Familial and genetic influences on heart rate variability

The Cardiorespiratory Network in Healthy First-Degree Relatives of Schizophrenic Patients

Impaired heart rate- and respiratory regulatory processes as a sign of an autonomic dysfunction seems to be obviously present in patients suffering from schizophrenia. Since the linear and non-linear couplings within the cardiorespiratory system with respiration as an important homeostatic control mechanism are only partially investigated so far for those subjects, we aimed to characterize instantaneous cardiorespiratory couplings by quantifying the casual interaction between heart rate (HR) and respiration (RESP). Therefore, we investigated causal linear and non-linear cardiorespiratory couplings of 23 patients suffering from schizophrenia (SZO), 20 healthy first-degree relatives (REL) and 23 healthy subjects, who were age-gender matched (CON). From all participants' heart rate (HR) and respirations (respiratory frequency, RESP) were investigated for 30 min under resting conditions. The results revealed highly significant increased HR, reduced HR variability, increased respiration rates and impaired cardiorespiratory couplings in SZO in comparison to CON. SZO were revealed bidirectional couplings, with respiration as the driver (RESP → HR), and with weaker linear and non-linear coupling strengths when RESP influencing HR (RESP → HR) and with stronger linear and non-linear coupling strengths when HR influencing RESP (HR → RESP). For REL we found only significant increased HR and only slightly reduced cardiorespiratory couplings compared to CON. These findings clearly pointing to an underlying disease-inherent genetic component of the cardiac system for SZO and REL, and those respiratory alterations are only clearly present in SZO seem to be connected to their mental emotional states.

Effects of manual cranial therapy on heart rate variability in children without associated disorders: Translation to clinical practice

BACKGROUND

and purpose: Heart rate variability (HRV) represents a marker of autonomic activity, self-regulation and psychiatric illness. Few studies of manual therapy have investigated the neurophysiological effects of manual cranial therapy (MC-t). This study assessed the neurophysiological short/medium-term effects of two manual therapy interventions: massage therapy (Mss-t) and MC-t.

MATERIALS AND METHODS

A double-blind clinical trial was conducted with 50 healthy children, randomized into two groups who received a Mss-t intervention or MC-t. The variables analysed included vital signs (temperature, respiratory rate, heart rate, blood pressure) and HRV components, including the root mean square of successive differences (RMSSD), high frequency (HF), low frequency (LF) and LF/HF ratio.

RESULTS

Both interventions produced short-term parasympathetic effects, although the effects of MC-t were more persistent.

CONCLUSION

The persistence of the MC-t intervention suggested a prominent vagal control and better self-regulation. Autonomic imbalances in mental pathologies may benefit from the neurophysiological effects of MC-t.

A Comparison of Heritability Estimates by Classical Twin Modeling and Based on Genome-Wide Genetic Relatedness for Cardiac Conduction Traits

Twin studies have found that ~50% of variance in electrocardiogram (ECG) traits can be explained by genetic factors. However, genetic variants identified through genome-wide association studies explain less than 10% of the total trait variability. Some have argued that the equal environment assumption for the classical twin model might be invalid, resulting in inflated narrow-sense heritability (h 2) estimates, thus explaining part of the 'missing h 2'. Genomic relatedness restricted maximum likelihood (GREML) estimation overcomes this issue. This method uses both family data and genome-wide coverage of common SNPs to determine the degree of relatedness between individuals to estimate both h 2 explained by common SNPs and total h 2. The aim of the current study is to characterize more reliably than previously possible ECG trait h 2 using GREML estimation, and to compare these outcomes to those of the classical twin model. We analyzed ECG traits (heart rate, PR interval, QRS duration, RV5+SV1, QTc interval, Sokolow-Lyon product, and Cornell product) in up to 3,133 twins from the TwinsUK cohort and derived h 2 estimates by both methods. GREML yielded h 2 estimates between 47% and 68%. Classical twin modeling provided similar h 2 estimates, except for the Cornell product, for which the best fit included no genetic factors. We found no evidence that the classical twin model leads to inflated h 2 estimates. Therefore, our study confirms the validity of the equal environment assumption for monozygotic and dizygotic twins and supports the robust basis for future studies exploring genetic variants responsible for the variance of ECG traits.

