher incidence of AF than did the control group, but not of stroke. Multivariate Cox regression analysis revealed that three chromosomal abnormalities were independent risk factors for AF, and Down Syndrome was independently associated with the risk of stroke. In conclusion, Down Syndrome, Turner Syndrome, and Klinefelter Syndrome showed an increased risk of AF. Down Syndrome patients only showed an increased risk of stroke. Therefore, AF surveillance and active stroke prevention would be beneficial in patients with these chromosomal abnormalities.

Artificial Neural Network Correlation and Biostatistics Evaluation of Physiological and Molecular Parameters in Healthy Young Individuals Performing Regular Exercise

Studies support that regular physical activity (PA) decelerates senescence-related decline of physiological and molecular parameters in the elderly. We have addressed the other end of this spectrum: healthy and young, inactive individuals participated in a 6-month long personal trainer-guided lifestyle program. We have measured physiological and molecular parameters (differentiating high- and low responders) and their correlation with PA (sedentary status). Cluster analysis helped to distinguish individuals with high- or low PA and differentiate high- and low-responders of each parameter. The assessed cardiovascular parameters (heart rate, blood pressure, 6-min walking distance, relative VO₂max), body composition parameters (body fat and muscle mass percentage) metabolic parameters (glucose, insulin, HDL, LDL), immune parameters (cortisol, CRP, lymphocyte counts, hTREC) all showed improvement. Artificial neural network analysis (ANN) showed correlation efficiencies of physiological and molecular parameters using a concept-free approach. ANN analysis appointed PA as the mastermind of molecular level changes. Besides sedentary status, insulin and hTREC showed significant segregation. Biostatistics evaluation also supported the schism of participants for their sedentary status, insulin concentration and hTREC copy number. In the future ANN and biostatistics, may predict individual responses to regular exercise. Our program reveals that high responder individuals of certain parameters may be low responders of others. Our data show that moderate regular PA is essential to counteract senescence in young and healthy individuals, despite individual differences in responsiveness. Such PA may not seem important in the everyday life of young and healthy adults, but shall become the base for healthy aging.

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.

Individual and family-based approaches to increase physical activity in adolescents with intellectual and developmental disabilities: Rationale and design for an 18 month randomized trial

Adolescents with intellectual and developmental disabilities (IDD) are less physically active and have lower cardiovascular fitness compared with their typically developing peers. This population faces additional barriers to participation in moderate-to-vigorous physical activity (MVPA) such as reliance on parents, lack of peer-support, and lack of inclusive physical activity opportunities. Previous interventions to increase MVPA in adolescents with IDD have met with limited success, at least in part due to requiring parents to transport their adolescent to an exercise facility. We recently developed a remote system to deliver MVPA to groups of adolescents with IDD in their homes via video conferencing on a tablet computer. This approach eliminates the need for transportation and provides social interaction and support from both a health coach and other participants. We will conduct a 18-mo. trial (6 mos. active, 6 mos. maintenance, 6 mos. no-contact follow-up) to compare changes in objectively assessed MVPA in 114 adolescents with IDD randomized to a single level intervention delivered only to the adolescent (AO) or a multi-level intervention delivered to both the adolescent and a parent (A + P). Our primary aim is to compare increases in MVPA (min/d) between the AO and A + P groups from 0 to 6 mos. Secondarily we will compare changes in MVPA, sedentary time, cardiovascular fitness, muscular strength, motor ability, quality of life, and the percentage of adolescents achieving the US recommendation of 60 min. MVPA/d across 18 mos. We will also explore the influence of process variables/participant characteristics on changes in MVPA across 18 mos. NCT registration: NCT03684512.

Sleep and sleep disordered breathing in children with down syndrome: Effects on behaviour, neurocognition and the cardiovascular system

Down syndrome (DS), the most common human chromosomal malformation, has an estimated annual incidence of one in 1000 live births worldwide. Sleep problems are common in children with DS, reported by parents in up to 65% of school-aged children, significantly higher rates than in typically developing (TD) children. Problems include difficulty in sleep initiation and maintenance together with obstructive sleep apnoea (OSA) which affects up to over 90%, of DS children compared with 1-5% in the general paediatric population. Any sleep problem has the potential to exert significant negative effects on daytime behaviour, learning and quality of life in TD children and there is now a growing body of evidence that children with DS are similarly affected. In addition to adverse effects on daytime functioning, OSA has adverse effects on the cardiovascular system and this is a particularly significant issue given the high rates of hypertension and premature cardiac disease in people with DS. This review discusses the effects of sleep problems and OSA on daytime functioning and cardiovascular function in children with DS and evidence of the effectiveness of treatment in improving outcomes and quality of life for these children.

Heart rate variability in individuals with Down syndrome - A systematic review and meta-analysis

INTRODUCTION

Down syndrome (DS) results in many changes, including dysfunction in cardiac autonomic modulation. Heart rate variability (HRV) analysis evaluates the autonomic function and it is a predictor of adverse cardiovascular events.

OBJECTIVE

To present results of a systematic review and a meta-analysis about heart rate variability in individuals with DS.

METHOD

A systematic review was performed on PubMed, PubMed Central and Web of science databases. We included articles that exhibited all the terms: "Down Syndrome", "heart rate variability", "autonomic nervous system", "autonomic dysfunction" and "cardiac autonomic modulation". We conducted the meta-analysis to compare "DS" to "controls" during rest. Random effects models were used, as were appropriate tests for heterogeneity.

