Short-term Heart Rate Variability Analysis Research Articles

Validity of the Polar V800 monitor for measuring heart rate variability in mountain running route conditions.

This study was conducted to test, in mountain running route conditions, the accuracy of the Polar V800™ monitor as a suitable device for monitoring the heart rate variability (HRV) of runners. Eighteen healthy subjects ran a route that included a range of running slopes such as those encountered in trail and ultra-trail races. The comparative study of a V800 and a Holter SEER 12 ECG Recorder™ included the analysis of RR time series and short-term HRV analysis. A correction algorithm was designed to obtain the corrected Polar RR intervals. Six 5-min segments related to different running slopes were considered for each subject. The correlation between corrected V800 RR intervals and Holter RR intervals was very high (r = 0.99, p < 0.001), and the bias was less than 1ms. The limits of agreement (LoA) obtained for SDNN and RMSSD were (- 0.25 to 0.32ms) and (- 0.90 to 1.08ms), respectively. The effect size (ES) obtained in the time domain HRV parameters was considered small (ES < 0.2). Frequency domain HRV parameters did not differ (p > 0.05) and were well correlated (r ≥ 0.96, p < 0.001). Narrow limits of agreement, high correlations and small effect size suggest that the Polar V800 is a valid tool for the analysis of heart rate variability in athletes while running high endurance events such as marathon, trail, and ultra-trail races.

A study of heart rate variability among non-diabetic offspring of type 2 diabetic parents

Background: Type 2 diabetes mellitus is an inheritable condition that runs in families as a disorder of impaired glycemic control and its complications. Among the complications of diabetes, autonomic neuropathy contributes to the development of cardiovascular disease states besides diabetic vascular complications. Sympathovagal imbalance is reported to be observed among the non-diabetic first-degree relatives of diabetic population. Aims and Objectives: To assess the heart rate variability (HRV) parameters in non-diabetic normotensive offspring of diabetic parents and infer the impairment in sympathovagal balance in them by comparing with the HRV findings of non-diabetic offspring of non-diabetic parents. Materials and Methods: This cross-sectional observational study was conducted on 30 healthy non-diabetic, normotensive volunteers with parental history of Type 2 diabetes and 30 non-diabetic normotensive volunteers without parental history of diabetes. The volunteers were between the age of 17 and 25 years with normal body mass index and no health condition that could influence the cardiovascular health. The basal cardiovascular parameters and a 5 min lead II electrocardiogram for short-term HRV analysis were recorded to assess the sympathovagal balance. Results: The HRV analysis reveals a statistically significant increase in the sympathetic components and decreased parasympathetic components in the nondiabetic offspring of diabetic parents when compared to the non-diabetic offspring of non-diabetic parents. Conclusion: From our study, it could be observed that the non-diabetic offspring of diabetic parents have enhanced sympathetic activity and attenuated vagal activity even in their non-diabetic state, thus inferring an early onset of sympathovagal imbalance that could predispose them to hypertension and its sequel.

Psychophysiological evaluation of patients with transient consciousness loss of uncertain origin

Psychological profile (PsyP) of patients with transient loss of consciousness (TLoC) is evidence of high prevalence of anxiety and depression. However, the mechanistic link between abnormal PsyP and TLoC is still unclear. This study aimed to evaluate: 1) prevalence of abnormal PsyP in TLoC patients; 2) cardiac autonomic response to head-up tilt test (HUTT) in patients with (PsyP+) or without abnormal PsyP (PsyP-), developing syncope (HUTT+) or not (HUTT-). Forty-one patients (66% female, mean age 36 ± 15 years), with history of TLoC, underwent PsyP before HUTT. Short-term heart rate variability analysis was carried out under baseline rest condition and at peak heart rate and/or onset of syncope induced by nitroglycerine (NTG), during HUTT. HUTT+ occurred in 17/41 patients, more frequently in females, who had higher levels of anxiety (p < 0.0001). PsyP+ was prevalent in 70.5% of HUTT+ patients (p < 0.05). Among PsyP+ patients HUTT+ had dominant sympathetic modulation (DSM) at rest, which increased at the onset of syncope, whereas in HUTT patients vagal modulation was prevalent at rest. Among NTG-induced HUTT+ patients, fourfold higher increases of very low frequency (VLF) power were found in PsyP- compared with PsyP+. 58% of patients with history of TLoC were PsyP+. In PsyP+ patients, DSM at rest correlates with higher prob-ability of NTG-induced syncope, which occurs with 60% increment of low frequency and 530% increment of VLF power. Conversely, in patients with prevalent vagal modulation at rest and a decrease in VLF power after NTG, syncope did not occur. This supports interpretation of VLF power as an index of stress-induced sympathetic activity.

