Heart rate variability during sleep and sleep apnoea in a population based study of 387 women

Increased sympathetic activity during sleep has been suggested as a link between obstructive sleep apnoea syndrome and cardiovascular disease. Heart rate variability (HRV) is a measure of autonomic effect on the heart. Different parameters have been associated with sympathetic and parasympathetic activity. We have studied HRV in different sleep stages and related the HRV‐pattern to sleep apnoea in a population‐based sample of 387 women. We investigated the HRV‐parameters standard deviation of all R‐R intervals (SDNN), root of the averaged square of successive differences (RMSSD), low frequency component (LF), high frequency component (HF), ratio of low frequency component to high frequency component LF/HF and VSAI [variation in sympathetic activity between rapid eye movement (REM) and slow wave sleep, defined as LF_REM?LF_SWS]. The HRV‐parameters were compared with the results of a full‐night polysomnography. Hourly incidence of obstructive episodes was used for classifying the subjects into four apnoea‐hypopnoea index (AHI)‐groups (<5, ≥5 and <15, 15–30 and >30 events). Individual sleep stages were analysed by pooling all recordings. Women with high AHI had higher heart rate and LF/HF ratio. In subjects with AHI >30, LF/HF ratio however dropped to same level as with AHI <5. Subjects with high AHI had low VSAI. Levels of SDNN, LF and LF/HF ratio during REM and light sleep were similar to wakefulness. In slow wave sleep the parameters decreased. In conclusion, moderately increased prevalence of obstructive apnoeas was associated with signs of higher sympathetic activity. High AHI was however associated with a HRV‐pattern suggestive of depressed sympathetic drive and lowered ability to increase it during REM.     

Role of Sympathovagal Balance in the Initiation of Idiopathic Ventricular Tachycardia Originating from Right Ventricular Outflow Tract

VT originating from the right ventricular outflow tract (RVOT) is prone to occur when sympathetic nervous activity is increased. β-Blockade is, therefore, effective in suppressing this VT. The purpose of this study was to determine the role of sympathovagal balance assessed by heart rate variability (HRV) in the spontaneous initiation of repetitive premature ventricular contractions (PVCs) and VT (five or more consecutive PVCs) arising from RVOT in seven patients without structural heart diseases. Frequency-domain measures of HRV were determined by analyzing 24-hour Holter electrocardiographic recording with the maximum entropy method over α 1,280-second period immediately before the onset of 35 single PVCs, 26 episodes of 2-4 consecutive PVCs, and 21 episodes of VT. High frequency component (HF: 0.15–0.40 Hz) was used as an index of parasympathetic activity, and the ratio of low frequency component (LF: 0.04–0.15 Hz) to HF (LF/HF ratio), as an index of sympathovagal balance. NN50(%), a time-domain variable of parasympathetic activity, was also determined. Mean RR interval and any measures of HRV did not change significantly before single PVCs. Mean RR interval shortened and HF decreased prior to repetitive PVCs and VT. The LF/HF ratio, however, increased only before the onset of VT. NN50(%) tended to decrease before repetitive PVCs and decreased significantly before VT. With propranolol (30–60 mg/day), frequency of repetitive PVCs was suppressed from 2,048 ± 1,201 to 746 ± 658/day and VT was totally abolished, but frequency of single PVCs did not change significantly. In conclusion, sympathetic predominance plays an important role in the initiation of repetitive PVCs and VT originating from RVOT in patients without structural heart diseases.     

