High-frequency Power Of Heart Rate Variability Research Articles

Differences in heart rate responses to upright posture are associated with variations in the high-frequency power of heart rate variability.

High resting heart rate is a cardiovascular risk factor, but limited data exist on the underlying hemodynamics and reproducibility of supine-to-upright increase in heart rate. We recorded noninvasive hemodynamics in 574 volunteers [age, 44.9 yr; body mass index (BMI), 26.4 kg/m2; 49% male] during passive head-up tilt (HUT) using whole body impedance cardiography and radial artery tonometry. Heart rate regulation was evaluated using heart rate variability (HRV) analyses. Comparisons were made between quartiles of supine-to-upright heart rate changes, in which heart rate at rest ranged 62.6-64.8 beats/min (P = 0.285). The average upright increases in heart rate in the quartiles 1-4 were 4.7, 9.9, 13.5, and 21.0 beats/min, respectively (P < 0.0001). No differences were observed in the low-frequency power of HRV, whether in the supine or upright position, or in the high-frequency power of HRV in the supine position. Upright high-frequency power of HRV was highest in quartile 1 with lowest upright heart rate and lowest in quartile 4 with highest upright heart rate. Mean systolic blood pressure before and during HUT (126 vs. 108 mmHg) and the increase in systemic vascular resistance during HUT (650 vs. 173 dyn·s/cm5/m2) were highest in quartile 1 and lowest in quartile 4. The increases in heart rate during HUT on three separate occasions several weeks apart were highly reproducible (r = 0.682) among 215 participants. To conclude, supine-to-upright increase in heart rate is a reproducible phenotype with underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. As heart rate at rest influences prognosis, future research should elucidate the prognostic significance of these phenotypic differences.NEW & NOTEWORTHY Subjects with similar supine heart rates are characterized by variable increases in heart rate during upright posture. Individual heart rate increases in response to upright posture are highly reproducible as hemodynamic phenotypes and present underlying differences in the modulation of cardiac parasympathetic tone and systemic vascular resistance. These results indicate that resting heart rate obtained in the supine position alone is not an optimal means of classifying people into groups with differences in cardiovascular function.

The Association Between Heart Rate Variability and Quality of Life in Patients with Functional Somatic Syndrome and Healthy Controls.

Functional somatic syndrome (FSS) includes a spectrum of somatic symptoms with insufficient medical explanation. Its underlying pathophysiology is considered to include dysfunctional stress-responsive systems or autonomic dysfunction. Among the autonomic dysfunction readouts, decreased heart rate variability (HRV) has been shown to be characteristic in patients with FSSs. However, its association with quality of life (QOL) has not been clearly examined. We examined the association between short-term resting HRV and QOL in patients with FSS (n = 47) and healthy controls (n = 28). The time domain parameters of HRV were mean heart rate per minute (HR), coefficient of variation of R-R intervals (CvRR) and root mean square of successive differences (RMSSD). The frequency domain parameters of HRV were low-frequency (LF) power and high-frequency (HF) power by power spectrum analysis. The Japanese version of the WHO's QOL scale (WHOQOL-BREF) (WHO/QOL26) was used for the QOL assessment. There was a significant positive association between the RMSSD and HF power of HRV and all the QOL domains in patients with FSSs who had lower QOL scores on average than controls, while there was no association between HRV and any of the QOL domains in the control group. HF power was more dominantly associated with QOL than the other variables in patients with FSS based on the analysis with a multiple linear regression model. The present study elucidated that the HF power of HRV was dominantly associated with QOL in patients with FSSs who had lower QOL than controls. Vagal index of HRV could be a valuable indicator of the pathological condition and a significant predictor of health-related QOL in patients with FSSs.

