Heart Rate Complexity Research Articles

The Effect of Different Antihypertensive Classes on the Complexity of Heart Rate and Blood Pressure Variability

Hypertension is associated with several physiological dysfunctions, including changes in the neurohumoral control of heart and vessels. Different classes of antihypertensive drugs may have distinct effects on the autonomic system and body homeostasis, but their individual effects on the complexity of cardiovascular regulation are still not established. We investigated the effect of five different classes of antihypertensive on the complexity of pulse interval (PI) and arterial pressure (AP) variability in an experimental model of renal hypertension (2 kidney 1 clip, 2K1C) in the rat. Hypertensive rats were treated (by gavage) during 15 days with: water (N=12), ramipril (2 mg/kg/day; N=7), losartan (10 mg/kg/day; N=8), atenolol (90 mg/kg/day; N=9), amlodipine (10 mg/kg/day; N=7) or hydrochlorothiazide (20 mg/kg/day; N=8). A normotensive (sham‐operated) control group (N=10) received water for the same period. After the treatment, rats had their raw AP recorded and beat‐by‐beat series of systolic AP and PI were created. The complexity of AP and PI was assessed by multiscale entropy (MSE) and detrended fluctuation analysis (DFA). For PI series, hypertensive rats treated with water showed decreased MSE and increased DFA in the middle range of scales. For AP series, hypertensive rats untreated or treated with amlodipine have lower MSE at short and middle time scales. Hypertensive rats treated with amlodipine also showed altered DFA in comparison to the other groups. All antihypertensive drugs were efficient to restore AP to normal levels. Moreover, 2K1C untreated (water) rats presented the lowest cardiovascular complexity and all antihypertensive drugs, except for amlodipine, were capable to restore the cardiovascular complexity to normal levels. Therefore, amlodipine seems to have a deleterious effect on the cardiovascular integrative control, probably due to the increased sympathetic activity induced by amlodipine.Support or Funding InformationThis study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior ‐ Brasil (CAPES) ‐ Finance Code 001, São Paulo Research Foundation (FAPESP, Proc. 2013/20549‐7) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Proc. 402076/2016‐8).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Measures of Compensatory Reserve are More Sensitive and Specific than Heart Rate Variability as Early Predictors of Hemodynamic Decompensation

BackgroundHemorrhage remains the leading cause of death following traumatic injury in both civilian and military settings. Heart rate variability (HRV) and complexity (HRC) have been recognized as potential “new vital signs” for monitoring trauma patients, although their benefit for triage decision support remains unclear. Another new paradigm, the compensatory reserve measurement (CRM), represents the integration of all mechanisms responsible for compensation during blood loss, designed to identify current physiologic status by estimating the progression toward hemodynamic decompensation. We hypothesized that CRM would provide greater sensitivity and specificity to detect progressive reductions in central circulating blood volume and onset of decompensation as compared to measurements of HRV and HRC.MethodsContinuous, noninvasive measurements of CRM and electrocardiogram (ECG) were made on 101 healthy volunteers (59 males, 42 females; mean±SD age 28±8 years) during stepwise progressive central hypovolemia to the point of decompensation. Lower body negative pressure (LBNP) was used to simulate hemorrhage by inducing the onset and progression of central hypovolemia. Time‐domain measures of HRV were taken from ECG signal data including R‐to‐R Interval Standard Deviation in milliseconds (ms), Root Mean Square Standard Deviation, percentage of RRI that vary by at least 50 ms, and amplitude measures of High Frequency Oscillations and Low Frequency Oscillations (CDMLF) obtained from the complex demodulation method. Measures of HRC included Sample Entropy, Fractal Dimension by Dispersion Analysis, Stationarity and Detrended Fluctuation Analysis. Data were analyzed using generalized estimating equations with compound symmetry covariance structures for longitudinal correlated data analysis of continuous variables, the results of which were used to report least‐square means with 95% confidence intervals at each LBNP level.ResultsCRM demonstrated superior ROC AUC (0.93) compared with all measures of HRV (≤ 0.84), and HRC (≤ 0.86). Sensitivity and specificity values at the ROC optimal thresholds were greater for CRM (SENS=0.84; SPEC=0.84) than HRV (SENS ≤ 0.78; SPEC ≤ 0.77) and HRC (SENS ≤ 0.79; SPEC ≤ 0.77). With standardized values across all levels of LBNP, CRM had a steeper decline, less variability, and explained a greater proportion of the variation in the data than both HRV and HRC during progressive hypovolemia.ConclusionConsistent with our hypothesis, CRM had greater sensitivity and specificity in detecting progressive reductions in circulating blood volume and decompensation than HRV and HRC. These findings add to the growing body of literature describing the advantages of CRM for detecting reductions in central blood volume. Most importantly, these results provide further support for the potential use of CRM in the triage and monitoring of patients at risk of circulatory shock following blood loss.Support or Funding InformationStudy funding was provided by a grant from the US Army Combat Casualty Care Research Program (D‐009‐2014‐USAISR).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Admission Heart Rate Is Associated With Coronary Artery Disease Severity and Complexity in Patients With Acute Coronary Syndrome.