Modulation of cardiac autonomic tone in non-hypotensive hypovolemia during blood donation

Non-hypotensive hypovolemia, observed during mild haemorrhage or blood donation leads to reflex readjustment of the cardiac autonomic tone. In the present study, the cardiac autonomic tone was quantified using heart rate and blood pressure variability during and after non-hypotensive hypovolemia of blood donation. 86 voluntary healthy male blood donors were recruited for the study (age 35 ± 9 years; weight 78 ± 12 kg; height 174 ± 6 cms). Continuous lead II ECG and beat-to-beat blood pressure was recorded before, during and after blood donation followed by offline time and frequency domain analysis of HRV and BPV. The overall heart rate variability (SDNN and total power) did not change during or after blood donation. However, there was a decrease in indices that represent the parasympathetic component (pNN50 %, SDSD and HF) while an increase was observed in sympathetic component (LF) along with an increase in sympathovagal balance (LF:HF ratio) during blood donation. These changes were sustained for the period immediately following blood donation. No fall of blood pressure was observed during the period of study. The blood pressure variability showed an increase in the SDNN, CoV and RMSSD time domain measures in the post donation period. These results suggest that mild hypovolemia produced by blood donation is non-hypotensive but is associated with significant changes in the autonomic tone. The increased blood pressure variability and heart rate changes that are seen only in the later part of donation period could be because of the progressive hypovolemia associated parasympathetic withdrawal and sympathetic activation that manifest during the course of blood donation.     

Analysis of Heart Rate Variability Five Minutes Before the Onset of Paroxysmal Atrial Fibrillation

BACKGROUND: Various experimental and clinical observations suggest changes in sympathetic and vagal neural regulatory mechanisms play a critical role in altering cardiac electrical properties and favor the occurrence of arrhythmic events. There is limited information about the influences of the autonomic tone on the development of episodes of paroxysmal atrial fibrillation in patients with no evidence of organic heart disease. The aim of this study was to investigate changes in sympatho-vagal balance 5 minutes before the onset of atrial fibrillation. METHODS: We evaluated 28 patients with no history of heart disease who were not undergoing pharmacological treatment and who had at least one episode of paroxysmal atrial fibrillation recorded during an 24-hour ECG Holter monitoring. We analyzed values of frequency domain heart rate variability parameters 5 minutes before the onset of atrial fibrillation (prefa period) compared to an equivalent period at least 1 hour after from atrial fibrillation (random period). RESULTS: Thirty-six episodes of atrial fibrillation were recorded and our results showed we had two types of episodes. Eighteen were classified as Type A, in which we had an increase of low frequency (LF) (79.15 +/- 10.76 in comparison with 62.64 +/- 19.55) (P = 0.004) and a decrease of high frequency (HF) (20.82 +/- 10.74 in comparison with 37.64 +/- 20.20) (P = 0.004) consistent with an increase of sympathetic tone; and 18 were classified as Type B in which there was a decrease of LF (62.82 +/- 15.38 in comparison with 85.97 +/- 8.48) (P < 0.001), and an increase of HF (36.79 +/- 14.72 compared with 14.01 +/- 8.48) (P < 0.001), consistent with an increase of parasympathetic tone. CONCLUSION: We observed abrupt changes in sympathovagal balance in the last 5 minutes preceding an episode of atrial fibrillation. This can be related to a double behavior in the neurogenic drive: in Type A episodes there is an increase of the LF spectrum, LF:HF ratio, and a decrease of the HF spectrum consistent with an increase of neurogenic sympathetic drive; in Type B episodes there is a reduction of the LF spectrum, LF/HF ratio, and an increase of HF spectrum consistent with an enhancement of the neurogenic parasympathetic drive. In some patients, we found that the two mechanisms operate during different hours of the day and that sometimes there is an increase of sympathetic tone, and in the same instances an increase of parasympathetic tone. Heart-rate variability measures fluctuation in autonomic inputs to the heart rather than the mean level of autonomic impulse; autonomic imbalance is probably more important than the vagal or sympathetic drive alone.     

