Protective effect of metoprolol on arrhythmia and heart rate variability in healthy people with 24 hours of sleep deprivation

Sleep Deficiency and Cardiometabolic Disease

Epidemiologic studies have demonstrated that short sleep duration is associated with an increased risk of cardio-metabolic health outcomes including cardiovascular disease mortality, coronary heart disease, type 2 diabetes mellitus, hypertension, and metabolic syndrome. Experimental sleep restriction studies have sought to explain these findings. This review describes the main evidence of these associations and possible mechanisms explaining them. Whether sleep extension reverses these now widely acknowledged adverse health effects and the feasibility of implementing such strategies on a public health level is discussed.

2024 HRS expert consensus statement on arrhythmias in the athlete: Evaluation, treatment, and return to play

Youth and adult participation in sports continues to increase, and athletes may be diagnosed with potentially arrhythmogenic cardiac conditions. This international multidisciplinary document is intended to guide electrophysiologists, sports cardiologists, and associated health care team members in the diagnosis, treatment, and management of arrhythmic conditions in the athlete with the goal of facilitating return to sport and avoiding the harm caused by restriction. Expert, disease-specific risk assessment in the context of athlete symptoms and diagnoses is emphasized throughout the document. After appropriate risk assessment, management of arrhythmias geared toward return to play when possible is addressed. Other topics include shared decision-making and emergency action planning. The goal of this document is to provide evidence-based recommendations impacting all areas in the care of athletes with arrhythmic conditions. Areas in need of further study are also discussed.

Acute combined effects of concurrent physical activities on autonomic nervous activation during cognitive tasks

Backgrounds: The validity of heart rate variability (HRV) has been substantiated in mental workload assessments. However, cognitive tasks often coincide with physical exertion in practical mental work, but their synergic effects on HRV remains insufficiently established. The study aims were to investigate the combined effects of cognitive and physical load on autonomic nerve functions. Methods: Thirty-five healthy male subjects (aged 23.5 ± 3.3 years) were eligible and enrolled in the study. The subjects engaged in n-back cognitive tasks (1-back, 2-back, and 3-back) under three distinct physical conditions, involving isotonic contraction of the left upper limb with loads of 0 kg, 3 kg, and 5 kg. Electrocardiogram signals and cognitive task performance were recorded throughout the tasks, and post-task assessment of subjective experiences were conducted using the NASA-TLX scale. Results: The execution of n-back tasks resulted in enhanced perceptions of task-load feelings and increased reaction times among subjects, accompanied by a decline in the accuracy rate (p < 0.05). These effects were synchronously intensified by the imposition of physical load. Comparative analysis with a no-physical-load scenario revealed significant alterations in the HRV of the subjects during the cognitive task under moderate and high physical conditions. The main features were a decreased power of the high frequency component (p < 0.05) and an increased low frequency component (p < 0.05), signifying an elevation in sympathetic activity. This physiological response manifested similarly at both moderate and high physical levels. In addition, a discernible linear correlation was observed between HRV and task-load feelings, as well as task performance under the influence of physical load (p < 0.05). Conclusion: HRV can serve as a viable indicator for assessing mental workload in the context of physical activities, making it suitable for real-world mental work scenarios.

Sleep Deficiency and Cardiometabolic Disease

Epidemiologic studies have demonstrated that short sleep duration is associated with an increased risk of cardio-metabolic health outcomes including cardiovascular disease mortality, coronary heart disease, type 2 diabetes mellitus, hypertension, and metabolic syndrome. Experimental sleep restriction studies have sought to explain these findings. This review describes the main evidence of these associations and possible mechanisms explaining them. Whether sleep extension reverses these now widely acknowledged adverse health effects and the feasibility of implementing such strategies on a public health level is discussed.