We evaluated the relationship between admission heart rate (HR) and coronary artery disease severity and complexity in patients with acute coronary syndrome (ACS). A total of 884 patients (mean age 59 [11] years, 24.7% female) who underwent coronary angiography for ACS and were treated with primary or selective percutaneous coronary intervention were included in this cross-sectional study. The measurement of admission HR was based on the first available resting electrocardiogram after admission. The SYNTAX score (SS) was calculated. Patients with an SS ≤ 22 (n = 538) were classified as the low SS group and those with an SS > 22 (n = 346) were classified as the intermediate-to-high SS group. Admission HR was greater in the intermediate-to-high SS group compared with the low SS group (75 [10] bpm vs 67 [8] bpm, P < .001). Admission HR was positively and significantly correlated with the SS (r = 0.475, P < .001). After multivariate analysis, admission HR (per 1 standard deviation, ie, 10 bpm) remained an independent predictor of intermediate-to-high SS (odds ratio: 3.135, 95% confidence interval: 2.538-3.873, P < .001). Admission HR is independently and positively associated with the SS. Thus, elevated admission HR may be useful to identify patients with ACS with a high coronary atherosclerotic plaque burden.

Uncertainty in heart rate complexity metrics caused by R-peak perturbations

Heart rate complexity (HRC) is a proven metric for gaining insight into human stress and physiological deterioration. To calculate HRC, the detection of the exact instance of when the heart beats, the R-peak, is necessary. Electrocardiogram (ECG) signals can often be corrupted by environmental noise (e.g., from electromagnetic interference, movement artifacts), which can potentially alter the HRC measurement, producing erroneous inputs which feed into decision support models. Current literature has only investigated how HRC is affected by noise when R-peak detection errors occur (false positives and false negatives). However, the numerical methods used to calculate HRC are also sensitive to the specific location of the fiducial point of the R-peak. This raises many questions regarding how this fiducial point is altered by noise, the resulting impact on the measured HRC, and how we can account for noisy HRC measures as inputs into our decision models. This work uses Monte Carlo simulations to systematically add white and pink noise at different permutations of signal-to-noise ratios (SNRs), time segments, sampling rates, and HRC measurements to characterize the influence of noise on the HRC measure by altering the fiducial point of the R-peak. Using the generated information from these simulations provides improved decision processes for system design which address key concerns such as permutation entropy being a more precise, reliable, less biased, and more sensitive measurement for HRC than sample and approximate entropy.

The complexity of heart rate during behaviour formed in different stages of ontogeny

The complexity of heart rate during behaviour formed in different stages of ontogeny

Analysis of heart rate signals during meditation using visibility graph complexity.

In the dynamics analysis of heart rate, the complexity of visibility graphs (VGs) is seen as a sign of short term variability in signals. The present study was conducted to investigate the possible impact of meditation on heart rate signals complexity using VG method. In this study, existing heart rate signals in Physionet database were used. The dynamics of the signals were then studied both before and during meditation by examining the complexity of VGs using graph index complexity (GIC). Generally, the obtained results showed that the heart rate signals were more complex during meditation. The simple process of calculating the GIC of VG and its adaptability to the chaotic nature of the biological signals can help in estimating the heart rate complexity in meditation.