RESULTS

From 271 studies, 13 were included in our review. These are conducted with volunteers from a wide age range, of either gender, and not taking medications. Meta-analysis displayed that there were no significant differences between the groups at rest, except the RMSSD, which revealed a significant (Z = -2.80, p = 0.005) main effect (Hedge's g = -0.55, 95% CI [-0.93; -0.16]), indicating difference in individuals with DS compared with controls.

CONCLUSION

There is autonomic dysfunction in individuals with DS, which may or may not be expressed at rest, but it is usually demonstrated in an autonomic task. Meta-analysis specified that there was no significant alteration between DS and the controls during rest, except RMSSD index which was lower in DS than controls.

PROSPERO

CRD42017068647.

Descripción de un caso de bradiarritmia en pacientes con síndrome de Down sin enfermedad cardiaca congénita

Introducción. Los pacientes con síndrome de Down sin enfermedad cardiaca estructural pueden presentar disfunción de la regulación autonómica cardiaca, lo cual se manifiesta mediante una contestación reducida de la frecuencia cardiaca (FC) frente a los estímulos. Con base en las respuestas hemodinámicas, se postuló que dichos pacientes tienen una reducción en las retirada vagales y la activación simpática. En esta revisión se explica el rol del sistema autonómico en el control de la FC y la respuesta cronotrópica atenuada observada en esta población.Objetivo. Describir, mediante la presentación de un caso clínico, la disfunción autonómica presente en los pacientes con síndrome de Down a fin de identificar las causas atribuidas por la evidencia científicaMateriales y métodos.Se describió un caso clínico y se realizó una búsqueda a través de PubMed con los términos: “Down Syndrome” AND “Bradycardia”, “VO2peak”, “Heart Rate Variability”, “Vagal Withdrawal”, “Sympathetic Activation”.Resultados. Los hallazgos sugieren que el ejercicio físico puede ser una intervención efectiva para mejorar la función cardiaca autonómica en personas con síndrome de Down. Además, las mejoras inducidas por el entrenamiento fueron alcanzadas por los participantes con niveles más bajos de modulación vagal al inicio del estudio en pacientes con y sin discapacidad, por lo que el entrenamiento puede ser eficaz para mejorar la aptitud cardiorespiratoria en quienes tienen un mayor grado de disfunción autonómica.Conclusión. Se presentó un caso clínico de síndrome de Down con disfunción sinusal, que podía estar relacionado con la disfunción de la regulación de la función cardiaca autonómica, dada por una FC reducida frente a los estímulos.

Cardiovagal modulation and efficacy of aerobic exercise training in obese individuals

Type 2 diabetes (T2D) is associated with poor exercise tolerance and peak aerobic capacity (V˙O2peak) even when compared to obese nondiabetic peers. Exercise training studies have demonstrated improvements in V˙O2peak among patients with T2D, yet there is a large amount of variability in this response. Recent evidence suggests that cardiac autonomic modulation may be an important factor when considering improvements in aerobic capacity.

PURPOSE

This study aimed to determine the effects of a 16-wk aerobic exercise program on V˙O2peak in obese individuals, with and without T2D, who were classified as having either high or low cardiovagal modulation (HCVM or LCVM) at baseline.

METHODS

Obese individuals (38 women and 19 men; body mass index = 36.1 kg·m(-2)) were studied in the fasted state. ECG recordings were obtained while seated for 3 min, before and after 4 months of exercise training (4 d·wk(-1), 65% V˙O(2peak)). The ECG recording was analyzed for HR variability in the spectral domain. Groups were split on a marker of CVM (normalized high frequency (HFnu)) at the 50th percentile, as either HCVM or LCVM.

RESULTS

V˙O(2peak) only increased with exercise training among those classified as having HCVM, regardless of diabetes status (T2D: HCVM = 20.3-22.5 mL·kg(-1)min(-1), LCVM = 24.3-25.0 mL·kg(-1)min(-1); obese nondiabetics: HCVM = 24.5-26.3 mL·kg(-1)min(-1), LCVM = 23.1-23.7 mL·kg(-1)min(-1)) (P < 0.05). No change in V˙O(2peak) was observed for the LCVM group. Changes in weight do not explain the change in V˙O(2peak) among the HCVM group. Glucose tolerance only improved among the LCVM group with T2D.

CONCLUSIONS

Obese individuals, with or without T2D, when classified as having relatively HCVM before exercise training, have a greater propensity to improve V˙O(2peak) after a 16-wk aerobic training program.

Accuracy of the prediction equation for the determination of maximum heart rate in adults with Down syndrome

BACKGROUND

The purpose of the study was to determine if the regression formula developed for the prediction of maximum heart rate (HR) is valid for adults with Down syndrome (DS).

METHODS

Thirty-six adults with DS (31.7 ± 6.8 years; 20 men, 16 women) completed a maximal aerobic test. Maximum HR and VO₂ peak were measured directly on a motorised treadmill with a metabolic analyser. Predicted HR was estimated with the regression equation developed for individuals with DS (Fernhall et al. 2001). Differences between measured versus predicted maximum HR were assessed with a dependent T-test and the relationship with Pearson correlational analyses. Agreement was assessed with Bland-Altman analysis.

RESULTS

There was a significant difference between directly measured maximum HR and predicted maximum HR (P < 0.01). There was no significant relationship between these variables. Bland-Altman analysis indicated that there was measurement bias (+4.7) and large limits of agreement (+26.7 and -17.4) between measured and predicted maximum HR. The Bland-Altman plot also demonstrated the presence of heteroscedasticity.

