Heart rate variability today

Acupuncture in subjects with cold hands sensation: study protocol for a randomized controlled trial

BACKGROUND

Cold hands sensation is a common disorder within the Korean population. Many Korean family physicians believe that it is a mild early manifestation of Raynaud's phenomenon (RP), or may be related to RP. RP is characterized by reversible digital vasospasm provoked by cold temperatures and/or emotional stress, and doctors often prescribe medications that are used in treatment of RP for subjects with cold hands. However, this has not shown a clear benefit, and these medications can cause unwanted side effects. It is also reported that traditional Korean medicine, including acupuncture, is widely used to treat cold hands, although the current level of evidence for this approach is also poor and to date, there have been no published randomized controlled clinical trials (RCTs) evaluating the efficacy and safety of acupuncture for cold hands. We have therefore designed a pilot RCT to obtain information for the design of a further full-scale trial.

METHODS/DESIGN

The proposed study is a five-week pilot RCT. A total of 14 subjects will be recruited and randomly allocated to two groups: an acupuncture plus medication group (experimental group) and a medication-only group (control group). All subjects will take nifedipine (5 mg once daily) and beraprost (20 mg three times daily) for three weeks. The experimental group will receive additional treatment with three acupuncture sessions per week for three weeks (nine sessions total). The primary outcome will be measured using a visual analogue scale. Secondary outcomes will be measured by blood perfusion in laser Doppler perfusion imaging of the hands, frequency and duration of episodes of cold hands, and heart rate variability. Assessments will be made at baseline and at one, three, and five weeks thereafter.

DISCUSSION

This study will provide an indication of the feasibility and a clinical foundation for a future large-scale trial.

TRIAL REGISTRATION

This study was registered at Korean Clinical Research Information Service (CRIS) registry on 5 August 2013 with the registration number #KCT0000817.

Left renal nerves stimulation facilitates ischemia-induced ventricular arrhythmia by increasing nerve activity of left stellate ganglion

INTRODUCTION

Renal sympathetic nerve (RSN) activity plays a key role in systemic sympathetic hyperactivity. Previous studies have shown that cardiac sympathetic hyperactivity, especially the left stellate ganglion (LSG), contributes to the pathogenesis of ventricular arrhythmias (VAs) after acute myocardial infarction (AMI).

METHODS AND RESULTS

Twenty-eight dogs received 3 hours of continuous left-sided electrical stimulation of RSN (LRS; Group-1, n = 9), sham RSN stimulation (Group-2, n = 9), or LSG ablation plus 3 hours of LRS (Group-3, n = 10) were included. AMI was induced by ligating the proximal left anterior descending coronary artery. LRS was performed using electrical stimulation on the adventitia of left renal artery at the voltage increasing the systolic blood pressure (BP) by 10%. BP, heart rate variability (HRV), serum norepinephrine (NE) level, and LSG function were measured at baseline and the end of each hour of LRS. C-fos and nerve growth factor (NGF) protein expressed in the LSG were examined in Group-1 and Group-2. Compared with baseline, 3 hours of LRS induced a significant increase in BP, sympathetic indices of HRV, serum NE level, and LSG function. The incidence of VAs in Group-1 was significantly higher than other groups. The expression of c-fos and NGF protein in the LSG was significantly higher in Group-1 than Group-2.

CONCLUSION

Three hours of LRS induces both systemic and cardiac sympathetic hyperactivity and increases the incidence of ischemia-induced VAs.

[Heart rate variability is significantly reduced in non-diabetic patients with hypertension]

INTRODUCTIONS

Heart rate variability is reduced among patients with hypertension and/or with diabetes mellitus. Hypertension and diabetes show frequent co-morbidity, but it is still not entirely clear whether heart rate variability is reduced in non-diabetic patients with hypertension.

AIM

The aim of the authors was to evaluate the heart rate variability in hypertensive patients with and without diabetes and in control subjects.

METHOD

130 patients with hypertension, 48 patients with hypertension and type 2 diabetes mellitus, and 87 control subjects were involved in the study. Minimum, mean and maximum heart rate, and parameters of heart rate variability were measured.

RESULTS

The mean of minimum heart rate did not differ significantly between the three groups. However, all other parameters were significantly reduced in patients with hypertension with and without diabetes as compared to the control group. No significant differences were observed between hypertensive patients with and without diabetes mellitus.