Estimation of confidence limits for descriptive indexes derived from autoregressive analysis of time series: Methods and application to heart rate variability.

The growing interest in personalized medicine requires making inferences from descriptive indexes estimated from individual recordings of physiological signals, with statistical analyses focused on individual differences between/within subjects, rather than comparing supposedly homogeneous cohorts. To this end, methods to compute confidence limits of individual estimates of descriptive indexes are needed. This study introduces numerical methods to compute such confidence limits and perform statistical comparisons between indexes derived from autoregressive (AR) modeling of individual time series. Analytical approaches are generally not viable, because the indexes are usually nonlinear functions of the AR parameters. We exploit Monte Carlo (MC) and Bootstrap (BS) methods to reproduce the sampling distribution of the AR parameters and indexes computed from them. Here, these methods are implemented for spectral and information-theoretic indexes of heart-rate variability (HRV) estimated from AR models of heart-period time series. First, the MS and BC methods are tested in a wide range of synthetic HRV time series, showing good agreement with a gold-standard approach (i.e. multiple realizations of the "true" process driving the simulation). Then, real HRV time series measured from volunteers performing cognitive tasks are considered, documenting (i) the strong variability of confidence limits' width across recordings, (ii) the diversity of individual responses to the same task, and (iii) frequent disagreement between the cohort-average response and that of many individuals. We conclude that MC and BS methods are robust in estimating confidence limits of these AR-based indexes and thus recommended for short-term HRV analysis. Moreover, the strong inter-individual differences in the response to tasks shown by AR-based indexes evidence the need of individual-by-individual assessments of HRV features. Given their generality, MC and BS methods are promising for applications in biomedical signal processing and beyond, providing a powerful new tool for assessing the confidence limits of indexes estimated from individual recordings.

Permutation entropy analysis of heart rate variability for the assessment of cardiovascular autonomic neuropathy in type 1 diabetes mellitus

Heart rate variability (HRV) analysis is a relevant tool for the diagnosis of cardiovascular autonomic neuropathy (CAN). To our knowledge, no previous investigation on CAN has assessed the complexity of HRV from an ordinal perspective. Therefore, the aim of this work is to explore the potential of permutation entropy (PE) analysis of HRV complexity for the assessment of CAN. For this purpose, we performed a short-term PE analysis of HRV in healthy subjects and type 1 diabetes mellitus patients, including patients with CAN. Standard HRV indicators were also calculated in the control group. A discriminant analysis was used to select the variables combination with best discriminative power between control and CAN patients groups, as well as for classifying cases. We found that for some specific temporal scales, PE indicators were significantly lower in CAN patients than those calculated for controls. In such cases, there were ordinal patterns with high probabilities of occurrence, while others were hardly found. We posit this behavior occurs due to a decrease of HRV complexity in the diseased system. Discriminant functions based on PE measures or probabilities of occurrence of ordinal patterns provided an average of 75% and 96% classification accuracy. Correlations of PE and HRV measures showed to depend only on temporal scale, regardless of pattern length. PE analysis at some specific temporal scales, seem to provide additional information to that obtained with traditional HRV methods. We concluded that PE analysis of HRV is a promising method for the assessment of CAN.

Relationship among Sleep Quality, Heart Rate Variability, Fatigue, Depression, and Anxiety in Adults

Purpose: The purpose of this study was to investigate the relationship among sleep quality, heart rate variability (HRV), fatigue, depression, and anxiety reported by Korean adults. Methods: A cross-sectional study of 208 adults aged 20~60 years was conducted using a short-term HRV analysis and self...

Approximate entropy profile: a novel approach to comprehend irregularity of short-term HRV signal