Shift Work and Heart Rate Variability Coherence: Pilot Study Among Nurses

This study used ambient heart rate monitoring among health care workers to determine whether a novel measure of heart rate variability (HRV), as well as sleep disturbances, fatigue, or cognitive performance differed among non-rotating night shift nurses relative to those working permanent day shifts. Continuous ambulatory HRV monitoring was performed among night nurses (n = 11), and a comparison group of permanent day nurses (n = 7), over a 36-h period coinciding with the last two 12-h shifts of each participant’s work week. Symptoms and psychomotor vigilance were assessed at the end of the ambient HRV monitoring period, and no differences between shifts were observed. Day nurses exhibited an increase in hourly mean HRV coherence ratios during their sleep period, suggesting a circadian pattern of cardiorespiratory phase coupling, whereas night nurses had no increase in HRV coherence ratios during their sleep period. The HRV coherence patterns were similar to high frequency HRV power among nurses on the same shift. To the authors knowledge, this study was the first to quantify patterns of the HRV coherence ratio among shiftworkers in a non-experimental (work/home) setting. The results suggest a pattern of autonomic dysregulation among night workers during their sleep period relative to those working day shifts. The HRV coherence ratio may serve as a novel indicator of HRV dysregulation among shift workers.

Chronic pain-related changes in cardiovascular regulation and impact on comorbid hypertension in a general population: the Tromsø study

Heart rate variability (HRV) and baroreflex sensitivity (BRS) are indexes reflecting the ability to maintain cardiovascular homeostasis amidst changing conditions. Evidence primarily from small studies suggests that both HRV and BRS may be reduced in individuals with chronic pain (CP), with potential implications for cardiovascular risk. We compared HRV and BRS between individuals with CP (broadly defined) and pain-free controls in a large unselected population sample. Participants were 1143 individuals reporting clinically meaningful CP and 5640 pain-free controls who completed a 106-second cold pressor test (CPT). Participants self-reported hypertension status. Resting HRV and BRS were derived from continuous beat-to-beat blood pressure recordings obtained before and after the CPT. Hierarchical regressions for the pre-CPT period indicated that beyond effects of age, sex, and body mass index, the CP group displayed significantly lower HRV in both the time domain (SDNN and rMSSD) and frequency domain (high-frequency HRV power), as well as lower BRS. Results were somewhat weaker for the post-CPT period. Mediation analyses indicated that for 6 of 7 HRV and BRS measures tested, there were significant indirect (mediated) effects of CP status on the presence of comorbid hypertension via reduced HRV or BRS. Results confirm in the largest and broadest sample tested to date that the presence of CP is linked to impaired cardiovascular regulation and for the first time provide support for the hypothesis that links between CP and comorbid hypertension reported in previous population studies may be due in part to CP-related decrements in cardiovascular regulation.

Aromatic effects of a Japanese citrus fruit-yuzu (Citrus junos Sieb. ex Tanaka)-on psychoemotional states and autonomic nervous system activity during the menstrual cycle: a single-blind randomized controlled crossover study.

BackgroundYuzu (Citrus junos Sieb. ex Tanaka), a yellow-golden colored citrus fruit, has traditionally been used to promote psychosomatic health in Japan. While the yuzu produces a distinctive, pleasing aroma of citrus and floral, the efficacy of its fragrance remains unknown. The present study investigated the soothing effects of the fragrance of yuzu essential oil from the perspective of autonomic nervous system activity, which plays a crucial role in the integrity of the mind-body connection.MethodsTwenty one women in their 20s participated in a single-blind randomized controlled crossover study. Subjects were examined twice each in the follicular and late-luteal phases. Two kinds of aromatic stimulation (yuzu and water as a control) were used. This experiment measured heart rate variability (HRV) reflecting autonomic nervous system activity and used the Profile of Mood States (POMS) as a psychological index before and after the aromatic stimulation.ResultsOnly a 10-min inhalation of the yuzu scent significantly decreased heart rate and increased high frequency power of HRV reflecting parasympathetic nervous system activity, regardless of menstrual phase. This significant physiological effect continued for at least 25 min. In addition, the POMS tests revealed that inhalation of the aromatic yuzu oil significantly decreased total mood disturbance, a global measure of affective state, together with two POMS subscales—tension-anxiety and fatigue, as long as 35 min after the aroma stimulation, both in the symptomatic late-luteal and non-symptomatic follicular phases.ConclusionsThe present study provides the novel information that yuzu’s aromatic effects could serve to alleviate negative emotional stress, which, at least in part, would contribute to the improvement of parasympathetic nervous system activity.

Female Listeners' Autonomic Responses to Dramatic Shifts Between Loud and Soft Music/Sound Passages: A Study of Heavy Metal Songs.

