Heart Rate Entropy Research Articles

The Impact of Prenatal Alcohol Exposure on the Autonomic Nervous System and Cardiovascular System in Rats in a Sex-Specific Manner.

Fetal Alcohol Spectrum Disorder (FASD) is a consequence of prenatal alcohol exposure (PAE) associated with a range of effects, including dysmorphic features, prenatal and/or postnatal growth problems, and neurodevelopmental difficulties. Despite advances in treatment methods, there are still gaps in knowledge that highlight the need for further research. The study investigates the effect of PAE on the autonomic system, including sex differences that may aid in early FASD diagnosis, which is essential for effective interventions. During gestational days 5 to 20, five pregnant female Wistar rats were orally administered either glucose or ethanol. After 22 days, 26 offspring were born and kept with their mothers for 21 days before being isolated. Electrocardiographic recordings were taken on the 29th and 64th day. Heart rate variability (HRV) parameters were collected, including heart rate (HR), standard deviation (SD), standard deviation of normal-to-normal intervals (SDNN), and the root mean square of successive differences between normal heartbeats (RMSSD). Additionally, a biochemical analysis of basic serum parameters was performed on day 68 of the study. The study found that PAE had a significant impact on HRV. While electrolyte homeostasis remained mostly unaffected, sex differences were observed across various parameters in both control and PAE groups, highlighting the sex-specific effects of PAE. Specifically, the PAE group had lower mean heart rates, particularly among females, and higher SDNN and RMSSD values. Additionally, there was a shift towards parasympathetic activity and a reduction in heart rate entropy in the PAE group. Biochemical changes induced by PAE were also observed, including elevated levels of alanine transaminase (ALT) and aspartate aminotransferase (AST), especially in males, increased creatinine concentration in females, and alterations in lipid metabolism. PAE negatively affects the development of the autonomic nervous system, resulting in decreased heart rate and altered sympathetic activity. PAE also induces cardiovascular abnormalities with sex-specific effects, highlighting a relationship between PAE consequences and sex. Elevated liver enzymes in the PAE group may indicate direct toxic effects, while increased creatinine levels, particularly in females, may suggest an influence on nephrogenesis and vascular function. The reduced potassium content may be linked to hypothalamus-pituitary-adrenal axis overactivity.

A Pilot Study Using Entropy for Optimizing Self-Pacing during a Marathon.

A new group of marathon participants with minimal prior experience encounters the phenomenon known as "hitting the wall," characterized by a notable decline in velocity accompanied by the heightened perception of fatigue (rate of perceived exertion, RPE). Previous research has suggested that successfully completing a marathon requires self-pacing according to RPE rather than attempting to maintain a constant speed or heart rate. However, it remains unclear how runners can self-pace their races based on the signals received from their physiological and mechanical running parameters. This study aims to investigate the relationship between the amount of information conveyed in a message or signal, RPE, and performance. It is hypothesized that a reduction in physiological or mechanical information (quantified by Shannon Entropy) affects performance. The entropy of heart rate, speed, and stride length was calculated for each kilometer of the race. The results showed that stride length had the highest entropy among the variables, and a reduction in its entropy to less than 50% of its maximum value (H = 3.3) was strongly associated with the distance (between 22 and 40) at which participants reported "hard exertion" (as indicated by an RPE of 15) and their performance (p < 0.001). These findings suggest that integrating stride length's Entropy feedback into new cardioGPS watches could improve marathon runners' performance.

Entropy of Heart Rate on Self-Selected Interval Exercises in Older Women

Entropy of Heart Rate on Self-Selected Interval Exercises in Older Women

MO747AN ASSESSMENT OF COMPLEXITY OF CARDIOVASCULAR SIGNALS USING ENTROPY IN HEMODIALYSIS SESSION AND GLUCOSE INJECTION DURING HEMODIALYSIS IN END STAGE RENAL DISEASE PATIENTS WITH AND WITHOUT DIABETES MELLITUS TYPE 2

