Ratio Of RR Interval Research Articles

Suitability of Ultra-Short-Term Heart Rate Variability in Military Trainees.

We aimed to (a) evaluate the agreement between ultra-short-term and criterion resting heart rate variability (HRV) measures in military trainees, and (b) compare associations between HRV recording lengths and body composition. HRV recordings were performed for 10 min in 27 military male students. Mean RR interval, the root-mean square of successive differences (RMSSD), RMSSD:RR interval ratio, standard deviation of normal-to-normal RR intervals (SDNN), and SDNN:RR interval ratio were determined from the last 5 min of the 10-min recording and considered the criterion. Parameters were also recorded in successive 1-min epochs from the 5-min stabilization period. No differences were observed between criterion values and any of the 1-min epochs (p > 0.05). Effect sizes ranged from −0.36–0.35. Intra-class correlations ranged from 0.83–0.99. Limits of agreement ranged from 38.3–78.4 ms for RR interval, 18.8–30.0 ms for RMSSD, 1.9–3.1 for RMSSD:RR, 24.1–31.4 ms for SDNN, and 2.5–3.0 for SDNN:RR. Body fat% was associated (p < 0.05) with all HRV parameters at varying time segments. A 1-min HRV recording preceded by a 1-min stabilization period seems to be a suitable alternative to criterion measures. Ultra-short procedures may facilitate routine HRV tracking in tactical populations for status-monitoring purposes.

Heart rate-adjusted PR as a prognostic marker of long-term ventricular arrhythmias and cardiac death in ICD/CRT-D recipients.

ObjectiveTo evaluate the PR to RR interval ratio (PR/RR, heart rate-adjusted PR) as a prognostic marker for long-term ventricular arrhythmias and cardiac death in patients with implantable cardioverter defibrillator (ICDs) and cardiac resynchronization therapy with defibrillators (CRT-D).MethodsWe retrospectively analyzed data from 428 patients who had an ICD/CRT-D equipped with home monitoring. Baseline PR and RR interval data prior to ICD/CRT-D implantation were collected from standard 12-lead electrocardiograph, and the PR/RR was calculated. The primary endpoint was appropriate ICD/CRT-D treatment of ventricular arrhythmias (VAs), and the secondary endpoint was cardiac death.ResultsDuring a mean follow-up period of 38.8 ± 10.6 months, 197 patients (46%) experienced VAs, and 47 patients (11%) experienced cardiac death. The overall PR interval was 160 ± 40 ms, and the RR interval was 866 ± 124 ms. Based on the receiver operating characteristic curve, a cut-off value of 18.5% for the PR/RR was identified to predict VAs. A PR/RR ≥ 18.5% was associated with an increased risk of VAs [hazard ratio (HR) = 2.243, 95% confidence interval (CI) = 1.665–3.022, P < 0.001) and cardiac death (HR = 2.358, 95%CI = 1.240–4.483, P = 0.009) in an unadjusted analysis. After adjustment in a multivariate Cox model, the relationship remained significant among PR/RR ≥ 18.5%, VAs (HR = 2.230, 95%CI = 1.555–2.825, P < 0.001) and cardiac death (HR = 2.105, 95%CI = 1.101–4.025, P = 0.024.ConclusionsA PR/RR ≥ 18.5% at baseline can serve as a predictor of future VAs and cardiac death in ICD/CRT-D recipients.

Autonomic Dysfunction in Wilson's Disease: A Comprehensive Evaluation during a 3-Year Follow Up.

Objectives: Wilson's disease is reported to have autonomic dysfunction, but comprehensive evaluation of autonomic function is lacking. Additionally, little is known about the change of autonomic function of Wilson's disease during continuous therapy. We assumed that patients with Wilson's disease had both sympathetic and parasympathetic autonomic impairments, and the autonomic dysfunction might be stable across a 3-year follow-up after years of optimal treatment.Methods: Twenty-six patients with Wilson's disease and twenty-six healthy controls were recruited. Twenty patients in the Wilson's disease group were examined again after a 3-year follow-up. All the participants were evaluated by a questionnaire on dysautonomia symptoms, 24-h blood pressure and heart rate monitoring, and cardiovascular autonomic function examination in various conditions including at rest, deep breathing, Valsalva maneuver, isometric handgrip test and passive tilting. Baroreflex sensitivity and spectral analyses were performed via trigonometric regressive spectral analysis.Results: Patients with Wilson's disease showed autonomic dysfunction mainly in the following aspects: (1) the heart rate was higher than the controls. (2) Valsalva ratio was lower in patients with Wilson's disease compared with the controls. (3) Heart rate increase during isometric hand gripping was smaller in the Wilson's disease patients than the controls. (4) Baroreflex sensitivity was lower during nearly all the cardiovascular autonomic function examinations compared with healthy controls. When tested 3 years later, baroreflex sensitivity at rest decreased compared with baseline. (5) There were mild declines of resting DBP and low frequency component of heart rate variability during the follow-up examination compared with baseline. (6) Subgroup analysis showed that patients initially presenting with neurological symptoms had a higher night-time heart rate, lower expiration: inspiration RR interval ratio (E/I ratio), lower expiration: inspiration RR interval difference (E-I difference), less increase of heart rate and diastolic blood pressure during the handgrip test, and lower baroreflex sensitivity during deep breathing than the control group. (7) Correlation analysis showed that the severity of neurological symptoms was associated with E/I ratio, E-I difference, Valsalva ratio, heart rate change during the handgrip test, and baroreflex sensitivity during deep breathing.Conclusions: The present study reveals cardiovascular autonomic dysfunction involving both sympathetic and parasympathetic branches in Wilson's disease patients, which is especially significant in the patients with neurological onset. Autonomic function is generally stable undergoing optimal maintenance treatment in patients with Wilson's disease. Though there might be mild changes of specific parameters.