Heart rate variability and its determinants in patients with severe or mild essential hypertension

How cardiac autonomic nervous control is related to the severity of essential hypertension in patients receiving long‐term antihypertensive therapy is not well known. The aim of this study was to examine heart rate variability (HRV), a non‐invasive measure of cardiac autonomic function, in patients with long‐term and medically treated mild and severe essential hypertension and healthy control subjects, and to assess the clinical determinants of HRV in these patients. Thirty‐four patients with severe essential hypertension (SEHT) and 29 with mild essential hypertension (MEHT) as well as healthy age‐ and sex‐matched control subjects were studied. HRV was assessed from 10 min ECG‐recordings during paced (0·2 Hz) breathing at rest and expressed as time and frequency domain measures. In the SEHT group time (SDNN, RMSSD) and frequency domain measures (total power, low‐frequency (LF) power and high‐frequency (HF) power of HRV in absolute units, and LF and HF power of HRV in normalized units) of HRV were significantly lower when compared with those of the control group. The MEHT and control groups did not differ from each other with respect to time or frequency domain measures of HRV. Comparison between the hypertensive groups showed that SDNN, total power, LF power and HF power were lower in the SEHT group compared with the MEHT group (P<0·05 for all). Among hypertensive patients RR‐interval, age, gender, systolic finger blood pressure and diastolic office blood pressure as well as 24‐h blood pressure were significant determinants of HRV. In conclusion, we found that the severity of chronic essential hypertension seems to be related to the severity of impairment of cardiac autonomic control.     

Physical training increases heart rate variability in healthy prepubertal children

BACKGROUND: The aim of the present study was to evaluate the effect of an endurance training program on heart rate variability (HRV) in prepubertal healthy children and to determine the relationships between HRV components and training-induced cardiac adaptations. METHODS: Nineteen prepubertal children (aged 10-11 years old) took part in this study: 12 children were assigned to participate in a 13-week endurance training program (3 x 1 h week-1; intensity, > 80% HRmax) and 7 children served as a control group. Before and after the 13-week study period, all the children were tested for maximal oxygen uptake (V O(2max)), HRV was measured by spectral and time domain analysis of 5 h night ECG recordings, and left ventricular (LV) cardiac morphology and function were assessed by means of Doppler-Echocardiography. RESULTS: V O(2max) increased significantly (+15.5% +/- 12.1; P < 0.01) after the training program. All the frequency domain components (absolute values) increased after training except the low (LF) to high (HF) frequency ratio. Also, LF and HF did not change when expressed relative to total power. For the time domain components, only N-N intervals, the standard deviation of all N-N and the average of all 5 min standard deviations of N-N increased after training. Our training program induced also an increase in LV internal diameter and mass as well as an enhancement in early diastolic passive LV filling with a concomitant reduction in late diastolic active LV filling. These cardiac morphological and functional adaptations did not correlate however, with the autonomous nervous system modifications due to training. CONCLUSION: Our study shows that an endurance training program had a positive effect on aerobic potential, morphological and functional cardiac parameters and on nocturnal global HRV in healthy prepubertal children without inducing sympathetic and parasympathetic modifications.     

Long‐term stability of heart rate variability in chronic stable angina pectoris,and the impact of an acute myocardial infarction

Background: Heart rate variability (HRV) reflects the balance between cardiac parasympathetic and sympathetic autonomic influences. Reduced HRV has adverse prognostic implications. The time course for changes in HRV over prolonged periods of time and the influence of an acute coronary event on HRV are not well established. Methods: Heart rate variability was assessed in patients with chronic stable angina pectoris, who were followed for 3 years within the Angina Prognosis Study in Stockholm. Patients who suffered an acute myocardial infarction after the study were re‐examined after this event. We assessed HRV by the simple geometric method differential index, and traditional time‐ and frequency‐domain measurements of HRV. Results: The differential index was essentially unchanged during the study (i.e. the ratio month 36/month 1 was 1·00 ± 0·06, n = 261). Also most other time and frequency indices of HRV (SDNN, r‐MSSD, SDNNIDX, total power, and VLF, LF, HF respectively; n = 63) remained largely unchanged; pNN50 and LF/HF were, however, less reproducible. In 21 patients with a subsequent acute myocardial infarction, SDNN, SDNNIDX, total power, LF and LF/HF were reduced following the event, whereas differential index, pNN50 and HF remained unchanged. Conclusions: Differential index and other indices of HRV are stable and reproducible in patients with chronic stable angina pectoris. High‐frequency HRV (reflecting cardiac parasympathetic activity) and the differential index changed little following an acute coronary event, and may be suitable for predictions of the future risk of sudden death even in the presence of a recent acute coronary event.     