CONCLUSIONS

Heart rate variability is significantly reduced in non-diabetic patients with hypertension. It seems that type 2 diabetes results in no further significant reduction of heart rate variability in patients with hypertension.

Inhalation of ultrafine carbon particles alters heart rate and heart rate variability in people with type 2 diabetes

BACKGROUND

Diabetes may confer an increased risk for the cardiovascular health effects of particulate air pollution, but few human clinical studies of air pollution have included people with diabetes. Ultrafine particles (UFP, ≤100 nm in diameter) have been hypothesized to be an important component of particulate air pollution with regard to cardiovascular health effects.

METHODS

17 never-smoker subjects 30-60 years of age, with stable type 2 diabetes but otherwise healthy, inhaled either filtered air (0-10 particles/cm3) or elemental carbon UFP (~107 particles/cm3, ~50 ug/m3, count median diameter 32 nm) by mouthpiece, for 2 hours at rest, in a double-blind, randomized, crossover study design. A digital 12-lead electrocardiogram (ECG) was recorded continuously for 48 hours, beginning 1 hour prior to exposure.

RESULTS

Analysis of 5-minute segments of the ECG during quiet rest showed reduced high-frequency heart rate variability with UFP relative to air exposure (p = 0.014), paralleled by non-significant reductions in time-domain heart rate variability parameters. In the analysis of longer durations of the ECG, we found that UFP exposure increased the heart rate relative to air exposure. During the 21- to 45-hour interval after exposure, the average heart rate increased approximately 8 beats per minute with UFP, compared to 5 beats per minute with air (p = 0.045). There were no UFP effects on cardiac rhythm or repolarization.

CONCLUSIONS

Inhalation of elemental carbon ultrafine particles alters heart rate and heart rate variability in people with type 2 diabetes. Our findings suggest that effects may occur and persist hours after a single 2-hour exposure.

The autonomic balance predicts cardiac responses after the first dose of fingolimod

BACKGROUND

Predictive markers of cardiac side effects would be helpful for the stratification and individualized monitoring of multiple sclerosis (MS) patients prescribed with fingolimod.

OBJECTIVE

To test whether the autonomic balance predicts a cardiac response after the first dose of fingolimod.

METHODS

A total of 55 consecutive relapsing-remitting MS (RRMS) patients underwent 'head-up tilt', Valsalva maneuver, deep breathing and handgrip tests before their first dose of fingolimod. The normalized unit of the high frequency (HF) component (HF normalized units; HFnu), reflecting mostly vagal activity; and the low frequency (LF) component (LF normalized units; LFnu) reflecting mostly sympathetic activity, were considered for the analysis of heart rate (HR) variability. The patients' HR and electrocardiographic parameters ((the interval between P wave and ventricular depolarization (PR); the interval between Q and T waves (QT)) were recorded during 6-hour post-dose monitoring.

RESULTS

We found significant correlations between measures of parasympathetic function and fingolimod-induced bradycardia. Subjects with higher Valsalva ratio and HR variation during deep breathing had, in fact, nadir HR ≤ 50 beats/minute (bpm) after the first fingolimod dose. Conversely, significant negative correlations were found between measures of sympathetic function and fingolimod-induced PR interval increase. Subjects with lower LFnu at rest and less increase of blood pressure on the handgrip test showed a PR interval increase > 20 ms after fingolimod.

CONCLUSIONS

Assessing autonomic control of cardiovascular functions can be useful to predict cardiac effects after the first fingolimod dose.

The relationship between sympathetic nervous activity and cerebral hemodynamics and oxygenation: a study using skin conductance measurement and functional near-infrared spectroscopy