Correlations between the Signal Complexity of Cerebral and Cardiac Electrical Activity: A Multiscale Entropy Analysis

The heart begins to beat before the brain is formed. Whether conventional hierarchical central commands sent by the brain to the heart alone explain all the interplay between these two organs should be reconsidered. Here, we demonstrate correlations between the signal complexity of brain and cardiac activity. Eighty-seven geriatric outpatients with healthy hearts and varied cognitive abilities each provided a 24-hour electrocardiography (ECG) and a 19-channel eye-closed routine electroencephalography (EEG). Multiscale entropy (MSE) analysis was applied to three epochs (resting-awake state, photic stimulation of fast frequencies (fast-PS), and photic stimulation of slow frequencies (slow-PS)) of EEG in the 1–58 Hz frequency range, and three RR interval (RRI) time series (awake-state, sleep and that concomitant with the EEG) for each subject. The low-to-high frequency power (LF/HF) ratio of RRI was calculated to represent sympatho-vagal balance. With statistics after Bonferroni corrections, we found that: (a) the summed MSE value on coarse scales of the awake RRI (scales 11–20, RRI-MSE-coarse) were inversely correlated with the summed MSE value on coarse scales of the resting-awake EEG (scales 6–20, EEG-MSE-coarse) at Fp2, C4, T6 and T4; (b) the awake RRI-MSE-coarse was inversely correlated with the fast-PS EEG-MSE-coarse at O1, O2 and C4; (c) the sleep RRI-MSE-coarse was inversely correlated with the slow-PS EEG-MSE-coarse at Fp2; (d) the RRI-MSE-coarse and LF/HF ratio of the awake RRI were correlated positively to each other; (e) the EEG-MSE-coarse at F8 was proportional to the cognitive test score; (f) the results conform to the cholinergic hypothesis which states that cognitive impairment causes reduction in vagal cardiac modulation; (g) fast-PS significantly lowered the EEG-MSE-coarse globally. Whether these heart-brain correlations could be fully explained by the central autonomic network is unknown and needs further exploration.

New method to measure and improve consistency of baroreflex sensitivity values

Baroreflex sensitivity (BRS) is an important prognostic index in cardiovascular diseases, however, its use is complicated by different methods difficult to compare and standardize, often providing conflicting results. We tested whether the simple ratio of RR interval to systolic blood pressure global variabilities (assessed by standard deviations) is a reliable measure of BRS, by measuring the agreement with six established methods. In addition, we tested whether high-pass filtering of data, by removing slow non-baroreflex-mediated fluctuations, could improve the agreement between different BRS methods. In 1,409 subjects, we compared 6 established methods (derived by cross-spectral and sequence analysis) and the new method, supine and in response to tilting (1,175 subjects). Data were analyzed after linear detrending, high-pass filtering at 0.025 and 0.05Hz. Although all seven methods showed a general agreement, the new method consistently showed the lowest distance from the median of the remaining methods (0.04±0.06ms/mmHg over 2,584 files, p<0.05 with respect to the second best method). High-pass filtering improved (p<0.001) the agreement between methods without reducing the sensitivity to changes induced by tilting. Only the new method could provide estimates in all 2,584 files tested. The new method intercepts the mean information of all other methods better than any other method, hence providing a simple, easy to standardize (no mathematical constraints) and yet robust and reliable BRS estimate. High-pass filtering markedly improves the agreement of all methods, without loss of sensitivity, and could be routinely used in clinical trials, to provide comparable BRS estimates.

Hemodynamic response to lower body negative pressure in children: A pilot study

Although head-up tilt and upright standing are common methods used to induce orthostatic stress, lower body negative pressure (LBNP) is another safe and easy technique that induces orthostatic stress independently of gravity. However, the use of LBNP in children has never been investigated. The purpose of this pilot study was to determine whether LBNP was capable of inducing hemodynamic adaptations in pre-pubertal boys. Ten healthy pre-pubertal boys (9 ± 1 years) were recruited and randomly exposed to 3 levels of LBNP (15, 20 and 25 mm Hg). Heart rate, manual and beat-by-beat systolic (SBP), diastolic and mean arterial blood pressure were monitored continuously. Aortic diameter was measured at rest and peak aortic blood velocity was recorded continuously for at least 1 min during each condition. R–R interval (RRI), heart rate, stroke volume (SV), cardiac output ( Q), total peripheral resistance (TPR), low frequency (LF) and high frequency (HF) baroreceptor sensitivity (BRS), as well as LF/HF RRI ratio were calculated. With increasing LBNP TPR increased while SBP decreased ( P ≤ 0.05). As well, a trend towards a decrease in SV ( P = 0.054) and Q ( P = 0.06) was found. However, LF and HF BRS, and LF/HF RRI ratio did not significantly change from baseline to LBNP 15, 20 or 25 mm Hg. In conclusion, the results of this pilot study suggest that low levels of LBNP are capable of inducing hemodynamic adaptations in children that are to be expected when undergoing an orthostatic stress. As well, LBNP is a safe and effective method of inducing orthostatic stress in children.