Heart rate differences between symptomatic and asymptomatic Brugada syndrome patients at night

Objective: Ventricular arrhythmias in Brugada syndrome (BS) mainly occur at rest, especially during nighttime, suggesting that parasympathetic activity at night may play an important role in the arrhythmogenesis of the disease. This study examined and compared the autonomic function of symptomatic and asymptomatic BS patients overnight. Approach: We analyzed various heart rate variability (HRV) and heart rate complexity (HRC) markers in a clinical series including 87 BS patients, where 23 were symptomatic. Main results: Statistically significant differences were found in markers MIRR, SDNN, SDANN, and SampEn, suggesting that symptomatic patients may be related to lower heart rate variability and complexity values, as well as to greater circadian fluctuations overnight. Significance: The results provide further evidence for the role of autonomic imbalance in the pathophysiology of BS, highlighting the relevance of nighttime analysis to the unmasking of significant ANS changes. Based on these outcomes, the role of HRV and HRC assessment at night could be a step forward towards the understanding of BS and the risk for the occurrence of symptoms in these patients, with a potential future impact on therapeutic strategies.

Diminished heart rate complexity in adolescent girls: a sign of vulnerability to anxiety disorders?

ABSTRACTBackground and Objectives: Diminished heart rate variability has been found to be associated with high anxiety symptomatology. Since adolescence is the period of onset for many anxiety disorders, this study aimed to determine sex- and anxiety-related differences in heart rate variability and complexity in adolescents.Methods: We created four groups according to sex and anxiety symptomatology: high-anxiety girls (n = 24) and boys (n = 25), and low-anxiety girls (n = 22) and boys (n = 24) and recorded their cardiac function while they performed regular school activities. A series of two-way (sex and anxiety) MANOVAs were performed on time domain variability, frequency domain variability, and non-linear complexity.Results: We obtained no multivariate interaction effects between sex and anxiety, but highly anxious participants had lower heart rate variability than the low-anxiety group. Regarding sex, girls showed lower heart rate variability and complexity than boys.Conclusions: The results suggest that adolescent girls have a less flexible cardiac system that could be a marker of the girls’ vulnerability to developing anxiety disorders.

Autonomic Modulation After Acute Resistance Exercise in Resistance-Trained Individuals

Differences in autonomic modulation between free-weight and weight machines resistance exercise is unknown. PURPOSE: To investigate the effects of acute free-weight (FW) and weight machines (WM) resistance exercise on heart rate complexity (HRC) and variability (HRV) in resistance-trained individuals. METHODS: Resistance- trained individuals were assigned to either a FW (n = 25) or a WM (n = 16) group. Autonomic modulation was collected at rest, and 15 (Rec1) and 25 (Rec2) min following acute resistance exercise (ARE) or a control. Sample Entropy (SampEn), indicative of vagal modulation, was used as a measure of HRC. HRV measurements included vagal modulation (normalized high frequency (HFnu)), and sympathovagal balance (LF/HF ratio). ARE for the FW group consisted of 3 sets of 10 repetitions at 75% 1-repetition maximum (1RM) on the squat, bench press, and deadlift, while the WM group utilized of 3 sets of 10 repetitions at 75% 1RM on the leg press, lat pull down, leg extension, chest press, and leg curl. A 2x2x3 ANCOVA was used to examine groups (FW, WM) across conditions (ARE, control) and time (Rest, Rec1, Rec2), with load as a covariate. RESULTS: The groups were similar (p>0.05) for age, height, weight, BMI, and baseline autonomic modulation, but differed for years of training. There was a significant group by condition by time interaction (p=0.03) for SampEn such that in the FW group (Rest: 1.5±0.3; Rec1: 1.1±0.3; Rec2: 1.1±0.4) it was attenuated during Rec1 and Rec2 after ARE compared to rest and the control. In the MW group, while there were no significant differences from rest to Rec1 or Rec2, there was a significant difference from Rec1 to Rec2 (Rest: 1.4±0.5; Rec1: 1.0±0.3; Rec2: 1.3±0.3) such that it differed from the control. There was also a significant group by time interaction for HFnu (Rest: 62.5±15.0%; Rec1: 29.5±18.9%; Rec2: 29.2±19.9%, p=0.002) such that it was attenuated compared to rest, and the control, in both groups. The LF/HF ratio (Rest: 61.0±52.1; Rec1: 420.0 ±424.7; Rec2: 456.7±390.2, p=0.007) was augmented such that it differed from rest, and the control, in both groups. CONCLUSIONS: Based on our data the use of free- weight resistance exercises results in significant reductions in vagal modulation that are immediate, and maintained, up to 30 min, which does not appear to occur when using weight machines.