Neurocardiac Responses to Vagoafferent Electrostimulation in Humans

To determine if cardiac vagal tone is enhanced by vagal electrostimulation (VES), we examined the heart rate autospectrum (HRA) in eight patients with implanted stimulators for complex partial seizures. In four patients the VES was activated at 30 Hz and 500-msec pulse (HiStim group) compared to 2 Hz and 130-msec pulse for the LoStim group (n = 4). Continuous ECG and respiratory waveforms were recorded for 45 minutes every 8 hours (7–8 AM; 3–4 PM 11–12 PM) during resting supine wakeful epochs both before and 15 days after surgical implantation. From the HRA cardiac sympathovagal balance was expressed as the ratio of the low frequency (LF) power to the high frequency (HF) power. RESULTS: There were no presurgical differences between the groups in heart rate, its variance, or the energies contained in any autospectral band. The LoStim group showed no significant change in heart rate (HR), HF peak power, or LF:HF ratios during 2 weeks of VES. Conversely, in the HiStim group, the LF:HF peak power ratio fan expression of sympathetic dominance) decreased from 2.5 ± 1.5 preimplant to 1.5 ± 0.49 (P < 0.02) with VES. During VES there was a significantly higher HF power in the HiStim compared to LoStim group. No diurnal variations in HRA values were seen for either group. CONCLUSIONS: (1) A relationship exists between selective vagal nerve electrostimulation and the HRA; and (2) high stimulation frequency of the vagus nerve in man is associated with sustained augmentation of cardiac vagal tone throughout a 24-hour cycle.     

Cardiac sympathovagal balance during endoscopic retrograde cholangiopancreatography

BACKGROUND AND STUDY AIMS: Cardiopulmonary complications have been reported during upper gastrointestinal endoscopy and endoscopic retrograde cholangiopancreatography (ERCP). The aim of this study was to evaluate the sympathovagal response to the stretching of the common bile duct caused by contrast medium injection during ERCP. PATIENTS AND METHODS: The 16 patients included in the study were assigned to two groups according to the size of common bile duct. Group A consisted of patients with normal-sized bile ducts, while Group B patients had dilated common bile ducts. The heart rate variability (HRV) technique was used to assess the sympathovagal balance. The HRV data were gathered using the Holter technique, and frequency domain analysis revealed two main spectral components of HRV: low frequency (LF) and high frequency (HF). RESULTS: In patients with normal-sized bile ducts, contrast injection initiated a rapid increase in the power spectra (ms2) of both the HF and LF components. In patients with dilated common bile ducts, this phenomenon was not observed. CONCLUSIONS: During ERCP, contrast injection into a dilated common bile duct does not stimulate the autonomic nervous system in the same way as it does when the common bile duct is of normal size.     

Model based and experimental investigation of respiratory effect on the HRV power spectrum

The role of respiration in the genesis of heart rate variability (HRV) has been the subject matter of many experimental and modeling studies. It is widely accepted that the high frequency (HF) peak of a HRV power spectrum, which is centered at the average respiratory frequency, is caused by mechanisms activated by respiration. On the other hand, there is a debate on the possible role of respiration in the genesis of the low frequency (LF) peak which is usually centered around 0.1 Hz. In this study, a comprehensive cardiorespiratory interaction model is used to test various hypotheses regarding the role of respiration in the LF peak of HRV. In this model, chest and abdomen circumference signals and lung volume signal are used as respiratory inputs. Simulations are made for periodic, spontaneous and slightly irregular respiratory patterns, and it is observed that the more low frequency (LF) power there in the respiratory signals, the more LF power there in the model-predicted HRV. Experiments on nine volunteers are also performed for the same respiratory patterns and similar results are observed. Furthermore, the actual measured respiratory signals are input to the model and the model predicted and the actual HRVs are compared both in time domain and also with respect to their power spectra. It is concluded in general that respiration not only is the major contributor to the genesis of the HF peak in the HRV power spectrum, but also plays an important role in the genesis of its LF peak. Thus, the LF/HF ratio, which is used to assess sympathovagal balance, cannot be correctly utilized in the absence of simultaneous monitoring of respiration during an HRV test.     