Abstract Background and Aims Few studies have focused on the imbalance of the autonomic nervous system during hemodialysis (HD), although it seems to be an important factor for the maintenance of blood pressure. The aim of this work was to assess the impact of hemodialysis (HD) and glucose injection upon entropy of heart rate and blood pressure during HD session in end stage renal disease (ESRD) patients with and without diabetes mellitus (DM) type 2. Method 21 patients without DM (NDO), in age 54,95 +/-13,08 y.o., and 10 DM patients, in age 69,70 +/- 8,27 y.o., were studied during HD. 30 minutes after dialysis begins, 40% glucose solution was administered in the amount of 0.5g/kg body dry-weight (constant rate of 1 mL/s). The cardiovascular signals were extracted from the recordings using Portapres® system. The analysis was performed using Amplitude Aware Permutation Entropy (AAPE). The parameters of AAPE were set as d=7, A=0.5. All statistical analysis were performed on significance level α=0.05. The comparisons between groups were conducted with Mann-Whitney test with Holm corrections. The comparisons in time points were performed using Friedman test with post-hoc (Wilcoxon test with Holm corrections). The calculations of AAPE and all statistical analysis were performed with Matlab R2020a and R. Results The results are presented in table. It was found that AAPE(HR) tends to decrease during dialysis (NS) and increases only in the DM group after glucose injection (p=0.019); without difference between groups. There were no differences in AAPE of blood pressure between the groups, but hemodialysis reduces AAPE(fiSYS) in both groups (p&amp;lt;0.001 in both DM and NDO groups) and AAPE(fiDIA) in NDO (p&amp;lt;0.01). AAPE(TPR) is high before dialysis, and decreases during HD in both groups (p&amp;lt;0.0001). There is no effect of glucose injection on AAPE(HR) in both groups, but AAPE(fiSYS) and AAPE(fiDIA) increase in NDO (p&amp;lt;0.001, p&amp;lt;0.01, p&amp;lt;0.05 respectively); without difference between groups. AAPE(TPR) tends to increase after glucose injection (p&amp;lt;0.05 for NDO, NS for DM). Conclusion AAPE(HR)tends to decrease during HD, and glucose injections increase AAPE(HR) in DM patients. Hemodialysis reduce, and glucose injections increase AAPE of blood pressure especially in NDO. A weaker response to hemodialysis and glucose injection in diabetic patients may be caused by impairment of the autonomic system, and may have clinical impact – may leads to faint. Glucose administration does not prevent autonomic system disorders in patients with DM.

Heart rate entropy is associated with mortality after intracereberal hemorrhage

BackgroundAutonomic nervous system changes have been associated with outcome after intracerebral hemorrhage (ICH) previously. We aimed to investigate the association of heart rate entropy (HRE) with mortality after ICH. MethodsSample HRE, heart rate variability and baroreflex sensitivity were examined in consecutive ICH patients. Hematoma volume, intraventricular hemorrhage, infratentorial origin, consciousness impairment and age were combined into standard ICH score. ResultsIn 47 patients suffering ICH (mean age 61 years, median hemorrhage volume 38 mL) the areas under the curve (AUC) for mortality were 0.86, 0.83, 0.76, 0.74, 0.72 and 0.7 for HRE, ICH-score, normalized low frequency powers, low frequency/high frequency powers ratio, normalized high frequency powers and BRS, respectively. HRE and ICH score were associated with mortality independently (adjusted odd ratio (aOR) 0.09, 95% confidence interval (CI) 0.1–0.8, p = .03 and aOR 2.6, CI 1.03–6.6, p = .04). Combining ICH score with HRE into a novel score resulted in an AUC of 0.94, CI 0.88–0.99, p < .001. ConclusionCompared to several autonomic markers HRE seems to bear the largest amount of information on death probability after ICH. Moreover, HRE may predict mortality comparable to ICH score. Combining HRE with ICH score may increase the predictive performance for mortality after ICH.