CONCLUSIONS

The results indicate that the regression formula developed for individuals with DS was not accurate in this sample of DS adults aged 19 to 46 years. Future studies should develop different prediction equations for more specific age and body mass index categories for individuals with DS.

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.

Effect of continuous aerobic vs. interval training on selected anthropometrical, physiological and functional parameters of adults with Down syndrome

BACKGROUND

A large percentage of adults with Down syndrome (DS) are overweight and have extremely low aerobic capacities compared with the general population and persons with intellectual disability without DS. Previous aerobic training intervention studies showed limited potential to significantly ameliorate anthropometrical and cardiovascular variables. The primary purpose of this study was to determine the effect of continuous aerobic training (CAT) vs. interval training (IT) on selected anthropometrical, health, physical and functional parameters of adults with DS.

METHODS

Forty-two adults with DS (25 men and 17 women) and a mean age of 33.8 (±8.6) years were randomly allocated to one of three groups (IT, CAT and control). Training was performed for 12 weeks. The IT group performed 10-30 s all out sprints with 90 s (1:3 work-rest ratio) of low cadence, low intensity cycling or walking. The CAT group performed continuous cycling and walking at an intensity of 70-80% of VO₂ peak. Heart rate monitors were used for monitoring training intensities. After 6 weeks of training, the intensity of the CAT was increased to 85% of VO₂ peak, whilst the intensity of the IT group remained 'all out'. An increase of 5 min in duration was implemented after 6 weeks for both training groups. To evaluate pre-post differences between groups, a repeated analysis of covariance with post hoc Bonferroni test was performed RESULTS: After 12 weeks of training, body weight and body mass index decreased significantly more in the IT group compared with control and CAT (P < 0.05). Participants in the IT group decreased their body weight from 71.4 ± 8 to 69.4 ± 8 kg and their body mass index from 29.3 ± 4 to 28.5 ± 4 kg/m² . Significant ameliorations for functional parameters and leg strength were shown for CAT compared with control (P < 0.05). Participants in the CAT group improved their performance in the 6 minute walk distance (499 ± 78 to 563 ± 75 m), 8-ft up-and-go (5.9 ± 1.2 to 4.8 ± 0.9) and leg strength (13.1 ± 2 to 15.2 ± 2). VO₂ peak and time to exhaustion significantly improved in both the IT and CAT group compared with control (P < 0.01). Moreover, a significant improvement for relative VO₂ peak was also determined for IT compared with CAT (P < 0.05). Participants in the IT group increased their VO₂ peak from 32 ± 8 to 37 ± 8 mL/min/kg. Submaximal heart rate and VO₂ values improved significantly within both exercise groups (P < 0.05).

CONCLUSION

Interval training and CAT can both be pursued by adults with DS to positively impact on various parameters of anthropometry, fitness and functional ability, with IT more appropriate for improving body weight and aerobic capacity.

Test-retest reliability and minimal detectable change scores of twelve functional fitness tests in adults with Down syndrome

AIM

The purpose of the study was to explore the test-retest reliability and minimal detectable change of selected functional fitness test items in adults with Down syndrome.

METHODS

Forty-three adults with Down syndrome (24 men and 19 women) aged 18-50 years completed a battery of tests twice in a two-week period. The battery of tests consisted of two balance items, two flexibility items, five muscular strength and endurance items, two aerobic items, and one functional task. All items were considered valid and reliable tests in a general elderly or intellectually disabled population. The test-retest relative reliability for all repeated tests was assessed with intraclass correlation coefficient performing one-way analysis of variance. The test-retest absolute variability was measured by using the standard error of measurement (SEM) to calculate the minimal detectable change at the 90% confidence interval (MDC90). Reliability data was visualised with a Bland-Altman plot.

RESULTS

All tests showed excellent intraclass correlation coefficients (ICC's>0.9). All SEM values demonstrated acceptable measurement precision (SEM<SD/2). Values for MDC90 are provided for all 12 tests. The analyses indicated that there was no major systematic bias in the plots. The scatter around the Bland-Altman was distributed randomly.

CONCLUSION

All twelve functional fitness tests demonstrated adequate feasibility and relative and absolute test-retest reliability in adults with Down syndrome in South Africa. Information of this nature will help to monitor performance alterations over time and success of training interventions.

Difference of catecholamine responses to exercise in men with trisomy 21, with or without chronotropic incompetence

OBJECTIVE

Our purpose was to analyse if catecholamine responses to exercise would be different in Down syndrome (DS) with or without chronotropic incompetence.

RESEARCH DESIGN AND METHODS

Twenty five men with DS (mean age 22.2 ± 3.2) and twenty six controls (CONT, mean age 22.5 ± 1.4) participated in the study, and are divided into 3 groups: CONT, DS with chronotropic incompetence (DS+) and DS without chronotropic incompetence (DS-). During two treadmill incremental tests, blood samples were collected for the determination of hormonal and metabolic variables.

RESULTS

Ten out of 25 DS had chronotropic incompetence whereas no CONT. At rest, compared to CONT, despite similar physical activity, DS with chronotropic incompetence had significantly higher subcutaneous fat mass (p<0.001), lower epinephrine concentration (p<0.01), and higher leptin (p<0.01) and insulin concentrations (p<0.05). At peak exercise, all DS had lower heart rate, oxygen uptake and blood lactate concentrations than controls (p<0.001). During a 'Submaximal incremental test', DS with chronotropic incompetence had lower HR and lactate values (p<0.001) compared to CONT and DS without chronotropic incompetence (p<0.01). They also had blunted epinephrine and impaired norepinephrine responses to exercise compared to DS without chronotropic incompetence and CONT (p<0.01 and p<0.05 respectively).