Acute Effects of Moxonidine on Cardiac Autonomic Modulation

Background: Moxonidine, an imidazoline I1 receptor agonist, is a centrally acting antihypertensive agent having sympatholytic effect. However, there are only limited data regarding the effects of this drug on autonomic cardiac functions. Methods and results: In this study we investigated the acute effects of moxonidine on cardiac autonomic modulation by heart rate variability (HRV) analysis. The effects of oral 0.4‐mg moxonidine were studied on 11 healthy male volunteers in a randomized, double‐blind, placebo controlled, and crossover study. After 15 minutes rest, time and frequency domain parameters of HRV were calculated from 5‐minute continue electrocardiography recordings in supine position, during controlled respiration (15 breath/min) and during handgrip exercise before and 1 hour after taking placebo or moxonidine. Baseline parameters before taking placebo and moxonidine were similar (P > 0.05). Moxonidine, but not placebo, caused an increase in heart failure (HF) (119 ± 21 vs 156 ± 23, P = 0.029) and HFnu (39 ± 4 vs 47 ± 4, P = 0.033) and decrease in LFnu (61 ± 4 vs 53 ± 4, P = 0.033) and LF/HF ratio (1.96 ± 0.36 vs 1.12 ± 0.35, P = 0.010) in supine position compared with baseline parameters. However, there was no difference in other time or frequency domain parameters during controlled breathing and handgrip exercise either with moxonidine or placebo administration (P > 0.05). Single dose of moxonidine administration increases cardiovagal tone but parasympathetic and sympathetic autonomic maneuvers attenuated its short term effects on HRV in healthy male subjects. (PACE 2010; 929–933)     

Effects of progressive exercise during phase I cardiac rehabilitation on the heart rate variability of patients with acute myocardial infarction

Purpose.?Heart rate variability (HRV) decreases after an acute myocardial infarction (AMI) due to changes in cardiac autonomic balance. The purpose of the present study, therefore, was to evaluate the effects of a progressive exercise protocol used in phase I cardiac rehabilitation on the HRV of patients with post-AMI.

Material and methods.?Thirty-seven patients who had been admitted to hospital with their first non-complicated AMI were studied. The treated group (TG, n?=?21, age?=?52?±?12 years) performed a 5-day programme of progressive exercise during phase I cardiac rehabilitation, while the control group (CG, n?=?16, age?=?54?±?11 years) performed only respiratory exercises. Instantaneous heart rate (HR) and RR interval were acquired by a HR monitor (Polar®S810i). HRV was analysed by frequency domain methods. Power spectral density was expressed as normalised units (nu) at low (LF) and high (HF) frequencies, and as LF/HF.

Results.?After 5 days of progressive exercise, the TG showed an increase in HFnu (35.9?±?19.5 to 65.19?±?25.4) and a decrease in LFnu and LF/HF (58.9?±?21.4 to 32.5?±?24.1; 3.12?±?4.0 to 1.0?±?1.5, respectively) in the resting position (p?<?0.05). No changes were observed in the CG.

Conclusions.?A progressive physiotherapeutic exercise programme carried out during phase I cardiac rehabilitation, as supplement to clinical treatment increased vagal and decreased sympathetic cardiac modulation in patients with post-AMI.     

