Spectral analysis of heart rate in diabetic autonomic neuropathy. A comparison with standard tests of autonomic function

Combining Heart Rate Variability and Oximetry to Improve Apneic Event Screening in Non-Desaturating Patients

In this paper, we thoroughly analyze the detection of sleep apnea events in the context of Obstructive Sleep Apnea (OSA), which is considered a public health problem because of its high prevalence and serious health implications. We especially evaluate patients who do not always show desaturations during apneic episodes (non-desaturating patients). For this purpose, we use a database (HuGCDN2014-OXI) that includes desaturating and non-desaturating patients, and we use the widely used Physionet Apnea Dataset for a meaningful comparison with prior work. Our system combines features extracted from the Heart-Rate Variability (HRV) and SpO₂, and it explores their potential to characterize desaturating and non-desaturating events. The HRV-based features include spectral, cepstral, and nonlinear information (Detrended Fluctuation Analysis (DFA) and Recurrence Quantification Analysis (RQA)). SpO₂-based features include temporal (variance) and spectral information. The features feed a Linear Discriminant Analysis (LDA) classifier. The goal is to evaluate the effect of using these features either individually or in combination, especially in non-desaturating patients. The main results for the detection of apneic events are: (a) Physionet success rate of 96.19%, sensitivity of 95.74% and specificity of 95.25% (Area Under Curve (AUC): 0.99); (b) HuGCDN2014-OXI of 87.32%, 83.81% and 88.55% (AUC: 0.934), respectively. The best results for the global diagnosis of OSA patients (HuGCDN2014-OXI) are: success rate of 95.74%, sensitivity of 100%, and specificity of 89.47%. We conclude that combining both features is the most accurate option, especially when there are non-desaturating patterns among the recordings under study.

Interpreting resting heart rate variability in complex populations: the role of autonomic reflexes and comorbidities

PURPOSE

Resting heart rate variability (HRV) is an important biomarker linking mental health to cardiovascular outcomes. However, resting HRV is also impaired in autonomic neuropathy, a common and underdiagnosed complication of common medical conditions which is detected by testing autonomic reflexes. We sought to describe the relationship between autonomic reflex abnormalities and resting HRV, taking into consideration medical comorbidities and demographic variables.

METHODS

Participants (n = 209) underwent a standardized autonomic reflex screen which was summarized as the Composite Autonomic Severity Score (CASS) and included measures of reflexive HRV, e.g., heart rate with deep breathing (HRDB). Resting HRV measures were: pNN50 (percentage of NN intervals that differ by > 50 ms) and cvRMSSD (adjusted root mean square of successive differences).

RESULTS

In univariate analyses, lower resting HRV was associated with: older age, higher CASS, neuropathy on examination, hypertension, diabetes, chronic obstructive pulmonary disease, chronic kidney disease, and psychiatric disease. Adaptive regression spline analysis revealed that HRDB explained 27% of the variability in resting HRV for participants with values of HRDB in the normal range. Outside this range, there was no linear relationship because: (1) when HRDB was low (indicating autonomic neuropathy), resting HRV was also low with low variance; and (2) when HRDB was high, the variance in resting HRV was high. In multivariate models, only HRDB was significantly independently associated with cvRMSSD and pNN50.

CONCLUSION

Subclinical autonomic neuropathy, as evidenced by low HRDB and other autonomic reflexes, should be considered as a potential confounder of resting HRV in research involving medically and demographically diverse populations.

Heart rate variability and the dawn of complex physiological signal analysis: methodological and clinical perspectives

Spontaneous beat-to-beat variations of heart rate (HR) have intrigued scientists and casual observers for centuries; however, it was not until the 1970s that investigators began to apply engineering tools to the analysis of these variations, fostering the field we now know as heart rate variability or HRV. Since then, the field has exploded to not only include a wide variety of traditional linear time and frequency domain applications for the HR signal, but also more complex linear models that include additional physiological parameters such as respiration, arterial blood pressure, central venous pressure and autonomic nerve signals. Most recently, the field has branched out to address the nonlinear components of many physiological processes, the complexity of the systems being studied and the important issue of specificity for when these tools are applied to individuals. When the impact of all these developments are combined, it seems likely that the field of HRV will soon begin to realize its potential as an important component of the toolbox used for diagnosis and therapy of patients in the clinic. This article is part of the theme issue 'Advanced computation in cardiovascular physiology: new challenges and opportunities'.

Information-based analysis of the coupling between brain and heart reactions to olfactory stimulation

BACKGROUND

Analysis of the heart activity is one of the important areas of research in biomedical science and engineering. For this purpose, scientists analyze the activity of the heart in various conditions. Since the brain controls the heart's activity, a relationship should exist among their activities.

OBJECTIVE

In this research, for the first time the coupling between heart and brain activities was analyzed by information-based analysis.

METHODS

Considering Shannon entropy as the indicator of the information of a system, we recorded electroencephalogram (EEG) and electrocardiogram (ECG) signals of 13 participants (7 M, 6 F, 18-22 years old) in different external stimulations (using pineapple, banana, vanilla, and lemon flavors as olfactory stimuli) and evaluated how the information of EEG signals and R-R time series (as heart rate variability (HRV)) are linked.