Negative cognitive emotion regulation as a predictor of adolescent heart rate variability and entropy under social stress

ABSTRACTBackground and Objectives: Negative cognitive emotion regulation (ER) strategies are particularly important within the framework of anxiety problems amongst youths and how they cope with stressful events. The aim of this study was to examine the associations between both negative and positive ER style and cardiac regulation under stressful conditions.Design: Eighty-nine adolescents (M = 13.31 years, SD = 0.68, 44.94% girls) were exposed to a socially relevant stress induction protocol.Methods: Participants’ emotion regulation strategies were assessed and their cardiac function was recorded.Results: A negative ER style predicted heart rate (HR) entropy at the stressful stage after controlling for anxiety scores. In addition, heart rate variability reactivity and recovery and HR entropy recovery were larger (p < .05) in the low negative ER style group (n = 16) than in the high negative ER style group (n = 23).Conclusions: Results suggest that individuals with a highly negative ER style have diminished autonomic flexibility.

Сдвиги в структуре иерархической системы гомеокинеза больных ИБС на фоне стрессорного воздействия

The article presents the data on the possibility of obtaining additional diagnostic information about the reactions of the systemic regulation of the body under stressful conditions implemented as a part of the stress-test in patients with coronary artery disease: stable exertional angina. The implementation of an alternative approach to the assessment of adaptation processes arising against the background of measured physical activity is based on the assessment of the shifts in the topology of the entropic attractor model of the sinus heart rate reflecting the phenomenon of systemic homeokinesis. Against the background of the transition process in systemic regulation during stress-test, at the attractor structure has been revealed the development of the heart rate entropy, being a complex object, with the effects of activation and consolidation of its levels, which are significantly more pronounced during the formation of myocardial ischemia. The proposed digital indicators reflecting the identified topological changes can be used for an objective quantitative diagnosis of the phenomenon of destabilization of the systemic body resistance during the exacerbation of acute somatic pathology.

Multiscale network representation of physiological time series for early prediction of sepsis

Objective and Approach: Sepsis, a dysregulated immune-mediated host response to infection, is the leading cause of morbidity and mortality in critically ill patients. Indices of heart rate variability and complexity (such as entropy) have been proposed as surrogate markers of neuro-immune system dysregulation with diseases such as sepsis. However, these indices only provide an average, one dimensional description of complex neuro-physiological interactions. We propose a novel multiscale network construction and analysis method for multivariate physiological time series, and demonstrate its utility for early prediction of sepsis. Main results: We show that features derived from a multiscale heart rate and blood pressure time series network provide approximately 20% improvement in the area under the receiver operating characteristic (AUROC) for four-hour advance prediction of sepsis over traditional indices of heart rate entropy ( versus ). Our results indicate that this improvement is attributable to both the improved network construction method proposed here, as well as the information embedded in the higher order interaction of heart rate and blood pressure time series dynamics. Our final model, which included the most commonly available clinical measurements in patients’ electronic medical records and multiscale entropy features, as well as the proposed network-based features, achieved an AUROC of . Significance: Prediction of the onset of sepsis prior to clinical recognition will allow for meaningful earlier interventions (e.g. antibiotic and fluid administration), which have the potential to decrease sepsis-related morbidity, mortality and healthcare costs.

Shifts in the light-dark cycle increase unpredictability of the cardiovascular system.

Physiological variables such as heart rate (HR) and blood pressure (BP) exhibit long-term circadian rhythms, which can be disturbed by shift work. On the other hand, short-term oscillations in HR and BP have a high prognostic value. Therefore, we aimed to determine if the short-term variability, complexity and entropy of HR and BP would be affected by a regular light/dark (LD) cycle and phase delay shifts of the LD cycle, leading to chronodisruption. Telemetry-monitored rats were exposed first to the regular LD cycle and then to shifts in LD for 8weeks. On the basis of long-term HR and BP recording and evaluation, we found circadian rhythms in HR and BP variability, complexity and entropy under regular LD cycles. Short-term exposure to shifts disturbed circadian rhythms of HR and BP variability, complexity and entropy, indicating chronodisruption. The power of circadian rhythms was suppressed after 8weeks of phase delay shifts. Long-term exposure to shifts increased variability (p=0.007), complexity (p<0.001) and dark-time entropy (p=0.006) of HR but not BP. This is the first study demonstrating long-term recording and estimation of HR and BP variability, complexity and entropy in conscious rats exposed to irregular lighting conditions. After long-term phase delay shifts, short-term variability of HR was less predictable than in controls. This study suggests that changes in short-term HR and BP oscillations induced by long-term shift work can negatively affect cardiovascular health.