Frequency-domain analysis of heart rate variability during positive and negative head-up tilt test: importance of age

The study of autonomic behavior during a head-up tilt test (HUT) has been deemed important to understand the loss of consciousness mechanism. Though HRV in patients with HUT(+) and HUT(-) has been compared, few trials emphasized the importance of age. HRV in frequency domain was analyzed based on 5-minute samples in the supine position, and between 5 and 10 minutes during early tilt test (R1) in 102 patients with one or more episodes of syncope (mean age 44.3 +/- 20.8, range 15-85 years, 55 women). Two subgroups were selected afterwards: (1) young patients between 15 and 35 years of age (41 patients) and (2) elderly patients aged 60 or more (36 patients). The following parameters were taken into account: the sum of low (LF) and high frequency (HF) (LF and HF in absolute values and in normalized units), the LF/HF ratio (L/H ratio), and the percentage of change between baseline and R1 values. The HRV behavior in young and elderly patients with positive and negative HUT was established. We then analyzed the correlation between HRV and age and HUT outcome. A multiple regression analysis encompassing age, HUT outcome, gender, and number of syncope episodes was performed. In young patients, the LF and HF areas and the L/H ratio changed significantly between baseline and R1. The L/H ratio increases from baseline to R1. Conversely, these differences were not significant in the elderly. No differences between HUT(+) and HUT(-) within the same age group were observed. Age related significantly to practically all HRV parameters analyzed, whereas the tilt test outcome correlates poorly with HF normalized units and LF normalized units during R1, and the L/H ratio changes between baseline and R1. By means of a multivariate analysis, only age shows a significant correlation with the HRV values. Despite an all age triggering of vasovagal syncope during HUT, the young and elderly patients' autonomic behavior differs. The young considerably increase their sympathovagal balance during HUT, whereas the elderly have a mitigated autonomic response. No significant differences were observed during the first minutes of the test between those with a HUT(+) and those with a HUT(-) within the same age group. Age, and not the HUT response, is the major determinant of the autonomic behavior during early HUT.     

Relationship Between Short- and Long-Term Measurements of Heart Rate Variahility in Patients at Risk of Sudden Cardiac Death

Because of technical difficulties in analyzing heart rate variability (HRV) from ambulatory Holter recordings over 24-hour periods, short-term recordings are more practical for the clinical application of HRV. However, the relationship between short- and long-term recordings is unclear. In this study, short-term (10 min) electrocardiograms were assessed in the supine position, during passive head-up tilt and on standing in 15 patients (aged 39 ± 14 years) with ventricular tachycardia/fibrillation not associated with coronary artery disease. Spectral HBV was computed as total frequency (TF: 0.01–1.00 Hz), low frequency (LF: 0.04–0.15 Hz), and high frequency (HF: 0.15–0.40 Hz) components. The short-term HRV parameters were compared with those obtained from long-term (24 hour) recordings from the same patients. There was a significant decrease in the HF component of HRV and a significant increase in LF/HF ratio during passive tilt or active standing compared with supine recordings, but no significant changes were observed in the TF or LF components. All frequency components of HRV for the 24-hour periods showed significant correlation with the values from short-term recordings (τ ranged from 0.67–0.87). Stepwise multivariate regression analysis showed that both the TF and HF components of HRV over 24 hours were predominantly related to the corresponding frequency components of HBV in the supine position, while the LF component of HRV over 24 hours was predominantly related to that on standing. Our observations suggest that the short-term HRV is related to the long-term value, but global HRV over 24 hours cannot completely be replaced by the short-term recordings. The postural effects on the frequency components of HRV should be taken into account when short-term HRV assessment is applied.     