CONCLUSIONS

Our results indicate that catecholamine adaptations to exercise are not adequate in DS+ and are associated with exercise intolerance. Thus, this endocrine profile at rest and during exercise may limit endurance performance of DS.

Cardiac autonomic modulation of children with Down syndrome

The aim of this study is to analyze the autonomic modulation in children with Down syndrome (DS). The study was conducted with a convenience sample of children with DS and without heart disease, from the Genetics Clinic of the Hospital Infantil Darcy Vargas and APAE São Paulo, São Paulo, SP, Brazil. The control group was matched for sex and age. The analysis of autonomic modulation was performed using the indices of heart rate variability (HRV). The children remained in the supine position with spontaneous breathing for 20 min. Heart rate was recorded beat-to-beat. HRV analysis was performed in time and frequency domain. For data analysis, we used Student's t test: unpaired and Mann-Whitney. It was considered statistically significant at p < 0.05. From 75 children with DS, 50 were excluded, a total of 25 children [16 boys, 8.6 (1.4) years] participated in this study, and the control group also consisted of 25 children [16 boys, 9.0 (1.2) years] without the syndrome. The BMI of the volunteers with DS was higher than the controls [19.1 (2.9) vs. 15.8 (1.2), p < 0.0001]. There were differences between groups in the indices in frequency domain: LFms(2) [1242.1 (788.25) vs. 786.44 (481.90), p = 0.040], LFun [69.104 (11.247) vs. 57.348 (11.683), p = 0.0004], HFun [30.896 (11.247) vs. 42.520 (11.634), p = 0.0004] and LF/HF [2.594 (1.104) vs. 1.579 (0.9982), p = 0.0004]. No differences were observed in time domain indices. The results indicate increased indices representing the sympathetic branch of the autonomic nervous system and those that indicate the overall modulation in children with DS.

Cardiac autonomic regulation in autism and Fragile X syndrome: a review

Despite the significance of efforts to understand the biological basis of autism, progress in this area has been hindered, in part, by the considerable heterogeneity in the disorder. Fragile X syndrome (FXS), a monogenic condition associated with high risk for autism, may pave the way for the dissection of biological heterogeneity within idiopathic autism. This article adopts a cross-syndrome biomarker approach to evaluate potentially overlapping profiles of cardiac arousal dysregulation (and broader autonomic dysfunction) in autism and FXS. Approaches such as this, aimed at delineating shared mechanisms across genetic syndromes, hold great potential for improving diagnostic precision, promoting earlier identification, and uncovering key systems that can be targeted in pharmaceutical/behavioral interventions. Biomarker approaches may be vital to deconstructing complex psychiatric disorders and are currently promoted as such by major research initiatives such as the NIMH Research Domain Criteria (RDoC). Evidence reviewed here supports physiological dysregulation in a subset of individuals with autism, as evidenced by patterns of hyperarousal and dampened parasympathetic vagal tone that overlap with the well-documented physiological profile of FXS. Moreover, there is growing support for a link between aberrant cardiac activity and core deficits associated with autism, such as communication and social impairment. The delineation of physiological mechanisms common to autism and FXS could lend insight into relationships between genetic etiology and behavioral endstates, highlighting FMR1 as a potential candidate gene. Research gaps and potential pitfalls are discussed to inform timely, well-controlled biomarker research that will ultimately promote better diagnosis and treatment of autism and associated conditions.

Increased P-wave and QT dispersions necessitate long-term follow-up evaluation of Down syndrome patients with congenitally normal hearts

Reports state that Down syndrome (DS) patients with congenitally normal hearts might experience the development of cardiac abnormalities such as cardiac autonomic dysfunction, valvular lesions, bradycardia, and atrioventricular block. However, the presence of any difference in terms of P-wave dispersion (PWd) and QT dispersion (QTd) was not evaluated previously. This study prospectively investigated 100 DS patients with structurally normal hearts and 100 age- and sex-matched healthy control subjects. Standard 12-lead electrocardiograms were used to assess and compare P-wave and QT durations together with PWd and QTd. The median age of the DS patients and control subjects was 48 months. Heart rates and P-wave and QT dispersions were significantly greater in the DS group than in the control group (113 ± 22.9 vs 98.8 ± 16.6 bpm, p < 0.001; 31.3 ± 9.5 vs 24 ± 8.6 ms, p < 0.001; and 46.6 ± 15.9 vs 26 ± 9.1 ms, p < 0.001, respectively). A positive correlation was found between PWd and age in the DS patients (p < 0.05; r = 0.2). All children with DS should be followed up carefully with electrocardiography in terms of increased P-wave and QT dispersions even in the absence of concomitant congenital heart disease for management of susceptibility to arryhthmias.

Assessment protocols of maximum oxygen consumption in young people with Down syndrome--a review

Maximum oxygen consumption is considered the gold standard measure of cardiorespiratory fitness. Young people with Down syndrome (DS) present low values of this indicator compared to their peers without disabilities and to young people with an intellectual disability but without DS. The use of reliable and valid assessment methods provides more reliable results for the diagnosis of cardiorespiratory fitness and the response of this variable to exercise. The aim of the present study was to review the literature on the assessment protocols used to measure maximum oxygen consumption in children and adolescents with Down syndrome giving emphasis to the protocols used, the validation process and their feasibility. The search was carried out in eight electronic databases--Scopus, Medline-Pubmed, Web of science, SportDiscus, Cinhal, Academic Search Premier, Scielo, and Lilacs. The inclusion criteria were: (a) articles which assessed VO2peak and/or VO2max (independent of the validation method), (b) samples composed of children and/or adolescents with Down syndrome, (c) participants of up to 20 years old, and (d) studies performed after 1990. Fifteen studies were selected and, of these, 11 measured the VO2peak using tests performed in a laboratory, 2 used field tests and the remaining 2 used both laboratory and field tests. The majority of the selected studies used maximal tests and conducted familiarization sessions. All the studies took into account the clinical conditions that could hamper testing or endanger the individuals. However, a large number of studies used tests which had not been specifically validated for the evaluated population. Finally, the search emphasized the small number of studies which use field tests to evaluate oxygen consumption.