RESULTS

The results indicate that the changes in the information of the R-R time series and EEG signals are strongly correlated (ρ=-0.9566).

CONCLUSION

We conclude that heart and brain activities are related.

Cardiovascular dysautonomia in Achalasia Patients: Blood pressure and heart rate variability alterations

Achalasia is a disease characterized by the inability to relax the esophageal sphincter due to a degeneration of the parasympathetic ganglion cells located in the wall of the thoracic esophagus. Achalasia has been associated with extraesophageal dysmotility, suggesting alterations of the autonomic nervous system (ANS) that extend beyond the esophagus. The purpose of the present contribution is to investigate whether achalasia may be interpreted as the esophageal manifestation of a more generalized disturbance of the ANS which includes alterations of heart rate and/or blood pressure. Therefore simultaneous non-invasive records of the heart inter-beat intervals (IBI) and beat-to-beat systolic blood pressure (SBP) of 14 patients (9 female, 5 male) with achalasia were compared with the records of 34 rigorously screened healthy control subjects (17 female, 17 male) in three different conditions: supine, standing up, and controlled breathing at 0.1 Hz, using a variety of measures in the time and spectral domains. Significant differences in heart rate variability (HRV) and blood pressure variability (BPV) were observed which seem to be due to cardiovagal damage to the heart, i.e., a failure of the ANS, as expected according to our hypothesis. This non-invasive methodology can be employed as an auxiliary clinical protocol to study etiology and evolution of achalasia, and other pathologies that damage ANS.

Is there cardiac autonomic neuropathy in prediabetes?

Although there is considerably more data showing an association between type 2 diabetes mellitus (T2DM) and autonomic neuropathy, accumulating evidence indicates that cardiovascular autonomic neuropathy (CAN) is common in persons with impaired glucose tolerance (IGT). Furthermore, CAN may occur early after a metabolic insult and obesity, especially among mean, and seems to play an important role in the early pathogenesis of CAN. Autonomic symptoms are common in subjects with IGT. In addition to defects in CAN, in subjects with IGT, there is impaired sudomotor function and abnormalities of endothelial peripheral vasoreactivity. At the present time, the only interventions that may be effective in preventing or reversing IGT associated autonomic neuropathy are lifestyle improvement. These include a tailored diet and exercise program. Other approaches that may be beneficial include modulation of oxidative stress and improvement of metabolic regulation in subjects with IGT. Interventions are most likely to be effective early in the course of disease and therefore it is extremely important to have early diagnosis of IGT and autonomic neuropathy.

Rationale and design of the EMPYREAN study

Aims

A sodium glucose cotransporter 2 (SGLT2) inhibitor was recently found to reduce heart failure hospitalization in the EMPA‐REG OUTCOME trial. We have hypothesized that autonomic nerve activity may be modulated by SGLT2 inhibition. The current study aims to investigate the impact of empagliflozin on sympathetic and parasympathetic nerve activity in patients with type 2 diabetes mellitus.

Methods and results

This ongoing study is a prospective, randomized, open‐label, multicentre investigation of 134 patients with type 2 diabetes mellitus. The patients are randomly allocated to receive either empagliflozin or sitagliptin with the treatment goal of the Japan Diabetes Society guidelines. Ambulatory electrocardiographic monitoring is performed at the baseline and at 12 and 24 weeks of treatment. Analyses of heart rate variability are conducted using the MemCalc method, which is a combination of the maximum entropy method for spectral analysis and the non‐linear least squares method for square analysis. The primary endpoint is the change in the low‐frequency (0.04–0.15 Hz)/high‐frequency (0.15–0.4 Hz) ratio from baseline to 24 weeks.

Conclusions

This investigation on the effect of EMPagliflozin on cardiac sYmpathetic and parasympathetic neRve activity in JapanEse pAtieNts with type 2 diabetes (EMPYREAN study) offers an important opportunity to understand the impact of SGLT2 inhibition on autonomic nerve activity in patients with type 2 diabetes.

Autonomic Function in Patients on Continuous Ambulatory Peritoneal Dialysis

Objective

To investigate sympathetic function in the peripheries of patients on chronic ambulatory peritoneal dialysis (CAPD) using noninvasive techniques.

Design

Comparison of peripheral blood flowresponses in sympathetic vasoconstrictor reflexes in CAPD patients and matched control subjects.

Setting

Tertiary care hospital and research institution.

Patients

Twenty-three clinically stable CAPD patients and 23 control subjects matched for age, sex, and drug therapy.

Main Outcome Measures

Sympathetic activity assessed from the reductions in hand and foot blood flow induced by a deep breath and by body surface cooling. Cardiac autonomic activity measured by the changes in heart rate produced by deep breathing, a Valsalva maneuver, and standing from lying.

