Heart rate variability during interictal epileptiform discharges

RATIONALE: Seizures may produce a variety of autonomic alterations. These alterations may occur due to evoked autonomic reflexes or as a direct cortical effect on autonomic control. In animal studies, lock step phenomena of interictal discharges to autonomic output have been repeatedly documented. However, the association of interictal discharges and autonomic output is not as well established in humans. METHODS: RR intervals timely locked to interictal epileptiform discharge (RR(n)) were compared to RR intervals immediately following (RR(n+1)) interictal discharges in 40 patients with focal onset epilepsy and low baseline heart beat variability. RESULTS: In 20 patients with 200 left sided interictal epileptiform discharges, RR(n) shortened in 100 and prolonged in 31 when compared to RR(n+1) intervals. While in 20 patients with 200 right sided interictal epileptiform discharges RR(n) intervals shortened in 17 and prolonged in 116 (Chi square P<0.001). No consistent differences in RR(n) intervals variability between frontal versus temporal localization of the interictal discharges from the same side was found. CONCLUSIONS: Interictal discharges, may influence autonomic control over the cardiac cycle and agree with animal studies. Further study of the relationship of interictal discharges to autonomic output is needed to delineate the potential lateralized influences over autonomic nervous system.     

Heart rate variability in preterm infants and maternal smoking during pregnancy

Objective  Tobacco smoke exposure increases the risk of premature birth and of dying of sudden infant death syndrome (SIDS). Prematurity significantly increases the risk of dying of SIDS, but mechanisms underlying this epidemiological finding are unclear. The cumulated effect of both prematurity and prenatal exposure to nicotine on autonomic heart rate control has not been studied. Methods  Using coarse-graining spectral analysis, we compared heart rate variability (HRV) indices of preterm newborns at 33–34 weeks post-conceptional age from smoking (n = 19) and non-smoking (n = 21) mothers. Assessment of tobacco exposure relied on maternal reports and newborns cotinine analysis. We observed how indicators of HRV depended on gestational age at birth. Results  At 33–34 weeks postconceptional age, the newborns from smoking mothers had lower HRV low frequency power normalised to the total spectral power (LF/TP) than the control group (median values: 8% vs. 15% respectively, p < 0.02). In the non-smoking group, RR-interval values and total HRV power were correlated with gestational age at birth, with a shorter RR and a lower total HRV power in lesser gestational ages (ρ = 0.67, p = 0.03, ρ = 0.71, p = 0.003 respectively). This correlation was not observed for RR values in the group with smoking mothers.     

Heart rate variability in multiple sclerosis during a stable phase

Objectives – Multiple sclerosis (MS) frequently causes disturbances of autonomic functions. Cardiovascular dysautonomia has been studied by classic autonomic tests and, recently, by heart rate variability analysis in some isolated periods. Multiple authors recommended performing heart rate variability analysis with a 24 h ECG recording to increase its sensitivity. Material and methods – We analyzed the heart rate variability in time and frequency domains in 34 MS patients and 24 age and sex-matched healthy control subjects, in order to evaluate the effects of MS on sympathetic and parasympathetic cardiovascular regulatory functions measured from 24-h electrocardiogram. Results – Low frequency power (0.01) and low frequency/high frequency power (0.01) were significantly higher in multiple sclerosis patients independently, all together or in subgroups. Very low frequency (0.01) and high frequency (0,001) power were higher in less affected multiple sclerosis patients. Variability in time domain (0.05) were lower in most affected multiple sclerosis patients. Conclusions – These results suggest that multiple sclerosis causes cardiovascular autonomic dysregulation manifesting as impaired heart rate variability. This illness seems to cause an increase in sympathetic cardiovascular tone; the parasympathetic tone is most variable and depends on clinical and paraclinical findings, but the illness progression seems to provoke a decrease in it.     