Long-Term Sleep Deprivation-Induced Myocardial Remodeling and Mitochondrial Dysfunction in Mice Were Attenuated by Lipoic Acid and N-Acetylcysteine

The impact of long-term sleep deprivation on the heart and its underlying mechanisms are poorly understood. The present study aimed to investigate the impact of chronic sleep deprivation (CSD) on the heart and mitochondrial function and explore an effective drug for treating CSD-induced heart dysfunction. We used a modified method to induce CSD in mice; lipoic acid (LA) and N-acetylcysteine (NAC) were used to treat CSD mice. Echocardiography, hematoxylin-eosin (H&E) staining, Sirius red staining, and immunohistochemistry were used to determine heart function and cardiac fibrosis. The serum levels of brain natriuretic peptide (BNP), superoxide Dismutase (SOD), micro malondialdehyde (MDA), and glutathione (GSH) were measured to determine cardiovascular and oxidative stress-related damage. Transmission electron microscopy was used to investigate mitochondrial damage. RNA-seq and Western blotting were used to explore related pathways. We found that the left ventricular ejection fraction (LVEF) and fraction shortening (LVFS) values were significantly decreased and myocardial hypertrophy was induced, accompanied by damaged mitochondria, elevated reactive oxygen species (ROS), and reduced SOD levels. RNA-sequence analysis of the heart tissue showed that various differentially expressed genes in the metabolic pathway were enriched. Sirtuin 1 (Sirt1) and Glutathione S-transferase A3 (Gsta3) may be responsible for CSD-induced heart and mitochondrial dysfunction. Pharmacological inhibition of ROS by treating CSD mice with LA and NAC effectively reduced heart damage and mitochondrial dysfunction by regulating Sirt1 and Gsta3 expression. Our data contribute to understanding the pathways of CSD-induced heart dysfunction, and pharmacological targeting to ROS may represent a strategy to prevent CSD-induced heart damage.

Effects of 24-h acute total sleep deprivation on physiological coupling in healthy young adults

Sleep deprivation is associated with dysregulation of the autonomic nervous system, adverse cardiovascular events, cognitive and complex motor performance impairment. Less is known about the effects of acute total sleep deprivation (ATSD) on physiological coupling. We aimed to determine the effects of 24-h ATSD on the physiological coupling between complex subsystems by evaluating the cardiorespiratory, cardiovascular and cortico-cardiac interactions. This study enrolled 38 young healthy participants aged 23.2 ± 2.4 years. Multiple synchronous physiological signals including electrocardiography, photoplethysmography, bio-electrical impedance, electroencephalography, and continuous hemodynamic data, were performed over a baseline night after regular sleep and after a night with 24-h ATSD in the supine position. The magnitude squared coherence, phase synchronization index, and heartbeat evoked potential amplitudes, were obtained from 10-min synchronous physiological recordings to estimate the coupling strength between two time series. Parameters of hemodynamic characteristics and heart rate variability were also calculated to quantify autonomic regulation. Results indicated that the magnitude squared coherence (0.38 ± 0.17 vs. 0.29 ± 0.12, p = 0.015) between respiration and heart rate variability along with the magnitude squared coherence (0.36 ± 0.18 vs. 0.27 ± 0.13, p = 0.012) between respiration and pulse transit time were significantly decreased after 24-h ATSD. There were no significant differences (all p > 0.05) in phase synchronization indices, heartbeat evoked potential amplitudes as well as other analyzed measurements between baseline and 24-h ATSD states. We conclude that exposure to 24-h ATSD appears to weaken the cardiorespiratory and respiratory-cardiovascular coupling strength of young healthy adults. These findings suggest that physiological coupling analysis may serve as a complementary approach for characterizing and understanding the complex effects of sleep deprivation.

Sleep Deficiency and Cardiometabolic Disease

Epidemiologic studies have demonstrated that short sleep duration is associated with an increased risk of cardio-metabolic health outcomes including cardiovascular disease mortality, coronary heart disease, type 2 diabetes mellitus, hypertension, and metabolic syndrome. Experimental sleep restriction studies have sought to explain these findings. This review describes the main evidence of these associations and possible mechanisms explaining them. Whether sleep extension reverses these now widely acknowledged adverse health effects and the feasibility of implementing such strategies on a public health level is discussed.

