Impaired Cardiac Autonomic Modulation Research Articles

0114 Interplay of School and Free Days on the Association of Circadian Misalignment with Heart Rate Variability in Adolescents

Abstract Introduction The circadian timing system, which governs the sleep-wake cycle, is involved in cardiometabolic and autonomic regulation. Heart rate variability (HRV), a marker of cardiac autonomic modulation (CAM), is known to predict cardiovascular morbidity. Therefore, circadian misalignment of the sleep-wake cycle, which is highly prevalent in adolescents and may express differently if youth are in school or free-days, is likely to impact CAM. We examined whether deviations in the circadian timing of sleep are associated with blunted HRV in adolescents as a function of being entrained to school or not. Methods We studied 337 population-based randomly-selected adolescents from the Penn State Child Cohort (median 16 years; 47% female; 21% racial/ethnic minority) who had at least 3-night at-home actigraphy (ACT), in-lab 9-h polysomnography (PSG) and 24-h Holter-monitoring heart rate variability (HRV) data. ACT-measured sleep midpoint (SM) was calculated as the midpoint of the sleep period for weekdays (5-nights) and weekends (2-nights), whereas ACT-measured sleep regularity (SR) was calculated as the intra-individual standard deviation of the SM across 5- and 7-nights. Frequency and time-domain HRV indices were primary outcomes. Linear regression models were stratified by “in school” and “on break” to test SM and SR as predictors of HRV indices while accounting for sex, race/ethnicity, age, BMI percentile, ACT-sleep duration, ACT-sleep variability, and PSG-apnea/hypopnea index. Results Lower SR on schooldays was associated with lower nighttime Log-HF, Log-LF and SDNN, yet higher HR (all p< 0.01); e.g., each standard deviation increase in SR on schooldays (i.e., 45m higher) was associated with -7.15ms (2.57) in nighttime SDNN (p=0.006). A later SM on free weekends was associated with lower nighttime Log-HF, Log-LF, SDNN and RMSSD, yet higher HR and LF-HF ratio (all p< 0.03); e.g., each standard deviation increase in SM on free weekends (i.e., 1.5h later) was associated with -7.33ms (2.85) in nighttime RMSSD (p=0.011). Conclusion A delayed and an irregular sleep midpoint during breaks and during schooldays, respectively, were associated with impaired CAM in adolescents. These data suggest that not only circadian misalignment contributes to adverse cardiovascular outcomes but its distinct metrics require measurement under different entrainment conditions in adolescents. Support (if any) NIH (R01HL136587,R01MH118308,UL1TR000127), American Heart Association (23PRE1011962).

Abstract 13: Circadian Misalignment is Associated With Impaired Heart Rate Variability in Adolescents

Introduction: Adequate sleep has been recognized by AHA as part of Life’s Essential 8 in the prevention of cardiovascular disease (CVD). The circadian system, which governs the sleep-cycle, is also involved in cardiac, metabolic and autonomic regulation. Heart rate variability (HRV), a marker of cardiac autonomic modulation (CAM), is known to predict CVD. As a result, circadian misalignment of the sleep-wake cycle, which is highly prevalent in adolescents, may impact CAM and be a potential risk factor for adverse CVD outcomes in early life. Hypothesis: We hypothesize that deviations in the circadian timing of sleep are associated with blunted HRV in adolescents. Methods: We analyzed data from 337 population-based randomly-selected adolescents from the Penn State Child Cohort (median 16 years; 47% female; 21% racial/ethnic minority) who had at least 3-night at-home actigraphy (ACT), in-lab 9-h polysomnography (PSG) and 24-h Holter-monitoring heart rate variability (HRV) data. ACT-sleep duration and sleep midpoint (SM) were calculated as the intra-individual mean total sleep time and midpoint of the sleep period, respectively. ACT-sleep variability and sleep regularity (SR) were calculated as the intra-individual standard deviation of sleep duration and sleep midpoint across nights, respectively. Frequency and time-domain HRV indices, including HR oscillations at high frequencies (HF), standard deviation between normal heart beats or R-R intervals (SDNN), and root mean square of successive differences between normal heartbeats (RMSSD), were primary outcomes. Linear regression models tested SM and SR as predictors of HRV indices, while accounting for sex, race/ethnicity, age, body mass index, ACT-sleep duration, ACT-sleep variability, and PSG-apnea/hypopnea index. Results: While there were no meaningful associations between SM or SR with daytime HRV, there were significant associations between SM with nighttime HRV. A later SM was associated with lower nighttime Log-HF, SDNN and RMSSD, yet higher nighttime LF/HF (all p<0.03). For each standard deviation increase in SM (i.e., 1.5 hours later), there was a decrease of -5.50ms (1.92) in nighttime RMSSD (p=0.004). More specifically, the nighttime RMSSD of adolescents with a SM at 5:30 (i.e., sleep onset at 2:00, sleep offset at 9:00), was 18.2ms (6.7) lower (p=0.007) than that of adolescents with a SM at 2:30 (i.e., sleep onset at 23:00, sleep offset at 6:00). Conclusions: A delayed sleep phase is associated with impaired CAM in adolescents. These data support that circadian misalignment of the sleep-wake cycle may independently contribute to CVD risk.

