Heart Rate Complexity Research Articles

Reliable real-time calculation of heart-rate complexity in critically ill patients using multiple noisy waveform sources

Heart-rate complexity (HRC) has been proposed as a new vital sign for critical care medicine. The purpose of this research was to develop a reliable method for determining HRC continuously in real time in critically ill patients using multiple waveform channels that also compensates for noisy and unreliable data. Using simultaneously acquired electrocardiogram (Leads I, II, V) and arterial blood pressure waveforms sampled at 360 Hz from 250 patients (over 375 h of patient data), we evaluated a new data fusion framework for computing HRC in real time. The framework employs two algorithms as well as signal quality indices. HRC was calculated (via the method of sample entropy), and equivalence tests were then performed. Bland-Altman plots and box plots of differences between mean HRC values were also obtained. Finally, HRC differences were analyzed by paired t tests. The gold standard for obtaining true means was manual verification of R waves and subsequent entropy calculations. Equivalence tests between mean HRC values derived from manually verified sequences and those derived from automatically detected peaks showed that the "Fusion" values were the least statistically different from the gold standard. Furthermore, the fusion of waveform sources produced better error density distributions than those derived from individual waveforms. The data fusion framework was shown to provide in real-time a reliable continuously streamed HRC value, derived from multiple waveforms in the presence of noise and artifacts. This approach will be validated and tested for assessment of HRC in critically ill patients.

Heart Rate Dynamics after Combined Strength and Endurance Training in Middle-Aged Women: Heterogeneity of Responses

The loss of complexity in physiological systems may be a dynamical biomarker of aging and disease. In this study the effects of combined strength and endurance training compared with those of endurance training or strength training alone on heart rate (HR) complexity and traditional HR variability indices were examined in middle-aged women. 90 previously untrained female volunteers between the age of 40 and 65 years completed a 21 week progressive training period of either strength training, endurance training or their combination, or served as controls. Continuous HR time series were obtained during supine rest and submaximal steady state exercise. The complexity of HR dynamics was assessed using multiscale entropy analysis. In addition, standard time and frequency domain measures were also computed. Endurance training led to increases in HR complexity and selected time and frequency domain measures of HR variability (P<0.01) when measured during exercise. Combined strength and endurance training or strength training alone did not produce significant changes in HR dynamics. Inter-subject heterogeneity of responses was particularly noticeable in the combined training group. At supine rest, no training-induced changes in HR parameters were observed in any of the groups. The present findings emphasize the potential utility of endurance training in increasing the complex variability of HR in middle-aged women. Further studies are needed to explore the combined endurance and strength training adaptations and possible gender and age related factors, as well as other mechanisms, that may mediate the effects of different training regimens on HR dynamics.

Initial fractal exponent of heart rate variability is associated with success of early resuscitation in patients with severe sepsis or septic shock: a prospective cohort study

IntroductionHeart rate variability (HRV) reflects autonomic nervous system tone as well as the overall health of the baroreflex system. We hypothesized that loss of complexity in HRV upon intensive care unit (ICU) admission would be associated with unsuccessful early resuscitation of sepsis. MethodsWe prospectively enrolled patients admitted to ICUs with severe sepsis or septic shock from 2009 to 2011. We studied 30 minutes of electrocardiogram, sampled at 500 Hz, at ICU admission and calculated heart rate complexity via detrended fluctuation analysis. Primary outcome was vasopressor independence at 24 hours after ICU admission. Secondary outcome was 28-day mortality. ResultsWe studied 48 patients, of whom 60% were vasopressor independent at 24 hours. Five (10%) died within 28 days. The ratio of fractal alpha parameters was associated with both vasopressor independence and 28-day mortality (P = .04) after controlling for mean heart rate. In the optimal model, Sequential Organ Failure Assessment score and the long-term fractal α parameter were associated with vasopressor independence. ConclusionsLoss of complexity in HRV is associated with worse outcome early in severe sepsis and septic shock. Further work should evaluate whether complexity of HRV could guide treatment in sepsis.