Evaluation of techniques for estimating the power spectral density of RR-intervals under paced respiration conditions

Heart rate variability (HRV) analysis is increasingly used in anaesthesia and intensive care monitoring of spontaneous breathing and mechanical ventilated patients. In the frequency domain, different estimation methods of the power spectral density (PSD) of RR-intervals lead to different results. Therefore, we investigated the PSD estimates of fast Fourier transform (FFT), autoregressive modeling (AR) and Lomb–Scargle periodogram (LSP) for 25 young healthy subjects subjected to metronomic breathing. The optimum method for determination of HRV spectral parameters under paced respiration was identified by evaluating the relative error (RE) and the root mean square relative error (RMSRE) for each breathing frequency (BF) and spectral estimation method. Additionally, the sympathovagal balance was investigated by calculating the low frequency/high frequency (LF/HF) ratio. Above 7 breaths per minute, all methods showed a significant increase in LF/HF ratio with increasing BF. On average, the RMSRE of FFT was lower than for LSP and AR. Therefore, under paced respiration conditions, estimating RR-interval PSD using FFT is recommend.     

Autonomic involvement in idiopathic premature ventricular contractions

Objective

To investigate autonomic involvement in different types of idiopathic premature ventricular contractions (PVCs) grouped by heart rate (HR) dependency.

Methods

One hundred and sixty PVC patients and 31 controls were enrolled. Holter ECG was used to evaluate PVC occurrence, and spectral analysis of heart rate variability (HRV) was calculated to represent cardiac autonomic control. PVCs were divided into fast rate-dependent (F-PVC), slow rate-dependent (S-PVC), and HR-independent PVC (I-PVC) based on the relationship between hourly PVC density and hourly HR. HRV among different types of PVCs were compared, and the association between PVC density with HR and HRV were analyzed. Furthermore, autonomic changes assessed by consecutive 5-min HRV in 30 min before PVC episodes were investigated.

Results

In 160 subjects, there were 73 F-PVC, 56 S-PVC, and 31 I-PVC. Hourly PVC density was positively associated with sympathetic indice (LF/HF) and negatively related to vagal indices (HF and HFnu) in F-PVC, and this trend was reversed in S-PVC. During 30 min before PVC onset, RR interval and HFnu decreased significantly with LF/HF showing an increasing trend in F-PVC, while in S-PVC both RR interval and HF increased significantly. It was noted that those changes were most evident during the last 5 min before PVC onset. In addition, PVC density in F-PVC was significantly decreased by β-blocker treatment.

Conclusions

HR dependency reflected autonomic modulation of idiopathic PVCs. F-PVC and S-PVC might be facilitated by sympathetic activation and vagal activation, respectively. HR dependency and the related autonomic mechanisms should be considered when treating idiopathic PVCs.     

甲亢病人的心率变异性及临床意义

目的 :通过对 31例甲状腺机能亢进症 (简称甲亢 )患者 (甲亢组 )和 31例正常人 (对照组 )的心率变异性 (HRV)的分析 ,进一步了解甲亢患者自主神经功能状况。方法 :对甲亢组和对照组进行 2 4hHRV对比分析。结果 :甲亢组与对照组比较其时域指标 :SDNN、SDANN明显降低 ,频域指标 :VLF、LF/HF增高 (P <0 .0 0 1,P <0 .0 5 ) ,LF、HF降低 ,与对照组有显著差异 (P<0 .0 0 1,P <0 .0 5 )。结论 :通过HRV的变化 ,进一步说明甲亢患者的交感神经受损和迷走神经失衡。     

Chronotropic incompetence to exercise separates low body weight from established anorexia nervosa