Heart rate variability in full-term normal and abnormal newborn infants during sleep

Heart rate variability was studied in normal and abnormal newborn infants during sleep in relation to the EEG background. The background EEGs of the full-term newborn infants were classified into normal, minimal depression, mild depression, moderate depression, burst-suppression and flat patterns in order of increasing severity. Nonsequential and sequential histograms were produced with the aid of a computer from some 500 consecutive RR intervals of the ECG recorded on a magnetic tape during polygraphic recordings. The seuential curves mainly showed fast oscillation during quiet sleep and slow oscillation during active sleep in normal infants. The infants who had moderately depresed EEGs presented pronounced oscillation. In those whose EEGs displayed burst-suppression and flat patterns, the sequential curves showed very little heart rate variability. They were often flat (fixed heart rate). Thus, heart rate variability was found to be one of the valuable parameters in evaluating abnormality of the CNS in newborn infants.     

Heart rate variability during static and dynamic breath-hold dives in elite divers

The purpose of this study was to assess the differences in cardiac autonomic modulation during maximal static (SA) and dynamic (DA) underwater apneas. Arterial oxygen saturation (SpO(2)), heart rate (HR) and HR variability (SD1 from Poincaré plot and short-term fractal-like scaling exponent, α(1)) were analyzed at the immersed baseline (3 min) and initial, mid- and end-phases (each 30s) of SA and DA in nine elite breath-hold divers. DA and SA lasted 78 ± 8 and 225 ± 20s (mean ± SEM), respectively, and resulted in similar decrements in end-stage SpO(2) (78 ± 3 and 75 ± 3%, p=0.352). During DA, initial increase in HR (from 80 ± 5 to 122 ± 5 bpm, p<0.001) was followed by gradual decrease towards the baseline at mid-apnea and end-apnea phase (101 ± 6 and 80 ± 8 bpm, respectively). During SA, HR decreased at mid-apnea (from 78 ± 4 to 66 ± 3 bpm, p=0.004) but did not decrease further at end-apnea phase (66 ± 4b pm). Decreased SD1 was observed at the initial phase of DA (from 28 ± 5 to 10 ± 4 ms, p=0.005) being lower compared with SA (24 ± 4 ms, p=0.005). At the end of DA and SA, SD1 tended to increase above the baseline (62 ± 16 and 66 ± 10 ms, p=0.128 and p=0.093, respectively, p=0.602 DA vs. SA). α(1) tended to be higher at the end of DA compared with SA (1.17 ± 0.10 vs. 0.79 ± 0.10, p=0.059). We concluded that apnea blunts the effects of exercise on cardiac vagal activity at the end of DA. However, higher HR during DA compared with SA indicates larger cardiac sympathetic activity during DA, as suggested also by slightly higher α(1).     

Heart rate variability during sleep in children with autism spectrum disorder

Purpose

Autonomic dysfunction has been reported in autism spectrum disorders (ASD). Less is known about autonomic function during sleep in ASD. The objective of this study is to provide insight into the autonomic cardiovascular control during different sleep stages in ASD. We hypothesized that patients with ASD have lower vagal and higher sympathetic modulation with elevated heart rate, as compared to typical developing children (TD).

Methods

We studied 21 children with ASD and 23 TD children during overnight polysomnography. Heart rate and spectral parameters were calculated for each vigilance stage during sleep. Data from the first four sleep cycles were used to avoid possible effects of different individual sleep lengths and sleep cycle structures. Linear regression models were applied to study the effects of age and diagnosis (ASD and TD).

Results

In both groups, HR decreased during non-REM sleep and increased during REM sleep. However, HR was significantly higher in stages N2, N3 and REM sleep in the ASD group. Children with ASD showed less high frequency (HF) modulation during N3 and REM sleep. LF/HF ratio was higher during REM. Heart rate decreases with age at the same level in ASD and in TD. We found an age effect in LF in REM different in ASD and TD.

Conclusion

Our findings suggest possible deficits in vagal influence to the heart during sleep, especially during REM sleep. Children with ASD may have higher sympathetic dominance during sleep but rather due to decreased vagal influence.