Multiscale sample entropy of heart rate and blood pressure: Methodological aspects.

The entropy of heart rate variability is one of the main features characterizing the complexity of the cardiovascular system. In order to take into account the multiscale nature of cardiovascular regulation, it was proposed to evaluate entropy with a multiscale approach, based on the estimation of Sample Entropy on progressively coarse-grained series (Multiscale Sample Entropy, MSE). Aim of this work is to investigate two methodological aspects related to MSE of cardiovascular signals. The first aspect regards the tolerance below which a couple of points are considered similar in a given embedding dimension, in particular how the way the tolerance is set at each level of coarse graining influences the MSE estimates. The second aspect regards whether heart rate and blood pressure (BP) signals are characterized by different MSE structures.To investigate these aspects, we analyzed 65 continuous BP recordings of more than 90-minute duration in healthy volunteers sitting at rest, and applied MSE estimators to beat-by-beat series of systolic BP, diastolic BP and pulse interval (inverse of heart rate). Results indicate that the way the tolerance is set during coarse graining influences substantially the MSE profile of cardiovascular signals, modifying the relative level of their unpredictability.

Zależność między entropią aproksymacji rytmu serca a strukturalną i funkcjonalną przebudową przedsionków oraz przebiegiem klinicznym napadowego i przetrwałego migotania przedsionków

Introduction. Atrial remodeling due to atrial fibrillation (AF) is characterized by electrical and structural changes of cardiomyocytes that are in response for arrhythmia self-perpetuation and resistance to sinus rhythm conversion. This project was designed to study nonlinear methods of heart rate variability (HRV) (such as approximate entropy of heart rate [ApEn]) that can best characterize LA structural and functional remodeling and its association with clinical course in patients with paroxysmal and persistent AF. Material and methods. Traditional time and frequency domain HRV indices were analyzed in 75 patients (mean age 55 [49–62] years, 79% male) with paroxysmal or persistent AF on a background of ischemic heart disease (IHD) and/or hypertension without significant structural myocardial damage and in 19 control patients without AF (mean age 56 [49–61] years, 63% male). Echocardiography was performed to assess size and function of left atrium (LA). Results. In patients with paroxysmal or persistent AF the ApEn value was significantly lower than in the control patients group. Echo-parameters of LA, characterizing its structure and function, were correlated with ApEn value. The AF duration was negatively correlated with the ApEn value. Its values less than 0.93 was associated with a larger LA size (> 39 mm) and more frequent AF. Conclusions. There is a strong correlation of ApEn value and atrial remodeling. ApEn values less than 0.93 are related to AF recurrence and can be considered as prognostic risk factor of structural and functional remodeling of the heart muscle in patients with AF.

Association of Diabetes Related Complications with Heart Rate Variability among a Diabetic Population in the UAE.

Microvascular, macrovascular and neurological complications are the key causes of morbidity and mortality among type II diabetes mellitus (T2DM) patients. The aim of this study was to investigate the alterations of cardiac autonomic function of diabetic patients in relation to three types of diabetes-related complications. ECG recordings were collected and analyzed from 169 T2DM patients in supine position who were diagnosed with nephropathy (n = 55), peripheral neuropathy (n = 64) and retinopathy (n = 106) at two hospitals in the UAE. Comparison between combinations of patients with complications and a control diabetic group (CONT) with no complication (n = 34) was performed using time, frequency and multi-lag entropy measures of heart rate variability (HRV). The results show that these measures decreased significantly (p<0.05) depending on the presence and type of diabetic complications. Entropy, (median, 1st- 3rd interquartile range) for the group combining all complications (1.74,1.37–2.09) was significantly lower than the corresponding values for the CONT group (1.77, 1.39–2.24) with lag-1 for sequential beat-to-beat changes. Odds ratios (OR) from the entropy analysis further demonstrated a significantly higher association with the combination of retinopathy and peripheral neuropathy versus CONT (OR: 1.42 at lag 8) and an even OR for the combination of retinopathy and nephropathy (OR: 2.46 at lag 8) compared to the other groups with complications. Also, the OR of low frequency power to high frequency power ratio (LF/HF) showed a higher association with these diabetic-related complications compared to CONT, especially for the patient group combining all complications (OR: 4.92). This study confirms that the type of microvascular or peripheral neuropathy complication present in T2DM patients have different effects on heart rate entropy, implying disorders of multi-organ connectivity are directly associated with autonomic nervous system dysfunction. Clinical practice may benefit from including multi-lag entropy for cardiac rhythm analysis in conjunction with traditional screening methods in patients with diabetic complications to ensure better preventive and treatment outcomes in the Emirati Arab population.