Results

A deep breath induced mean decreases in hand blood flow of 65.1% in the patients and 82.8% in their matched controls. Corresponding reductions in the foot were 46.0% and 70.0%. Body surface cooling reduced mean hand blood flow by 50.3% in the patients an d 71.8% in the control subjects. Corresponding values in the foot were 26.7% and 43.6%. The differences in response between the patients and their matched control subjects were all significant (p < 0.01). Cardiac autonomic function assessed by standard tests of heart rate variability was significantly impaired in the patients compared with the control subjects in two of the three tests used (p < 0.001).

Conclusions

Cardiovascular autonomic impairment can affect the peripheral circulation as well as the heart in patients on dialysis, and this may have implications for cardiovascular homeostasis.

Comparison of methods for the assessment of nonlinearity in short-term heart rate variability under different physiopathological states

Despite the widespread diffusion of nonlinear methods for heart rate variability (HRV) analysis, the presence and the extent to which nonlinear dynamics contribute to short-term HRV are still controversial. This work aims at testing the hypothesis that different types of nonlinearity can be observed in HRV depending on the method adopted and on the physiopathological state. Two entropy-based measures of time series complexity (normalized complexity index, NCI) and regularity (information storage, IS), and a measure quantifying deviations from linear correlations in a time series (Gaussian linear contrast, GLC), are applied to short HRV recordings obtained in young (Y) and old (O) healthy subjects and in myocardial infarction (MI) patients monitored in the resting supine position and in the upright position reached through head-up tilt. The method of surrogate data is employed to detect the presence and quantify the contribution of nonlinear dynamics to HRV. We find that the three measures differ both in their variations across groups and conditions and in the percentage and strength of nonlinear HRV dynamics. NCI and IS displayed opposite variations, suggesting more complex dynamics in O and MI compared to Y and less complex dynamics during tilt. The strength of nonlinear dynamics is reduced by tilt using all measures in Y, while only GLC detects a significant strengthening of such dynamics in MI. A large percentage of detected nonlinear dynamics is revealed only by the IS measure in the Y group at rest, with a decrease in O and MI and during T, while NCI and GLC detect lower percentages in all groups and conditions. While these results suggest that distinct dynamic structures may lie beneath short-term HRV in different physiological states and pathological conditions, the strong dependence on the measure adopted and on their implementation suggests that physiological interpretations should be provided with caution.

Comparison of Heart Rate Variability Parameters to the Autonomic Reflex Screen in Postural Orthostatic Tachycardia Syndrome and Neurogenic Orthostatic Hypotension

PURPOSE

The clinical significance of heart rate variability (HRV) in the context of autonomic dysfunction continues to be a matter of debate. Therefore, the purpose of the current study was to investigate the clinical relevance of HRV in the context of autonomic dysfunction.

METHODS

Heart rate variability data from 225 volunteers consisting of controls (n = 166) and patients with mild (n = 25) and severe (n = 34) autonomic dysfunction were retrospectively analyzed. Time and frequency parameters were correlated against baseline and standardized tests of autonomic function.

RESULTS

During baseline, resting HR was negatively correlated with time (SD of all normal RR interval, r = -0.511; RMSSD, r = -0.585; pNN50, r = -0.545) and frequency (low-frequency, r = -0.362; high-frequency, r = -0.421) parameters (P < 0.01). Resting systolic blood pressure demonstrated similar significant correlations (P < 0.01). During head-up tilt, SD of all normal RR intervals was positively correlated with [INCREMENT]HR and change in systolic blood pressure (r = 0.340; r = 0.538, respectively; P < 0.01). Similarly, low-frequency, high-frequency, and low-frequency/high-frequency ratios were correlated with [INCREMENT]HR (r = 0.422, r = 0.176, r = 0.470) and change in systolic blood pressure (r = 0.451, r = 0.407, and r = 0.185) (P < 0.01). Time parameters (SD of all normal RR intervals, RMSSD, and pNN50) were all significantly correlated with deep breathing (r = 0.600; r = 0.556; r = 0.516; P < 0.01, respectively). Low-frequency and high-frequency power were also correlated (r = 0.596; r = 0.580, respectively) (P < 0.01).

CONCLUSIONS

Time and frequency parameters showed significant negative correlations with baseline hemodynamics. During a test of sympathetic activation and parasympathetic withdrawal, this relationship shifted to reveal significant positive correlations between HRV parameters and hemodynamics. Last, during a test of parasympathetic activation, there were significant positive correlations with cardiovagally mediated HRV parameters. Overall, these results suggest broader clinical relevance for HRV parameters within the spectrum of autonomic functioning.

Cardiovascular autonomic dysfunction predicts increasing albumin excretion in type 1 diabetes

OBJECTIVE

To determine the potential role of cardiovascular autonomic dysfunction in the development of renal complications in young people with type 1 diabetes (T1D).

METHODS

In this prospective study, 199 children and adolescents recruited to the Oxford Regional Prospective Study underwent assessment of autonomic function ~5 years after diagnosis, and were subsequently followed with longitudinal assessments of HbA_1c and urine albumin-creatinine ratio (ACR) over 8.6 ± 3.4 years. Autonomic function was assessed with 4 standardized tests of cardiovascular reflexes: heart rate (HR) response to (1) Valsalva Maneuver, (2) deep breathing, (3) standing, and (4) blood pressure (BP) response to standing. Linear mixed models were used to assess the association between autonomic parameters and future changes in ACR.