     

Heart rate variability in childhood obesity

Obesity is characterized by hemodynamic and metabolic alterations. Autonomic control on cardiac function involvement is controversial. The aim of the study was to assess early sign of cardiac autonomic dysfunction in obesity, using time- and frequency-domain heart rate variability (HRV) analysis in a pediatric population. Methods: 32 obese children (OB) (17 M, 15 F; 13.9±1.7 y) were compared with 13 healthy lean subjects (7M, 6F; 12.9±1.6y). For each participant, the authors performed a clinical examination, laboratory testing, blood pressure (BP) measurements, and 24-hour electrocardiograph/ambulatory BP monitoring. The spectral power was quantified in total power, low-frequency (HF) power, index of sympathetic tone, high-frequency (HF) power, index of vagal tone, and LF/HF ratio. Low frequency and HF were averaged to obtain 3 measures: 24-hour, daytime, and nighttime levels. Total, long-term, and short-term time-domain HRV values were calculated. Results: The obese children had higher casual and ambulatory BP, and higher fasting glucose, insulin, and triglyceride levels. Overall HRV values were not significantly lower in OB. The obese children had significantly lower 24-hour and nighttime high-frequency normalized units, and time-domain measures of vagal activity. Low-frequency power showed an inverse but not significant pattern. The OB group had significantly greater 24-hour and nighttime LF/HF ratios. Conclusions: The authors found an increase in heart rate and in BP associated with parasympathetic heart rate control decrease in stabilized obese normotensive children.     

Heart rate variability in brain death

The sensitivity and specificity of heart rate variability (HRV) in the corroboration of brain death diagnosis in patients with acute traumatic intracranial lesions was evaluated in 20 patients with clinical criteria of brain death, nine patients in deep coma (Glasgow scale <7) and 18 normal controls, all age matched. The electrocardiogram was sampled at 650 Hz and several parameters of HRV were calculated, in both time and frequency domains. The HRV parameters were significantly lower in the brain death group compared with the deep coma group. Linear discriminant analysis between brain death and deep coma patients was performed on a data set made of nine randomly selected patients with clinical criteria of brain death and nine patients in deep coma. Cross-validation was performed on the remaining 11 patients with clinical criteria of brain death. All patients in the data set were correctly classified (sensitivity and specificity of 100%). All patients in the cross-validation set were correctly classified (sensitivity of 100%). Further studies are necessary to evaluate the specificity of the method in the independent set of deep coma patients and in the follow-up of comatose and vegetative patients to identify irreversibility of HRV. Nevertheless, these results suggest that HRV analysis constitutes a fully sensitive and specific method for assessing brain death in potential organ donors with acute traumatic lesions of the brain. This fast, quantitative and bedside method seems very promising for the early confirmation of brain death, which is an important factor for the success of transplantation procedures and could have a high predictive value of brain death in comatose patients with brain injuries without fully diagnostic criteria.     

Heart rate variability during sleep and the early development of posttraumatic stress disorder

Background

Noradrenergic function has been linked to posttraumatic stress disorder (PTSD) and might have a role in mediating sleep disturbances of the disorder. Our objective was to relate a peripheral manifestation of noradrenergic function, sympathetic nervous system activity as indexed by heart rate variability during sleep, to the development of PTSD in subjects with recent traumatic injuries.

Methods

Subjects who had recall of life-threatening experiences were recruited from one of two regional trauma centers. Select subjects received a polysomnographic recording within 1 month of the trauma. Digitized electrocardiogram recordings were extracted from early and late rapid-eye-movement (REM) and preceding non-REM sleep periods. Autoregression was applied to R-R interval time series to calculate the ratios of low-frequency to high-frequency spectral densities (LF/HF ratios), which index sympathetic activation. Posttraumatic stress disorder status was determined at 2 months.

Results

There was a significant state × group interaction: LF/HF ratios were higher during the REM sleep of the nine subjects who were positive for PTSD symptoms, compared with the 10 subjects who were PTSD negative.

Conclusions

Our findings are consistent with the possibility that increased noradrenergic activity during REM sleep contributes to the development of PTSD.     

