Age-associated alteration of sympatho-vagal balance in a female population assessed through the tone-entropy analysis

Sesame lignans increase sympathetic nerve activity and blood flow in rat skeletal muscles

Beneficial effects of sesame lignans, especially antioxidative effects, have been widely reported; however, its potential effects on autonomic nerves have not yet been investigated. Therefore, the current study aimed to investigate the effect of sesame lignans on the autonomic nervous system. The sympathetic nerve activity in rat skeletal muscle was measured using electrophysiological approaches, with blood flow determined using the laser Doppler method. Sesame lignans were administered intragastrically at 2 and 20 mg/kg, and after 60 min, the sympathetic nerve activity was observed to increase by 45.2% and 66.1%, respectively. A significant increase in blood flow (39.6%) was also observed for the 20-mg/kg dose when measured at 55 min after administration. These sympathomimetic effects were completely prevented by subdiaphragmatic vagotomy, and the increase in blood flow was eliminated in the presence of the beta2-adrenergic receptor inhibitor butoxamine. Thus, it is proposed that sesame lignans can increase the blood flow of skeletal muscle, possibly by exciting sympathetic nerve activity through the afferent vagal nerve.

Improvement of Menopausal Symptoms with Acupuncture Not Reflected in Changes to Heart Rate Variability

Hypothesis

Studies indicate that menopausal symptoms are relieved by acupuncture. Additional studies have suggested that acupuncture may affect heart rate variability (HRV). This paper reports a pilot study that investigated whether menopausal symptoms responded to acupuncture, and if changes in the spectral analysis of HRV, either suppression of low frequency or augmentation of high frequency bands, corresponded with symptom report.

Methods/interventions

12 healthy menopausal subjects were enrolled in this feasibility study. At baseline, subjects were experiencing moderately distressing menopausal symptoms, scoring at least 22 of a possible 44 points on the Menopausal Rating Scale. 10 traditional Chinese medicine-based, protocol acupuncture treatments were administered over a 4 week period, three times a week for 2 weeks, followed by twice a week for 2 weeks.

Outcome measures

Menopausal Rating Scale questionnaire, 11 menopausal symptoms were evaluated on a zero to four severity scale via self-administered daily checklist for 4 weeks. Dynamic measures of HRV (autoregressive model) were captured before, during and after acupuncture at each session. Spectral analysis of the heart rate was used to compute power in the low frequency and high frequency bands, and their ratio.

Results

All subjects complied fully with the protocol without any reported adverse events. While all 11 symptoms showed significant improvement, and one HRV measure changed, on average over the study period, there was essentially no support for a relationship between HRV, menopausal symptom report and acupuncture intervention.

Age alters cardiac autonomic modulations during and following exercise-induced heat stress in females

The aim of this study was to examine the effect of natural ageing on heart rate variability during and following exercise-induced heat stress in females. Eleven young (∼24 years) and 13 older (∼51 years), habitually active females completed an experimental session consisting of baseline rest, moderate intensity intermittent exercise (four 15-min bouts separated by 15-min recovery) and 1-hour of final recovery in a hot and dry (35°C, 20% relative humidity) environment. Respiratory and heart rate recordings were continuously logged with 10-min periods analysed at the end of: baseline rest; each of the exercise and recovery bouts; and during the 1-hour final recovery period. Comparisons over time during exercise and recovery, and between groups were conducted via two-way repeated-measures ANCOVAs with rest values as the covariate. During baseline rest, older females exhibited lower heart rate variability compared to young females with similar levels of respiration and most (∼71-79%) heart rate variability measures during repeated exercise and recovery. However, older females exhibited heart rate variability metrics suggestive of greater parasympathetic modulation (greater long axis of Poincare plot, cardiac vagal index; lower low-high frequency ratio) during repeated exercise with lower indices during the latter stage of prolonged recovery (less very low frequency component, Largest Lyapunov Exponent; greater cardiac sympathetic index). The current study documented several unique, age-dependent differences in heart rate variability, independent of respiration, during and following exercise-induced heat stress for females that may assist in the detection of normal heat-induced adaptations as well as individuals vulnerable to heat stress.

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.

Methodological Comparisons of Heart Rate Variability Analysis in Patients With Type 2 Diabetes and Angiotensin Converting Enzyme Polymorphism

Angiotensin converting enzyme (ACE) polymorphism has been shown to be important in hypertension progression and also in diabetes complications, especially associated with heart disease. Heart rate variability (HRV) is an established measure for classification of autonomic function regulating heart rate, based on the interbeat interval time series derived from a raw ECG recording. Results of this paper show that the length (number of interbeat intervals) and preprocessing of the tachogram affect the HRV analysis outcome. The comparison was based on tachogram lengths of 250, 300, 350, and 400 RR-intervals and five preprocessing approaches. An automated adaptive preprocessing method for the heart rate biosignal and tachogram length of 400 interbeat intervals provided the best classification. HRV results differed for the Type 2 Diabetes Mellitus (T2DM) group between the I/I genotype and the I/D and D/D genotypes, whereas for controls there was no significant difference in HRV between genotypes. Selecting an appropriate length of recording and automated preprocessing has confirmed that there is an effect of ACE polymorphism including the I/I genotype and that I/I should not be combined with I/D genotype in determining the extent of autonomic modulation of the heart rate.