Chronotropic incompetence (CI), characterized by an attenuated heart rate (HR) response to exercise could participate to the limitation of exercise capacity in anorexia nervosa (AN). Therefore, we evaluated the role of cardiac sympathetic responsiveness in AN patients. In addition, the ambulatory value of autonomic control using spectral analysis of heart rate variability (HRV) was determined and correlated to maximal exercise performance. Twenty-two patients hospitalized for weight loss and suspicion of AN were included in the study. All performed a symptom-limited exercise test with measurement of gas exchange for chronotropic response to exercise evaluation. Holter ECG recordings allowed daytime and night-time spectral domain HRV analysis in order to evaluate the alteration of sympathetic control of HR in free-living conditions. CI defined as a failure to achieve 80% of heart rate reserve (%HRR) was observed in 13 (59%) patients (CI+). This group presented a higher body mass deficit than the group without CI (CI-; -35.1 +/- 8.7% versus -26.1 +/- 10.7%; P<0.05). Obviously, patients with a lower body mass index (BMI < 16 kg m(-2), n = 14) revealed a more severe limitation to maximal exercise with a lower peak HR, a lower peak Vo(2), and a lower maximal O(2) pulse (P<0.05). BMI was significantly correlated to peak Vo(2), maximal HR, and %HRR achieved at peak exercise. Daytime HRV parameters reflecting the sympathetic autonomic equilibrium (LF nu, LF/HF ratio) were significantly lower in CI+ patients. Blunted sympathetic response to maximal exercise is frequent and correlated to weight deficit. The present data suggest a major autonomic derangement in AN characterized by a cardiac sympathetic withdrawal.     

Specificity of the glucose oxidase reaction and interference with the quantitative glucose oxidase—peroxidase—0-dianisidine method

Abstract

Although ambulatory measurements of heart rate variability (HRV) are widely used, the reproducibility and seasonal variation of ambulatory sampled short-term HRV measurements in healthy participants has not been investigated before. In the present study we collected ambulatory ECGs from 19 healthy participants monthly for 12 months, and for a sub-group of 12 participants weekly for one month. Frequency-domain HRV-metrics were calculated for 5 min ECG segments during (i) a 15-min self-selected rest period (awake period), and (ii) a 30-min sleep period starting 45 min after estimated sleep onset. Total, within- and between-subject coefficient of variation (CV) and seasonal variation were estimated for ln (TP), ln (LFP), ln (HFP), ln (LF/HF), LFnu, HFnu, the mean heart period and the ECG derived respiratory frequency. The within- and between-subject CV varied considerably between different variables, from < 10% for ln (TP) and ln (LFP) to >100% for ln (LF/HF). Within- and between-subject CV of ln (HFP), LFnu and HFnu were 10-40%. A weak, but significant, seasonal variation was found for ln (TP) (p = 0.05), ln (LFP) (p<0.05) and the respiratory frequency (p<0.01), but the seasonal variation did not affect the within-subject CV. Furthermore, sample size calculations demonstrated that the reproducibility was sufficient for ambulatory HRV measurements to be used to study autonomic cardiac regulation in healthy populations.     

Power spectral analysis of heart rate variability in HIV-infected and AIDS patients

Background: In HIV‐infected patients the risks for cardiovascular disease are multifactorial. Autonomic dysfunction has been detected in the early phase of HIV infection as well as in AIDS patients with advanced cardiomyopathy. Methods: Forty AIDS patients receiving highly active antiretroviral therapy (HAART), 40 HIV+ naïve of HAART, and 40 control subjects were studied. Computerized analysis of heart rate variability was performed using an analog to digital converter. R‐R intervals were obtained from a standard ECG, recorded in DII lead in supine rest and after the cold‐face and tilt tests. The series of R‐R intervals were assessed in time and frequency domains using an autoregressive algorithm. Results: There was no difference regarding to mean values of R‐R intervals and variance in baseline. The normalized power of the low‐frequency (LF) component and the low‐frequency/high‐frequency (HF) ratio (LF/HF) was significantly decreased in the HIV group. Responses of normalized HF and LF/HF ratio during the cold‐face test were significantly decreased in the HIV group, as compared to the control. During the tilt test, a higher augmentation of normalized LF and the LF/HF ratio was observed in the HIV group compared with the control. The AIDS group was similar to the control in baseline and after cold‐face and tilt tests. Conclusion: The HIV group presented in baseline conditions, a shift of cardiac sympathovagal balance, an exacerbated response of the LF component during the tilt test, and an ineffective cardiac vagal response to the cold‐face test suggesting sympathetic and parasympathetic dysfunction. AIDS patients receiving HAART did not present these autonomic alterations.