Corrigendum to “Multifractal-Multiscale Analysis of Cardiovascular Signals: A DFA-Based Characterization of Blood Pressure and Heart-Rate Complexity by Gender”

Corrigendum to “Multifractal-Multiscale Analysis of Cardiovascular Signals: A DFA-Based Characterization of Blood Pressure and Heart-Rate Complexity by Gender”

Chronic vagus nerve stimulation reverses heart rhythm complexity in patients with drug-resistant epilepsy: An assessment with multiscale entropy analysis

ObjectiveVagus nerve stimulation (VNS) is an adjunctive treatment in drug-resistant epilepsy. The alterations in heart rate dynamics through VNS are not well understood. This study aimed to determine changes in heart rhythm complexity in association with VNS and to relate the findings to the outcome of VNS treatment in patients with drug-resistant epilepsy. MethodsWe prospectively analyzed 32 patients with drug-resistant epilepsy, who underwent VNS implantation, and 32 age- and sex-matched healthy control subjects. The interictal heartbeat intervals were analyzed using the heart rhythm complexity with multiscale entropy (MSE) and traditional heart rate variability (HRV) analyses based on ambulatory 24-hour electrocardiograms (ECGs). ResultsPatients had significantly decreased complexity indices (Slope 5, Area 1–5, Area 6–15, Area 6–20) on MSE analysis and decreased HRV measurements (standard deviation of the heartbeat interval (SDNN), square root of the mean of sum of squares of the differences between adjacent RR intervals (RMSSD), pNN50, very low frequency (VLF), low frequency (LF), high frequency (HF), total power (TP)) in time and frequency domain analyses. After one year of VNS treatment in patients with drug-resistant epilepsy, there was a trend in an elevated MSE profile with significant higher values between the scales 1 and 9. Vagus nerve stimulation induces a more significant increase of MSE in VNS responders than those in the nonresponders. The conventional HRV measurements did not change. ConclusionOur results suggest that heart rhythm complexity is impaired in patients with drug-resistant epilepsy, and this is at least partially reversed by VNS treatment. Furthermore, VNS-induced effects on heart rate complexity may be associated with the therapeutic response to VNS in patients with drug-resistant epilepsy.

Mapping the dynamics of heart rate variability and complexity changes with progressive focal status epilepticus. (P3.275)

Mapping the dynamics of heart rate variability and complexity changes with progressive focal status epilepticus. (P3.275)

High-intensity handgrip training lowers blood pressure and increases heart rate complexity among postmenopausal women: a pilot study.

Handgrip exercise is an emerging strategy for resting blood pressure (BP) reduction requiring minimal time and exercise effort. However, the research literature is currently limited to handgrip protocol designs predominantly prescribing sustained grip contractions, with little assessment of alternative options. Furthermore, our understanding of the utility of handgrip exercise would be strengthened by an evaluation of the physiological mechanisms driving BP reductions and an assessment of the interindividual response variability. As such, this research was designed to perform an initial evaluation of the pragmatic effectiveness of a novel at-home, high-intensity, unilateral (nondominant) handgrip exercise training program in reducing resting BP, while simultaneously exploring mediators of BP change including a neurocardiac index of autonomic nervous control [heart rate (HR) variability], measures of arterial stiffness (radial augmentation index and carotid-radial pulse wave velocity), and cardiovascular reactivity to psychophysiological stressors. Postmenopausal women were recruited to complete 8 weeks of handgrip exercise training. Aforementioned measures of resting BP and mediators of BP change were acquired at the midway point and end of training. All participants (n=17) completed training with high self-reported adherence (96.9%) and improvement in grip strength (2.7±2.4kg, P<0.05). Handgrip training reduced resting systolic BP (-5.1±7.7 mmHg, P<0.05) and improved HR complexity (sample entropy: 0.24±0.31, P<0.05), without significant changes to resting diastolic BP, HR, or arterial stiffness (all P>0.05). This pilot study successfully shows the potential utility of high-intensity intermittent handgrip exercise for improvements in cardiovascular health among postmenopausal women, with additional research required to further explore the underlying physiological mechanisms driving such improvements.

Correspondence between the heart rate complexity and system characteristics of performed behavior

Correspondence between the heart rate complexity and system characteristics of performed behavior

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.

Effects of prolonged and repeated immersions on heart rate variability and complexity in military divers.