Respiration and heart rate complexity: Effects of age and gender assessed by band-limited transfer entropy

Aging and disease are accompanied with a reduction of complex variability in the temporal patterns of heart rate. This reduction has been attributed to a break down of the underlying regulatory feedback mechanisms that maintain a homeodynamic state. Previous work has established the utility of entropy as an index of disorder, for quantification of changes in heart rate complexity. However, questions remain regarding the origin of heart rate complexity and the mechanisms involved in its reduction with aging and disease. In this work we use a newly developed technique based on the concept of band-limited transfer entropy to assess the aging-related changes in contribution of respiration and blood pressure to entropy of heart rate at different frequency bands. Noninvasive measurements of heart beat interval, respiration, and systolic blood pressure were recorded from 20 young (21–34 years) and 20 older (68–85 years) healthy adults. Band-limited transfer entropy analysis revealed a reduction in high-frequency contribution of respiration to heart rate complexity (p<0.001) with normal aging, particularly in men. These results have the potential for dissecting the relative contributions of respiration and blood pressure-related reflexes to heart rate complexity and their degeneration with normal aging.

Development and validation of a novel fusion algorithm for continuous, accurate, and automated R-wave detection and calculation of signal-derived metrics

PurposePrevious studies have shown that heart rate complexity may be a useful indicator of patient status in the critical care environment but will require continuous, accurate, and automated R-wave detection (RWD) in the electrocardiogram (ECG). Although numerous RWD algorithms exist, accurate detection remains a challenge. The purpose of this study was to develop and validate a novel fusion algorithm (Automated Electrocardiogram Selection of Peaks, or AESOP) that combines the strengths of several well-known algorithms to provide a more reliable real-time solution to the RWD problem. Materials and MethodsThis study involved the ECGs of 108 prehospital patient records and 32 ECGs from a conscious sedated porcine model of hemorrhagic shock. The criterion standard for validation was manual verification of R waves. ResultsFor 108 human ECG records, the AESOP algorithm overall outperformed each of its component algorithms. In addition, for 32 swine ECG records, AESOP achieved an R-wave sensitivity of 97.9% and a positive predictive value of 97.5%, again outperforming its component algorithms. ConclusionBy fusing several best algorithms, AESOP uses the strengths of each algorithm to perform more robustly and reliably in real time. The AESOP algorithm will be integrated into a real-time heart rate complexity software program for decision support and triage in critically ill patients.

Development of a Rugged handheld Device for Real-Time Analysis of heart Rate: Entropy in Critically Ill Patients

The usefulness of heart rate variability (HRV) and heart rate complexity (HRC) analysis as a potential triage tool has been limited by the inability to perform real-time analysis on a portable, handheld monitoring platform. Through a multidisciplinary effort of academia and industry, we report on the development of a rugged, handheld and noninvasive device that provides HRV and HRC analysis in real-time in critically ill patients.After extensive re-engineering, real-time HRV and HRC analyses were incorporated into an existing, rugged, handheld monitoring platform. Following IRB approval, the prototype device was used to monitor 20 critically ill patients and 20 healthy controls to demonstrate real-world discriminatory potential. Patients were compared to healthy controls using a Student?s t test as well as repeated measures analysis. Receiver operator characteristic (ROC) curves were generated for HRV and HRC.Critically ill patients had a mean APACHE-2 score of 15, and over 50% were mechanically ventilated and requiring vasopressor support. HRV and HRC were both lower in the critically ill patients compared to healthy controls (p < 0.0001) and remained so after repeated measures analysis. The area under the ROC for HRV and HRC was 0.95 and 0.93, respectively.This is the first demonstration of real-time, handheld HRV and HRC analysis. This prototype device successfully discriminates critically ill patients from healthy controls. This may open up possibilities for real-world use as a trauma triage tool, particularly on the battlefield.