Kolmogorov–Sinai entropy-based irregularity measures such as approximate entropy (ApEn), sample entropy and fuzzy entropy are widely used for short-term heart rate variability analysis. These entropy statistics are estimated for a specific value of the tolerance parameter (r) that is mostly chosen from a common recommended range. Entropy measurement on short-term signals is highly sensitive to the choice of r. An incorrect selection of r results in an inaccurate entropy value, thereby leading to unreliable information retrieval. By addressing this inaccuracy due to r selection, the quality and reliability of information retrieval can be improved. Thus, we hypothesize that generating a complete entropy profile using all potential r values will give a more complete and useful information about signal irregularity in contrast to the case of finding entropy at a single selected value of r. In order to do so, one must be able to accurately select all potential r candidates. In this paper, we use a data-driven algorithm based on cumulative histograms to automatically select potential r values for an individual signal based on its dynamics. An appropriate set of r values is designated by the algorithm for generating a series of ApEn values (ApEn profile) instead of a single value of ApEn. ApEn profile- based secondary measures such as TotalApEn and SDApEn have been used as features to classify sets of synthetic and physiologic data. Our study proves that secondary measures obtained from an ApEn profile are more efficient in indicating irregularity levels in comparison with the traditional measure of ApEn evaluated at a single r value, specially in the case of short length data.

Assessment of heart rate variability and reaction time in traffic policemen

Introduction: Air Pollution can have a deleterious effect on cardiovascular function and cognition. Heart rate variability (HRV), which is a non-invasive and objective measure of cardiac autonomic function, is a cardiovascular risk predictor. Reaction time is a simple method of assessing the perceptual-cognitive processing capability of the central nervous system. Hence, the aim of the study was to assess the heart rate variability and reaction time in traffic police officers of Puducherry. Methods: Fifty-five age and BMI matched traffic police and healthy controls were recruited. Basal cardiovascular parameters; basal heart rate, systolic and diastolic blood pressure (BHR, SBP, DBP) were assessed. Short term HRV analysis was done. Time and frequency domain indices were computed. Simple and Choice Auditory and Visual reaction time (SART, CART, SVRT, CVRT) were measured. Results: BHR and DBP were significantly increased in traffic police. Time domain indices (Mean RR, SDNN, RMSSD, pNN50) were significantly reduced in traffic police. In frequency domain, Total Power was significantly reduced. LF-HF ratio was increased, though not significant. SVRT was significantly delayed in traffic police. CVRT, SART and CART were delayed in traffic police though not significant. Conclusion: Traffic police have decreased HRV with increased sympathetic and decreased vagal tone, and delayed reaction time.

Validation of PC-based Sound Card with Biopac for Digitalization of ECG Recording in Short-term HRV Analysis.

Background:Heart rate variability (HRV) analysis is a simple and noninvasive technique capable of assessing autonomic nervous system modulation on heart rate (HR) in healthy as well as disease conditions. The aim of the present study was to compare (validate) the HRV using a temporal series of electrocardiograms (ECG) obtained by simple analog amplifier with PC-based sound card (audacity) and Biopac MP36 module.Materials and Methods:Based on the inclusion criteria, 120 healthy participants, including 72 males and 48 females, participated in the present study. Following standard protocol, 5-min ECG was recorded after 10 min of supine rest by Portable simple analog amplifier PC-based sound card as well as by Biopac module with surface electrodes in Leads II position simultaneously. All the ECG data was visually screened and was found to be free of ectopic beats and noise. RR intervals from both ECG recordings were analyzed separately in Kubios software. Short-term HRV indexes in both time and frequency domain were used.Results:The unpaired Student's t-test and Pearson correlation coefficient test were used for the analysis using the R statistical software. No statistically significant differences were observed when comparing the values analyzed by means of the two devices for HRV. Correlation analysis revealed perfect positive correlation (r = 0.99, P < 0.001) between the values in time and frequency domain obtained by the devices.Conclusion:On the basis of the results of the present study, we suggest that the calculation of HRV values in the time and frequency domains by RR series obtained from the PC-based sound card is probably as reliable as those obtained by the gold standard Biopac MP36.

Short-term heart rate variability (HRV) in healthy dogs.

Heart rate variability (HRV) is a well established mortality risk factor in both healthy dogs and those with heart failure. While the standards for short-term HRV analysis have been developed in humans, only reference values for HRV parameters determined from 24-hour ECG have been proposed in dogs. The aim of this study was to develop the reference values for short-term HRV parameters in a group of 50 healthy dogs of various breeds (age 4.86 ± 2.74 years, body weight 12.2 ± 3.88 kg). The ECG was recorded continuously for at least 180 min in a dark and quiet room. All electrocardiograms were inspected automatically and manually to eliminate atrial or ventricular premature complexes. Signals were transformed into a spectrum using the fast Fourier transform. The HRV parameters were measured at fixed times from 60-min ECG segments. The following time-domain parameters (ms) were analyzed: mean NN, SDNN, SDANN, SDNN index, rMSSD and pNN50. Moreover, frequency-domain parameters (Hz) were determined, including very low frequency (VLF), low frequency (LF) and high frequency (HF) components, total power (TP) and the LF/HF ratio. The results (means ± SD) were as follows: mean NN = 677.68 ± 126.89; SDNN = 208.86 ± 77.1; SDANN = 70.75 ± 30.9; SDNN index = 190.75 ± 76.12; rMSSD = 259 ± 120.17, pNN50 = 71.84 ± 13.96; VLF = 984.96 ± 327.7; LF = 1501.24 ± 736.32; HF = 5845.45 ± 2914.20; TP = 11065.31 ± 3866.87; LF/HF = 0.28 ± 0.11.