The influence of prolonged and repeated water immersions on heart rate variability (HRV) and complexity was examined in 10 U.S. Navy divers who completed six-hour resting dives on five consecutive days. Pre-dive and during-dive measures were recorded daily. Dependent variables of interest were average heart rate (HR), time-domain measures of HRV [root mean square of successive differences of the normal RR (NN) interval (RMSSD), standard deviation of the NN interval (SDNN)], frequency-domain measures of HRV [low-frequency power spectral density (psd) (LFpsd), low-frequency normalized (LFnu), high-frequency psd (HFpsd), high-frequency normalized (HFnu), low-frequency/ high-frequency ratio (LF/HF)], and non-linear dynamics of HRV [approximate entropy (ApEn)]. A repeated-measures ANOVA was performed to examine pre-dive measure differences among baseline measures. Hierarchical linear modeling (HLM) was performed to test the effects of prolonged and repeated water immersion on the dependent variables. Pre-dive HR (P=0.005) and RMSSD (P⟨0.001) varied significantly with dive day while changes in SDNN approached significance (P=0.055). HLM indicated that HR decreased during daily dives (P=0.001), but increased across dive days (P=0.011); RMSSD increased during daily dives (P=0.018) but decreased across dive days (P⟨0.001); SDNN increased during daily dives (P⟨0.001); LF measures increased across dive days (LFpsd P⟨0.001; LFnu P⟨0.001), while HF measures decreased across dive days (HFpsd P⟨0.001; HFnu P⟨0.001); LF/HF increased across dive days (P⟨0.001); ApEn decreased during daily dives (P⟨0.02) and across dive days (P⟨0.001). These data suggest that the cumulative effect of repeated dives across five days results in decreased vagal tone and a less responsive cardiovascular system.

Impairment of heart rhythm complexity in patients with drug-resistant epilepsy: An assessment with multiscale entropy analysis

ObjectiveEpilepsy and seizures can have dramatic effects on the cardiac function. The aim of this study was to investigate the heart rhythm complexity in patients with drug-resistant epilepsy (DRE). MethodsAmbulatory 24-h electrocardiograms (ECG) from 70 DRE patients and 50 healthy control subjects were analyzed using conventional heart rate variability (HRV) and multiscale entropy (MSE) methods The variation of complexity indices (CI), which was calculated from MSE profile, was determined. ResultsDRE patients had significantly lower time domain (Mean RR, SDNN, RMSSD, pNN50) and frequency domain (VLF, LF, HF, TP) HRV measurements than healthy controls. Of the MSE analysis, MSE profile, CI including Slope 5, Area 1–5, Area 6–15 and Area 6–20 were significantly lower than those in the healthy control group. In receiver operating characteristic (ROC) curve analysis, VLF had the greatest discriminatory power for the two groups. In both net reclassification improvement (NRI) model and integrated discrimination improvement (IDI) models, CI derived from MSE profiles significantly improved the discriminatory power of Mean RR, SDNN, RMSSD, pNN50, VLF, LF, HF and TP. SignificanceThe heart rate complexity is impaired for DRE patients. CI are useful to discriminate DRE patients from subjects with normal cardiac complexity. These findings indicate that MSE method may serve as a complementary approach for characterizing and understanding abnormal heart rate dynamics in epilepsy. Furthermore, the CI may potentially be used as a biomarker in monitoring epilepsy.

Acute Resistance Exercise Effects on Autonomic Modulation Between Resistance-Trained Men and Women