Heart rate variability in bipolar mania and schizophrenia

Background

Autonomic nervous system (ANS) dysfunction and reduced heart rate variability (HRV) have been reported in a wide variety of psychiatric disorders, but have not been well characterized in bipolar mania. We recorded cardiac activity and assessed HRV in acutely hospitalized manic bipolar (BD) and schizophrenia (SCZ) patients compared to age- and gender-matched healthy comparison (HC) subjects.

Method

HRV was assessed using time domain, frequency domain, and nonlinear analyses in 23 manic BD, 14 SCZ, and 23 HC subjects during a 5 min rest period. Psychiatric symptoms were assessed by administration of the Brief Psychiatric Rating Scale (BPRS) and the Young Mania Rating Scale (YMRS).

Results

Manic BD patients demonstrated a significant reduction in HRV, parasympathetic activity, and cardiac entropy compared to HC subjects, while SCZ patients demonstrated a similar, but non-significant, trend towards lower HRV and entropy. Reduction in parasympathetic tone was significantly correlated with higher YMRS scores and the unusual thought content subscale on the BPRS. Decreased entropy was associated with increased aggression and diminished personal hygiene on the YMRS scale.

Conclusion

Cardiac function in manic BD individuals is characterized by decreased HRV, reduced vagal tone, and a decline in heart rate complexity as assessed by linear and nonlinear methods of analysis. Autonomic dysregulation is associated with more severe psychiatric symptoms, suggesting HRV dysfunction in this disorder may be dependent on the phase of the illness.     

Heart rate variability, sleep and sleep disorders

Heart rate (HR) is modulated by the combined effects of the sympathetic and parasympathetic nervous systems. Therefore, measurement of changes in HR over time (heart rate variability or HRV) provides information about autonomic functioning. HRV has been used to identify high risk people, understand the autonomic components of different disorders and to evaluate the effect of different interventions, etc. Since the signal required to measure HRV is already being collected on the electrocardiogram (ECG) channel of the polysomnogram (PSG), collecting data for research on HRV and sleep is straightforward, but applications have been limited. As reviewed here, HRV has been applied to understand autonomic changes during different sleep stages. It has also been applied to understand the effect of sleep-disordered breathing, periodic limb movements and insomnia both during sleep and during the daytime. HRV has been successfully used to screen people for possible referral to a Sleep Lab. It has also been used to monitor the effects of continuous positive airway pressure (CPAP). A novel HRV measure, cardiopulmonary coupling (CPC) has been proposed for sleep quality. Evidence also suggests that HRV collected during a PSG can be used in risk stratification models, at least for older adults. Caveats for accurate interpretation of HRV are also presented.     

Heart rate, tonic cardiac variability and evaluation

Heart rate (HR) and various measures of heart rate variability (HRV) were measured while 29 male and 15 female student volunteers individually rated slide stimuli presented in one-minute intervals. Ratings were factor analyzed and factor scores analyzed as variables. Factor one: “evaluation” accounted for 52.5% of the variances. HR and HRV were not significantly related to the experimental conditions although factor one was related. HR was correlated to measures of HRV [such as the coefficient of variability (CV), coefficient of temporal variability (CVT), a cosine function (FREQ) and to a lesser degree the auto-correlation (RA)]. HR also correlated linearly to evaluation. CVT, CV and RA were also linearly correlated to evaluation. HRV (BURST) was independent of HR, other forms of HRV, and curvilinearly related to evaluation. A cyclic HRV function (FREQ) was found with a mode of 18.7 sec and accounted for 21.4% of the variance of the heart beat data. This cyclic function, not reported previously, should be further investigated.     

Heart rate variability and autonomic dysfunction in SSPE

Autonomic nervous system involvement in subacute sclerosing panencephalitis was studied in 29 patients by analysis of heart rate variability and compared with a control group which consisted of 20 age- and sex-matched healthy subjects. Holter recordings for 24 hours were obtained, and all recordings were analyzed using time-domain parameters. The patients with subacute sclerosing panencephalitis were found to have significantly lower values of standard deviation of all normal sinus intervals and triangular index when compared with the control group. Of 23 patients who had regular follow-up, 15 died in a period ranging from 1 to 13 months. Twelve of these patients had heart rate variability parameters lower than normal, but no significant difference was observed between the heart rate variability values of patients who survived or died. Also, there was no association between brain magnetic resonance imaging findings and heart rate variability indices. It is concluded that patients with subacute sclerosing panencephalitis have autonomic dysfunction; and this was thought to be mainly due to central involvement.     