Heart rate variability among caregivers of chronically bedridden patients

Background: Caregivers of chronically bedridden patients are likely to suffer from mental and physical exhaustion leading to stress. This is important in view of the prevailing socioeconomic as well as the healthcare system available in a developing country like India. Therefore, the present study is designed to measure heart rate variability (HRV) among this special group of population who give care to long-term bedridden patients. Materials and Methods: Fifteen female subjects were enrolled from among attendants of patients admitted with an immediate history of a cerebrovascular accident with locomotor deficits, who required constant care. They were free from any type of physical and mental health issues, nonsmokers and nonaddicts. Each care giver was subjected to HRV analysis on three occasions: The first record was performed in the 1 st week of their arrival in the hospital as caregivers. The second observation was recorded after 3 months of caregiving. The final HRV analysis was done after 6 months of care giving. Two types of parameters were analyzed: Time domain and frequency domain. Statistical analysis was done using paired t-test. Results: Both the HRV parameters: Time and frequency domain, showed decreased values during the 3 rd and 6 th month recording as compared to the 1 st week recording. The decrease is much more during the 6 th month recording as compared to the 3 rd month recording. Statistically significant decrease is observed in mean RR interval, heart rate, very low frequency (VLF), and LF only when the 1 st week recording is compared with the 3 rd month recording, but when the 1 st week recording was compared with the 6 th month recording significant decrease was found in mean RR interval and heart rate. Conclusion: Subjects involved in taking care of chronically ill bedridden patients are likely to undergo a lot of physical and mental stress, thus affecting their autonomic status. HRV analysis using short term electrocardiogram (ECG) recording was used to detect changes consequent to this stress. It was found that almost all HRV parameters measuring heart rate complexity were decreased in the period of caregiving.

A study of heart rate variability among caregivers from a rural background in a busy urban infirmary

Background: Urban life in modern times is completely laden with stressors. Caregivers of chronically sick patients are likely to suffer from mental and physical exhaustion leading to stress. This is important in view of the prevailing socioeconomic conditions as well as the healthcare system available in any developing country. Therefore, the present study was designed to measure the heart rate variability (HRV) in this special group of population who gives care to long-term bedridden patients in an urban setting. Materials and Methods: Fifteen female subjects were enrolled from among the attendants of patients admitted with immediate history of a cerebrovascular accident with locomotor deficits, who required constant care. They were free from any type of physical and mental health issues, nonsmokers, and nonaddicts. Each caregiver was subjected to HRV analysis on three occasions: the first record was performed in the 1st week of their arrival in the hospital as caregivers and the second observation was recorded after 4 months of caregiving. Two types of parameters were analyzed: time domain and frequency domain. Statistical analysis was done using paired t-test. Results: Both the HRV parameters - time and frequency domains - showed decreased values during the 3rd month and 6th month recording as compared to the 1st week recording. The decrease was much more during the 6th month recording as compared to the 3rd month recording. Statistically significant decrease was observed in the mean RR interval, heart rate, Very Low FrequencyVLF, and Low Frequency LF]. On comparing the 1st week recording with the 4th month recording significant decrease was found in mean RR interval and heart rate. Conclusion: Subjects involved in taking care of chronically ill bedridden patients are likely to undergo a lot of physical and mental stress, thus affecting their autonomic status. HRV analysis with short-term electrocardiogram (ECG) recording was used to detect changes consequent to this stress. It was found that almost all HRV parameters measuring heart rate complexity were decreased in the period of caregiving.

A Study of Heart Rate Variability among Gutkha Chewers from a Rural Farming Background in India