Although music and the emotion it conveys unfold over time, little is known about how listeners respond to shifts in musical emotions. A special technique in heavy metal music utilizes dramatic shifts between loud and soft passages. Loud passages are penetrated by distorted sounds conveying aggression, whereas soft passages are often characterized by a clean, calm singing voice and light accompaniment. The present study used heavy metal songs and soft sea sounds to examine how female listeners’ respiration rates and heart rates responded to the arousal changes associated with auditory stimuli. The high-frequency power of heart rate variability (HF-HRV) was used to assess cardiac parasympathetic activity. The results showed that the soft passages of heavy metal songs and soft sea sounds expressed lower arousal and induced significantly higher HF-HRVs than the loud passages of heavy metal songs. Listeners’ respiration rate was determined by the arousal level of the present music passage, whereas the heart rate was dependent on both the present and preceding passages. Compared with soft sea sounds, the loud music passage led to greater deceleration of the heart rate at the beginning of the following soft music passage. The sea sounds delayed the heart rate acceleration evoked by the following loud music passage. The data provide evidence that sound-induced parasympathetic activity affects listeners’ heart rate in response to the following music passage. These findings have potential implications for future research on the temporal dynamics of musical emotions.

Orthostatic Stress Induced Changes in Heart Rate Variability, Pulse Transit Time and QRS Duration

Studies have shown the application of non-invasive cardiovascular parameters like heart rate variability (HRV), pulse transit time (PTT) and QRS duration. However no information is available about effects of orthostatic stress on these parameters. Our objective was to study the changes in HRV, PTT and QRS duration caused by orthostatic stress. Electrocardiogram (ECG) and photoplethysmogram (PPG) data was collected from 22 subjects in supine and upright positions. Comparison of parameters in supine and upright positions revealed that every parameter was effected by orthostatic stress. High frequency power of HRV showed the largest response (75%), while QRS duration had the smallest response of (7%). We found that gender played a significant role in PTT, R-R interval and QRS duration values, with male subjects showing higher values of all three parameters. Subject height also played a distinguishing role, with taller subjects showing higher values of R-R interval and PTT. The results allow us to better understand the interaction between various parameters and how they reflect the hemodynamic changes caused by orthostatic stress.

Efficacy of paced breathing for insomnia: enhances vagal activity and improves sleep quality.

Fourteen self-reported insomniacs (SRI) and 14 good sleepers (GS) had their cardiac neuronal activity assessed by heart rate variability (HRV) under controlled respiration at a slow frequency rate of 0.1 Hz, and a forced rate of 0.2 Hz during daytime rest. Nighttime sleep was measured by polysomnography. The SRI showed depressed high frequency power of HRV compared to the GS. An increased total power of HRV was observed among the SRI during slow, paced breathing compared with spontaneous breathing and 0.2 Hz. Sleep onset latency, number of awakenings, and awakening time during sleep were decreased and sleep efficiency was increased if SRI practiced slow, paced breathing exercises for 20 min before going to sleep. Our results indicate that there is autonomic dysfunction among insomniacs, especially in relation to vagal activity; however, this decreased vagal activity can be facilitated by practicing slow, paced breathing, thereby improving sleep quality.

Non-linear HRV indices under autonomic nervous system blockade.

Heart rate variability (HRV) has been studied as a non-invasive technique to characterize the autonomic nervous system (ANS) regulation of the heart. Non-linear methods based on chaos theory have been used during the last decades as markers for risk stratification. However, interpretation of these nonlinear methods in terms of sympathetic and parasympathetic activity is not fully established. In this work we study linear and non-linear HRV indices during ANS blockades in order to assess their relation with sympathetic and parasympathetic activities. Power spectral content in low frequency (0.04-0.15 Hz) and high frequency (0.15-0.4 Hz) bands of HRV, as well as correlation dimension, sample and approximate entropies were computed in a database of subjects during single and dual ANS blockade with atropine and/or propranolol. Parasympathetic blockade caused a significant decrease in the low and high frequency power of HRV, as well as in correlation dimension and sample and approximate entropies. Sympathetic blockade caused a significant increase in approximate entropy. Sympathetic activation due to postural change from supine to standing caused a significant decrease in all the investigated non-linear indices and a significant increase in the normalized power in the low frequency band. The other investigated linear indices did not show significant changes. Results suggest that parasympathetic activity has a direct relation with sample and approximate entropies.