Simultaneous measurement of cortical and peripheral affective processing is relevant in many neuroscientific research fields. The aim was to investigate the influence of different affective task components on the coherence between cortical hemodynamic signals and peripheral autonomic skin potential signals. Seventeen healthy subjects performed four tasks, i.e. a finger-tapping task, a hyperventilation task, a working memory task and a risk-taking task. Cortical hemodynamic responses were measured using functional near-infrared spectroscopy (fNIRS). Peripheral skin conductance responses (SCRs) were assessed using electrodermal activity (EDA). Coherence between the fNIRS and the EDA time series was calculated using the S transform coherence (STC), a method that tests the temporal dynamics between two time series for consistent phase relationships and thus for a functional relationship. The following characteristics of fNIRS-EDA coherence were observed: (1) Simple motor performance was not a contributor to enhanced coherence, as revealed by the finger-tapping task. (2) Changes in respiration rate and/or heart rate acted as relevant contributors to enhanced coherence, as revealed by the hyperventilation task. (3) Working memory performance did not induce changes in coherence, (4) whereas risk-taking behavior was a significant contributor to enhanced coherence. (5) Based on all four tasks, we also observed that coherence may be subject to habituation or sensitization effects over the trial-to-trial course of a task. Increased fNIRS-EDA coherence may be an indicator of a psychophysiological link between the underlying cortical and peripheral affective systems. Our findings are relevant for several neuroscientific research areas seeking to evaluate the interplay between cortical and peripheral affective performance.

A brief review and clinical application of heart rate variability biofeedback in sports, exercise, and rehabilitation medicine

CONTEXT

An important component of the effective management of chronic noncommunicable disease is the assessment and management of psychosocial stress. The measurement and modulation of heart rate variability (HRV) may be valuable in this regard.

OBJECTIVE

To describe the measurement and physiological control of HRV; to describe the impact of psychosocial stress on cardiovascular disease, metabolic syndrome, and chronic respiratory disease, and the relationship between these diseases and changes in HRV; and to describe the influence of biofeedback and exercise on HRV and the use of HRV biofeedback in the management of chronic disease.

DATA SOURCES AND STUDY SELECTION

The PubMed, Medline, and Embase databases were searched (up to August 2013). Additional articles were obtained from the reference lists of relevant articles and reviews. Articles were individually selected for further review based on the quality and focus of the study, and the population studied.

RESULTS

Heart rate variability is reduced in stress and in many chronic diseases, and may even predict the development and prognosis of some diseases. Heart rate variability can be increased with both exercise and biofeedback. Although the research on the effect of exercise is conflicting, there is evidence that aerobic training may increase HRV and cardiac vagal tone both in healthy individuals and in patients with disease. Heart rate variability biofeedback is also an effective method of increasing HRV and cardiac vagal tone, and has been shown to decrease stress and reduce the morbidity and mortality of disease.

CONCLUSION

The assessment and management of psychosocial stress is a challenging but important component of effective comprehensive lifestyle interventions for the management of noncommunicable disease. It is, therefore, important for the sports and exercise physician to have an understanding of the therapeutic use of HRV modulation, both in the reduction of stress and in the management of chronic disease.

Prognostic significance of heart rate turbulence parameters in patients with chronic heart failure

Background

This study is aimed to evaluate the clinical significance of heart rate turbulence (HRT) parameters in predicting the prognosis in patients with chronic heart failure (CHF).

Methods

From June 2011 to December 2012, a total of 104 CHF patients and 30 healthy controls were enrolled in this study. We obtained a 24-hour Holter ECG recording to assess the HRT parameters, included turbulence onset (TO), turbulence slope (TS), standard deviation of N-N intervals (SDNN), and resting heart rate (RHR). The relationships between HRT parameters and the prognosis of CHF patients were determined.

Results

The assessment follow-up period lasted until January 31, 2013. The overall mortality of CHF patients was 9.6% (10/104). Our results revealed that CHF patients had higher levels of TO than those of healthy subjects, but the TS levels of CHF patients were lower than that of the control group. CHF patients with NYHA grade IV had higher HRT_1/2 rate than those with NYHA grade II/III. There were statistical differences in TS, LVEF, SDNN and RHR between the non-deteriorating group and the non-survivor group. Significant differences in TS among the three groups were also found. Furthermore, CHF patients in the non-survivor group had lower levels of TS than those in the deteriorating group. Correlation analyses indicated that TO negatively correlate with SDNN, while TS positively correlated with SDNN and left ventricular ejection fraction (LVEF). We also observed negative correlations between TS and left ventricular end-diastolic cavity dimension (LVEDD), RHR, homocysteine (Hcy) and C-reactive protein (CRP). Multivariate Cox regression analysis further confirmed that LVEF (≤30%), HRT₂, SDNN and RHR were independent risk factors which can indicate poor prognosis in CHF patients.

Conclusions

Our findings indicate that HRT may have good clinical predictive value in patients with CHF. Thus, quantifying HRT parameters could be a useful tool for predicting mortality in CHF patients.