Individual differences in physiologic measures are stable across repeated exposures to total sleep deprivation

Some individuals show severe cognitive impairment when sleep deprived, whereas others are able to maintain a high level of performance. Such differences are stable and trait‐like, but it is not clear whether these findings generalize to physiologic responses to sleep loss. Here, we analyzed individual differences in behavioral and physiologic measures in healthy ethnic‐Chinese male volunteers (n = 12; aged 22–30 years) who were kept awake for at least 26 h in a controlled laboratory environment on two separate occasions. Every 2 h, sustained attention performance was assessed using a 10‐min psychomotor vigilance task (PVT), and sleepiness was estimated objectively by determining percentage eyelid closure over the pupil over time (PERCLOS) and blink rate. Between‐subject differences in heart rate and its variability, and electroencephalogram (EEG) spectral power were also analyzed during each PVT. To assess stability of individual differences, intraclass correlation coefficients (ICC) were determined using variance components analysis. Consistent with previous work, individual differences in PVT performance were reproducible across study visits, as were baseline sleep measures prior to sleep deprivation. In addition, stable individual differences were observed during sleep deprivation for PERCLOS, blink rate, heart rate and its variability, and EEG spectral power in the alpha frequency band, even after adjusting for baseline differences in these measures (range, ICC = 0.67–0.91). These findings establish that changes in ocular, ECG, and EEG signals are highly reproducible across a night of sleep deprivation, hence raising the possibility that, similar to behavioral measures, physiologic responses to sleep loss are trait‐like.

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Individual differences in physiologic measures were examined in healthy ethnic‐Chinese males who underwent sleep deprivation in the laboratory on two different occasions. We found that between‐subject differences in ocular, electrocardiogram, and electroencephalogram measures were highly stable, even after adjusting for baseline individual differences in these measures. These results suggest that the brain responds predictably to the challenge of sleep deprivation and raise the possibility that physiologic responses to sleep loss are trait‐like.

Sex differences in cardiac autonomic regulation and in repolarisation electrocardiography

The review summarises the present knowledge on the sex differences in cardiac autonomic regulations and in related aspects of electrocardiography with particular attention to myocardial repolarisation. Although some of the sex differences are far from fully established, multitude of observations show consistent differences between women and men. Despite more pronounced parasympathetic cardiac regulation, women have higher resting heart rate and lower baroreflex sensitivity. Of the electrocardiographic phenomena, women have longer QT interval duration, repolarisation sequence more synchronised with the inverse of the depolarisation sequence, and likely increased regional heterogeneity of myocardial repolarisation. Studies investigating the relationship of these sex disparities to hormonal differences led frequently to conflicting results. Although sex hormones seem to play a key role by influencing both autonomic tone and electrophysiological properties at the cellular level, neither the truly relevant hormones nor their detailed actions are known. Physiologic usefulness of the described sex differences is also unknown. The review suggests that new studies are needed to advance the understanding of the physiologic mechanisms responsible for these inequalities between women and men and provides key methodological suggestions that need to be followed in future research.

Autonomic dysfunction in unaffected first-degree relatives of patients suffering from schizophrenia

Recent studies revealed cardiac autonomic dysfunction in patients with acute schizophrenia, which appears to be mainly related to reduced vagal and increased sympathetic modulation. To understand the significance of cardiac autonomic function in patients with schizophrenia, we extended these studies to relatives of patients. In this study, we assessed cardiac autonomic modulation in healthy first-degree relatives of patients with schizophrenia (n = 36) to investigate a putative genetic influence. Data were compared with control subjects matched for age, gender, and physical activity as well as to patients suffering from schizophrenia. First-degree relatives showed an attenuated, yet identical pattern in autonomic dysfunction as patients with decreased vagal modulation of heart rate, decreased baroreflex sensitivity, but no difference in blood pressure variability could be detected. The patients' relatives also showed a similar pattern in regards to QT variability. In addition, the subgroup comparison of offspring vs. siblings showed a significant difference in heart rate variability suggesting a higher degree of heritability in offspring. In conclusion, the pattern of autonomic dysfunction seen in patients and relatives might indicate underlying disease-inherent genetic vulnerability, especially because autonomic parameters are heritable. In addition, these findings may be of value to identify the high-risk group of patients' relatives in regards to serious cardiovascular events so that early preventive measures can be taken.