High Fasting Glycemia Predicts Impairment of Cardiac Autonomic Control in Adults With Type 2 Diabetes: A Case-Control Study.

IntroductionType 2 diabetes (T2D) is characterized by a metabolic disorder that elevates blood glucose concentration. Chronic hyperglycemia has been associated with several complications in patients with T2D, one of which is cardiac autonomic dysfunction that can be assessed from heart rate variability (HRV) and heart rate recovery (HRR) response, both associated with many aspects of health and fitness, including severe cardiovascular outcomes.ObjectiveTo evaluate the effects of T2D on cardiac autonomic modulation by means of HRV and HRR measurements.Materials and MethodsThis study has an observational with case-control characteristic and involved ninety-three middle-aged adults stratified into two groups (control group - CG, n = 34; diabetes group - DG, n = 59). After signing the free and informed consent form, the patients were submitted to the evaluation protocols, performed biochemical tests to confirm the diagnosis of T2D, collection of R-R intervals for HRV analysis and cardiopulmonary effort test to quantify HRR.ResultsAt rest, the DG showed a reduction in global HRV (SDNN= 19.31 ± 11.72 vs CG 43.09 ± 12.74, p < 0.0001), lower parasympathetic modulation (RMSSD= 20.49 ± 14.68 vs 52.41 ± 19.50, PNN50 = 4.76 ± 10.53 vs 31.24 ± 19.24, 2VD%= 19.97 ± 10.30 vs 28.81 ± 9.77, p < 0.0001 for both indices) and higher HRrest when compared to CG. After interruption of physical exercise, a slowed heart rate response was observed in the DG when compared to the CG. Finally, a simple linear regression showed that fasting glycemia was able to predict cardiac autonomic involvement in volunteers with T2D.ConclusionPatients with T2D presented lower parasympathetic modulation at rest and slowed HRR after physical exercise, which may be associated with higher cardiovascular risks. The findings show the glycemic profile as an important predictor of impaired cardiac autonomic modulation.

Reduced heart-rate variability and increased risk of hypertension-a prospective study of the ELSA-Brasil.