Fetal right ventricular contraction and relaxation times at 11-13 weeks' gestation on speckle tracking imaging

OBJECTIVE

To examine the contraction time and relaxation time of the right ventricle at 11-13 weeks' gestation in trisomy 21 and euploid fetuses by speckle tracking ultrasound imaging.

METHODS

Measurement of fetal nuchal translucency (NT) thickness, Doppler assessment for tricuspid regurgitation and reversed A-wave in the ductus venosus (DV) and fetal echocardiography were performed immediately before chorionic villus sampling for fetal karyotyping at 11-13 weeks' gestation. Digital videoclips of the four-chamber view of the fetal heart were recorded and analyzed offline using speckle tracking imaging software. The contraction time, which is the time between the highest and lowest peaks in the right ventricular area, and relaxation time, which is the time between the lowest and the subsequent highest area peak, were measured and expressed as a percentage of the duration of the cardiac cycle. Values in trisomy 21 and euploid fetuses were compared.

RESULTS

Mean contraction time and relaxation time in 119 euploid fetuses were 52.1% (95% CI, 51.6-52.8%) and 47.8% (95% CI, 47.2-48.4%), respectively. In 21 trisomy 21 fetuses, mean contraction time was significantly higher (57.0% (95% CI, 55.2-58.9%); P<0.01) and relaxation time lower (42.9% (95% CI, 41.1-44.8%); P<0.01) than in euploid fetuses. Multiple regression analysis showed that significant contributions to contraction time and relaxation time were provided by fetal karyotype, NT and tricuspid regurgitation, but not by reversed A-wave in the DV or the presence of a cardiac defect.

CONCLUSION

In first-trimester fetuses with trisomy 21 and in euploid fetuses with increased NT and tricuspid regurgitation there is evidence of increased right ventricular contraction time and shortening of the relaxation time.

Evidence-based risk assessment and recommendations for physical activity clearance: cognitive and psychological conditions

Physical activity has established mental and physical health benefits, but related adverse events have not received attention. The purpose of this paper was to review the documented adverse events occurring from physical activity participation among individuals with psychological or cognitive conditions. Literature was identified through electronic database (e.g., MEDLINE, psychINFO) searching. Studies were eligible if they described a published paper examining the effect of changes on physical activity behaviour, included a diagnosed population with a cognitive or psychological disorder, and reported on the presence or absence of adverse events. Quality of included studies was assessed, and the analyses examined the overall evidence by available subcategories. Forty trials passed the eligibility criteria; these were grouped (not mutually exclusively) by dementia (n = 5), depression (n = 10), anxiety disorders (n = 12), eating disorders (n = 4), psychotic disorders (n = 4), and intellectual disability (n = 15). All studies displayed a possible risk of bias, ranging from moderate to high. The results showed a relatively low prevalence of adverse events. Populations with dementia, psychological disorders, or intellectual disability do not report considerable or consequential adverse events from physical activity independent of associated comorbidities. The one exception to these findings may be Down syndrome populations with atlantoaxial instability; in these cases, additional caution may be required during screening for physical activity. This review, however, highlights the relative paucity of the reported presence or absence of adverse events, and finds that many studies are at high risk of bias toward reporting naturally occurring adverse events.

Cardiorespiratory fitness in individuals with intellectual disabilities--a review

Cardiorespiratory fitness is the ability of the circulatory, respiratory and muscular systems to supply oxygen during sustained physical activity. Low cardiorespiratory fitness levels have been found in individuals with intellectual disabilities (ID), which puts them at higher risk for cardiovascular diseases and all-cause mortality. The aims of this review were to update previous reviews about (a) the cardiorespiratory fitness levels and their determinants in individuals with ID, and (b) the validity and reliability of cardiorespiratory fitness testing in individuals with ID. We searched the databases of Pubmed and Embase for relevant studies, resulting in 31 included articles. These studies mainly included younger participants with mild to moderate ID. Results confirmed previous findings of low cardiorespiratory fitness levels in individuals with ID. Cardiorespiratory fitness levels of children and adolescents with ID are already low, with further decline with increasing age. Furthermore, females have lower cardiorespiratory fitness levels than males. Physical inactivity and chronotropic incompetence are most likely to contribute to low cardiorespiratory fitness levels. Peak cardiorespiratory fitness levels of individuals with ID can be assessed with maximal treadmill protocols, after allowing for familiarization sessions. Although, predicting maximal oxygen uptake from field tests is problematic, field tests have been found valid and reliable as indicators of cardiorespiratory fitness.

The functional fitness capacity of adults with Down syndrome in South Africa

BACKGROUND

It is well established that there is a relationship between physical inactivity and increased risk for diseases of lifestyle. Persons with Down syndrome (DS) are especially at risk because of physical and health impairments, as well as perceived and real barriers to participation in exercise. The purpose of the study was to establish the functional fitness capacity and predictors of performance of DS adults.