Heart rate variablity indices are poor predictors of exercise capacity in healthy type 1 diabetics (LB664)

People with diabetes often have chronotropic incompetence and reduced exercise tolerance. Chronotropic incompetence has been associated with autonomic dysfunction, thus we determined the ability of resting heart rate variability (HRV) to predict an altered exercise response in healthy individuals with type 1 diabetes (T1D). Baseline measures were taken followed by quantification of HRV with power spectral analysis during controlled breathing (15 breaths·min‐1) in 20 T1D (10 male &amp; 10 female) screened for ischaemic cardiac disease and 12 age‐, weight‐, and training‐matched non‐diabetics (CON: 7 male &amp; 5 female). These measurements were followed by a VO2max test (with ECG). Resting HR (73 ± 10 vs. 64 ± 10 beats·min‐1; P = 0.01) was higher and mean arterial blood pressure (92 ± 12 vs. 90 ± 11 mm Hg; P = 0.68) was not different between T1D and CON respectively. HR reserve (104 ± 17 vs. 121 ± 11 beats·min‐1; P &lt; 0.001), VO2max (31 ± 9 vs. 41 ± 9 mL·min‐1·Kg‐1; P =0.005), HRV total power (1317 ± 1146 vs. 7493 ± 15080 ms2; P = 0.024), and HRV high frequency power (441 ± 491 vs. 3840 ± 9883 ms2; P = 0.029) were lower in T1D vs. CON respectively. Absolute max HR (177 ± 15 vs. 185 ± 10 beats·min‐1; P = 0.09), % of age predicted max HR (95 ± 6 vs. 97 ± 2 %; P = 0.07), and HRV low frequency power (328 ± 279 vs. 1672 ± 3433 ms2; P = 0.09) were not different in T1D vs. CON respectively. Despite group differences in HRV, linear correlations showed that resting HRV total, high frequency, and low frequency power accounted for &lt; 20% of the variability in resting HR, HR reserve, max HR, and VO2max in T1D. Resting HRV indices are poor predictors of cardiovascular exercise response in healthy T1D.Grant Funding Source: Supported by Anderson's trust

Short-Term Stability of Sleep and Heart Rate Variability in Good Sleepers and Patients with Insomnia: For Some Measures, One Night is Enough

Quantify the short-term stability of multiple indices of sleep and nocturnal physiology in good sleeper controls and primary insomnia patients. Intra-class correlation coefficients (ICC) were used to quantify the short-term stability of study outcomes. Sleep laboratory. Fifty-four adults with primary insomnia (PI) and 22 good sleeper controls (GSC). Visually scored sleep outcomes included indices of sleep duration, continuity, and architecture. Quantitative EEG outcomes included power in the delta, theta, alpha, sigma, and beta bands during NREM sleep. Power spectral analysis was used to estimate high-frequency heart rate variability (HRV) and the ratio of low- to high-frequency HRV power during NREM and REM sleep. With the exception of percent stage 3+4 sleep; visually scored sleep outcomes did not exhibit short-term stability across study nights. Most QEEG outcomes demonstrated short-term stability in both groups. Although power in the beta band was stable in the PI group (ICC = 0.75), it tended to be less stable in GSCs (ICC = 0.55). Both measures of cardiac autonomic tone exhibited short-term stability in GSCs and PIs during NREM and REM sleep. Most QEEG bandwidths and HRV during sleep show high short-term stability in good sleepers and patients with insomnia alike. One night of data is, thus, sufficient to derive reliable estimates of these outcomes in studies focused on group differences or correlates of QEEG and/or HRV. In contrast, one night of data is unlikely to generate reliable estimates of PSG-assessed sleep duration, continuity or architecture, with the exception of slow wave sleep.