Although autonomic disturbances are known to precede hypertension onset, the risks underlying different ranges of blood pressure and impaired cardiac autonomic modulation are still unknown. This study aimed to identify the risk of hypertension incidence related to low heart-rate variability profile in normotensive blood pressure subcategories: normal (<120/80 mmHg) and prehypertension (120/80-139/89 mmHg) in a 4-year follow-up. 7665 participants free of hypertension at baseline were examined. They were allocated into one of two groups (<P25 and ≥P25) based on age-specific value distributions of heart-rate variability ranges presented in the literature. The relationship between heart-rate variability parameters (SDNN, RMSSD, VLF, LF, and HF) and hypertension incidence was analyzed using Poisson regression. The reference for the independent variable in these regressions was the dataset with all HRV values ≥P25. After full adjustments for age, sex, ethnicity, educational level, body mass index, smoking status, glucose, insulin, dyslipidemia, alcohol consumption, and physical activity, low values for all heart-rate variability indices were significantly associated with an increased relative risk of developing hypertension in the overall sample. Individuals with normal BP levels presented an increased risk for low SDNN, VLF, and LF values, whereas the risk in prehypertensive participants was only verified for low VLF. In conclusion, cardio autonomic disturbances precede the incidence of clinical hypertension and are potentially involved in its pathophysiological basis and progression. Even individuals with normal blood pressure may be at an increased risk for future hypertension in the presence of reduced cardio autonomic control.

Dysautonomic Arrhythmogenesis: A Working Hypothesis in Chronic Chagas Cardiomyopathy

Abstract Sudden cardiac arrest (SCA) represents the most dramatic course of chronic Chagas cardiomyopathy (CCC) and is closely related to the presence of ventricular arrhythmias and heart disease. Although several aspects of ventricular arrhythmias in CCC have been elucidated in the last decades, such as the role of impaired cardiac autonomic modulation reported in pre-clinical studies, important questions remain unresolved regarding these cardiac problems and SCA. The aim of this article is to discuss recent developments in the understanding of [...]

In peripheral artery disease, diabetes is associated with reduced physical activity level and physical function and impaired cardiac autonomic control: A cross-sectional study.

Diabetes has been considered a major risk factor for peripheral artery disease (PAD). The effect of diabetes on daily physical activity level and cardiovascular function in PAD patients is poorly known. To analyze the effect of diabetes on physical activity level, physical function and cardiovascular health parameters in patients with PAD and claudication symptoms. Cross-sectional study of 267 PAD patients, 146 without and 121 with diabetes. Physical activity levels were objectively measured by using an accelerometer, and time spent in sedentary (0-100 counts/min), light (101-1040 counts/min) and moderate to vigorous (≥1041 counts/min) physical activity was obtained. Physical function assessment included the 6-min walk test, handgrip strength test and short physical performance battery. Cardiovascular health parameters measured were brachial blood pressure, heart rate variability, and arterial stiffness. Diabetic PAD patients spent more time in sedentary behavior (P=0.001, effect size [ES] 0.234) and less time in light (P=0.003, ES=0.206) and moderate-to-vigorous physical activity (P<0.001, ES=0.258) than non-diabetic PAD patients. Diabetic PAD patients presented lower 6-min walk distance (P=0.005, ES=0.194) and impaired cardiac autonomic modulation (standard deviation of all NN intervals [SDNN], P<0.001, ES=0.357; square root of the mean of the sum of the squares of differences between adjacent NN intervals [RMSSD], P<0.001, ES=0.280; and NN50 count divided by the total number of all NN intervals [pNN50], P<0.001, ES=0.291) as compared with non-diabetic PAD patients. After adjustment for confounders, diabetes remained associated with sedentary behavior (P=0.011), light (P=0.020) and moderate-to-vigorous physical activity (P=0.008), 6-min walk distance (P=0.030), SDNN (P<0.001), RMSSD (P=0.004), and PNN50 (P=0.004). Diabetic PAD patients presented lower physical activity level, reduced physical function and impaired autonomic modulation as compared with non-diabetic PAD patients.