RESULTS

Independent of HbA_1c , each SD increase in HR response to Valsalva Maneuver predicted an ACR increase of 2.16% [95% CI: 0.08; 4.28] per year (P = .04), while each SD increase in diastolic BP response to standing predicted an ACR increase of 2.55% [95% CI: 0.37; 4.77] per year (P = .02). The effect of HR response to standing on ACR reached borderline significance (-2.07% [95% CI: -4.11; 0.01] per year per SD increase, P = .051).

CONCLUSIONS

In this cohort of young people with T1D, enhanced cardiovascular reflexes at baseline predicted future increases in ACR. These results support a potential role for autonomic dysfunction in the pathogenesis of diabetic nephropathy.

Utility of Time and Frequency Domain Parameters of Heart Rate Variability in the Context of Autonomic Disorders Characterized by Orthostatic Dysfunction

PURPOSE

The clinical significance of heart rate variability in the context of autonomic dysfunction continues to be a matter of debate. A consensus is lacking on the best heart rate variability measures for clinical purposes. Therefore, the purpose of this study was to investigate the utility of heart rate variability parameters in healthy versus autonomic dysfunction.

METHODS

Healthy young (n = 134), healthy older (n = 32), and patients with mild (postural tachycardia syndrome; n = 25) and severe (neurogenic orthostatic hypotension; n = 34) autonomic dysfunction were included. Time and frequency parameters during baseline, head-up tilt (HUT), and heart rate response to deep breathing (HRDB) were compared.

RESULTS

Cardiovagal time parameters were significantly reduced during HUT in healthy young and postural tachycardia syndrome (P < 0.001). Healthy young had significantly higher time parameters during baseline, HUT, and HRDB (P < 0.01). This was reflected by a significantly lower resting heart rate (HR) (61.4 ± 9.0 bpm vs. 76.8 ± 13.6 bpm; P < 0.001) and a smaller [INCREMENT]HR during HUT (32.8 ± 10.5 bpm vs. 44.4 ± 13.3 bpm; P < 0.001). Time parameters increased in young and postural tachycardia syndrome during HRDB, which was characterized by a nonsignificant difference in [INCREMENT]HR between both groups. Time parameters were significantly higher in healthy old versus neurogenic orthostatic hypotension at rest and during HRDB (P < 0.05). During HUT, only the SD of all normal RR intervals remained significantly higher. Heart rate changes corroborated these findings. Resting HR was significantly lower in healthy older (62.6 ± 11.0 bpm vs. 70.7 ± 12.4 bpm), and [INCREMENT]HR during HRDB was significantly higher (15.9 ± 9.2 bpm vs. 3.9 ± 4.2 bpm; P < 0.001). During HUT, [INCREMENT]HR showed no significant differences.

CONCLUSIONS

Time domain parameters of heart rate variability have a greater utility than frequency parameters in clinical autonomic disorders.

Cardiac autonomic neuropathy: Risk factors, diagnosis and treatment

Cardiac autonomic neuropathy (CAN) is a serious complication of diabetes mellitus (DM) that is strongly associated with approximately five-fold increased risk of cardiovascular mortality. CAN manifests in a spectrum of things, ranging from resting tachycardia and fixed heart rate (HR) to development of “silent” myocardial infarction. Clinical correlates or risk markers for CAN are age, DM duration, glycemic control, hypertension, and dyslipidemia (DLP), development of other microvascular complications. Established risk factors for CAN are poor glycemic control in type 1 DM and a combination of hypertension, DLP, obesity, and unsatisfactory glycemic control in type 2 DM. Symptomatic manifestations of CAN include sinus tachycardia, exercise intolerance, orthostatic hypotension (OH), abnormal blood pressure (BP) regulation, dizziness, presyncope and syncope, intraoperative cardiovascular instability, asymptomatic myocardial ischemia and infarction. Methods of CAN assessment in clinical practice include assessment of symptoms and signs, cardiovascular reflex tests based on HR and BP, short-term electrocardiography (ECG), QT interval prolongation, HR variability (24 h, classic 24 h Holter ECG), ambulatory BP monitoring, HR turbulence, baroreflex sensitivity, muscle sympathetic nerve activity, catecholamine assessment and cardiovascular sympathetic tests, heart sympathetic imaging. Although it is common complication, the significance of CAN has not been fully appreciated and there are no unified treatment algorithms for today. Treatment is based on early diagnosis, life style changes, optimization of glycemic control and management of cardiovascular risk factors. Pathogenetic treatment of CAN includes: Balanced diet and physical activity; optimization of glycemic control; treatment of DLP; antioxidants, first of all α-lipoic acid (ALA), aldose reductase inhibitors, acetyl-L-carnitine; vitamins, first of all fat-soluble vitamin B1; correction of vascular endothelial dysfunction; prevention and treatment of thrombosis; in severe cases-treatment of OH. The promising methods include prescription of prostacyclin analogues, thromboxane A2 blockers and drugs that contribute into strengthening and/or normalization of Na⁺, K⁺-ATPase (phosphodiesterase inhibitor), ALA, dihomo-γ-linolenic acid (DGLA), ω-3 polyunsaturated fatty acids (ω-3 PUFAs), and the simultaneous prescription of ALA, ω-3 PUFAs and DGLA, but the future investigations are needed. Development of OH is associated with severe or advanced CAN and prescription of nonpharmacological and pharmacological, in the foreground midodrine and fludrocortisone acetate, treatment methods are necessary.