Aberrant autonomic pattern during the post-exercise recovery phase in long QT syndrome patients

OBJECTIVES

It is well-established that the autonomic nervous system (ANS) plays a central role in arrhythmogenesis. During and after exercise the ANS is particularly active, and since long QT syndrome (LQTS) patients have an increased risk of lethal arrhythmias during physical activity, it is important to investigate the autonomic function in these patients. In this study we investigate the ANS response during and after exercise in LQTS patients and healthy age and sex matched controls.

METHODS

Forty-four genotype-verified adult LQTS patients and forty-four healthy age- and sex-matched controls performed a submaximal bicycle exercise stress test. Heart rate recovery (HRR) and heart rate variability (HRV) were analyzed from registered electrocardiogram (ECG) and vector electrocardiogram (VCG) recordings collected throughout rest, exercise and in the post-exercise phase.

RESULTS

LQTS patients had a slower HRR than controls at 1- and 4-min post-exercise (p < 0.001). During the post-exercise phase, LQTS patients had a lower total power (p < 0.001), low frequency power (p < 0.001) and high frequency power (p < 0.001) than controls. In the same phase, LQTS patients off betablocker (BB) treatment showed a lower high frequency power (p = 0.01) and different low frequency/high frequency ratio (p = 0.003) when comparing with LQTS patients on BB treatment.

CONCLUSIONS

The parasympathetic effect on both HRR and HRV after exercise appears depressed in this LQTS patient cohort compared to healthy controls. This indicates an aberrant ANS response during the post-exercise phase which might be compensated by BB treatment. Our findings emphasize the importance of performing further investigations to identify the role of the ANS in LQTS arrhythmogenesis.

The Acute Readiness Monitoring Scale: Assessing Predictive and Concurrent Validation

To complement and enhance readiness-monitoring capability, the Acute Readiness Monitoring Scale (ARMS) was developed: a widely applicable, simple psychometric measure of perceived readiness. While this tool may have widespread utility in sport and military settings, it remains unknown if the ARMS demonstrates predictive and concurrent validity. Here, we investigated whether the ARMS is: (1) responsive to an acute manipulation of readiness using sleep deprivation, (2) relates to biological markers of readiness [cortisol/heart-rate variability (HRV)], and (3) predicts performance on a cognitive task. Thirty young adults (aged 23 ± 4 years; 18 females) participated. All participants engaged in a 24-h sleep deprivation protocol. Participants completed the ARMS, biological measures of readiness (salivary cortisol, HRV), and cognitive performance measures (psychomotor vigilance task) before, immediately after, 24-, and 48-h post-sleep deprivation. All six of the ARMS subscales changed in response to sleep deprivation: scores on each subscale worsened (indicating reductions in perceived readiness) immediately after sleep deprivation, returning to baseline 24/48 h post. Lower perceived readiness was associated with reduced awakening responses in cortisol and predicted worse cognitive performance (slower reaction time). No relationship was observed between the ARMS and HRV, nor between any biological markers of readiness (cortisol/HRV) and cognitive performance. These data suggest that the ARMS may hold practical utility in detecting, or screening for, the wide range of deleterious effects caused by sleep deprivation; may constitute a quick, cheap, and easily interpreted alternative to biological measures of readiness; and may be used to monitor or mitigate potential underperformance on tasks requiring attention and vigilance.

Pharmacological Evaluation of the Effects of Phenylcarbamic Acid Derivatives on Cardiovascular Functions in Rats