Identifying increased risk of post-infarct people with diabetes using multi-lag Tone-Entropy analysis

Diabetes mellitus is associated with multi-organ system dysfunction. One of the key causative factors is the increased blood sugar level that leads to an increase in free radical activity and organ damage including the cardiovascular and nervous system. Heart rhythm is extrinsically modulated by the autonomic nervous system and cardiac autonomic neuropathy or dysautonomia has been shown to lead to sudden cardiac death in people with diabetes due to the decrease in heart rate variability (HRV). Current algorithms for determining HRV describe only beat-to-beat variation and therefore do not consider the ability of a heart beat to influence a train of succeeding beats. Therefore mortality risk analysis based on HRV has often not been able to discern the presence of an increased risk. This study used a novel innovation of the tone-entropy algorithm by incorporating increased lag intervals and found that both the sympatho-vagal balance and total activity changed at larger lag intervals. Tone-Entropy was found to be better risk identifier of cardiac mortality in people with diabetes at lags higher than one and best at lag seven.

Association of cardiovascular risk using non-linear heart rate variability measures with the framingham risk score in a rural population

Cardiovascular risk can be calculated using the Framingham cardiovascular disease (CVD) risk score and provides a risk stratification from mild to very high CVD risk percentage over 10 years. This equation represents a complex interaction between age, gender, cholesterol status, blood pressure, diabetes status, and smoking. Heart rate variability (HRV) is a measure of how the autonomic nervous system (ANS) modulates the heart rate. HRV measures are sensitive to age, gender, disease status such as diabetes and hypertension and processes leading to atherosclerosis. We investigated whether HRV measures are a suitable, simple, noninvasive alternative to differentiate between the four main Framingham associated CVD risk categories. In this study we applied the tone-entropy (T-E) algorithm and complex correlation measure (CCM) for analysis of HRV obtained from 20 min. ECG recordings and correlated the HRV score with the stratification results using the Framingham risk equation. Both entropy and CCM had significant analysis of variance (ANOVA) results [F (172, 3) = 9.51; <0.0001]. Bonferroni post hoc analysis indicated a significant difference between mild, high and very high cardiac risk groups applying tone-entropy (p < 0.01). CCM detected a difference in temporal dynamics of the RR intervals between the mild and very high CVD risk groups (p < 0.01). Our results indicate a good agreement between the T-E and CCM algorithm and the Framingham CVD risk score, suggesting that this algorithm may be of use for initial screening of cardiovascular risk as it is noninvasive, economical and easy to use in clinical practice.

Risk stratification of cardiac autonomic neuropathy based on multi-lag Tone-Entropy

Cardiac autonomic neuropathy (CAN) is an irreversible condition affecting the autonomic nervous system, which leads to abnormal functioning of the visceral organs and affects critical body functions such as blood pressure, heart rate and kidney filtration. This study presents multi-lag Tone-Entropy (T-E) analysis of heart rate variability (HRV) at multiple lags as a screening tool for CAN. A total of 41 ECG recordings were acquired from diabetic subjects with definite CAN (CAN+) and without CAN (CAN-) and analyzed. Tone and entropy values of each patient were calculated for different beat sequence lengths (len: 50-900) and lags (m: 1-8). The CAN- group was found to have a lower mean tone value compared to that of CAN+ group for all m and len, whereas the mean entropy value was higher in CAN- than that in CAN+ group. Leave-one-out (LOO) cross-validation tests using a quadratic discriminant (QD) classifier were applied to investigate the performance of multi-lag T-E features. We obtained 100 % accuracy for tone and entropy with len = 250 and m = {2, 3} settings, which is better than the performance of T-E technique based on lag m = 1. The results demonstrate the usefulness of multi-lag T-E analysis over single lag analysis in CAN diagnosis for risk stratification and highlight the change in autonomic nervous system modulation of the heart rate associated with cardiac autonomic neuropathy.

Evaluating cardiovascular risk using the tone-entropy algorithm

Currently the Framingham equation is the most often used cardiovascular risk calculator in health care. The equation requires data for age, gender, cholesterol status, blood pressure, diabetes status and smoking. A large proportion of the morbidity and mortality associated with cardiovascular disease is due to arrhythmic events that are multifactorial including dysregulation by the autonomic nervous system. In this study we applied the tone-entropy algorithm for analysis of heart rate variability obtained from 20 minute ECG recordings and compared the outcome with the Framingham risk stratification. Our results indicate a good agreement between the T-E algorithm and the Framingham risk equation suggesting that this algorithm may be of use for initial screening of cardiovascular risk as it is noninvasive, economical and easy to use in clinical practice.