Association between severity of hypoglycemia and loss of heart rate variability in patients with type 1 diabetes mellitus

BACKGROUND

The occurrence of hypoglycemia has been associated with the presence of cardiovascular autonomic neuropathy. Cardiovascular autonomic reflex tests are the gold standard diagnostic method for cardiovascular autonomic neuropathy. Nevertheless, impaired heart rate variability indices on spectral analysis have been reported before cardiovascular autonomic reflex test abnormalities arise. The objective of the present study was to analyse the association between the severity of hypoglycemia and indices of heart rate variability on spectral analysis.

METHODS

Consecutive type 1 diabetes patients were prospectively enrolled. Heart rate variability indices were assessed by spectral analysis. One abnormal test result was used to define impaired spectral analysis. The severity of hypoglycemia was evaluated by a hypoglycemia score and patients were classified into absent/minor or moderate/severe hypoglycemia groups.

RESULTS

Patients with moderate/severe hypoglycemia were older, had longer duration of diabetes and had higher rates of diabetic complications. After adjusting for baseline clinical characteristics, impaired spectral analysis (OR: 3.85; 95% IC 1.23 - 12.02; p = 0.020), nephropathy (OR: 4.15, 95% IC 1.27 - 13.54; p = 0.018) and macrovascular complications (OR: 12.18, 95% IC 1.14 - 129.84; p = 0.038) remained independent predictors of moderate/severe hypoglycemia. Patients with moderate/severe hypoglycemia had lower heart rate variability in the high frequency band of spectral analysis, reflecting a decreased parasympathetic tonus on the heart. These patients also had higher low frequency/high frequency ratios, ultimately denoting the occurrence of cardiovascular autonomic imbalance.

CONCLUSIONS

Impaired heart rate variability on spectral analysis, nephropathy and macrovascular complication were shown to independently predict moderate/severe hypoglycemia. Patients with moderate/severe hypoglycemia showed loss of the cardio protective effect of vagal activity according to spectral analysis. Copyright © 2016 John Wiley & Sons, Ltd.

Loss of Breathing Modulation of Heart Rate Variability in Patients with Recent and Long Standing Diabetes Mellitus Type II

Healthy subjects under rhythmic breathing have heart interbeat intervals with a respiratory band in the frequency domain that can be an index of vagal activity. Diabetes Mellitus Type II (DM) affects the autonomic nervous system of patients, thus it can be expected changes on the vagal activity. Here, the influence of DM on the breathing modulation of the heart rate is evaluated by analyzing in the frequency domain heart interbeat interval (IBI) records obtained from 30 recently diagnosed, 15 long standing DM patients, and 30 control subjects during standardized clinical tests of controlled breathing at 0.1 Hz, supine rest and standing upright. Fourier spectral analysis of IBI records quantifies heart rate variability in different regions: low-frequencies (LF, 0.04–0.15 Hz), high-frequencies (HF, 0.15–0.4 Hz), and a controlled breathing peak (RP, centered around 0.1 Hz). Two new parameters are introduced: the frequency radius r_f (square root of the sum of LF and HF squared) and β (power of RP divided by the sum of LF and HF). As diabetes evolves, the controlled breathing peak loses power and shifts to smaller frequencies, indicating that heart rate modulation is slower in diabetic patients than in controls. In contrast to the traditional parameters LF, HF and LF/HF, which do not show significant differences between the three populations in neither of the clinical tests, the new parameters r_f and β, distinguish between control and diabetic subjects in the case of controlled breathing. Sympathetic activity that is driven by the baroreceptor reflex associated with the 0.1 Hz breathing modulations is affected in DM patients. Diabetes produces not only a rigid heartbeat with less autonomic induced variability (r_f diminishes), but also alters the coupling between breathing and heart rate (reduced β), due to a progressive decline of vagal and sympathetic activity.

Twenty-four-hour blood pressure profile, orthostatic hypotension, and cardiac dysautonomia in elderly type 2 diabetic hypertensive patients

PURPOSE

The aim of this study was to evaluate the relationship between orthostatic hypotension (OH), defined as a decrease in systolic blood pressure (SBP) ≥20 mmHg and/or a decrease in diastolic blood pressure (DBP) ≥10 mmHg, and 24-h ambulatory BP profile in elderly hypertensive type 2 diabetic patients.

METHODS

After a 2-week antihypertensive wash-out period, 200 hypertensive well-controlled diabetic outpatients, aged 65-75 years, underwent a clinical examination, including BP measurements, ECG, 24-h ABP monitoring (ABPM), an orthostatic test, and three tests for cardiovascular autonomic function assessment [deep breathing, heart rate (HR) variability, resting HR].