Abstract 20061: Towards Predicting the Rate and Rhythm of Rearrest After Out-of-hospital Cardiac Arrest

Background/Aims: Rearrest (RA) after resuscitation from out-of-hospital cardiac arrest (OHCA) has been shown to be an independent predictor of death before hospital discharge. The aim of this study was to understand how heart rate and rhythm transitions relate to the timing and presentation of rearrest. Methods: Case data for emergency medical services (EMS)-treated OHCA were obtained from the Resuscitation Outcomes Consortium (ROC) for the period 2006-2008. Cases with analyzable electrocardiogram (ECG) signals were included in the study. RA events were ascertained by an inferential scheme involving the presence of a life-threatening ECG rhythm and/or presence of chest compressions. ROSC-RA ECG intervals were extracted from defibrillator source files and imported into custom software for calculation of several heart rate characteristics for 30s, 1min, 3min, and 5min epochs beginning at the onset of ROSC, including: mean heart rate, standard deviation for heart rate (SD-HR), root mean square of the successive differences (RMSSD), and approximate entropy of heart rate (ApEn). Frequency-based heart rate variability measures including normalized high frequency power (HFN), normalized low frequency power (LFN), and ratio of low and high frequency power (LFHF) were calculated. Multivariable generalized estimating equations (GEE) were used to assess the relationship between heart rate characteristics and time-to-RA while controlling for RA event number, presenting OHCA ECG rhythm, and RA ECG rhythm. Rhythm transitions were assessed and compared with Fisher’s exact test. Results: In univariate analyses RMSSD in the 30s and 1-minute epoch epochs, SD-HR in the 5-minute epoch, ApEn in the 5-minute epoch, presenting ECG rhythm ventricular fibrillation / ventricular tachycardia (VF/VT), and RA event number were predictive of time-to-RA. In a multivariable model, only SD-HR in the 5-minute epoch was related to time-to-RA (coeff. = -764.16; 95%CI: -1405.92 , -122.40; p = 0.020). The most common first rhythm transition was from VF/VT to VF/VT. Conclusions: At least one heart rate-derived measure, SD-HR, was related to time-to-RA event, independent of RA ECG rhythm, presenting OHCA ECG rhythm or RA event number.

Энтропия сердечного ритма в серии проб с ритмическим дыханием

Энтропия сердечного ритма в серии проб с ритмическим дыханием

Real-time heart rate entropy predicts the need for lifesaving interventions in trauma activation patients

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 utility of real-time, automated, instantaneous, hand-held heart rate entropy analysis in predicting the need for lifesaving interventions (LSIs). We hypothesized that real-time HRC would predict LSIs. Prospective enrollment of patients who met criteria for trauma team activation was conducted at a Level I trauma center (September 2011 to February 2012). A novel, hand-held, portable device was used to measure HRC (by sample entropy) and time-domain heart rate variability continuously in real time for 2 hours after the moment of presentation. Electric impedance cardiography was used to determine cardiac output. 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. Of 82 patients enrolled, 21 (26%) received 67 LSIs within 24 hours of hospital arrival. Initial systolic blood pressure was similar in both groups. LSI patients had a lower Glasgow Coma Scale (GCS) score (9.2 [5.1] vs. 14.9 [0.2], p < 0.0001). The mean (SD) 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 < 0.0001). With the use of 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%, and 53%, respectively, with an accuracy of 77% for predicting an LSI. Decreased HRC on hospital arrival is an independent predictor of the need for LSI in trauma activation patients. Real-time HRC may be a useful adjunct to standard vital signs monitoring and predicts LSIs. Prognostic and diagnostic study, level III.