While it has been reported that women have greater vagal withdrawal during aerobic exercise and supramaximal exercise compared to men, the sex-specific responses to an acute bout of resistance exercise are unknown. PURPOSE: To determine the effects of an acute bout of free-weight resistance exercise consisting of the squat, bench press, and deadlift on heart rate variability (HRV) and heart rate complexity (HRC) between the sexes. METHODS: Twenty-three resistance-trained (aged 23±3 yrs; mean±SD) men (n=13) and women (n=10) with a minimum of 1 year of resistance training volunteered for the study. Autonomic modulation was assessed at rest as well as 15-20 minutes (Rec1) and 25-30 minutes (Rec2) after an acute bout of resistance exercise utilizing 3 sets of 10 repetitions at 75% 1-repetition maximum on the squat, bench press and deadlift. Two minutes of rest was given between sets and exercises. A quiet control condition of the same duration was also utilized for each participant. Measures of HRV were analyzed in the frequency domain and included measures of vagal modulation (normalized high frequency (HFnu)), sympathetic modulation (normalized low frequency (LFnu)), and sympathovagal balance (LF/HF ratio). Sample Entropy (SampEn), indicative of vagal modulation, was used as a measure of HRC. A repeated measures ANOVA was used to compare the effects of sex (men and women) across the two conditions (resistance exercise and control) and time (rest, Rec1 and Rec2). T-tests were used for post-hoc testing if the ANOVA was significant with a Benjamini-Hochberg correction factor. RESULTS: There were no significant sex differences at rest for any of the variables. Furthermore, there were no significant sex x condition x time interactions for any variable. Compared with Rest LFnu (Rest: 35.5±15.3%; Rec1: 73.0±18.0; Rec2: 66.0±25.1%, p=0.0001), LnLF/HF (Rest: 4.0±0.9%; Rec1: 5.1±1.1%; Rec2: 5.2±1.1%, p=0.002) were augmented at Rec1 and Rec2. HFnu (Rest: 61.2±17.1%; Rec1: 40.3±22.3%; Rec2: 38.4±21.8%, p=0.0001) and SampEn (Rest: 1.5±0.3units; Rec1: 1.2±0.3units; Rec2: 1.3±0.5units, p=0.0001) were decreased at Rec1 and Rec2 compared to Rest after the acute resistance exercise. CONCLUSIONS: These data suggest that acute RE using free-weights has a profound impact on autonomic modulation that is similar between the sexes.

Low pre-operative heart rate variability and complexity are associated with hypotension after anesthesia induction in major abdominal surgery.

Significant hypotension after induction of general anesthesia is common and has the potential for serious complications. This study aimed to determine if pre-operative heart rate variability (HRV) was associated with post-induction hypotension in patients undergoing major abdominal surgery. Patients undergoing semi-elective major abdominal surgery were consecutively recruited during pre-admission clinic assessment. Exclusion criteria included cardiac conduction disease, arrhythmias or severe liver or renal disease. Ten minutes of electrocardiogram at 1024Hz were recorded a median of 3 days pre-operatively. Pre-operative HRV parameters were compared in patients who experienced significant hypotension (fall in systolic and mean arterial pressure (MAP) >30% baseline and MAP ≤60mmHg) versus those who remained haemodynamically stable after induction of general anesthesia with propofol and fentanyl. Patients who experienced hypotension after general anesthesia induction had significantly lower pre-operative HRV (SDNN 16 vs. 37ms, p < 0.001), reduced spectral power (total power 262 vs. 1236 ms2, p = 0.002) and reduced correlation dimension, a measure of signal complexity (0.11 vs. 2.13, p < 0.001). Hypotension occurred relatively frequently in our cohort and was associated with a higher ASA grade (36 vs. 6% ASA 3, p = 0.036), hence post-induction hypotension and lower HRV may be associated with severity of illness or poor physiological reserve. Pre-operative HRV was a useful screening tool in identifying patients undergoing major abdominal surgery who were at risk of haemodynamic instability after anesthesia induction.

Cardiac Autonomic Alteration and Metabolic Syndrome: An Ambulatory ECG-based Study in A General Population

Metabolic syndrome (MetS) has been associated with chronic damage to the cardiovascular system. This study aimed to evaluate early stage cardiac autonomic dysfunction with electrocardiography (ECG)-based measures in MetS subjects. During 2012–2013, 175 subjects with MetS and 226 healthy controls underwent ECG recordings of at least 4 hours starting in the morning with ambulatory one-lead ECG monitors. MetS was diagnosed using the criteria defined in the Adult Treatment Panel III, with a modification of waist circumference for Asians. Conventional heart rate variability (HRV) analysis, and complexity index (CI1–20) calculated from 20 scales of entropy (multiscale entropy, MSE), were compared between subjects with MetS and controls. Compared with the healthy controls, subjects with MetS had significantly reduced HRV, including SDNN and pNN20 in time domain, VLF, LF and HF in frequency domain, as well as SD2 in Poincaré analysis. MetS subjects have significantly lower complexity index (CI1–20) than healthy subjects (1.69 ± 0.18 vs. 1.77 ± 0.12, p < 0.001). MetS severity was inversely associated with the CI1–20 (r = −0.27, p < 0.001). MetS is associated with significant alterations in heart rate dynamics, including HRV and complexity.