RESULTS

According to their nighttime BP profile, patients were divided into three groups: dippers (n = 86) (BP fall during nighttime ≥10 %), non-dippers (n = 80) (BP fall during nighttime 0-10 %), and reverse dippers (n = 34) (nighttime BP > daytime BP). Orthostatic test produced a significantly greater orthostatic SBP fall in dippers and even more in reverse dippers. In these latter, a significant fall was observed also in DBP. Prevalence of OH was 9.3 % in dippers, 30 % in non-dippers, and 79.4 % in reverse dippers.

CONCLUSIONS

In elderly hypertensive type 2 diabetics, a blunted nocturnal BP fall is associated with OH and autonomic dysfunction. These data suggest that ABPM should be performed in the assessment of hypertensive diabetic patients in whom the cardiovascular dysautonomia is suspected or the signs of it are present (such as OH).

Heart Rate and Systolic Blood Pressure Variability in the Time Domain in Patients with Recent and Long-Standing Diabetes Mellitus

Diabetes Mellitus (DM) affects the cardiovascular response of patients. To study this effect, interbeat intervals (IBI) and beat-to-beat systolic blood pressure (SBP) variability of patients during supine, standing and controlled breathing tests were analyzed in the time domain. Simultaneous noninvasive measurements of IBI and SBP for 30 recently diagnosed and 15 long-standing DM patients were compared with the results for 30 rigorously screened healthy subjects (control). A statistically significant distinction between control and diabetic subjects was provided by the standard deviation and the higher moments of the distributions (skewness, and kurtosis) with respect to the median. To compare IBI and SBP for different populations, we define a parameter, α, that combines the variability of the heart rate and the blood pressure, as the ratio of the radius of the moments for IBI and the same radius for SBP. As diabetes evolves, α decreases, standard deviation of the IBI detrended signal diminishes (heart rate signal becomes more "rigid"), skewness with respect to the median approaches zero (signal fluctuations gain symmetry), and kurtosis increases (fluctuations concentrate around the median). Diabetes produces not only a rigid heart rate, but also increases symmetry and has leptokurtic distributions. SBP time series exhibit the most variable behavior for recently diagnosed DM with platykurtic distributions. Under controlled breathing, SBP has symmetric distributions for DM patients, while control subjects have non-zero skewness. This may be due to a progressive decrease of parasympathetic and sympathetic activity to the heart and blood vessels as diabetes evolves.

Principal component analysis of heart rate variability data in assessing cardiac autonomic neuropathy

Heart rate variability (HRV) is recognized to carry early diagnostic value regarding cardiac autonomic neuropathy (CAN). A number of different HRV analysis algorithms have been proposed for the assessment of CAN, each of them providing partly differing information about HRV time series. Instead of confining to a limited set of HRV features, a multi-dimensional approach incorporating a multitude of HRV parameters could be an optimal way of assessing the changes in HRV related to CAN. In this paper, principal component analysis (PCA) is used for analysing multi-dimensional HRV data of 11 patients with definite CAN and 71 subjects without CAN. Using the two most significant principal components, patients with CAN were separated from subjects without CAN with 87% accuracy.

Complexity of heart rate variability in type 2 diabetes - effect of hyperglycemia

Heart rate variability (HRV) is reduced in diabetes mellitus (DM) patients, suggesting dysfunction of cardiac autonomic regulation which has been associated with increased risk for pathological cardiac events. In this paper, we examined changes in HRV complexity in association to blood glucose level (BGL) and duration of diabetes. Resting HRV and BGL measurements of 32 healthy controls and 54 type 2 DM (T2DM) patients were analyzed. HRV complexity was assessed using Shannon entropy, sample entropy (SampEn), multiscale entropy (MSE), and multiscale Renyi entropy. HRV complexity increased with hyperglycemia indicated by increases in Shannon entropy and MSE and decreases in Renyi entropy for negative orders. Diabetes duration was strongly associated with Renyi entropy which increased for positive orders and decreased for negative orders as a function of disease duration. Shannon entropy, SampEn and MSE did not correlate with disease duration.

Autonomic control during acute hypoglycemia in type 1 diabetes mellitus

PURPOSE

We hypothesized that adults with type 1 diabetes mellitus (T1DM) would exhibit impaired heart rate variability (HRV), QT interval, T-wave amplitude, and baroreflex sensitivity (BRS) when compared with healthy controls. In addition, we hypothesized that acute hypoglycemia would result in further adverse changes in measures of autonomic and cardiovascular function.

METHODS

A single 180-min hyperinsulinemic (2 mU/kg TBW/min), hypoglycemic (~3.3 umol/mL) clamp was completed in 10 healthy adults and 13 adults with T1DM. Counterregulatory hormones were assessed and measures of heart rate (electrocardiogram) and blood pressure (intra-arterial catheter or finger photoplethysmography) were analyzed at baseline and during the hypoglycemic clamp for measures of HRV, QT interval, T-wave amplitude, and spontaneous cardiac BRS (sCBRS).