Heart rate variability in ischemic heart disease

Major untoward events, such as life-threatening arrhythmias and acute coronary events, have been suggested to be triggered by the activation of the autonomic nervous system in patients with coronary artery disease. Analysis of heart rate variability by conventional time and frequency domain methods, as well as by newer methods derived from nonlinear system theory, has offered a novel approach for studying the abnormalities in cardiovascular neural regulation in ischemic heart disease. Heart rate variability has been shown to be altered among patients with ischemic heart disease as compared to their age-matched controls without the evidence of ischemic heart disease. There are also obvious differences in various measures of heart rate variability between patients with uncomplicated coronary artery disease and those with coronary artery disease with complicated myocardial infarction. Impaired high-frequency oscillations of heart rate is the most prominent feature in patients with uncomplicated coronary artery disease, suggesting mainly an impairment in vagal autonomic regulation. Patients with prior myocardial infarction have a reduced overall heart rate variability, and a specific spectral pattern with a reduced low-frequency spectral component has been observed in patients with prior myocardial infarction and impaired left ventricular function. Recent studies have shown that the new nonlinear measures, particularly fractal analysis methods of heart rate dynamics, can detect subtle changes in heart rate behavior that are not easily detected by traditional analysis methods from ambulatory recordings. Patients with prior myocardial infarction have steeper power-law slope analyzed from the ultra and very low-frequency spectral bands, and they also have more random short-term heart rate dynamics analyzed by the detrended fluctuation method. A large body of data indicate that reduced overall heart rate variability is associated with an increased risk of mortality and nonfatal cardiac events in patient with ischemic heart disease. Of particular note, recent studies indicate that fractal analysis methods perform even better than the traditional analysis methods of heart rate variability as predictors of death and the onset of life-threatening arrhythmic events in post-infarction populations. These findings support the notion that heart rate variability analysis methods, such as fractal and complexity measures as well as conventional techniques, give valuable clinical information among patients with ischemic heart disease.     

Heart rate variability in premenstrual dysphoric disorder

Measuring heart rate variability (HRV) is a way to assess the autonomic regulation of the heart. Decreased HRV, indicating reduced parasympathetic tone, has previously been found in depression and anxiety disorders. The objective of this study was to assess HRV in women with premenstrual dysphoric disorder (PMDD). To this end, time domain variables and frequency domain variables were assessed in 28 women with PMDD and in 11 symptom-free controls during both the symptomatic luteal phase and the non-symptomatic follicular phase of the menstrual cycle. Two variables reflecting vagal activity in the time domain, the root mean square of differences of successive normal RR intervals (rMSSD) and standard deviation of normal RR intervals (SDNN) were lower in PMDD patients, but this difference was statistically significant in the follicular phase only. The most important vagal measure in the frequency domain, supine high frequency (HF), also appeared lower in PMDD subjects during the follicular phase. It is suggested that PMDD may be associated with reduced vagal tone compared to controls and that this difference is most apparent in the non-symptomatic follicular phase of the menstrual cycle.     

Heart rate variability in facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is the third most frequent form of muscular dystrophy. Heart rate variability (HRV) analysis is a means of evaluating the activity of the autonomic nervous system. The aim of this study was to evaluate HRV in FSHD patients. Fifty-five consecutive FSHD patients were enrolled (31 men, age 26-72 years). Muscular impairment was measured using a clinical severity scale (CSS). Patients were compared with a control group of 55 healthy subjects, matched for age and sex. HRV was analyzed in the time domain and in the frequency domain. Patients showed increased spectral power of the low-frequency band. Spectral power of the high-frequency band was inversely correlated with CSS score. FSHD is associated with a slight increase in sympathetic output and with a decrease in parasympathetic output. These modifications become more evident with the progression of the disease and could increase the risk of arrhythmias and other cardiovascular events.