Four phenylcarbamic acid derivatives, (1-(4-fluorophenyl)- 4-[3-(4-methoxyphenylcarbamoyloxy)-2-hydroxypropyl]piperazinium chloride (1), (1-(2-methylphenyl)-4-[3-(4-methoxyphenylcarbamoyloxy)- 2-hydroxypropyl]piperazinium chloride) (2), (1-(2-methylphenyl)-4-[3-(4-ethoxyphenylcarbamoyloxy)- 2-hydroxypropyl]piperazinium chloride) (3) and (1-(3-trifluoromethylphenyl)-4-[3-(4-methoxyphenylcarbamoyloxy)- 2-hydroxypropyl]piperazinium chloride) (4) were investigated for their ability to affect various cardiovascular functions and to establish their chemical structure-biological activity relationship. The compounds were evaluated for their antiarrhythmic efficacy using ouabain-induced rhythm disturbances and the ability to inhibit the positive chronotropic effect of isoproterenol in isolated atria of Wistar rats. Electrocardiogram (ECG) parameters in isolated hearts of spontaneously hypertensive rats (SHR) perfused according to the Langendorff method and ability to decrease phenylephrine- -induced contraction of the aortic strips after repeated administration of the compounds were also analyzed. Only compound 3 delayed significantly the evaluated parameter of arrhythmogenicity and was able to antagonize the isoproterenol- induced positive chronotropic effect in normotensive rats' atria. Similarly, in SHR rats, only compound 3 was able to decrease heart frequency significantly without influencing the duration of QT (time between the start of the Q wave and the end of the T wave) and QTc (frequency corrected QT) intervals. The evaluated endothelial function was improved after administration of compound 2. Fluorine-containing structures (1 and 4) were less effective compared to 2´-methylphenylpiperazine derivatives (2 and 3). The latter two compounds showed suitable efficacy, which supported their use for futher pharmacological research.

Effect of Ling-Gui-Zhu-Gan decoction major components on the plasma protein binding of metoprolol using UPLC analysis coupled with ultrafiltration

Using traditional Chinese medicine formula Ling-Gui-Zhu-Gan decoction (LGZGD) plus selective β1-adrenergic receptor inhibitor metoprolol to treat arrhythmia of coronary heart disease can significantly improve efficiency with no adverse reactions. However, the effect of major components of LGZGD on the plasma protein binding of metoprolol is unclear. Firstly, this study aimed to computationally predict the molecular interactions between metoprolol, the major components of LGZGD, and bovine serum albumin (BSA). Secondly, the plasma protein binding of metoprolol combined with major components of LGZGD was investigated by UPLC analysis coupled with ultrafiltration. The MOE (2008.10) software package was used to investigate the molecular interactions among metoprolol, the major components of LGZGD, and BSA. Using in vitro experiments, BSA was separately spiked with a mixtures of metoprolol and the major components of LGZGD. The results showed that metoprolol interacted with BSA mainly through arene-arene interactions, as did cinnamic acid and liquiritin. However, the energy scores of cinnamic acid and liquiritin were lower than that of metoprolol. There were no interactions between metoprolol and the major components of LGZGD. Further studies in vitro showed that the presence of the major components of LGZGD did not change the plasma protein binding of metoprolol. We adopted molecular docking to predict the drug-herb plasma protein binding interactions of metoprolol and then used ultrafiltration to verify the docking results. There were no drug-herb interactions between metoprolol and LGZGD in BSA, which indicated that this combination therapy might be safe and feasible.

Physiological and autonomic stress responses after prolonged sleep restriction and subsequent recovery sleep in healthy young men

Purpose

Sleep restriction is increasingly common and associated with the development of health problems. We investigated how the neuroendocrine stress systems respond to prolonged sleep restriction and subsequent recovery sleep in healthy young men.

Methods

After two baseline (BL) nights of 8 h time in bed (TIB), TIB was restricted to 4 h per night for five nights (sleep restriction, SR, n = 15), followed by three recovery nights (REC) of 8 h TIB, representing a busy workweek and a recovery weekend. The control group (n = 8) had 8 h TIB throughout the experiment. A variety of autonomic cardiovascular parameters, together with salivary neuropeptide Y (NPY) and cortisol levels, were assessed.