Twenty-four-hour ambulatory recording of cerebral hemodynamics, systemic hemodynamics, electrocardiography, and actigraphy during people's daily activities

The feasibility and utility of wearable 24-h multimodality neuromonitoring during daily activities are demonstrated. We have developed a fourth-generation ambulatory near infrared spectroscopy device, namely NINscan 4. NINscan 4 enables recording of brain function (via cerebral hemodynamics), systemic hemodynamics, electrocardiography, and actigraphy simultaneously and continuously for up to 24 h at 250-Hz sampling rate, during (and with minor restriction to) daily activities. We present initial 24-h human subject test results, with example analysis including (1) comparison of cerebral perfusion and oxygenation changes during wakefulness and sleep over a 24-h period and (2) capturing of hemodynamic changes prior, during and after sudden waken up in the night during sleep. These results demonstrate the first ambulatory 24-h cerebral and systemic hemodynamics monitoring, and its unique advantages including long-term data collection and analysis capability, ability to catch unpredictable transient events during activities of daily living, as well as coregistered multimodality analysis capabilities. These results also demonstrate that NINscan 4's motion artifact at 1-g head movement is smaller than physiological hemodynamic fluctuations during motionless sleep. The broader potential of this technology is also discussed.

Bright light therapy for depression: a review of its effects on chronobiology and the autonomic nervous system

Bright light therapy (BLT) is considered among the first-line treatments for seasonal affective disorder (SAD), yet a growing body of literature supports its use in other neuropsychiatric conditions including non-seasonal depression. Despite evidence of its antidepressant efficacy, clinical use of BLT remains highly variable internationally. In this article, we explore the autonomic effects of BLT and suggest that such effects may play a role in its antidepressant and chronotherapeutic properties. After providing a brief introduction on the clinical application of BLT, we review the chronobiological effects of BLT on depression and on the autonomic nervous system in depressed and non-depressed individuals with an emphasis on non-seasonal depression. Such a theory of autonomic modulation via BLT could serve to integrate aspects of recent work centered on alleviating allostatic load, the polyvagal theory, the neurovisceral integration model and emerging evidence on the roles of glutamate and gamma-hydroxybutyric acid (GABA).

Biological and psychological markers of stress in humans: focus on the Trier Social Stress Test

Validated biological and psychological markers of acute stress in humans are an important tool in translational research. The Trier Social Stress Test (TSST), involving public interview and mental arithmetic performance, is among the most popular methods of inducing acute stress in experimental settings, and reliably increases hypothalamic-pituitary-adrenal axis activation. However, although much research has focused on HPA axis activity, the TSST also affects the sympathetic-adrenal-medullary system, the immune system, cardiovascular outputs, gastric function and cognition. We critically assess the utility of different biological and psychological markers, with guidance for future research, and discuss factors which can moderate TSST effects. We outline the effects of the TSST in stress-related disorders, and if these responses can be abrogated by pharmacological and psychological treatments. Modified TSST protocols are discussed, and the TSST is compared to alternative methods of inducing acute stress. Our analysis suggests that multiple readouts are necessary to derive maximum information; this strategy will enhance our understanding of the psychobiology of stress and provide the means to assess novel therapeutic agents.

Impact of personally measured pollutants on cardiac function

Epidemiological studies have shown associations between ambient air pollution and changes in heart rate variability (HRV). However, studies using personal air pollution measurements, especially with exposure averages <24h, are still rare. Between February and March 2008 HRV data as well as personal exposure to particulate matter <2.5μm (PM2.5), and particle number concentrations (PNC) were collected in five volunteers for up to 8.3h on a 5min resolution. Information about the participant's whereabouts was also collected. Mixed models were used to analyze concurrent and up to 30min delayed effects of air pollutants as well as being in traffic on 5min-averages of heart rate (HR), high and low frequency power (HF and LF), standard deviation of all normal-to-normal intervals (SDNN), and the root mean square of successive interval differences (RMSSD). Results are presented as %-change from the mean per increase in interquartile range of air pollutant. In total, 474 5-min segments were available for analysis. We observed concurrent and delayed reductions in SDNN of about 0.8-1.0% in association with a 5.4μg/m(3) increase in PM2.5. However, being in traffic by car led to an increase of about 20% 10-14min and 15-19min later. An increase in PM2.5 or PNC was associated with lagged decreases for RMSSD and HF. We detected concurrent reductions in RMSSD (-17.6% [95%-confidence interval: 29.1; -4.3]) when being in traffic by bike/foot. Being in traffic by car was associated with an immediate reduction in LF while more delayed increases in LF were observed when being in traffic by bike/foot. Air pollution and traffic effects on HR were less consistent. These rapid changes in HRV within 30min might be mediated by the autonomic nervous system in response to direct reflexes from receptors in the lungs.