Short-term heart rate variability--influence of gender and age in healthy subjects.

In the recent years, short-term heart rate variability (HRV) describing complex variations of beat-to-beat interval series that are mainly controlled by the autonomic nervous system (ANS) has been increasingly analyzed to assess the ANS activity in different diseases and under various conditions. In contrast to long-term HRV analysis, short-term investigations (<30 min) provide a test result almost immediately. Thus, short-term HRV analysis is suitable for ambulatory care, patient monitoring and all those applications where the result is urgently needed. In a previous study, we could show significant variations of 5-min HRV indices according to age in almost all domains (linear and nonlinear) in 1906 healthy subjects from the KORA S4 cohort. Based on the same group of subjects, general gender-related influences on HRV indices are to be determined in this study. Short-term 5-min HRV indices from linear time and frequency domain and from nonlinear methods (compression entropy, detrended fluctuation analysis, traditional and segmented Poincaré plot analysis, irreversibility analysis, symbolic dynamics, correlation and mutual information analysis) were determined from 782 females and 1124 males. First, we examined the gender differences in two age clusters (25–49 years and 50–74 years). Secondly, we investigated the gender-specific development of HRV indices in five age decade categories, namely for ages 25–34, 35–44, 45–54, 55–64 and 65–74 years. In this study, significant modifications of the indices according to gender could be obtained, especially in the frequency domain and correlation analyses. Furthermore, there were significant modifications according to age in nearly all of the domains. The gender differences disappeared within the last two age decades and the age dependencies disappeared in the last decade. To summarize gender and age influences need to be considered when performing HRV studies even if these influences only partly differ.

Using heart rate variability for automated identification of exercise exertion levels.

Heart rate monitoring is being used to estimate activity of autonomous nervous system by analysing heart rate variability (HRV). HRV has been recently shown to be effective means to monitor efficacy of exercise in patients with cardiovascular conditions and older adults. Whether HRV can be used to identify exercise exertion levels is unknown. There are multiple approaches to analyse HRV however it is not clear which approach is optimal in assessing cycling exercise. Previous studies demonstrated potential of analysis of short-term sequences of beat-by-beat heart rate data in a time domain for continuous monitoring of levels of physiological stress. The goal of this study was to assess the potential value of short-term HRV analysis during cycling exercise for automated identification of exercise exertion level. HRV indices were compared during rest, height of exercise exertion, and exercise recovery. Comparative analysis of HRV during cycling exercise demonstrated responsiveness of time-domain indices to different phases of an exercise program. Using discriminant analysis, canonical discriminant functions were built which correctly identified 100% of 'highest level of exertion' and 80.0% of 'rest' episodes. HRV demonstrated high potential in monitoring autonomic balance and exercise exertion during cycling exercise program.

English

The aim of this study is to analyse and compare the heart rate variability (HRV) of normal and hypertension cases using time domain, frequency domain, and nonlinear methods. For short term HRV analysis, a five-minute electrocardiogram (ECG) of 57 normal and 56 hypertension subjects were recorded with prior verification of their clinical status by a cardiologist. Most time domain features of hypertension cases have clearly reduced values over normal subjects, frequency domain features, like power in different spectral bands, also have the distinguishable decreased values, whereas sympathovagal balance has clear edge over hypertension cases than normal cases. Nonlinear parameters of Poincare plot, approximate entropy and sample entropy, have higher values in normal cases when compared with hypertension cases. Support vector machine-based binary system classifies these two classes with 100 per cent accuracy and 100 per cent sensitivity when all time domain, frequency domain, and nonlinear features were used. It may work as a better predictor for in patients with hypertension. Science Journal, Vol. 64, No. 6, November 2014, pp.542-548, DOI:http://dx.doi.org/10.14429/dsj.64.7867

Short term heart rate variability for early assessment of autonomic neuropathy in patients with type 2 diabetes mellitus: A comparative cross-sectional study