Heart Rate Variability and Psychological Recovery from Exhaustive Exercise: an Exploratory Investigation

PURPOSE: Increased high frequency (HF) modulation of heart rate variability (HRV) is associated with high cardiac parasympathetic tone, while low HRV has been linked to a variety of chronic negative affective states, as well as mood disturbance following exercise withdrawal (Weinstein et al., 2007). Therefore, HRV has the potential to explain interindividual variability in anxiety and affective responses to acute exhaustive exercise, independent of cardiovascular fitness (which is also associated with high HRV). METHODS: Ten male and ten female healthy participants (age 30.7 ± 9.26 years) completed an incremental exercise test to volitional exhaustion. Participants were fitted with a Lead II ECG at rest for 20 min pre-exercise to collect HRV data. Assessments of affect (Activation-Deactivation Adjective Check List) and anxiety (State Anxiety Inventory) were made pre-exercise (pre-ex) and 10 minutes post-exercise (post-ex). Peak oxygen consumption (VO2peak; ml.kg.min-1) was measured using indirect calorimetry. RESULTS: From pre- to post-ex, significant (p<.01) reductions in calmness (13.85 ± 3.33 vs. 10.45 ± 4.24) and tiredness (11.9 ± 4.18 vs. 7.65 ± 2.72) were observed, as was an increase in energy (10.25 ± 4.38 vs. 15.35 ± 3.39). The impact of the normalized HF HRV power on post-ex affect and anxiety were assessed using a series of hierarchical regression analyses. Controlling for fitness and baseline affect or anxiety, results indicated that HF HRV power explained variation in post-ex calmness (B =.517; R2change = 0.264; p<.05) and state anxiety (B = -.493; R2change = 0.223; p<.05). CONCLUSION: Normalized HF HRV was positively associated with calmness and negatively associated with anxiety after exhaustive exercise, when baseline fitness and calmness/anxiety were controlled for. These preliminary data suggest that variation in cardiac parasympathetic modulation may help explain some individual variability in the post-exercise recovery of affective states.

Heart rate and heart rate variability in subjectively reported insomnia

According to epidemiological studies, insomnia is associated with cardiovascular mortality. However, it is yet to be determined whether this link is mediated by known cardiovascular risk factors. The current study aimed at investigating the association between primary insomnia, defined as subjectively reported sleep disturbance in the absence of any other pathology or substance intake, and alterations in polysomnographically determined nocturnal heart rate (HR) and heart rate variability (HRV). A total of 4,581 nocturnal short-term electrocardiographic recordings (5 min each) from 104 participants (58 with primary insomnia, 46 healthy controls) were evaluated for HR as well as for time and frequency domain measures of HRV. In the primary insomnia group, we found a lower wake-to-sleep HR reduction and a lower standard deviation of RR intervals (SDNN) compared to healthy controls. However, between-group differences in resting HR were not found, and previous results of an increase in sympathovagal balance and a decrease in parasympathetic nocturnal activity in objectively determined insomnia could not be confirmed in our sample of self-report insomnia patients. When restricting our analyses to insomnia patients with objectively determined short sleep duration, we found reduced parasympathetic activity as indicated by decreased high frequency power of HRV, as well as decreased root mean square of successive RRI differences (RMSSD) and percentage of successive RRIs that differ by more than 50 ms (pNN50) values. A lower wake-to-sleep HR reduction and alterations in HRV variables might, at least partially, mediate the increased rates of cardiovascular morbidity and mortality observed in insomnia patients.

The Effects of a Brief Relaxation Program on Symptom Distress and Heart Rate Variability in Cancer Patients

To determine whether a 15-minute, one-time guided relaxation program for cancer patients could improve symptom distress as measured by the Edmonton Symptom Assessment System (ESAS). In addition, we were interested in characterizing the changes of the autonomic nervous system, as demonstrated by heart rate variability (HRV) high-frequency (HF) spectral analysis, before and after this relaxation program. Nonrandomized pilot study. Comprehensive cancer center. Twenty cancer patients underwent a 15-minute relaxation program. The ESAS and a 5-minute HRV recording were completed before and after the relaxation program. The differences between the pre- and post-summed ESAS score and HRV values were compared by a paired t-test. The summed ESAS scores were significantly lower after the relaxation program (P<.01), with an average 31% decrease in total score. However, no differences were found in HRV HF power. There was no correlation between the change in HRV HF and change in symptom distress, as measured by ESAS. A brief guided relaxation program can significantly improve symptoms as measured by ESAS. More research is required to understand the effects of relaxation on HF HRV power.