METHODS

Data were collected at various intellectual disability centres and private homes in seven provinces of South Africa. Three hundred and seventy-one DS individuals (199 men and 172 women) from 18 to 66 years were tested for balance, flexibility, coordination, muscular strength and endurance, aerobic capacity and functional ability. Data were categorised according to gender and age groups (18-25, 26-35, 36-45, and >45 years). Multiple regression analysis was performed to determine the relationship between the functional task and physical test items.

RESULTS

Down syndrome men performed significantly better on all but two tests compared with the women (P < 0.05). DS women performed better on the sit-and-reach flexibility item and the chair stand test; however, differences were not statistically significant from the men. Significant differences across age groups were observed for nine of the 13 functional fitness tests (P < 0.05). Muscular strength items, especially leg strength, significantly predicted functional performance in DS men and women. Aerobic capacity only predicted functional performance in DS men and sit-and-reach flexibility and dynamic balance only in DS women.

CONCLUSIONS

Findings of this study provide important information on the functional capacity of DS adults and show which physical attributes contribute to functional performance. Consequently appropriate training programmes can be tailored for this population whom is known to have poor functional fitness.

Adults with Down syndrome have reduced cardiac response after light exercise testing

Objective

Physical fitness is reduced in adults with Down syndrome (DS). The present study was conducted to elucidate the exercise response in adults with DS.

Design

Case controlled before-after trial.

Setting

Residential centre for people with intellectual disabilities.

Participants

96 Adults with DS, 25 non-DS adults with an intellectual disability, 33 controls.

Interventions

Echocardiography to exclude heart defects and to measure cardiac index (CI) in the supine position, supine position with raised legs, and following ten knee bends.

Main outcome measure

Exercise testing

Results

At rest, mean CI was not significantly different between persons with DS and controls (2.3 vs. 2.4 l/min/m², p = 0.3). However, mean CI after exercise was significantly lower in DS (2.9 vs. 3.7 l/min/m², p < 0.001) and mean CI increase from rest to exercise was more than 50% lower in DS. On the contrary, CI after exercise was similar among controls and non-DS adults with an intellectual disability. Significantly lower stroke volumes in DS were found with insufficient heart rate response.

Conclusions

CI at rest was similar in adults with DS and controls; however persons with DS have a diminished cardiac response to exercise. Stroke volumes were significantly lower in DS during exercise and a compensated heightened heart rate was absent.

Cardiac and sympathetic activation are reduced in children with Down syndrome and sleep disordered breathing

STUDY OBJECTIVES

Sleep disordered breathing (SDB) occurs at an increased incidence in children with Down Syndrome (DS) compared to the general pediatric population. We hypothesized that, compared with typically developing (TD) children with SDB, children with DS have a reduced cardiovascular response with delayed reoxygenation after obstructive respiratory events, and reduced sympathetic drive, providing a potential explanation for their increased risk of pulmonary hypertension.

DESIGN

Beat-by-beat heart rate (HR) was analyzed over the course of obstructive events (pre, early, late, post-event) and compared between groups. Also compared were the time for oxygen resaturation post-event and overnight urinary catecholamines.

SETTING

Pediatric sleep laboratory.

PATIENTS

Sixty-four children aged 2-17 y referred for investigation of SDB (32 DS; 32 TD) matched for age and obstructive apnea/hypopnea index.

MEASUREMENT AND RESULTS

Children underwent overnight polysomnography with overnight urine collection. Compared to TD children, those with DS had significantly reduced HR changes post-event during NREM (DS: 21.4% ± 1.8%, TD: 26.6% ± 1.6%, change from late to post-event, P < 0.05). The time to resaturation post-event was significantly increased in the DS group (P < 0.05 for both NREM and REM sleep). Children with DS had significantly reduced overnight urinary noradrenaline (P < 0.01), adrenaline (P < 0.05) and dopamine levels (P < 0.01) compared with TD children.

CONCLUSION

Children with DS and SDB exhibit a compromised acute cardio-respiratory response and dampened sympathetic response to SDB compared with TD children with SDB. These data may reflect autonomic dysfunction in children with DS that may place them at increased risk for cardiovascular complications such as pulmonary hypertension.

Comparison of blood and saliva lactate level after maximum intensity exercise

Several studies have described high correlation of salivary and blood lactate level during exercise. Measuring the effectiveness and intensity of training, lactate concentration in blood, and lately in saliva are used.The aim of our study was to evaluate the correlation between the concentration and timing of salivary and blood lactate level in endurance athletes and non-athletes after a maximal treadmill test, and to identify physiological and biochemical factors affecting these lactate levels.Sixteen volunteers (8 athletes and 8 non-athletes) performed maximal intensity (Astrand) treadmill test. Anthropometric characteristics, body composition and physiological parameters (heart rate, RR-variability) were measured in both studied groups. Blood and whole saliva samples were collected before and 1, 4, 8, 12, 15, 20 min after the exercise test. Lactate level changes were monitored in the two groups and two lactate peaks were registered at different timeperiods in athletes. We found significant correlation between several measured parameters (salivary lactate - total body water, salivary lactate - RR-variability, maximal salivary lactate - maximal heart rate during exercise, salivary- and blood lactate -1 min after exercise test). Stronger correlation was noted between salivary lactate and blood lactate in athletes, than in controls.