Background: Cardiovascular autonomic diabetic neuropathy (CADN) is an important diabetes-associated complication. Reduced heart rate variation is the earliest indicator of CADN. Aims: The aim was to study the prospect of using short term heart rate variability (HRV) analysis for early diagnosis of CADN. Settings and Design: The type of this study was hospital-based comparative cross-sectional study. Materials and Methods: A total of 30 asymptomatic, type 2 diabetic male patients with duration of diabetes of 1-5 years with random blood sugar ≥200 mg/dl (11.1 mmol/L) or fasting blood sugar ≥126 mg/dl (7 mmol/L) in the age group of 30-65 years were selected as subjects. Thirty age and sex matched healthy nondiabetics were selected as controls. HRV analysis was performed using electrocardiogram recorded in lead II, at rest, in the supine position for 5 min. Results: Total power, low frequency power, high frequency power, standard deviation of all R-R intervals, root mean square of successive RR-interval differences, number of intervals differing by >50 ms from adjacent interval (NN50), and percentage of NN50 (pNN50) were significantly less in diabetics when compared to nondiabetics ( P Conclusion: Data from the study demonstrated that asymptomatic diabetics with <5 years history had already developed autonomic neuropathy. Short term analysis of HRV can be used as a valuable tool for early diagnosis of autonomic neuropathy.

Effect of Yoga Therapy on Heart Rate, Blood Pressure and Cardiac Autonomic Function in Heart Failure

It is well known that a hall mark of heart failure is adverse changes in autonomic function. Elevated blood pressure is a powerful predictor of congestive heart failure and other Cardiovascular Disease (CVD) outcomes. In this study, we planned to examine the effects of a 12 week yoga therapy on blood pressure, heart rate, heart rate variability, and rate pressure product (RPP). Out of 130 heart failure patients recruited for the study, 65 patients were randomly selected to receive 12 week yoga therapy along with standard medical therapy (yoga group). Other patients (n=65) received only standard medical therapy (control group). Heart rate, blood pressure, cardiac autonomic function (by short-term heart-rate variability analysis) and myocardial oxygen consumption (by RPP) were assessed before and after 12 weeks. In the yoga group, 44 patients and in the control group, 48 patients completed the study. There was a significant decrease in heart rate, blood pressure and RPP in yoga group compared to control group. Also, LFnu and LF-HF ratio decreased significantly and HFnu increased significantly in yoga group compared to control group. Twelve-week yoga therapy significantly improved the parasympathetic activity and decreased the sympathetic activity in heart failure patients (NYHA I&II).

Association of hypertension status and cardiovascular risks with sympathovagal imbalance in first degree relatives of type 2 diabetics.

As reports show cardiovascular (CV) risks in first-degree relatives (FDR) of type2 diabetics, and autonomic imbalance predisposing to CV risks, in the present study we have assessed the contribution of sympathovagal imbalance (SVI) to CV risks in these subjects. Body mass index (BMI), waist-to-hip ratio (WHR), basal heart rate (BHR), blood pressure (BP), rate pressure product (RPP), and spectral indices of heart rate variability (HRV) were reordered and analyzed in FDR of type2 diabetics (study group, n=293) and in subjects with no family history of diabetes (control group, n=405). The ratio of low-frequency (LF) to high-frequency (HF) power of HRV (LF-HF), a sensitive marker of SVI, was significantly increased (P<0.001) in the study group compared with the control group. The SVI in the study group was due to concomitant sympathetic activation (increased LF) and vagal inhibition (decreased HF). In the study group, the LF-HF ratio was significantly correlated with BMI, WHR, BHR, BP and RPP. Multiple regression analysis showed an independent contribution of LF-HF to hypertension status (P=0.000), and bivariate logistic regression showed significant prediction (odds ratio 2.16, confidence interval 1.130-5.115) of LF-HF to increased RPP, the marker of CV risk, in the study group. Sympathovagal imbalance in the form of increased sympathetic and decreased parasympathetic activity is present in FDR of type2 diabetics. Increased resting heart rate, elevated hypertension status, decreased HRV and increased RPP in these subjects make them vulnerable to CV risks. SVI in these subjects contributes to CV risks independent of the degree of adiposity.