Multi-scale Tone Entropy in differentiating physiologic and synthetic RR time series

Heart rhythm is extrinsically modulated by the autonomic nervous system and recently, the Tone-Entropy (TE) measurement was reported as a measure of autonomic balance and activity in time domain HRV analysis. Current algorithm for T-E measurement describes only beat-to-beat or influence of a heart beat on a train of succeeding beats on a single scale. Therefore, conventional T-E analysis has often not been able to discern various physiological conditions using heart rate variability (HRV) signal. In this study, we will present a mathematical framework to define multi-scale T-E analysis, apply this in differentiating physiological and synthetic RR time series. Finally, we compare the performance of proposed parameters with conventional T-E measurements.

Association of cardiac autonomic neuropathy with alteration of sympatho-vagal balance through heart rate variability analysis

Early sub-clinical assessment of severity of cardiac autonomic neuropathy (CAN) and intervention are of prime importance for risk stratification and early treatment in preventing sudden death due to silent myocardial infarction. The Ewing battery is currently the diagnostic tool of choice but is unable to detect sub-clinical disease and requires patient cooperation. Time and frequency domain analysis have several shortcomings including sensitivity to recording length, respiratory activity and non-stationarities in the ECG signal. An important step forward is to have a non-invasive method of detecting CAN that is robust against these shortcomings and has a higher sensitivity for the presence of both sub-clinical and overt clinical disease. This study presents a novel parameter, tone-entropy (T-E) that analyses heart rate variability (HRV) of 20 min lead II ECG recordings. Tone (T) represents sympatho-vagal balance and entropy (E) the autonomic regularity activity. Thirteen normal subjects without (CAN-) and 21 with CAN (CAN+) participated in this study. Among 21 CAN+ subjects, 13 are early CAN+ (eCAN+), eight are definite CAN+ (dCAN+) according to autonomic nervous system function tests as described by Ewing. The results showed that tone was higher and the entropy was lower in the dCAN+ group (T=-0.033 to -0.010 and E=1.73-2.24) compared with the eCAN+ (T=-0.0927 to -0.0311 and E=2.0-2.65) and normal (T=-0.128 to -0.0635 and E=2.64-3.15) group. The research verified that T-E is a suitable method to determine the presence of CAN that correctly identifies experimentally induced changes in cardiac function akin to parasympathetic and sympathetic dysfunction and differentiates between stages in CAN disease progression identified using the Ewing battery.

Evaluation of diabetic neuropathy using the tone-entropy analysis, a noninvasive method to estimate the autonomic nervous function

It is clinically important to diagnose diabetic neuropathy at the early stage. In this study, the toneentropy analysis of electrocardiogram was applied to diabetic patients to evaluate its usability in the screening of diabetic neuropathy. Consecutive 102 diabetic patients were invited to the study. Electrocardiogram was obtained and analyzed for the tone and the entropy using an original software developed previously. Nerve conduction velocity (NCV) was examined on the median, the posterior tibial and the sural nerves. Patients were divided into quartile subpopulations according to the NCVs in the analysis. Both the tone and the entropy significantly correlated with NCVs, while coefficient of variation in R-R intervals did not show a significant correlation. The correlation was most significant between the entropy and the NCV on the sural nerve. When a multivariate analysis (ordinary regression) was applied to examine independent effects of the factors influencing the NCV on the sural nerve, the entropy was the most potent independent factor (beta = 1.14 +/- 0.32, P = 0.0004) along with sex (beta = 0.43 +/- 0.19, P = 0.02) and BMI (beta = 0.11 +/- 0.05, P = 0.04). The tone-entropy analysis on electrocardiogram may be a promising non-invasive screening method for diabetic neuropathy.

Sevoflurane anesthesia decreases cardiac vagal activity and heart rate variability

We evaluated cardiac vagal activity during sevoflurane anesthesia in neurosurgical patients. Heart rate variability was determined by power spectral analysis and entropy with the patient awake and during sevoflurane anesthesia. High frequency power (0.15-0.50 Hz) and heart rate entropy decreased during sevoflurane and these effects were significantly correlated (r = 0.71 +/- 0.12, P < 0.05). The results confirm that cardiac vagal activity was the primary determinant of heart rate variability, which was attenuated by sevoflurane.

Autonomic activity during desflurane anesthesia in patients with brain tumors

OBJECTIVE

Although intracranial tumors may affect autonomic function, there are few reports of autonomic changes during anesthesia. The purpose of this study was to evaluate autonomic effects of anesthesia in patients with brain tumors compared to neurosurgical controls.