Heart rate variability is related to impaired haemorheology in older women with type 2 diabetes

Impaired heart rate variability (HRV)and haemorheology are independently associated with cardiovascular disease and diabetic complications. The aim of the present study was to investigate the relationships between parameters of HRV,and red blood cell (RBC) aggregation and deformability, in older women with type 2 diabetes. Twenty women (age 69 ± 2 yr) with uncomplicated type 2 diabetes and twenty controls (age 69 ± 3 yr) participated in the study. Beat-to-beat cardiac (RR) intervals over 5 min were analysed for HRV parameters in the time and frequency domains. Blood was sampled for RBC deformability, as well as RBC aggregation in two suspending mediums: haematocrit adjusted plasma and 3% dextran 70. RBC aggregation was increased and HRV was impaired for those with type 2 diabetes when compared with control. RBC aggregation was negatively related to low frequency power of HRV, and was positively related to high frequency power of HRV, for subjects with type 2 diabetes. RBC deformability was positively related to HRV only for those with type 2 diabetes. Impaired haemorheology is associated with reduced HRV in older women with type 2 diabetes, suggesting changes in the microcirculation may result in impaired modulation of cardiac cycles.

The effects of a brief relaxation program on heart rate variability in cancer patients

e20713 Background: Objectives were: (1) To characterize the physiologic changes of the autonomic nervous system, demonstrated by heart rate variability (HRV) high frequency (HF) spectral analysis, before and after a 15 minute, one-time, guided relaxation program for cancer patients. (2) To assess whether changes of HRV correlate with subjective feeling for anxiety, based on the Edmonton Symptom Assessment Scale (ESAS), and the summed ESAS score. Methods: 20 patients with any cancer diagnosis and normal cognition were recruited for the study. The ECG electrodes were attached and a 5-minute period of heart rate variability was recorded (HRVbefore) after 15 minutes of supine resting. The patient then began the brief relaxation program via recorded audio. Another 5 minute period of HRV was then recorded (HRVafter). The ESAS was completed before and immediately after the relaxation program. Parasympathetic activity assessed by heart rate variability, as measured by high frequency spectral analysis, was the primary outcome measure. The differences between the pre and post values of low and high frequency HRV, of the ESAS anxiety score, and of the summed ESAS score were compared using a Wilcoxan signed rank test. Results: No statistically significant differences were found in HF HRV power between the pre and post relaxation program. However, the summed ESAS scores were significantly lower after the relaxation program (p &lt;0.001). There was also a trend of decrease in the ESAS anxiety score (p = 0.086). There was no correlation between the change in HRV HF and change in the ESAS anxiety score. Conclusions: A brief guided relaxation program can significantly improve symptoms as measured by ESAS, but not HF HRV power. No significant financial relationships to disclose.

Heart rate recovery after exercise is associated with resting QTc interval in young men

Heart rate recovery (HRR) after exercise and spectral decomposition of heart rate variability (HRV), measures of autonomic nervous system function, are predictors of cardiovascular morbidity/mortality. QT interval, an index of ventricular depolarization and repolarization attained from surface ECG, is also associated with morbidity/mortality and is strongly influenced by autonomic tone. The purpose of this study was to assess the association between HRR after exercise, resting HRV and resting rate corrected QT interval in young healthy men. HRR was assessed in 37 men (23.3 +/- 0.6 years) 1 minute after a graded exercise test. Resting QT interval was derived from ECG recordings and rate corrected using five formulae (Bazett, Fridericia, Hodges, Framingham, and the nomogram method of Karjalainen). Resting HRV was spectrally decomposed using an autoregressive approach. A negative correlation was detected for QTc interval and HRR for each method (r = -0.36 to -0.48, P < 0.05). There was no correlation between high frequency power of HRV (a marker of parasympathetic modulation) and QTc interval. There was a negative relationship between absolute LF power (a marker of both sympathetic and parasympathetic modulation) and QTc interval for Karjalainen, Framingham, and Bazett correction methods (r = -0.33 to -0.47, P < 0.05). Resting LF power of HRV and HRR after exercise are inversely associated with resting QTc interval in young healthy men, supporting a relationship between cardiac autonomic nervous system function and ventricular depolarization and repolarization.

Acute resistance exercise reduces heart rate complexity and increases QTc interval.