Health-related physical fitness in children and adolescents with Down syndrome and response to training

Physical fitness is related to health at all ages. Information about physical fitness in the Down syndrome (DS) population, however, is scarce, especially when we consider children and adolescents. A review of the current data available on this topic would be both timely and important as it would serve as a starting point to stimulate new research perspectives. The data we reviewed from the literature showed a general trend toward lower values of physical fitness parameters and worse body composition variables in children and adolescents with DS compared with the population without intellectual disability (ID) or even with the population with ID without DS. Notably, children and adolescents with DS have been described as less active or overprotected; however, these factors may not be the cause of their poor physical fitness. Many of the training programs carried out in children and adolescents with DS did not yield the desired responses, and the reasons are still unknown. The purpose of this review is to summarize the current available literature on health-related physical fitness in children and adolescents with DS, and the effect of training on these variables. From the literature available, it is clear that more data on this population are necessary.

Cardiac autonomic function during submaximal treadmill exercise in adults with Down syndrome

This study determined whether the cardiac autonomic function of adults with Down syndrome (DS) differs from that of nondisabled persons during submaximal dynamic exercise. Thirteen participants with DS and 12 nondisabled individuals performed maximal and submaximal treadmill tests with metabolic and heart rate (HR) measurements. Spectral analysis of HR variability was performed on the last 256 consecutive R-R intervals obtained under the following conditions: (1) rest, (2) submaximal treadmill exercise (at constant relative intensity below the ventilatory threshold) and (3) recovery. Participants with DS presented lower chronotropic response than those without DS to peak and submaximal exercise (p<0.05). Nevertheless, the fractional utilization of peak HR during treadmill walking was similar between groups (∼60% peak HR). Even though there were no between-group differences at rest or during recovery, the participants with DS showed a higher LF/HF ratio during exercise (p<0.05). Similarly, the LF power of participants with DS during exercise was greater than that of nondisabled participants (p<0.05). In contrast, both groups exhibited similar HF power at each physiological condition. In conclusion, these findings suggest that adults with DS demonstrate appropriate vagal withdrawal, but heightened sympathetic modulation of HR variability at ∼60% of their peak HR. Despite this, the absolute change in HR from rest to exercise was attenuated in these individuals compared to persons without disabilities. This indicates that DS may be associated with poor cardiac responsiveness to changes in autonomic modulation during exercise at intensities below the ventilatory threshold.

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.

The heart rate response to spontaneous arousal from sleep is reduced in children with Down syndrome referred for evaluation of sleep-disordered breathing

Arousal from sleep in healthy adults is associated with a large, transient increase in heart rate (HR). Individuals with Down syndrome (DS) have attenuated cardiovascular responses to autonomic tests during wakefulness. We tested the hypothesis that the HR response to arousal from sleep is reduced in children with DS and obstructive sleep apnea (OSA) compared with healthy children. Twenty children aged 3-17 yr referred for investigation of sleep-disordered breathing (10 DS, and 10 OSA controls) matched for age and obstructive apnea/hypopnea index underwent routine overnight polysomnography. In addition, 10 nonsnoring controls from the general community were studied. Beat-by-beat HR was analyzed from 15 s pre- to 15 s post-spontaneous arousals and compared between groups using two-way ANOVA with repeated measures. Data are presented as means + or - SE. For both rapid eye movement (REM) and non-REM (NREM), arousals were associated with a significant increase in HR in all groups (peak response NREM: DS, 118 + or - 1% at 3 s; OSA controls, 124 + or - 2% at 4 s; and healthy controls, 125 + or - 3% at 4 s; and peak response REM: DS, 116 + or - 2% at 4 s; OSA controls, 123 + or - 3% at 4 s; and healthy controls, 125 + or - 4 at 4 s; P < 0.001 for all). Post hoc analysis revealed that HR in the DS group was significantly lower than both control groups at 1-4 s in NREM and at 4 to 5 s in REM (P < 0.05 for all). In conclusion, the HR response to spontaneous arousal from sleep is reduced in children with DS and OSA compared with healthy children. This attenuated cardiovascular response could be due to reduced sympathetic activation or blunted vagal withdrawal and may have implications for the child with DS and OSA.

Six-minute walk test in patients with Down syndrome: validity and reproducibility

OBJECTIVES

To examine the validity of the six-minute walk test (6MWT) as a tool to evaluate functional exercise performance in patients with Down syndrome (DS).

DESIGN

Comparison of the six-minute walk distance (6MWD) in 2 distinct groups of DS patients: with and without severe cardiac disease. To test reproducibility, a group of patients with DS performed the 6MWT twice.

SETTING

Tertiary referral centers for patients with congenital heart defects and outpatient clinics for people with intellectual disabilities.

PARTICIPANTS

Adult patients with DS with (n=29) and without (n=52) severe cardiac disease categorized by cardiac echocardiography.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

Distance walked on the 6MWT.

RESULTS

The mean 6MWD in the group with severe cardiac disease was 289+/-104 m and in the group without severe cardiac disease 280+/-104 m (P=.70). Older age, female sex, and severe level of intellectual disability were all found to be independently and significantly correlated with a lower 6MWD (r=.67, P<.001). The paired 6MWD was not significantly different (310+/-88 m vs 317+/-85 m; P=.40) in patients who performed the 6MWT twice. The coefficient of variation was 11%.

CONCLUSIONS

The 6MWD between the 2 groups was not significantly different. However, the walking distance inversely correlated with the level of intellectual disability. Therefore, the 6MWT is not a valid test to examine cardiac restriction in adult patients with DS.