Abstract P339: Impaired Cardiac Autonomic Modulation in Adolescents: Role of Insomnia Symptoms, Objective Short Sleep Duration and Night-To-Night Sleep Variability

Introduction: Impaired cardiac autonomic modulation (CAM), as measured by heart rate variability (HRV), has been associated with increased risk of cardiovascular morbidity. Inadequate sleep has been shown to contribute to impaired CAM, however, it is not clear what sleep problems are independently associated with impaired CAM in adolescents, a population in which insomnia symptoms, short sleep duration and night-to-night sleep variability are highly prevalent. Hypothesis: Insomnia symptoms, objective short sleep duration and high sleep variability are independently associated with worse HRV indices in adolescents. Methods: Data from the Penn State Child Cohort, a randomly-selected sample of 421 adolescents (12-23y) was used. Insomnia symptoms were defined by the presence of self-reported difficulties falling and/or staying asleep on the Pediatric Sleep Questionnaire. All subjects underwent 9-hour, in-lab polysomnography (PSG) and wore an actigraphy (ACT) monitor in the non-dominant wrist for 7 days. Mixed-effect regression models predicting HRV indices included insomnia symptoms, PSG sleep duration and ACT sleep duration and its variability (standard deviation) adjusted for each other as well as for sex, race, age, body mass index, and apnea/hypopnea index. Results: Shorter PSG sleep duration and higher ACT sleep variability were independently associated with decreased parasympathetic and increased sympathetic nervous activity [e.g., SDNN: 2.05±0.70, p&lt;0.01 and -4.50±1.14, p&lt;0.01 and Log-HF: 0.10±0.03, p&lt;0.0 and -0.10±0.05, p=0.05, respectively], while ACT sleep duration or self-reported insomnia symptoms were not [e.g., SDNN: -0.57±0.84, p=0.49 and 0.90±1.26, p=0.47 and Log-HF: -0.06±0.04, p=0.12 and 0.05±0.06, p=0.37, respectively]. Conclusions: Objective, but not subjective, measures of sleep are associated with impaired CAM in adolescents. Interestingly, short PSG sleep duration and high ACT sleep variability are independently associated with impaired CAM, which indicates that these two objective measures may help identify distinct sleep phenotypes associated with increased cardiovascular risk in adolescents. Future studies should examine whether a more severe type of insomnia symptoms, i.e., chronic insomnia, is associated with impaired CAM in adolescents.

Cardiac Autonomic Dysfunction in Offspring of Hypertensive Parents During Exercise.

Offspring of hypertensive parents present autonomic dysfunction at rest and during physiological maneuvers. However, the cardiac autonomic modulation during exercise remains unknown. This study tested whether the cardiac autonomic modulation would be reduced in offspring of hypertensive parents during exercise. Fourteen offspring of hypertensive and 14 offspring of normotensive individuals were evaluated. The groups were matched by age (24.5±1.0 vs. 26.6±1.5 years; p=0.25) and BMI (22.8±0.6 vs. 24.2±1.0 kg/m2; p=0.30). Blood pressure and heart rate were assessed simultaneously during 3 min at baseline followed by 3-min isometric handgrip at 30% of maximal voluntary contraction. Cardiac autonomic modulation was evaluated using heart rate variability. Primary variables were subjected to two-way ANOVA (group vs. time). P value<0.05 was considered statistically significant. Blood pressure and heart rate were similar between groups during exercise protocol. In contrast, offspring of hypertensive subjects showed a reduction of SDNN (Basal=34.8±3.5 vs. 45.2±3.7 ms; Exercise=30.8±3.3 vs. 41.5±3.9 ms; p group=0.01), RMSSD (Basal=37.1±3.7 vs. 52.0±6.0 ms; Exercise=28.6±3.4 vs. 41.9±5.3 ms; p group=0.02) and pNN50 (Basal=15.7±4.0 vs. 29.5±5.5%; Exercise=7.7±2.4 vs. 18.0±4.3%; p group=0.03) during the exercise protocol in comparison with offspring of normotensive parents. We concluded that normotensive offspring of hypertensive parents exhibit impaired cardiac autonomic modulation during exercise.

Birth Weight and Its Relationship with the Cardiac Autonomic Balance in Healthy Children.