Results

In the control group, none of the parameters changed. In the experimental group, heart rate increased from 60 ± 1.8 beats per minute (bpm) at BL, to 63 ± 1.1 bpm after SR and further to 65 ± 1.8 bpm after REC. In addition, whole day low-frequency to-high frequency (LF/HF) power ratio of heart rate variability increased from 4.6 ± 0.4 at BL to 6.0 ± 0.6 after SR. Other parameters, including salivary NPY and cortisol levels, remained unaffected.

Conclusions

Increased heart rate and LF/HF power ratio are early signs of an increased sympathetic activity after prolonged sleep restriction. To reliably interpret the clinical significance of these early signs of physiological stress, a follow-up study would be needed to evaluate if the stress responses escalate and lead to more unfavourable reactions, such as elevated blood pressure and a subsequent elevated risk for cardiovascular health problems.

Decreases in heart rate variability are associated with postoperative complications in hip fracture patients

Background

To explore relevant associations between deviations in linear and nonlinear heart rate variability (HRV) scores, and short-term morbidity and mortality in patients undergoing hip-surgery after a fracture.

Methods

165 patients with hip fractures being admitted for surgery at two hospitals were included in a prospective cohort study. A short-term ECG was recorded within 24 hours of arrival. 15 patients had to be excluded due to insufficient quality of the ECG recordings. 150 patients were included in the final analysis. Linear parameters were calculated in time domain: standard deviation of NN intervals (SDNN), root mean square of successive differences (rMSSD); and frequency domain: Total Power (TP), High Frequency Power (HF), Low Frequency Power (LF), Very Low Frequency Power (VLF), and the ratio of LF/HF. Postoperative outcome was evaluated at the time of discharge. This included occurrence of pneumonia, overall infection rate, stroke, myocardial infarction, and all-cause mortality.

Results

Patients experiencing complications had significantly lower rMSSD (p = 0.04), and TP (p = 0.03) preoperatively. Postoperative infections were predicted by decreased VLF preoperatively (p = 0.04). There was a significant association between pneumonia and LF/HF<1 (p = 0.03). The likelihood ratio to develop pneumonia when LF/HF < 1 was 6,1.

Conclusion

HRV seems to reflect the general frailty of the patient with hip fracture and might be used to identify patients in need of increased surveillance or prophylactic treatment.

Effects of Statin on Arrhythmia and Heart Rate Variability in Healthy Persons With 48-Hour Sleep Deprivation

BACKGROUND

It has been reported that sleep deprivation is associated with cardiac autonomic disorder, inflammation, and oxidative stress. Statins have significant cardiovascular protective effects in patients with cardiovascular disease. This study aimed to investigate the protective effect of statins on arrhythmia and heart rate variability in young healthy persons after 48-hour sleep deprivation.

METHODS AND RESULTS

This study enrolled 72 young healthy participants aged 26.5±3.5 years. All participants received 48-hour continuous ambulatory electrocardiogram monitoring. Arrhythmia, time, and frequency domain parameters were analyzed for all participants. The primary end point, low/high frequency ratio, was significantly lower in the statin group than in the control group (2.48±1.12 versus 3.02±1.23, P<0.001). After 48-hour sleep deprivation, low frequency-the frequency of premature atrial complexes and premature ventricular complexes-was significantly decreased in the statin group compared with the control group (P<0.05). There was also a significant increase in high frequency in the statin group compared with the control group (P<0.05). There was a significant decrease in serum high-sensitivity C-reactive protein and malondialdehyde levels after 48-hour sleep deprivation in the statin group compared with the control group (P<0.05).

CONCLUSIONS

Statin use might be associated with improvement in arrhythmia and heart rate variability in healthy persons with 48-hour sleep deprivation. This finding should be confirmed by larger scale trials.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02496962.

Sleep Disruption is Associated with Increased Ventricular Ectopy and Cardiac Arrest in Hospitalized Adults

STUDY OBJECTIVES

To determine whether sleep disruption increases ventricular ectopy and the risk of cardiac arrest in hospitalized patients.