Background: Modernisation of life style has affected the population even in rural areas leading to addiction. Smokeless tobacco is presumed to be less of an evil by the rural folk. Gutkha addicts are likely to suffer from mental and physical exhaustion leading to stress. This is important in view of the prevailing socio-economic as well as the healthcare system available in any developing country. Therefore the present study is designed to measure heart rate variability among this special group of population. Methods: 15 male subjects were enrolled from among the rural farm labors who regularly chewgutkha. They were free from any type of physical and mental health issues, non smokers. Each individual volunteer was subjected to HRV analysis on three occasions: the first record was performed on the first day of their arrival in the hospital as subjects during the lean season. The second observation was recorded after 3 months of farming activity. The final HRV analysis was done after 6 months of farming activity. Two types of parameters were analysed: time domain and frequency domain. Statistical analysis was done using paired t-test. Results: Both the HRV parameters – time and frequency domain, showed decreased values during the third month and sixth month recording as compared to the first week recording. The decrease is much more during the sixth month recording as compared to the third month recording. Statistically significant decrease is observed in mean RR interval, heart rate, VLF and LF only when the first week recording is compared with the third month recording but when the first week recording was compared with the sixth month recording significant decrease was found in mean RR interval and heart rate. Conclusion: Subjects involved in taking gutkha are likely to undergo a lot of physical and mental stress, thus affecting their autonomic status. This adds up to the stress induced by their occupation. HRV analysis using short term ECG recording was used to detect changes consequent to this stress. It was found that almost all HRV parameters measuring heart rate complexity were decreased in the period of farming activity.

The timing and degree of fetal systemic and cerebral inflammatory responses correlate with a subset of heart rate variability measures: Evidence of cholinergic anti-inflammatory pathway activation in sepsis

48 Real-time heart rate complexity on hospital arrival predicts the need for life-saving interventions in trauma activation patients Ali Mejaddam, Oscar Birkhan, Antonis Sideris, Gwen Van Der Wilden, Ayesha Imam, John Hwabejire, Yuchiao Chang, George Velmahos, Hasan Alam, Peter Fagenholz, Daniel Yeh, Marc Demoya Massachusetts General Hospital, Boston, MA, USA Objectives:Heart rate complexity (HRC), commonly described as a “new vital sign,” has shown promise in predicting injury severity, but its use in clinical practice has been precluded by the absence of real-time data. This study was conducted to evaluate the use of realtime, automated, instantaneous entropy analysis in predicting the need for lifesaving interventions (LSI). Methods: Prospective enrollment of patients who met the criteria for trauma code activation was conducted at a level I trauma center (September 2011–February 2012). Electric impedance cardiography was used to calculate HRC and time-domain heart rate variability continuously in real time for 2 hours with a portable, handheld device from the moment of arrival in the trauma center. Patients who received an LSI were compared with patients without any intervention (non-LSI). Multivariable analysis was performed to control for differences between the groups. Results: Of 82 patients enrolled, 21 (26%) received 67 LSIs within 24 hours of hospital arrival. Initial systolic blood pressure was similar in both groups, but heart rate was significantly higher in the LSI group. Also, LSI patients had a lower Glasgow Coma Score (9.2 ± 5.1 vs 14.9 ± 0.2, P b .0001). The mean HRC value on presentation was 0.8 ± 0.6 in the LSI group compared with 1.5 ± 0.6 in the non-LSI group (P b .0001). Using logistic regression, initial HRC was the only significant predictor of LSI. A cutoff value for HRC of 1.1 yields sensitivity, specificity, negative predictive value, and positive predictive value of 86%, 74%, 94%, 53%, respectively, with an accuracy of 77% for predicting an LSI. Conclusions: Decreased HRC on hospital arrival is an independent predictor of the need for LSI in patients with trauma activation. RealtimeHRCmay be a useful adjunct to standard vital signsmonitoring. http://dx.doi.org/10.1016/j.jcrc.2012.10.064

Real-time heart rate complexity on hospital arrival predicts the need for life-saving interventions in trauma activation patients

Real-time heart rate complexity on hospital arrival predicts the need for life-saving interventions in trauma activation patients

Robust real-time calculation of heart-rate complexity using multiple noisy waveform sources