Several studies indicate that the fetal environment plays a significant role in the development of cardiometabolic disease later in life. However, a few studies present conflicting data about the correlation between birth weight and the impairment of cardiac autonomic modulation. The purpose of the present study was to provide further knowledge to elucidate this contradictory relationship. One hundred children aged 5 and 14 years had anthropometric parameters, body composition and blood pressure levels determined. Heart rate variability (HRV) was evaluated by heart rate monitoring, including measurements of both the time and frequency domains. The results showed inverse correlation between the HRV parameters with BMI (RMSSD: P = 0.047; PNN50: P = 0.021; HF: P = 0.041), systolic (RMSSD: P = 0.023; PNN50: P = 0.032) and diastolic (PNN50: P = 0.030) blood pressure levels. On the other hand, there were consistent positive correlations between the HRV parameters and birth weight (RMSSD: P = 0.001; PNN50: P = 0.001; HF: P = 0.002). To determine the effect of birth weight on HRV parameters, we perform multivariate linear regression analysis adjusted for potentially confounding factors (prematurity, gender, age, BMI, physical activity index and SBP levels). These findings were preserved even after adjusting for these confounders. Our results suggested that impaired cardiac autonomic modulation characterized by a reduction in the parasympathetic activity occurs in children with low birth weight. One possible interpretation for these data is that a vagal withdrawal, rather than a sympathetic overactivity, could precede the development of hypertension and other cardiometabolic diseases in children with low birth weight. However, long-term studies should be performed to investigate this possibility.

Abstract P062: Individual Level Fine Particulate Air Pollution is Associated with Acute Impairment of Cardiac Autonomic Modulation in Adolescents

Introduction: Fine particulate (PM 2.5 ) air pollution has been associated with impaired cardiac autonomic modulation (CAM) in adults. The association between PM 2.5 exposure and CAM in adolescents is rarely investigated. Hypothesis: We assessed the hypothesis that PM 2.5 air pollution is related to acute impairment of CAM in adolescents. Methods: We used data from 421 adolescents in the Penn State Child Cohort follow-up examination. We obtained 24-hour ECG data using a 12-lead Holter ECG from each participant. After removing artifacts and arrhythmic beats, we performed heart rate variability (HRV) analysis on normal RR intervals to compute 30-min based high frequency (HF) and low frequency (LF) powers, standard deviation of RRs (SDNN), and the square root of mean of the sum of the squared differences of the adjacent RRs (RMSSD). Individual level 24-hour PM 2.5 concentration was obtained by a personal PM 2.5 monitor. We then calculated, on a 30-min basis, the corresponding time-specific exposure to PM 2.5 . Distributed lag models under a framework of linear mixed-effects model, with a first-order autoregressive covariance structure, were used to assess the segment-specific and cumulative effect of 30-min based PM 2.5 and HRV indices. Results: As shown in the table, both individual lag and cumulative effects of PM 2.5 on HRV, based on the lag 0-6 model, were significant after controlling for major covariates. For instance, for a 10 μg/m 3 increase in cumulative PM 2.5 , HF and SDNN decreased by 0.023 (SE=0.006) ms 2 and 0.61 (SE=0.16) ms, respectively. A 10 μg/m 3 increase in PM 2.5 was also significantly associated with elevated heart rate (0.25 (SE=0.09) beat/min). Individual lag effects of PM 2.5 were most consistently associated within 1.5 hours. Conclusion: Individual level exposure to PM 2.5 in adolescents is associated with impaired CAM, towards an elevated sympathetic and decreased parasympathetic outflow. The time to the apparent cumulative effect is about 3 hours, with the most consistent individual lag effects within 1.5 hours.

Effects of posteroanterior thoracic mobilization on heart rate variability and pain in women with fibromyalgia.