METHODS

Hospital emergency codes (HEC) trigger multiple hospital-wide overhead announcements. In 2014 an electronic "code white" program was instituted to protect staff from violent patients. This resulted in an increase in nocturnal HEC. Telemetry data was examined between September 14 and October 2, 2014. The frequency of nocturnal announcements was correlated with changes in frequency of premature ventricular complexes per hour (PVC/h). Cardiac arrest data were examined over a 3-y period. All HEC were assumed to have triggered announcements. The relationship between nocturnal HEC and the incidence of subsequent cardiac arrest was examined.

RESULTS

2,603 hours of telemetry were analyzed in 87 patients. During nights with two or fewer announcements, PVC/h decreased 33% and remained 30% lower the next day. On nights with four or more announcements, PVC/h increased 23% (P < 0.001) and further increased 85% the next day (P = 0.001). In 2014, following the introduction of the code white program, the frequency of all HEC increased from 1.1/day to 6.2/day (P < 0.05). The frequency of cardiac arrest/24 h rose from 0.46/day in 2012-2013 to 0.62/day in 2014 (P = 0.001). During daytime hours (06:00-22:00), from 2012 through 2014, the frequency of cardiac arrest following zero, one or at least two nocturnal HEC were 0.331 ± 0.03, 0.396 ± 0.04 and 0.471 ± 0.09 respectively (R(2) = 0.99, P = 0.03).

CONCLUSIONS

Sleep disruption is associated with increased ventricular ectopy and increased frequency of cardiac arrest.

Genetic, Epigenetic, and Environmental Factors Influencing Neurovisceral Integration of Cardiovascular Modulation: Focus on Multiple Sclerosis

Thought to be an autoimmune inflammatory CNS disease, multiple sclerosis (MS) involves multiple pathologies with heterogeneous clinical presentations. An impaired neurovisceral integration of cardiovascular modulation, indicated by sympathetic and parasympathetic autonomic nervous system (ANS) dysfunction, is among common MS clinical presentations. ANS dysfunction could not only enhance MS inflammatory and neurodegenerative processes, but can also lead to clinical symptoms such as depression, fatigue, sleep disorder, migraine, osteoporosis, and cerebral hemodynamic impairments. Therefore, factors influencing ANS functional activities, in one way or another, will have a significant impact on MS disease course. This review describes the genetic and epigenetic factors, and their interactions with a number of environmental factors contributing to the neurovisceral integration of cardiovascular modulation, with a focus on MS. Future studies should investigate the improvement in cardiovascular ANS function, as a strategy for preventing and minimizing MS-related morbidities, and improving patients' quality of life.

Cardiac autonomic changes after 40 hours of total sleep deprivation in women

OBJECTIVES

The effect of total sleep deprivation on heart rate variability (HRV) in groups of postmenopausal women on oral hormone therapy (HT) (on-HT, n = 10, 64.2 (1.4) years), postmenopausal women without HT (off-HT, n = 10, 64.6 (1.4) years) and young women (n = 11, 23.1 (0.5) years) was studied using a prospective case-control setup.

METHODS

Polysomnography was performed over an adaptation night, a baseline night, and a recovery night after 40 h of total sleep deprivation. Time and frequency domain and nonlinear HRV from overnight electrocardiogram recordings were compared between groups during baseline and recovery nights. Further, the changes in HRV from baseline to recovery were analysed and compared between groups. Finally, correlations of HRV to percentages of sleep stages and measures of sleep fragmentation were analysed during baseline and recovery.

RESULTS

Young women had higher HRV than older women; the most marked difference was between young and on-HT postmenopausal women. Sleep deprivation induced a decrease in frequency domain HRV in young and in off-HT women, an increase in α2 in off-HT women, and an increase in mean heart rate in on-HT women. The sleep deprivation effect was mainly uncorrelated to changes in sleep parameters.

CONCLUSIONS

Acute total sleep deprivation has a deleterious effect on the autonomic nervous system in young women, but an even more pronounced effect in postmenopausal women. Hormone therapy use in late postmenopause does not give protection against these changes. These harmful effects may partly explain the increased cardiovascular morbidity and overall mortality associated with sleep loss.

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.