Multiscale, multiorgan and multivariate complexity analyses of cardiovascular regulation

Cardiovascular system complexity is confirmed by both its generally variegated structure of physiological modelling and the richness of information detectable from processing of the signals involved in it, with strong linear and nonlinear interactions with other biological systems. In particular, this behaviour may be accordingly described by means of what we call MMM paradigm (i.e. multiscale, multiorgan and multivariate). Such an approach to the cardiovascular system emphasizes where the genesis of its complexity is potentially allocated and how it is possible to detect information from it. No doubt that processing signals from multi-leads of the same system (multivariate), from the interaction of different physiological systems (multiorgan) and integrating all this information across multiple scales (from genes, to proteins, molecules, cells, up to the whole organ) could really provide us with a more complete look at the overall phenomenon of cardiovascular system complexity, with respect to the one which is obtainable from its single constituent parts. In this paper, some examples of approaches are discussed for investigating the cardiovascular system in different time and spatial scales, in studying a different organ involvement (such as sleep, depression and multiple organ dysfunction) and in using a multivariate approach via various linear and nonlinear methods for cardiovascular risk stratification and pathology assessment.

Heritability and linkage study on heart rates in a Mongolian population

Elevated heart rate has been proposed as an independent risk factor for cardiovascular diseases, but their interrelationships are not well understood. In this study, we performed a genome-wide linkage scan in 1,026 individuals (mean age 30.6 years, 54.5% women) from 73 extended families of Mongolia and determined quantitative trait loci that influence heart rate. The DNA samples were genotyped using deCODE 1,039 microsatellite markers for 3 cM density genome-wide linkage scan. Correlation analysis was carried out to evaluate the correlation of the covariates and the heart rate. T-tests of the heart rate were also performed on sex, smoking and alcohol intake. Consequently, this model was used in a nonparametric genome-wide linkage analysis using variance component model to create a multipoint logarithm of odds (LOD) score and a corresponding P value. In the adjusted model, the heritability of heart rate was estimated as 0.32 (P<.0001) and a maximum multipoint LOD score of 2.03 was observed in 77 cM region at chromosome 18. The second largest LOD score of 1.52 was seen on chromosome 5 at 216 cM. Genes located on the specified locations in chromosomes 5 and 18 may be involved in the regulation of heart rate.

PER3 polymorphism and cardiac autonomic control: effects of sleep debt and circadian phase

A variable number tandem repeat polymorphism in the coding region of the circadian clock PERIOD3 (PER3) gene has been shown to affect sleep. Because circadian rhythms and sleep are known to modulate sympathovagal balance, we investigated whether homozygosity for this PER3 polymorphism is associated with changes in autonomic nervous system (ANS) activity during sleep and wakefulness at baseline and after sleep deprivation. Twenty-two healthy participants were selected according to their PER3 genotype. ANS activity, evaluated by heart rate (HR) and HR variability (HRV) indexes, was quantified during baseline sleep, a 40-h period of wakefulness, and recovery sleep. Sleep deprivation induced an increase in slow-wave sleep (SWS), a decrease in the global variability, and an unbalance of the ANS with a loss of parasympathetic predominance and an increase in sympathetic activity. Individuals homozygous for the longer allele (PER3(5/5)) had more SWS, an elevated sympathetic predominance, and a reduction of parasympathetic activity compared with PER3(4/4), in particular during baseline sleep. The effects of genotype were strongest during non-rapid eye movement (NREM) sleep and absent or much smaller during REM sleep. The NREM-REM cycle-dependent modulation of the low frequency-to-(low frequency + high frequency) ratio was diminished in PER3(5/5) individuals. Circadian phase modulated HR and HRV, but no interaction with genotype was observed. In conclusion, the PER3 polymorphism affects the sympathovagal balance in cardiac control in NREM sleep similar to the effect of sleep deprivation.

Nonlinear analyses of heart rate variability in monochorionic and dichorionic twin fetuses

AIMS

To examine whether the heart rate dynamics of a monochorionic diamniotic (MD) twin fetus is different from a dichorionic diamniotic (DD) twin fetus by nonlinear methods of time series analysis.

METHODS

32 fetal heart rate (FHR) recordings from healthy MD twin fetuses and 58 recordings from healthy DD twin fetuses were used. Nonlinear analyses included attractor reconstruction, calculation of the largest Lyapunov exponents, and estimation of correlation dimension.

RESULTS

FHR of healthy twin fetuses was shown to have unique nonlinear characteristics. The largest Lyapunov exponent significantly increased during the pregnancy period. In 30-36 weeks, correlation dimension in MD twins was significantly lower than that in DD twins. In DD twins, we observed a significant increase of correlation dimension from 22-29 to 30-36 weeks. In 22-29 weeks, the difference of the values of correlation dimension in each MD twin pair was significantly lower than that in each DD twin pair.

CONCLUSIONS

The heart rate dynamics of healthy MD and DD twin fetuses becomes more chaotic according to gestational age. From the viewpoint of the FHR-regulating system, a pair of MD twins seems to have a more strict binding than a pair of DD twins before 30 weeks' gestation.