Fibromyalgia (FM) has been associated with cardiac autonomic abnormalities and pain. Heart rate variability (HRV) is reduced in FM with autonomic tone dominated by sympathetic activity. The purpose of this study was to evaluate the effects of one session of a posteroanterior glide technique on both autonomic modulation and pain in woman with FM. This was a controlled trial with immediate followup; twenty premenopausal women were allocated into 2 groups: (i) women diagnosed with FM (n = 10) and (ii) healthy women (n = 10). Both groups received one session of Maitland mobilization grade III posteroanterior central pressure glide, at 2 Hz for 60 s at each vertebral segment. Autonomic modulation was assessed by HRV and pain by a numeric pain scale before and after the intervention. For HRV analyses, heart rate and RR intervals were recorded for 10 minutes. FM subjects demonstrated reduced HRV compared to controls. Although the mobilization technique did not significantly reduce pain, it was able to improve HRV quantified by an increase in rMSSD and SD1 indices, reflecting an improved autonomic profile through increased vagal activity. In conclusion, women with FM presented with impaired cardiac autonomic modulation. One session of Maitland spine mobilization was able to acutely improve HRV.

Heart rate variability and autonomic modulation in children with obstructive sleep apnea syndrome

To investigate whether obstructive sleep apnea syndrome (OSAS) is associated with impaired heart rate variability (HRV) indices, indicating impairment of cardiac autonomic modulation in children. Children with snoring and 5 years of age or elder who came to the Sleep center of Beijing Children’s Hospital were enrolled. All subjects underwent polysomnography and 24-h Holter monitoring with continuous time dependent and spectral analysis of heart rate variability. HRV analysis included time and frequency domain indices. Ninety-three subjects were recruited into the study. Forty-seven met the criteria for OSAS, 46 were non-OSAS. There were no difference between the two groups with respect to age and gender. The OSAS group had significantly higher apnea hyopnea index (AHI), obstructive apnea index (OAI) and oxygen desaturation index (ODI) than the non-OSAS group. The HRV analysis showed that OSAS children had decreased N-N interval, SDNN (the standard deviation of NN intervals) and SDANN (the standard deviation of the average NN intervals calculated over 5 min) with P value of 0.007, 0.003, and 0.01 respectively. SDNN was significantly different and declined with the degree of severity of OSAS ( P value < 0.01). In children with OSAS, the nocturnal PNN50 was decreased while low frequency/high frequency (LF/HF) was elevated compared to the non- OSAS controls ( p value 0.025 and 0.026 respectively). Multiple regression analysis showed that SDNN was related to AHI and age ( p value 0.03 and 0.006). OSAS in children is significantly associated with impaired cardiac autonomic modulation, i.e., sympathetic overflow and weaker parasympathetic modulation. Thanks to Ms. Yunxiao WU and Bei Li for their helping with ECG monitoring.

Deep Breathing Heart Rate Variability is Associated with Inspiratory Muscle Weakness in Chronic Heart Failure

There is a synchronism between the respiratory and cardiac cycles. However, the relationship of inspiratory muscle weakness in chronic heart failure (CHF) on cardiac autonomic modulation is unknown. The purpose of the present investigation was to evaluate the impact of inspiratory muscle strength on the magnitude of respiratory sinus arrhythmia. Ten CHF (62 ± 7 years--left ventricle eject fraction of 40 ± 5% and New York Heart Association class I-III) and nine matched-age healthy volunteers (64 ± 5 years) participated in this study. Heart rate variability (HRV) was obtained at rest and during deep breathing manoeuvre (DB-M) by electrocardiograph. CHF patients demonstrated impaired cardiac autonomic modulation at rest and during DB-M when compared with healthy subjects (p < 0.05). Moreover, significant and positive correlations between maximal inspiratory pressure and inspiratory-expiratory differences (r = 0.79), expiratory/inspiratory ratio (r = 0.83), root mean square of the successive differences (r = 0.77), standard deviation of NN intervals (r = 0.77), low frequency (r = 0.77), and high frequency (r = 0.70) were found during DB-M. At rest, significant correlations were found also. Patients with CHF presented impaired cardiac autonomic modulation at rest. In addition, cardiac autonomic control of heart rate was associated with inspiratory muscle weakness in CHF. Based on this evidence, recommendations for future research applications of respiratory muscle training can bring to light a potentially valuable target for rehabilitation.