METHODS

Two groups were evaluated: group 1 = 10 neurosurgical patients undergoing spinal cord surgery, group 2 = 10 patients with intracranial tumors. After placement of electrocardiogram and Response Entropy electroencephalogram (EEG) electrodes, 10 min baseline measures were made. Heart periods were transformed into a percentage index and heart rate entropy determined as a measure of variance of autonomic activity. Tone was evaluated as the balance between accelerator and inhibitory activity. Tone-entropy was measured during propofol anesthetic induction and the first 60 min of desflurane anesthesia before the start of surgery.

RESULTS

Blood pressure and heart rate were similar between the groups. Starting at awake levels, vagal heart tone was observed. Anesthesia decreased vagal dominance to near zero in both groups. Heart rate entropy and EEG activity decreased during anesthesia with no significant difference between the groups. Desflurane concentrations required to maintain anesthesia were significantly lower in patients in brain tumors.

CONCLUSION

Tone-entropy analysis of heart rate indicates anesthetic related depression of autonomic activity with no difference between groups. Normal titration of desflurane concentrations to maintain adequate blood pressure produced desflurane requirements that were lower in patients with brain tumors, while autonomic and EEG activity were similar.

Autonomic activity during dexmedetomidine or fentanyl infusion with desflurane anesthesia

STUDY OBJECTIVE

To evaluate autonomic activity with dexmedetomidine or fentanyl infusion and desflurane anesthesia during laparoscopic gastric banding.

STUDY DESIGN

Randomized, single-blinded, open-label study.

SETTING

Operating rooms at a university hospital.

SUBJECTS

40 patients scheduled for laparoscopic gastric banding with a mean body mass index of 50 kg/m2.

INTERVENTIONS

Patients received either dexmedetomidine (0.5 microg/kg given intravenously over 10 minutes, 0.4 microg.kg-1.h-1, n=20) or fentanyl (0.5 microg.kg-1 bolus, 1 microg.kg-1.h-1, n=20) during anesthesia. Response entropy of the electroencephalogram was maintained at 45+/-5 by adjusting end-tidal desflurane concentration.

MEASUREMENTS

In the operating room, blood pressure, heart rate (HR), response entropy, end-tidal desflurane concentration, tone entropy, and power-spectral analysis of HR were measured with the patient awake; 20, 40, and 60 minutes from intubation and the start of drug infusion; and at extubation.

MAIN RESULTS

The mean end-tidal desflurane concentration during anesthesia was 4.0%+/-0.6% with dexmedetomidine and 4.1%+/-0.7% with fentanyl, indicating a similar anesthetic requirement in both groups. Autonomic activity, determined by tone entropy and spectral analysis of HR, decreased by 50% during anesthesia in both groups. The dexmedetomidine group showed a greater decrease in sympathovagal balance during anesthesia.

CONCLUSION

Both dexmedetomidine and fentanyl facilitated anesthesia and attenuated autonomic activity. Dexmedetomidine produced a greater decrease in sympathovagal balance than fentanyl.

A comparative scale of autonomic function with age through the tone-entropy analysis on heart period variation

Tremendous numbers of heart rate variability studies have aimed to elucidate age-associated alterations of autonomic function in the past decades. However, the studies, far from clarifying ageing mechanisms, fell into confusion by a lack of common scales. The purpose of this study is to show a possibility to establish a comparative scale of autonomic function through a method, tone-entropy (T-E) analysis on heart period variation, whose validity has been already examined on typical physiological cases (Oida et al. in J Appl Physiol 82:1794-1801, 1997; Oida et al. in J Gerontol 54A:M219-M224, 1999a; Oida et al. in Acta Physiol Scand 165:129-134, 1999b; Oida et al. in Acta Physiol Scand 165:421-422, 1999c; Amano et al. in Eur J Appl Physiol 94:602-610, 2005). In this study, 276 subjects from teens to seventies were examined at rest by T-E analysis together with conventional time and frequency domain analyses. The tone (negativity represents vagal predominance) became significantly high [-0.174 +/- 0.026 (teens) to -0.024 +/- 0.004 (seventies), P < 0.05 for one-way ANOVA], and the entropy (total autonomic activity), significantly low [4.40 +/- 0.12 (teens) to 2.90 +/- 0.09 bit (seventies), P < 0.05] with advancing age. The result, plotted in 2-D T-E space, showed that the ageing traced a curvi-linear relation from right-bottom to left-top, and was consistent with previously studied typical physiological cases. The conventional analyses showed almost the same autonomic reduction as T-E did, but failed in detecting delicate alteration of autonomic balance. The results, showing that autonomic activity reduced in both pathways impairing vagal predominance significantly with ageing, suggested a possibility to assess autonomic function in 2-D T-E space in a comparative way.