Role of genetic and environmental influences on heart rate variability in middle-aged men

Our aim was to estimate causal relationships of genetic factors and different specific environmental factors in determination of the level of cardiac autonomic modulation, i.e., heart rate variability (HRV), in healthy male twins and male twins with chronic diseases. The subjects were 208 monozygotic (MZ, 104 healthy) and 296 dizygotic (DZ, 173 healthy) male twins. A structured interview was used to obtain data on lifetime exposures of occupational loading, regularly performed leisure-time sport activities, coffee consumption, smoking history, and chronic diseases from 12 yr of age through the present. A 5-min ECG at supine rest was recorded for the HRV analyses. In univariate statistical analyses based on genetic models with additive genetic, dominance genetic, and unique environmental effects, genetic effects accounted for 31–57% of HRV variance. In multivariate statistical analysis, body mass index, percent body fat, coffee consumption, smoking, medication, and chronic diseases were associated with different HRV variables, accounting for 1–11% of their variance. Occupational physical loading and leisure-time sport activities did not account for variation in any HRV variable. However, in the subgroup analysis of healthy and diseased twins, occupational loading explained 4% of the variability in heart periods. Otherwise, the interaction between health status and genetic effects was significant for only two HRV variables. In conclusion, genetic factors accounted for a major portion of the interindividual differences in HRV, with no remarkable effect of health status. No single behavioral determinant appeared to have a major influence on HRV. The effects of medication and diseases may mask the minimal effect of occupational loading on HRV.

Decreased chaos of heart rate time series in children of patients with panic disorder

This study examined the differences of heart rate variability measures between children of parents with panic disorder and children of healthy controls using linear as well as nonlinear techniques. Supine and standing heart rate variability indices were measured in all children using power spectral analysis and a measure of chaos, the largest Lyapunov exponent (LLE) of heart rate time series. No significant differences emerged between the children of panic disorder parents and children of normal controls on any of the spectral heart rate variability measures. However, children of patients with panic disorder had significantly lower LLE of heart rate time series in supine posture, suggesting a relative decrease of cardiac vagal function in this group of children. This suggests a possible heritable effect of certain measures of heart rate variability, as previous studies showed decreased heart rate variability in patients with panic disorder using spectral as well as nonlinear techniques. Recent evidence also suggests that some of these nonlinear measures are superior or of additional value to the traditional time and frequency domain measures of heart rate variability to predict serious ventricular arrhythmias and sudden death.

Altered heart rate and blood pressure variability in mice lacking the Mas protooncogene

Heart rate variability is a relevant predictor of cardiovascular risk in humans. A significant genetic influence on heart rate variability is suggested, although the genes involved are ill-defined. The Mas-protooncogene encodes a G-protein-coupled receptor with seven transmembrane domains highly expressed in testis and brain. Since this receptor is supposed to interact with the signaling of angiotensin II, which is an important regulator of cardiovascular homeostasis, heart rate and blood pressure were analyzed in Mas-deficient mice. Using a femoral catheter the blood pressure of mice was measured for a period of 30 min and 250 data values per second were recorded. The mean values and range of heart rate and blood pressure were then calculated. Neither heart rate nor blood pressure were significantly different between knockout mice and controls. However, high resolution recording of these parameters and analysis of the data by non-linear dynamics revealed significant alterations in cardiovascular variability in Mas-deficient animals. In particular, females showed a strong reduction of heart rate variability. Furthermore, the data showed an increased sympathetic tone in knockout animals of both genders. The marked alterations detected in Mas-deficient mice of both genders suggest that the Mas-protooncogene is an important determinant of heart rate and blood pressure variability.

Heritability of ECG measurements in adult male twins

To assess the genetic contribution to electrocardiographic (ECG) measurements, heritability analysis was performed on ECG data collected on 251 pairs of adult male twins during the second examination of the National Heart, Lung and Blood Institute twin study, a multicenter study of cardiovascular risk factors. Resting 12-lead ECGs were obtained on each twin, pair and, the R-R, QRS, QT, and JT intervals were measured. Both the R-R and QT intervals demonstrated significant heritable components, accounting for 77% and 36%, respectively, of the variability. No significant heritable component of the QRS complex could be identified. Although the MZ intraclass correlation was higher than the DZ intraclass correlation, the JT interval did not demonstrate significant heritability. Therefore, in adult males both heart rate and the duration of ventricular repolarization have significant heritable components. These heritable components may need to be considered when using ECG measurements to screen for patients at risk for cardiovascular disorders or sudden cardiac death.