Recently, we demonstrated that the steroid-hormone testosterone reduces interpersonal trust in humans. The neural mechanism which underlies this effect is however unknown. It has been proposed that testosterone increases social vigilance via neuropeptide systems in the amygdala, augmenting communication between the amygdala and the brain stem. However, testosterone also affects connectivity between the orbitofrontal cortex (OFC) and the amygdala, which could subsequently lead to increased vigilance by reduced top-down control over the amygdala. Here, in a placebo-controlled testosterone administration study with 16 young women, we use functional magnetic resonance imaging to get more insights into neural mechanisms whereby testosterone acts on trust. Several cortical systems, among others the OFC, are involved in the evaluation of facial trustworthiness. Testosterone administration decreased functional connectivity between amygdala and the OFC during judgments of unfamiliar faces, and also increased amygdala responses specifically to the faces that were rated as untrustworthy. Finally, connectivity between the amygdala and the brain stem was not affected by testosterone administration. Although speculative, a neurobiological explanation for these findings is that in uncertain social situations, testosterone induces sustained decoupling between OFC and amygdala by a prefrontal-dopaminergic mechanism, subsequently resulting in more vigilant responses of the amygdala to signals of untrustworthiness.

Heart rate dynamics during acute pain in newborns

Autonomic nervous system modulation of heart rate is significantly altered during painful procedures in newborns. Most studies investigating pain employed only linear-based analysis methods, thus ignoring the complex, non-linear nature of heart rate control mechanisms. The emergences of dynamic, nonlinear analysis methods enable us to uncover information embedded in the fluctuations of heart rate not otherwise noticeable. Our objective was to examine how cardiac dynamics change in newborns who undergo heel lancing by analyzing linear and nonlinear characteristics of heart rate fluctuations. We used dynamic nonlinear analyses methods to reveal heart rate variability and complexity alterations during painful stimulus in newborns. Poincaré plots were applied to examine the dynamics of the system, sample entropy to investigate the complexity of the system, and detrended fluctuation analysis, to reveal the fractal properties of the system. Heart rate significantly increased (165 vs.123 beats per minute, p < 0.001) while variability decreased. Sample entropy and the quantitative measures of the Poincaré plots (SD1 and SD2) significantly decreased during heel lancing (0.75 vs. 1.0, p < 0.01; 6.4 vs. 12.8, p < 0.001; and 30.4 vs. 50.5, p < 0.01, respectively). Detrended fluctuation analysis showed a significant decrease in the short-term scaling exponent α1 (1.06 vs. 1.3, p < 0.001), and an increase in the long-term scaling exponent α2 (1.5 vs. 1.1, p < 0.001). Our results indicate altered complexity of heart rate variability during painful stimulus in newborns and disruption of the mechanisms that regularly control it. Such alterations resemble certain pathological conditions and may represent stress reaction.

Patterns of cardiorespiratory coordination in young women with recurrent major depressive disorder treated with escitalopram or venlafaxine

Evidence from previous studies suggests autonomic dysregulation in patients with major depressive disorder (MDD). Antidepressant treatment may also affect central autonomic function. We investigated whether the type of antidepressant might be associated with the pattern of cardiorespiratory coordination in non-depressed women with recurrent MDD. Resting electrocardiograms and respiratory signals were simultaneously recorded from 38 euthymic women with recurrent MDD who were treated with either escitalopram (n=19) or venlafaxine (n=19) monotherapy and from 38 healthy women. Linear measures of heart rate variability were extracted to assess cardiac autonomic control. Sample entropy (SampEn) was computed to assess the complexity of heart rate and respiratory signals, and cross-SampEn was calculated to measure the nonlinear interaction of both signals. Significant decreases in the cardiovagal tone and cardiorespiratory coupling of women with recurrent MDD receiving venlafaxine, and tendencies toward lower cardiovagal tone and cardiorespiratory coupling in women with recurrent MDD receiving escitalopram were observed when compared with healthy controls. Effect sizes for these differences were large between women receiving venlafaxine and healthy controls. We found a positive association between cardiorespiratory decoupling and venlafaxine dose. Norepinephrine-enhancement, within a therapeutic dose range, seems to be closely associated with decreased vagal tone and reduced nonlinear coupling between heart rate and respiration in euthymic women with recurrent MDD. However, the effects of serotonin enhancement on cardiovagal tone should be considered. Our results suggest that the pharmacodynamic properties of antidepressants may affect autonomic regulation of women with recurrent MDD even in euthymic state.