Assessment of sympatholytic properties from short-term heart rate variability analysis in cynomolgus monkeys

Assessment of sympatholytic properties from short-term heart rate variability analysis in cynomolgus monkeys

Heart rate variability indices for very short-term (30 beat) analysis. Part 1: survey and toolbox

Heart rate variability (HRV) analysis over very short (<60s) periods may be useful for monitoring dynamic changes in autonomic nervous system activity where steady-state conditions are not maintained (e.g. during drug administration, or the start or end of exercise). From the 1980s there has been a wealth of HRV indices produced in the quest for better measures of the change in parasympathetic and sympathetic activity. Many of the indices have been sparingly used and have not been investigated for application to short-term use. This study surveyed published methods of HRV analysis searching for indices that could be applied to very short time HRV analysis. The survey included measures of time domain, frequency domain, respiratory sinus arrhythmia, Poincaré plot, and heart rate characteristics. Indices were tested with short segments of archived data to remove those that produced invalid results, or were mathematically equivalent to, but less well known than other indices. The survey identified a comprehensive list of 115 indices that were subsequently coded and screened. Of these, 70 were unique and produced a finite number with 60s data, so are included in the Toolbox. These indices require validation against physiological data before they can be applied to short-term HRV analysis of cardiac autonomic nervous system activity.

Evaluation of Autonomic Functions by Heart Rate Variability after Stenting in Patients with Carotid Artery Stenosis

Although carotid stenting is an effective treatment for severe carotid stenosis, it has been associated with alterations in autonomic functions during or shortly after the procedure. Heart rate variability (HRV) is an established tool for the asessment of autonumic functions. In this study, our aim was to investigate the relation between the alterations in autonomic functions and HRV by Holter monitoring parameters. Patients (19 male, 8 female) that are suitable for carotid artery stenting, without a history of hypertension, diabetes mellitus, severe coronary artery or valvular heart disease, were enrolled to our study. Short-term HRV analysis recordings were obtained at the beginning, and after the procedure. The square root of the mean squared differences of successive NN intervals (RMSSD), total frequency, low frequency (LF), high frequency (HF), normalized units LF (LFnu), normalized units HF (HFnu), LF/HF ratios were analyzed. Results were statistically analysed by using Wilcoxon test. Total frequency did not show any significant changes after the procedure (1101 ± 829, 981 ± 855). While RMSSD and HFnu values significantly increased respectively (23 ± 12/33 ± 22, and 22 ± 10/35 ± 10, p < 0.05) after the procedure, HF values increased nonsignificantly after the procedure (82 ± 92/92 ± 108). LF, LFnu, and LF/HF values were significantly decreased after the procedure. (228 ± 166/112 ± 100, 70 ± 15/55 ± 18, 4 ± 2.5/2.1 ± 2, respectively, p < 0.05) While RMSSD and HF are used as markers of vagal activity, LF is a marker of sympathetic modulation and LF/HF ratio shows sympathovagal balance. In our study, we showed that carotid artery stenting is associated with increase in parasympathetic activation, and this finding is demonstrated by HRV parameters.

Decreased Autonomic Modulation of Heart Rate and Altered Cardiac Sympathovagal Balance in Patients with Cushing's Syndrome: Role of Endogenous Hypercortisolism

Background/Aims: Endogenous Cushing's syndrome is associated with a higher risk of cardiovascular morbidity and mortality. Previous literature suggested multiple possible links by which hypercortisolism may alter the autonomic control of cardiovascular functions. We investigated the impact of chronic endogenous hypercortisolism on the autonomic regulation of cardiac functions by short-term heart rate variability analysis. Methods: Eighteen patients with endogenous Cushing's syndrome and 20 age-, gender- and BMI-matched controls participated in the study. ECG signal was acquired in lead II configuration for 5 min and heart rate variability assessment was made in both time and frequency domain using the extracted RR interval data. Results: All time and frequency domain measures of heart rate variability were significantly (p < 0.05) lower in the patient group compared to the control group. The patient group had an altered sympathovagal balance with low frequency/high frequency band ratio significantly higher than the control group [1.857 (0.6747-2.610) vs. 0.8581 (0.4779-1.352); p = 0.0253]. A significant negative correlation was obtained between normalized high frequency power of heart rate variability and basal cortisol levels (r = -0.6594; p = 0.0029). Multiple linear regression analysis identified age, disease duration (in months), basal cortisol levels and systolic blood pressure as independent predictors of normalized high frequency power. Conclusion: Findings of the study clearly portrayed the diminished autonomic modulation of heart rate in endogenous Cushing's syndrome and its possible relationship with hypercortisolism as the main causative factor. Diminished heart rate variability may be an indicator of the increased risk of cardiac mortality in these patients.