RESULTS

Baseline measures of HRV, sCBRS, and T-wave amplitude were blunted in adults with T1DM when compared with healthy controls. Hypoglycemia resulted in significant reductions in HRV, sCBRS, and T-wave amplitude and prolonged QT intervals; these changes were not different between adults with T1DM and healthy controls.

CONCLUSIONS

Results from the current study show that adults with T1DM exhibit impaired autonomic and cardiovascular function. Additionally, novel findings highlight an effect of acute hypoglycemia to further reduce measures of autonomic and cardiovascular function similarly between adults with T1DM and healthy controls. These results suggest that acute hypoglycemia may worsen impairments in autonomic and cardiovascular control in patients with T1DM, thus increasing the risk of ventricular arrhythmias and cardiovascular mortality.

Neural innervation of white adipose tissue and the control of lipolysis

White adipose tissue (WAT) is innervated by the sympathetic nervous system (SNS) and its activation is necessary for lipolysis. WAT parasympathetic innervation is not supported. Fully-executed SNS-norepinephrine (NE)-mediated WAT lipolysis is dependent on β-adrenoceptor stimulation ultimately hinging on hormone sensitive lipase and perilipin A phosphorylation. WAT sympathetic drive is appropriately measured electrophysiologically and neurochemically (NE turnover) in non-human animals and this drive is fat pad-specific preventing generalizations among WAT depots and non-WAT organs. Leptin-triggered SNS-mediated lipolysis is weakly supported, whereas insulin or adenosine inhibition of SNS/NE-mediated lipolysis is strongly supported. In addition to lipolysis control, increases or decreases in WAT SNS drive/NE inhibit and stimulate white adipocyte proliferation, respectively. WAT sensory nerves are of spinal-origin and sensitive to local leptin and increases in sympathetic drive, the latter implicating lipolysis. Transsynaptic viral tract tracers revealed WAT central sympathetic and sensory circuits including SNS-sensory feedback loops that may control lipolysis.

Effects of fluid overload on heart rate variability in chronic kidney disease patients on hemodialysis

Background

While fluid overload (FO) and alterations in the autonomic nervous system (ANS) such as hypersympathetic activity, are known risk factors for cardiovascular morbidity and mortality in patients on chronic hemodialysis (HD), their relationship has not been thoroughly studied.

Methods

In this observational study involving 69 patients on chronic HD, FO was assessed by whole body bioimpedance measurements before the midweek HD session and ANS activity reflected by Heart Rate Variability (HRV) was measured using 24-hour Holter electrocardiogram recordings starting before the same HD treatment. In total, 13 different HRV indices were analyzed, comprising a mixture of time domain, frequency domain and complexity parameters. A correlation analysis was performed between the HRV indices and hydration status indices. Successively, patients were retrospectively assigned to a high FO (H, FO > 2.5 L) or low FO (L, FO ≤ 2.5 L) group and these were further compared also after stratification by diabetes mellitus. Finally, a small number of patients without diabetes with significant and persistent FO were followed up for 3 months post-study to investigate how normalization of fluid status affects HRV.

Results

SDANN, VLF, LZC and HF% parameters significantly correlate with FO (correlation coefficients were respectively r = –0.40, r = –0.37, r = –0.28 and r = 0.26, p-value < 0.05). Furthermore, LF% and LF/HF were inversely correlated with hydration status (correlation coefficients were respectively r = –0.31 and r = -0.33, p-value < 0.05). These results indicate an association between FO and reduced HRV, higher parasympathetic activation and reduced sympathetic response to the HD session. Indeed, group H tended to have lower values of SDANN, VLF and LZC, and higher values of HF% than patients in the L group. Finally, there was a trend towards lower LF% measured during the last 30 minutes of HD for the H group versus the L group. Reduction in FO achieved over 3 months by implementation of a strict fluid management plan resulted in an increase of HRV.

Conclusions

Our results suggest that depressed HRV is associated with fluid overload and that normalization of hydration status is accompanied by improved HRV.

Cardiac autonomic function and insulin resistance for the development of hypertension: a six-year epidemiological follow-up study

BACKGROUND AND AIMS

To explore the impact of cardiac autonomic function (CAF) and insulin resistance (IR) on incident hypertension.

METHODS AND RESULTS

In 1996, 1638 subjects finished baseline examination, which included anthropometry, blood pressures, CAF, blood biochemistry, plasma insulin, urine examination and electrocardiogram. CAF included standard deviation of normal-to-normal intervals or RR intervals (SDNN), low- and high-frequency power spectrum (LF and HF), and LF/HF ratio at supine for 5 min, the RR interval changes during lying-to-standing maneuver, and the ratio between the longest RR interval during expiration and the shortest RR interval during inspiration (E/I ratio). We used homeostasis model assessment to define beta cell function (HOMA-B) and insulin resistance (HOMA-IR). In total, 992 non-hypertensive participants completed the follow-up assessment in 2003 and 959 participants were included for the final analysis. Incident hypertension was determined by blood pressure status at follow-up. In unadjusted model, both square root of HOMA-IR (OR:3.37, 95%CI: 2.10-6.64) and HOMA-B (OR:0.996, 95%CI: 0.992-0.999) were related to incident hypertension. In multivariate model, square root of HOMA-IR (OR:1.97, 95%CI: 1.05-3.70), but not HOMA-B, was associated with incident hypertension. After further adjustment for baseline CAF, the positive relationship between the square root of HOMA-IR and incident hypertension disappeared. In contrast, LF/HF ratio (OR:1.18, 95%CI: 1.01-1.37), HF power (OR:0.98, 95%CI: 0.96-0.999), and E/I ratio (OR:0.71, 95%CI: 0.54-0.95) were each independently associated with incident hypertension after further adjustment for HOMA measures.