Aging and Down syndrome: implications for physical therapy

The number of people over the age of 60 years with lifelong developmental delays is predicted to double by 2030. Down syndrome (DS) is the most frequent chromosomal cause of developmental delays. As the life expectancy of people with DS increases, changes in body function and structure secondary to aging have the potential to lead to activity limitations and participation restrictions for this population. The purpose of this update is to: (1) provide an overview of the common body function and structure changes that occur in adults with DS as they age (thyroid dysfunction, cardiovascular disorders, obesity, musculoskeletal disorders, Alzheimer disease, depression) and (2) apply current research on exercise to the prevention of activity limitations and participation restrictions. As individuals with DS age, a shift in emphasis from disability prevention to the prevention of conditions that lead to activity and participation limitations must occur. Exercise programs appear to have potential to positively affect the overall health of adults with DS, thereby increasing the quality of life and years of healthy life for these individuals.

The effects of a glucose load and sympathetic challenge on autonomic function in obese women with and without type 2 diabetes mellitus

This study examined the effect of glucose ingestion on cardiac autonomic function in nonobese women and obese women with and without type 2 diabetes mellitus. Heart rate variability was measured via continuous electrocardiogram, and beat-by-beat blood pressure was recorded using finger photoplethysmography (Portapres, TNO Biomedical Instrumentation, Amsterdam, The Netherlands) in a fasted state and in response to a 75-g glucose load in 42 middle-aged women (40-60 years). Upright tilt was also used as an orthostatic stress to provide a clinically relevant challenge to the cardiovascular system. Significant main effects for log-transformed (Ln) total power (TP, square milliseconds) were observed with upright tilt (P < .01) and glucose challenge (P < .05). LnTP decreased in all groups in both the fasted and fed state with upright tilt (P < .01), but glucose ingestion resulted in higher LnTP in the supine position only (P = .008). Tilt resulted in a significant main effect for low-frequency (LFnu, calculated in normalized units) and high-frequency (HFnu, calculated in normalized units) power (P < .000), whereas the glucose challenge had no effect on LFnu or HFnu power. LFnu approached significance for group differences (P = .07), such that the nonobese had lower LF power than either of the obese groups. Sympathovagal balance (LnLF/HF ratio) was affected by position (P < .000) and group (P < .05), with a lower LnLF/HF in the nonobese than in the obese women. Baroreceptor sensitivity decreased (P < .01) during upright tilt but was not changed by the glucose challenge. In conclusion, basal sympathovagal balance is higher in obese individuals with and without type 2 diabetes mellitus. Women with type 2 diabetes mellitus showed no differences in autonomic function with an orthostatic challenge or glucose load than nondiabetic, obese women. The glucose load did alter total spectral power in all of these middle-aged women but had no impact on baroreceptor sensitivity.

Baroreflex Sensitivity during Static Exercise in Individuals with Down Syndrome

INTRODUCTION

Individuals with Down syndrome (DS) have altered heart rate (HR) and blood pressure (BP) responses to orthostatic challenges and isometric handgrip (IHG) exercise, suggesting possible alteration in baroreflex sensitivity.

PURPOSE

This study investigated baroreflex sensitivity (BRS) as a potential mechanism contributing to chronotropic incompetence during IHG in persons with DS.

METHODS

Heart rate and BP were continually recorded in 12 individuals with DS and 10 controls, at rest and during 2 min of IHG, at 30% of maximal voluntary contraction (MVC). Spontaneous BRS was derived via the sequence method.

RESULTS

No differences were seen in HR at rest between groups. Systolic BP (SBP) was significantly lower in the DS group at rest (106.1+/- 2.9 vs 116.5+/- 3.9 mm Hg, P < 0.05) and during IHG (123.9+/- 4.6 vs 150.1+/- 5.3 mm Hg, P<0.001). A significant group-by-task interaction was found for both change in HR and change in SBP with IHG, because of an attenuated HR and SBP response to IHG in participants with DS (P<0.05). When controlling for resting SBP, the DS group had a lower BRS at rest (16.0+/-1.7 vs 21.2+/-4.2 ms.mm Hg, P< 0.05) and during IHG (7.8 +/-1.0 vs 12.1+/- 2.6 ms.mm Hg, P< 0.05).

CONCLUSIONS

Individuals with DS have lower BRS at rest and during IHG than controls and this may be related to their attenuated HR response during perturbation.

Altered autonomic cardiac regulation in individuals with Down syndrome

We tested the hypothesis that individuals with Down syndrome, but without congenital heart disease, exhibit altered autonomic cardiac regulation. Ten subjects with Down syndrome (DS) and ten gender-and age-matched healthy control subjects were studied at rest and during active orthostatism, which induces reciprocal changes in sympathetic and parasympathetic traffic to the heart. Autoregressive power spectral analysis was used to investigate R-R interval variability. Baroreflex modulation of sinus node was assessed by the spontaneous baroreflex sequences method. No significant differences between DS and control subjects were observed in arterial blood pressure at rest or in response to standing. Also, R-R interval did not differ at rest. R-R interval decreased significantly less during standing in DS vs. control subjects. Low-frequency (LFNU) and high-frequency (HFNU) (both expressed in normalized units) components of R-R interval variability did not differ between DS and control subjects at rest. During standing, significant increase in LFNU and decrease in HFNU were observed in control subjects but not in DS subjects. Baroreflex sensitivity (BRS) did not differ between DS and control subjects at rest and underwent significant decrease on going from supine to upright in both groups. However, BRS was greater in DS vs. control subjects during standing. These data indicate that subjects with DS exhibit reduced HR response to orthostatic stress associated with blunted sympathetic activation and vagal withdrawal and with a lesser reduction in BRS in response to active orthostatism. These findings suggest overall impairment in autonomic cardiac regulation in DS and may help to explain the chronotropic incompetence typically reported during exercise in subjects with DS without congenital heart disease.