Autonomic response to a visceral stressor is dysregulated in irritable bowel syndrome and correlates with duration of disease

BACKGROUND

Previous studies reported altered autonomic nervous system (ANS) responses in irritable bowel syndrome (IBS) at baseline and to colonic balloon distension. This study examined heart rate variability (HRV) and plasma catecholamines as an index of ANS responsiveness in IBS during flexible sigmoidoscopy (FS) and explored associations of HRV with clinical measures.

METHODS

Rome III-positive IBS patients and healthy controls completed questionnaires measuring gastrointestinal and psychological symptoms. Heart rate variability measures were calculated using electrocardiogram (ECG) data at rest and during FS. Plasma catecholamines were measured before and after the FS. Linear mixed effects models were used to compare HRV with IBS status and IBS duration across six time points. Significance was assessed at the 0.05 level.

KEY RESULTS

Thirty-six IBS patients (53% F, mean age 37.89) and 31 controls (58% F, mean age 37.26) participated. After adjusting for age, sex, body mass index, and current anxiety symptoms, IBS patients had a non-significant lower cardiovagal tone (P = 0.436) and higher cardiosympathetic balance (P = 0.316) at rest. During FS, controls showed a transient increase in cardiosympathetic balance and decrease in cardiovagal tone. However, IBS patients had significantly less cardiosympathetic and cardiovagal responsiveness both leading up to (P = 0.003, P = 0.005) and following (P = 0.001) this stimulus. Those with longer duration of disease had less cardiosympathetic (P = 0.014) and cardiovagal (P = 0.009) responsiveness than those with shorter duration. No differences in catecholamines between IBS and controls were found.

CONCLUSIONS & INFERENCES

Irritable bowel syndrome demonstrated dysregulated ANS responses to a visceral stressor which could be related to disease duration. Therefore, autonomic dysregulation is an objective physiologic correlate of IBS.

Reduced sympathetic activity in idiopathic rapid-eye-movement sleep behavior disorder and Parkinson's disease

BACKGROUND

More than 50% of patients with idiopathic REM sleep behavior disorder (iRBD) will develop Parkinson's disease or Lewy body dementia. In a previous study, we found attenuated heart rate responses in iRBD and Parkinson's disease patients during sleep. The current study aimed to evaluate heart rate variability further in order to identify possible changes in these components during wakefulness and sleep in patients with iRBD and Parkinson's disease.

METHODS

We evaluated heart rate variability in 5-minute electrocardiography segments from wakefulness, and non-REM and REM sleep in 11 iRBD patients and 23 Parkinson's disease patients, and compared these with 10 control subjects.

RESULTS AND CONCLUSIONS

Patients with iRBD had attenuated sympathetic nervous system activity compared with controls and this was more pronounced in patients with Parkinson's disease. The cardiac parasympathetic nervous system seems to be relatively well preserved in patients with iRBD and Parkinson's disease. The progressive reduction of sympathetic nervous activity is in line with the postganglionic sympathetic nervous dysfunction seen in early Parkinson's disease.

Meditation: should a cardiologist care?

Meditation refers to a family of practices that may share many similarities, but can have differences in underlying methods and goals. Religious and spiritual associations are common but are not requisite for meditation practice and it should be recognized that the basis of many if not all practices is the training of the brain and body, a process that appears to have profound effects on both structure and function. In recent decades there has been interest regarding the effects of these ancient practices on the cardiovascular system, as meditation has intuitive appeal for benefit in this area. Though there is a relative shortage of quality data, available evidence suggests that meditation may exert beneficial effects on autonomic tone, autonomic reflexes, and decrease blood pressure acutely and after long term practice. In addition, meditation has the potential to positively influence the cardiovascular system through the mind-heart connection and the anti-inflammatory reflex. There is limited but promising data to suggest that meditation based interventions can have beneficial effects on patients with established cardiovascular disease. More high quality and unbiased studies of meditation practices on relevant endpoints in cardiovascular disease are needed, including the effects of such practices on inflammation, baseline heart rate variability, arrhythmias, myocardial infarction, and cardiovascular mortality.