Changes of Heart and Respiratory Rate Dynamics During Weaning From Mechanical Ventilation

Abstract Purpose The aim of the study was to investigate heart rate (HR) and respiratory rate (RR) complexity in patients with weaning failure or success, using both linear and nonlinear techniques. Materials and Methods Forty-two surgical patients were enrolled in the study. There were 24 who passed and 18 who failed a weaning trial. Signals were analyzed for 10 minutes during 2 phases: (1) pressure support (PS) ventilation (15-20 cm H 2 O) and (2) weaning trials with PS (5 cm H 2 O). Low- and high-frequency (LF, HF) components of HR signals, HR multiscale entropy (MSE), RR sample entropy, cross-sample entropy between cardiorespiratory signals, Poincare plots, and α 1 exponent were computed in all patients and during the 2 phases of PS. Results Weaning failure patients exhibited significantly decreased RR sample entropy, LF, HF, and α 1 exponent, compared with weaning success subjects ( P P α 1 exponent, RR, and cross-sample entropies predicted better weaning outcome compared with RSBI, airway occlusion pressure at 0.1 second (P 0.1 ), and RSBI × P 0.1 (conventional model, R 2 = 0.887 vs 0.463; P P Conclusions We suggest that nonlinear analysis of cardiorespiratory dynamics has increased prognostic impact upon weaning outcome in surgical patients.

Isometric handgrip training lowers blood pressure and increases heart rate complexity in medicated hypertensive patients

Hypertension is characterized by elevated blood pressure (BP) and autonomic dysfunction, both thought to be improved with exercise training. Isometric handgrip (IHG) training may represent a beneficial, time-effective exercise therapy. We investigated the effects of IHG training on BP and traditional and nonlinear measures of heart rate variability (HRV). Pre- and post-measurements of BP and HRV were determined in 23 medicated hypertensive participants (mean ± SEM, 66 ± 2 years) following either 8 weeks of IHG training (n = 13) or control (n = 10). IHG exercise consisted of four unilateral 2-min isometric contractions at 30% of maximal voluntary contraction, each separated by 4 min of rest. IHG training was performed 3 days/week for 8 weeks. IHG training decreased systolic BP (125 ± 3 mmHg to 120 ± 2 mmHg, P < 0.05) and mean BP (90 ± 2 mmHg to 87 ± 2 mmHg, P < 0.05), while sample entropy was increased (1.07 ± 0.1 to 1.35 ± 0.1, P < 0.05) and the fractal scaling distance score was decreased (0.34 ± 0.1 to 0.19 ± 0.1, P < 0.05). No significant changes were observed in traditional spectral or time-domain measures of HRV or control participants. IHG training improves nonlinear HRV, but not traditional HRV, while reducing systolic and mean BP. These results may highlight the benefits of IHG training for patients with primary hypertension.

Correlation between Mortality of Prehospital Trauma Patients and Their Heart Rate Complexity

Heart rate complexity (HRC) is a measure of the beat-to-beat variations in heart rate which can be used in patients to identify their physiologic deterioration caused by critical injury. This measurement is the results of nonlinear analysis to the R-to-R interval (RRI) of the electrocardiogram (ECG) of pre-hospital trauma patients. Power spectra, entropy, fractal dimension, auto-correlation function and auto-correlation time are some tools for this nonlinear analysis of ECG signal. However, the measurements of these tools for some RRI data in the heart rates for healthy subjects and those with congestive heart failure are so close and hard to distinguish and use for further emergency care. In this case, surrogating raw data by some manipulated data will provide more informative vital signs. In this article, we will compare the nonlinear analysis of raw data by manipulated data using dominant frequency extraction. Here, we will use real data of 270-beat sections of ECG from 45 emergency patients brought to Shiraz Rejaee Hospetal prior to any medication.