Acute resistance exercise (RE) has been shown to reduce cardiac vagal control. Whether this would in turn affect QTc interval (an index of ventricular depolarization/repolarization) or heart rate complexity is not known. Heart rate variability (HRV), heart rate complexity (SampEn), and QT interval (rate corrected using Bazett, Fridericia, Hodges, and Framingham) were measured before and 5 min after an acute RE bout in twelve healthy young men. Normalized high frequency power of HRV (an index of cardiac parasympathetic modulation; HF (nu)), and SampEn were reduced following RE (p < 0.05). Bazett corrected QTc interval increased following RE (p < 0.05). Change in HF (nu) from rest to recovery was correlated with both change in SampEn (r = 0.51, p < 0.05) and change in QTc interval for each method of correction (r = - 0.67 to - 0.70, p < 0.05). Acute RE reduced HF spectral power of HRV and this was related to both reduced heart rate complexity and increased QTc length. Thus, during recovery from acute RE, there is prolongation of depolarization and repolarization of the ventricles concomitant with reduced cardiac irregularity, and this may be related to a reduction in cardiac vagal control.

Upsurge in T-Wave Alternans and Nonalternating Repolarization Instability Precedes Spontaneous Initiation of Ventricular Tachyarrhythmias in Humans

Analysis of repolarization instability, manifested by T-wave alternans (TWA), has proved useful for arrhythmia risk assessment. However, temporal relations between TWA and the spontaneous initiation of ventricular tachyarrhythmias (VTA) in humans are unknown. We examined continuous dynamics of repolarization in Holter electrocardiograms with spontaneous sustained (>30 seconds) VTA. Ambulatory electrocardiograms from 42 patients (79% with ischemic heart disease; left ventricular ejection fraction, 37+/-15%) were digitized, and the lead with the highest magnitude of the T wave was selected for analysis. TWA was examined by the modified moving average and intrabeat average analyses. To examine non-TWA (longer-period) oscillations in the repolarization segment, spectral energy of oscillations of consecutive T-wave amplitudes was calculated with the use of the short-time Fourier transform. Heart rate variability was assessed with the Fourier transform as well. TWA increased before the onset of VTA and reached a peak value of 23.6+/-11.7 microV 10 minutes before the event (P=0.0007). Spectral power of the oscillations of consecutive T-wave amplitudes increased nonuniformly, with the greatest increase in the respiratory range (2.6 microV2; P=0.005). In the TWA range, the change was smaller but highly pronounced relative to the 60- to 120-minute level (65%; P=0.003). The low-frequency and high-frequency heart rate variability power declined before the arrhythmia (P=0.04 and P=0.06, respectively). The magnitude of repolarization instability, manifested by TWA and beat-to-beat oscillations of T-wave amplitudes at other frequencies, increased before the onset of VTA. Tracking of these dynamics can facilitate timely detection of high-risk periods and may be useful for initiation of preventive treatments.

Assessment of Cardiovascular Autonomic Function in Patients with Liver Cirrhosis Using Heart Rate Variability, Blood Pressure Variability and Baroreflex Sensitivity

Background: Liver cirrhosis is associated with several hemodynamic abnormalities, including an impairment of autonomic nervous system reflexes, but very few have compared the disease severity with cardiovascular autonomic dysfunction assessed by spectral analysis of blood pressure and electrocardiogram. The aim of this study was to investigate the relationship between Child-Turcotte-Pugh (CTP) score and autonomic indices in patients with liver cirrhosis using the heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS). Methods: Fifty patients scheduled for liver transplantation recipients under general anesthesia were enrolled in the study. Beat-to-beat blood pressure and RR interval were measured for five minutes before anesthesia induction. HRV and BPV were estimated by power spectral analysis of RR interval and systolic blood pressure. BRS was estimated by both the sequence method (Sequence BRS) and high frequency (HF) gain of transfer function analysis (HF BRS). Results: Significant inverse correlations between CTP score and Sequence BRS (r = -0.61), HF BRS (r = -0.59), low frequency (LF) and HF power of HRV (r = -0.57, r = -0.46), LF power of BPV (r = -0.37) were found. However, no significant correlations were observed between CTP score and LF/HF ratio of HRV (r = -0.02) and HF power of BPV (r = 0.27). Conclusions: These results showed that autonomic dysfunction assessed by spectral analysis was associated with increasing severity of liver cirrhosis. Further study will be needed to clarify relationship between our findings and hemodynamic fluctuations during anesthesia for liver transplantation.