Insights into the clinical and functional significance of cardiac autonomic dysfunction in Chagas disease

Exclusive or associated lesions in various structures of the autonomic nervous system occur in the chronic forms of Chagas disease. In the indeterminate form, the lesions are absent or mild, whereas in the exclusive or combined heart and digestive disease forms, they are often more pronounced. Depending on their severity these lesions can result mainly in cardiac parasympathetic dysfunction but also in sympathetic dysfunction of variable degrees. Despite the key autonomic effect on cardiovascular functioning, the pathophysiological and clinical significance of the cardiac autonomic dysfunction in Chagas disease remains unknown. Review of data on the cardiac autonomic dysfunction in Chagas disease and their potential consequences, and considerations supporting the possible relationship between this disturbance and general or cardiovascular clinical and functional adverse outcomes. We hypothesise that possible consequences that cardiac dysautonomia might variably occasion or predispose in Chagas disease include: transient or sustained arrhythmias, sudden cardiac death, adverse overall and cardiovascular prognosis with enhanced morbidity and mortality, an inability of the cardiovascular system to adjust to functional demands and/or respond to internal or external stimuli by adjusting heart rate and other hemodynamic variables, and immunomodulatory and cognitive disturbances. Impaired cardiac autonomic modulation in Chagas disease might not be a mere epiphenomenon without significance. Indirect evidences point for a likely important role of this alteration as a primary predisposing or triggering cause or mediator favouring the development of subtle or evident secondary cardiovascular functional disturbances and clinical consequences, and influencing adverse outcomes.

Obesity is associated with impaired cardiac autonomic modulation in children

To examine the cross-sectional association between measurements of obesity and subclinical impairment of cardiac autonomic modulation (CAM) in a population-based sample of children. Data from 616 grade K-5 children randomly selected from Central Pennsylvania were utilized. Obesity was defined using the International Obesity Task Force (IOTF) age- and sex-specific cut-off criteria and classified as normal weight, overweight, and obese. CAM was measured by heart rate variability (HRV) analysis of beat-to-beat RR intervals, including time domain measures i.e., the standard deviation of all RR intervals (SDNN), the square root of the mean of the sum of squares of differences between adjacent RR intervals (RMSSD), and mean heart rate (HR); and frequency domain measures i.e., high frequency power (HF), low frequency power (LF), and LF/HF ratio. The prevalence of obesity and overweight in children was 12.3%, and 16.5%, respectively. Age, race, sex, and sleep disorder breathing (SDB) adjusted means (standard error, SE) of SDNN were 98 (1.24), 90.2 (2.58), and 81.9 (3.03) milliseconds (ms) in normal weight, overweight, and obese groups, respectively; and that for (log) HF were 6.83 (0.04), 6.56 (0.08), and 6.35 (0.09) ms(2), respectively. Comparing the magnitude of effects from body mass index (BMI), weight, and height percentiles, and waist circumference on HRV indices revealed that body weight was the strongest correlate of HRV indices. Childhood obesity is significantly associated with lower HRV, indicative of sympathetic overflow unopposed by parasympathetic modulation. These findings support the need to target childhood-obesity before traditional "high risk age" for cardiac events.

Insomnia Symptoms and Sleep Duration Are Associated with Impaired Cardiac Autonomic Modulation in Children