Heart rate complexity in response to upright tilt in persons with Down syndrome

People with Down syndrome (DS) show altered autonomic response to sympatho-excitation. Cardiac autonomic modulation may be examined with heart rate (HR) complexity which is associated uniquely with cardiovascular risk. This study examined whether the response of HR complexity to passive upright tilt differs between persons with and without DS and whether potential between-group differences in this response are accounted for by differences in body mass index (BMI). The electrocardiogram of 16 persons with DS (8 women, 8 men) and 16 persons without DS (8 women, 8 men) was recorded during 10 min of supine rest and 10 min of upright tilt. For each participant, 550 continuous, steady state, and ectopy-free R-R intervals under each condition were analyzed. Dependent variables were approximate entropy, correlation dimension, StatAv, and the mean R-R interval. In response to tilt, changes in approximate entropy and correlation dimension were reduced in participants with DS (p<0.05). These differences were explained by higher BMI in participants with DS. StatAv increased in persons with DS (p < 0.05) and stayed the same in those without DS even when controlling for BMI. The response of R-R interval did not differ between groups. None of the variables differed between groups at rest. Therefore, people with DS show smaller decrease in HR complexity in response to upright tilt than people without DS partially due to their higher BMI. Resting HR complexity does not differ between persons with and without DS. These results may have implications for cardiovascular risk in people with DS.

The effect of orthostatic stress on multiscale entropy of heart rate and blood pressure

Cardiovascular control acts over multiple time scales, which introduces a significant amount of complexity to heart rate and blood pressure time series. Multiscale entropy (MSE) analysis has been developed to quantify the complexity of a time series over multiple time scales. In previous studies, MSE analyses identified impaired cardiovascular control and increased cardiovascular risk in various pathological conditions. Despite the increasing acceptance of the MSE technique in clinical research, information underpinning the involvement of the autonomic nervous system in the MSE of heart rate and blood pressure is lacking. The objective of this study is to investigate the effect of orthostatic challenge on the MSE of heart rate and blood pressure variability (HRV, BPV) and the correlation between MSE (complexity measures) and traditional linear (time and frequency domain) measures. MSE analysis of HRV and BPV was performed in 28 healthy young subjects on 1000 consecutive heart beats in the supine and standing positions. Sample entropy values were assessed on scales of 1–10. We found that MSE of heart rate and blood pressure signals is sensitive to changes in autonomic balance caused by postural change from the supine to the standing position. The effect of orthostatic challenge on heart rate and blood pressure complexity depended on the time scale under investigation. Entropy values did not correlate with the mean values of heart rate and blood pressure and showed only weak correlations with linear HRV and BPV measures. In conclusion, the MSE analysis of heart rate and blood pressure provides a sensitive tool to detect changes in autonomic balance as induced by postural change.

Benefits of achieving vigorous as well as moderate physical activity recommendations: Evidence from heart rate complexity and cardiac vagal modulation

The aim of this study was to examine differences in traditional heart rate variability measurements and heart rate complexity (sample entropy) in young adults grouped by objectively measured achievement of either moderate or both moderate and vigorous physical activity recommendations. Of 168 young adults tested (86 females, 82 males; age 20.5 ± 1.2 years), 119 achieved only recommendations for moderate physical activity (moderate group) and 49 achieved recommendations for both moderate and vigorous physical activity (vigorous group). Analysis of covariance controlling for sex, weekly minutes of moderate physical activity, and percentage of body fat was used to assess between-group differences in heart rate variability and heart rate complexity. Logistic regression analysis was used to determine the group characteristics that best predicted high heart rate complexity and vagal indices of heart rate variability. The majority of the autonomic measures were higher (P < 0.05) in the vigorous group, and regression analysis showed that vigorous physical activity was the only multivariate predictor of higher heart rate complexity and higher heart rate variability. Young adults engaged in regular vigorous physical activity were more than twice as likely to have high heart rate complexity than those involved in predominantly moderate exercise. These findings suggest that vigorous physical activity is more closely associated with high heart rate complexity than moderate physical activity in young adults.