Effects of long-term angiotensin converting enzyme inhibition on cardiovascular variability in aging rats

We studied the effects of chronic (4 weeks) angiotensin converting enzyme inhibition with captopril on arterial pressure (AP) and heart rate (HR) variability, as well as on cardiac baroreflex sensitivity (BRS), in aged (20 months) rats. Series of basal RR interval (RRi) and systolic AP (SAP) were studied by autoregressive spectral analysis with oscillations quantified in low (LF: 0.2–0.8 Hz) and high frequency (HF: 0.8–2.5 Hz). BRS was measured by linear regression between HR and MAP changes. Captopril did not affect the spectra of RRi or SAP in young rats. Aged rats presented a reduction in variance (time domain) and in LF and HF oscillations of RRi and SAP. Captopril induced, in aged rats, a decrease in absolute and normalized LF oscillations and in LF/HF ratio of RRi. Captopril also reduced the variance, without changing its LF or HF components of SAP. Reflex tachycardia was reduced in aged as compared to young rats (− 1.1 ± 0.2 versus − 3.4 ± 0.5 bpm/mm Hg) and captopril did not affect it. Reflex bradycardia was also reduced in aged rats (− 0.7 ± 0.5 versus − 2.0 ± 0.4 bpm/mm Hg), but captopril prevented this attenuation in aged rats (− 2.3 ± 0.3 versus − 0.7 ± 0.5 bpm/mm Hg). These data indicate that there is a reduction in HR and SAP variability during aging, suggesting impairment of cardiovascular autonomic control. Captopril was able to change the power of oscillatory components of RRi, suggesting a shift in cardiac sympatho/vagal balance toward parasympathetic predominance. In addition, blockage of ACE improved the reflex bradycardia, but not the reflex tachycardia in aged rats.

Enhanced central hypercapnic chemosensitivity is related to autonomic imbalance in patients with heart failure

Purpose: The role of central hypercapnic chemosensitivity in autonomic imbalance remains obscure in patients with heart failure. The purpose of this study is to elucidate whether enhanced central hypercapnic chemosensitivity is related to sympathetic activation and parasympathetic withdrawal in this syndrome. Methods: In 40 patients with chronic heart failure, the central hypercapnic chemosensitivity and plasma norepinephrine were measured in the supine resting position. A stationary 6-minute period tracings of blood pressure and electrocardiogram served for measurements of high-frequency(HF) components of heart rate variability and the α-index, the ratio of RR interval and systolic blood pressure variability. Results: The patients with increased sympathetic tone showed a greater chemosensitivity and a resultant augmentation in exercise ventilation. In contrast, the chemosensitivity had an inverse relationship with HF power of heart rate variability (r = −0.38, p < 0.05) and the α-index (r = −0.41, p < 0.01). There were no significant correlations between the hypercapnic chemosensitivity and left ventricular function and between the chemosensitivity and exercise capacity. Conclusions: The enhanced central hypercapnic chemoreflex would potentially underlie autonomic imbalance in patients with chronic heart failure.

Effect of passive tilt on sympathetic and parasympathetic components of heart rate variability in normal subjects

Decreased heart rate (HR) variability has been shown to be an independent predictor of poor outcome after acute myocardial infarction. Presumably, both reduced parasympathetic activity and increased sympathetic activity contribute to this observed HR variability response. To elucidate the physiologic contributions of the sympathetic and parasympathetic nervous systems to HR variability, the effect of passive head-up tilt (+70 °) was investigated on 4 indexes of HR variability in 17 healthy subjects. The standard deviation of the mean of 512 consecutive RR intervals, a traditional marker of HR variability and a purported index of cardiac parasympathetic neural tone, was compared with the mean difference of 512 consecutive RR intervals, with the maximal expiratory RR interval to minimal inspiratory RR interval ratio (respiratory RR ratio) and with the low- and high-frequency components of the power spectrum of 512 consecutive RR intervals. Passive tilt produced a nonsignificant decrease in the standard deviation of RR intervals. There was, however, a highly significant decrease in the mean difference of consecutive RR intervals and the high-frequency component of the RR-interval spectrum. Both the respiratory RR ratio and the low-frequency component of the RR-interval spectrum increased with tilt. It was concluded that the mean difference of consecutive RR intervals and the high-frequency component of the RR-interval spectrum are potentially superior indexes of “pure” parasympathetic neural tone and may be preferable for future use in cardiovascular studies of autonomic dysfunction.