Limited population-based data from children are available to investigate the associations between insomnia and sleep duration in relationship to impaired cardiac autonomic modulation (CAM). Therefore, the objective of this study is to examine the cross-sectional associations between insomnia symptoms, sleep duration, and CAM in a population-based sample of children. All 616 children were randomly selected from Central Pennsylvania to participate in a one-night polysomnography (PSG) study in a sleep laboratory. The Pediatric Behavior Scale was used to assess parent-reported insomnia. Sleep duration was assessed objectively by PSG. CAM was measured by heart rate variability (HRV) analysis of 9-hour-beat-to-beat RR intervals. Multivariate linear regression models were used to assess the association between insomnia, sleep duration and HRV. The mean (SD) age was 9.2 (1.7) years, with 25.5% non-white and 48.9% male. After adjusting for age, race, gender, BMI percentile, %REM sleep, apnea-hypopnea-index, sleep latency, and sleep efficiency, the means(SE) of HRV indices were lower in children with insomnia than in children without: 6.56 (0.07) vs. 6.78 (0.04) m2 on logHF, respectively; and 6.47 (0.06) vs. 6.61 (0.03) m2 on logLF, respectively (all P < 0.05). There is a trend towards a significant lower time domain HRV indices, faster HR, and higher LF/HF ratio in children with insomnia symptoms. There is a similar pattern of association between shorter objective sleep duration and HRV. Insomnia symptoms and shorter objective sleep duration are associated with lower HRV and higher HR and LF/HF ratio, indicative of disturbance of CAM towards more sympathetic and lower parasympathetic modulation. These data provide supporting evidence of physiological activation associated with insomnia and short sleep duration even in very young children.

Sleep-disordered breathing and cardiac autonomic modulation in children

Objectives To investigate the adverse cardiac autonomic effects of sleep-disordered breathing (SDB) in a large population-based sample and a clinical sample of children. Methods Subjects included a population-based sample of 700 and a clinically diagnosed sample of 43 SDB children. SDB was defined based on an apnea hypopnea index (AHI) ⩾ 1 during one night of polysomnography. Cardiac autonomic modulation was measured by heart rate variability (HRV) analysis of the beat-to-beat RR interval data collected during polysomnography. Results The mean (SD) age was 112 (21) months, with 49% male and 25% non-white. About 73.0% had AHI < 1 (no SDB), 25.8% had 1–5 AHI (mild SDB), and 1.2% had ⩾5 AHI (moderate SDB). Among individuals with moderate SDB in the population-based sample and the clinically diagnosed SDB patients, the mean (SE) of HRV-high frequency power (HF) was significantly lower compared to children without SDB [6.00 (0.32) and 6.24 (0.14), respectively, vs. 6.68 (0.04) ms 2, p < 0.05 and p < 0.01, respectively], whereas the low frequency power to high frequency power ratio (LF/HF) was significantly higher [1.62 (0.20) and 1.74 (0.09), respectively, vs. 0.99 (0.02), both p < 0.01)]. Conclusions SDB in healthy young children and in clinical patients is significantly associated with impaired cardiac autonomic modulation, i.e., sympathetic overflow and weaker parasympathetic modulation, which may contribute to increased risk of acute cardiac events in persons with SDB, even before reaching the “high risk age.”

Deep breathing heart rate variability is associated with respiratory muscle weakness in patients with chronic obstructive pulmonary disease

BACKGROUNDA synchronism exists between the respiratory and cardiac cycles. However, the influence of the inspiratory muscle weakness in chronic obstructive pulmonary disease (COPD) on cardiac autonomic control is unknown. The purpose of the present investigation was to evaluate the influence of respiratory muscle strength on autonomic control in these patients.METHODSTen chronic obstructive pulmonary disease patients (69±9 years; FEV1/FVC 59±12% and FEV1 41±11% predicted) and nine age-matched healthy volunteers (64±5 years) participated in this study. Heart-rate variability (HRV) was obtained at rest and during respiratory sinusal arrhythmia maneuver (RSA-M) by electrocardiograph.RESULTSChronic obstructive pulmonary disease patients demonstrated impaired cardiac autonomic modulation at rest and during RSA-M when compared with healthy subjects (p<0.05). Moreover, significant and positive correlations between maximal inspiratory pressure (MIP) and the inspiratory-expiratory difference (ΔIE) (r = 0.60, p<0.01) were found.CONCLUSIONPatients with chronic obstructive pulmonary disease presented impaired sympathetic-vagal balance at rest. In addition, cardiac autonomic control of heart rate was associated with inspiratory muscle weakness in chronic obstructive pulmonary disease. Based on this evidence, future research applications of respiratory muscle training may bring to light a potentially valuable target for rehabilitation.