Trigonometric regressive spectral analysis: an innovative tool for evaluating the autonomic nervous system

Biological rhythms, describing the temporal variation of biological processes, are a characteristic feature of complex systems. The analysis of biological rhythms can provide important insights into the pathophysiology of different diseases, especially, in cardiovascular medicine. In the field of the autonomic nervous system, heart rate variability (HRV) and baroreflex sensitivity (BRS) describe important fluctuations of blood pressure and heart rate which are often analyzed by Fourier transformation. However, these parameters are stochastic with overlaying rhythmical structures. R-R intervals as independent variables of time are not equidistant. That is why the trigonometric regressive spectral (TRS) analysis--reviewed in this paper--was introduced, considering both the statistical and rhythmical features of such time series. The data segments required for TRS analysis can be as short as 20 s allowing for dynamic evaluation of heart rate and blood pressure interaction over longer periods. Beyond HRV, TRS also estimates BRS based on linear regression analyses of coherent heart rate and blood pressure oscillations. An additional advantage is that all oscillations are analyzed by the same (maximal) number of R-R intervals thereby providing a high number of individual BRS values. This ensures a high confidence level of BRS determination which, along with short recording periods, may be of profound clinical relevance. The dynamic assessment of heart rate and blood pressure spectra by TRS allows a more precise evaluation of cardiovascular modulation under different settings as has already been demonstrated in different clinical studies.

Detection of structural changes in tachogram series for the diagnosis of atrial fibrillation events

Atrial Fibrillation (AF) is the most common cardiac arrhythmia. It naturally tends to become a chronic condition, and chronic Atrial Fibrillation leads to an increase in the risk of death. The study of the electrocardiographic signal, and in particular of the tachogram series, is a usual and effective way to investigate the presence of Atrial Fibrillation and to detect when a single event starts and ends. This work presents a new statistical method to deal with the identification of Atrial Fibrillation events, based on the order identification of the ARIMA models used for describing the RR time series that characterize the different phases of AF (pre-, during, and post-AF). A simulation study is carried out in order to assess the performance of the proposed method. Moreover, an application to real data concerning patients affected by Atrial Fibrillation is presented and discussed. Since the proposed method looks at structural changes of ARIMA models fitted on the RR time series for the AF event with respect to the pre- and post-AF phases, it is able to identify starting and ending points of an AF event even when AF follows or comes before irregular heartbeat time slots.

Evaluation of remifentanil anesthesia for off-pump coronary artery bypass grafting surgery using heart rate variability

Heart rate variability (HRV) was used in the present study to evaluate a target-controlled approach compared with a constant-rate infusion for remifentanil anesthesia during off-pump coronary artery bypass grafting (OP-CABG) surgery. A total of 65 patients with American Society of Anesthesiologists (ASA) physical status II or III, who were aged 60–85 years and scheduled for OP-CABG, were selected for the study. All patients were administered an intramuscular premedication of 10 mg morphine and 0.3 mg scopolamine. In group I, remifentanil was infused using a target-controlled approach at 1.5–5.0 ng/ml, and in group II, remifentanil was infused at a constant-rate of 0.05–1.0 μg/kg/min and at additional single increments of 1 μg/kg when appropriate. The heart rate and other hemodynamic monitoring indices of the patients, including the mean arterial pressure, central venous pressure, pulmonary artery pressure and pulmonary capillary wedge pressure, were monitored at various time points, including prior to induction (T₀), at extubation (performed intraoperatively; T₇) and at 24 h post-surgery. The HRV indices, including total power (TP), low frequency (LF) and the LF/high frequency (HF) ratio of power (LF/HF), were reduced following induction at T₀ and remained low at 24 h post-surgery. At T₅ (right coronary or left circumflex artery anastomosis) and T₇ (tracheal extubation), all the HRV indices, with the exception of the HF power, were significantly increased (P<0.05). Additionally, the TP, LF and LF/HF values in group II were higher at T₅ compared with those in group I (P<0.05). Remifentanil target-controlled infusion is superior to constant-rate infusion in suppressing the stress response during OP-CABG, maintaining the balance of the cardiac autonomic nervous system and promoting the recovery of the autonomic function following surgery.