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.

Comparison of different methods of heart rate entropy analysis during acute anoxia superimposed on a chronic rat model of pulmonary hypertension

Acute life-threatening situations are particularly critical when superimposed on chronic diseases. The objective of this study was the assessment of heart rate (HR) dynamics during episodes of acute anoxia superimposed on a rat model of chronic pulmonary hypertension. In 10 adult Wistar rats, five weeks after pulmonary hypertension induction with Monocrotaline, we analysed eight 1-min HR segments, during episodes of baseline, mechanical ventilation and acute anoxia, using linear indices, approximate entropy (ApEn), sample entropy (SampEn) and multiscale entropy (MSE). The transition from baseline or mechanical ventilation to early anoxia was identified through almost all indices, but SampEn(2,0.6) was the index that better identified all the transitions. MSE presented limited performance, possibly due to the non-stationary nature and short duration of the acute anoxia episodes. A systematic evaluation of all computed HR indices may help to identify which indices or combination of indices more adequately discriminates and monitors critical acute events superimposed on chronic clinical conditions.

Cardio-respiratory coupling in untreated patients with major depression

Depressive disorders are known to be associated with higher risks of cardiovascular diseases. Several studies have reported an imbalance within the autonomic nervous system (ANS) as one putative cause. Previous investigations showed decreased cardio-respiratory coupling in depressive patients that were treated with nortriptyline. We aimed to compare parameters of heart rate variability and cardio-respiratory coupling between unmedicated patients suffering from major depressive disorder (MDD) and healthy controls in order to further understand autonomic dysfunction in the disease. We investigated eighteen unmedicated patients with major depressive disorder and eighteen matched healthy controls. Electrocardiogram and respiratory signals were obtained during a twenty minute resting period. Time- and frequency based parameters of HRV, respiratory sinus arrhythmia (RSA), approximate entropy of heart rate (ApEn(RR)) and respiratory rate (ApEn(Resp)) were calculated. Additionally, cross-ApEn between RR-intervals and respiration time series was determined, reflecting coupling of both signals. Patients showed an increased heart rate and LF/HF-ratio. Respiratory sinus arrhythmia (RSA) and ApEn(RR) were reduced in patients in comparison to controls. Breathing rate, ApEn(Resp) and cross-ApEn did not differ between the two groups. Increased heart rate, increased LF/HF-ratio, reduced RSA and reduced ApEn(RR) indicate a decrease of cardiac vagal modulation in depressive patients. No difference of cardio-respiratory coupling was observed. Respiratory parameters and cross-ApEn did not differ between both groups, and thus we conclude that diminished vagal modulation is mainly limited to cardiac modulation.

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.

Influence of Olanzapine on QT Variability and Complexity Measures of Heart Rate in Patients With Schizophrenia

Previous studies have shown that untreated patients with acute schizophrenia present with reduced heart rate variability and complexity as well as increased QT variability. This autonomic dysregulation might contribute to increased cardiac morbidity and mortality in these patients. However, the additional effects of newer antipsychotics on autonomic dysfunction have not been investigated, applying these new cardiac parameters to gain information about the regulation at sinus node level as well as the susceptibility to arrhythmias. We have investigated 15 patients with acute schizophrenia before and after established olanzapine treatment and compared them with matched controls. New nonlinear parameters (approximate entropy, compression entropy, fractal dimension) of heart rate variability and also the QT-variability index were calculated. In accordance with previous results, we have observed reduced complexity of heart rate regulation in untreated patients. Furthermore, the QT-variability index was significantly increased in unmedicated patients, indicating increased repolarization lability. Reduction of the heart rate regulation complexity after olanzapine treatment was seen, as measured by compression entropy of heart rate. No change in QT variability was observed after treatment. This study shows that unmedicated patients with acute schizophrenia experience autonomic dysfunction. Olanzapine treatment seems to have very little additional impact in regard to the QT variability. However, the decrease in heart rate complexity after olanzapine treatment suggests decreased cardiac vagal function, which may increase the risk for cardiac mortality. Further studies are warranted to gain more insight into cardiac regulation in schizophrenia and the effect of novel antipsychotics.