CONCLUSION

Sympathovagal imbalance with an apparently decreased parasympathetic tone is an important predictor of incident hypertension independent of IR.

Decreased heart rate variability parameters in amitriptyline treated depressed patients: biological and clinical significance

One hundred-four depressed patients treated with amitriptyline (mean dosage: 163 mg/d; mean plasma level: 239 ng/ml) and 52 normal control subjects matched for age and sex underwent a standardized cardiovascular test battery (various autonomic cardiac parameters, which are largely independent from heart rate, namely the coefficients of variation (CV) while resting and during deep respiration, a spectral analysis of heart rate, the Valsalva ratio, and a posture index were determined). The tests included the determination of time and frequency-derived measurements of heart rate variability (HRV), which is rather independent from heart rate. As compared to the controls the patients showed a significant plasma concentration-dependent decrease of R-R variation in the electrocardiogram (p < 0.0001), while their heart rate was significantly elevated (p < 0.0001). The markedly reduced parameters of sinus arrhythmia in amitriptyline treated patients are suggested to be mainly due to the anticholinergic effect of this drug, although it can not be excluded that the affective disorder itself might be associated with low heart rate variability. The results indicate that autonomic heart rate parameters are a valuable tool for the detection of tricyclic antidepressant (TCA) intake in unconscious patients, especially in intensive care and emergency wards.

Heart rate variability and plasma norepinephrine concentration in diabetic dogs at rest

Cardiac autonomic neuropathy in dogs with diabetic mellitus (DM) was evaluated using measurement of heart rate variability (HRV) and plasma norepinephrine (NE) concentration. Dogs were divided into 2 groups; the control non-DM group (n = 13) and the diabetic group (n = 22) which was further divided into the well-controlled DM (n = 11) and the poorly-controlled DM subgroups (n = 11) according to their fasting plasma fructosamine concentrations. The electrocardiogram (ECG) was recorded continuously for at least 30 min to yield HRV. The results showed that in the poorly-controlled DM subgroup, the average of normal R-R interval (mean N-N), SD of the mean of all 5-min segments of normal RR intervals (SDANN) were lower than the control group while heart rate was higher (P < 0.05). The NNA, SDNN, SDNN index and pNN50% were significantly lower when compared with the well-controlled DM subgroup (P < 0.05). The high frequency (HF) and total power were significantly lower while the ratio of low to high frequency (LF/HF) was higher (P < 0.05) when compared with the well-controlled DM subgroup. Moreover, in the poorly-controlled DM subgroup, plasma NE concentration was lower than the control group (210 ± 37 vs. 479 ± 74 pg/ml, P < 0.05). There was a significantly negative correlation between plasma NE and plasma fructosamine concentrations. It is concluded that cardiac autonomic neuropathy occurred in poorly-controlled DM dogs. The sympathetic activity was suppressed as shown by decrease in both plasma NE concentration and LF component.

Sex Differences and Heritability of Two Indices of Heart Rate Dynamics: A Twin Study

We investigated whether women show larger heart rate variability (HRV) than men after controlling for a large number of health-related covariates, using two indices of HRV, namely respiratory sinus arrhythmia (RSA) and approximate entropy (ApEn). In a twin design, the heritability of both indices was examined. The covariation between RSA and ApEn, a measure of heart rate dynamics derived from nonlinear dynamical systems theory, was decomposed into genetic and environmental components. Subjects were 196 male and 210 female middle-aged twins. Females showed larger HRV than men before (ApEn: p < .001; RSA: p = .052) and after adjustment for covariates (ApEn: p < .001; RSA: p = .015). This sex difference was confirmed by significant intrapair differences in the opposite-sex twin pairs for both ApEn (p < .001) and RSA (p = .03). In addition to sex, only heart period and age (both p < .001) were found to be independent predictors of ApEn, whereas RSA was also influenced by respiration rate and smoking (both p < .001). Age explained 16% and 6% of the variance in RSA and ApEn, respectively. Oral contraceptive use and menopausal status had no effect on HRV. Genetic model fitting yielded moderate heritability estimates for RSA (30%) and ApEn (40%) for both males and females. The correlation between RSA and ApEn (r = .60) could be attributed to genetic factors (48%), environmental factors (36%) and age (16%). The present study found support for a gender difference in HRV with women having greater HRV than men even after controlling for a large number of potential confounders. Indices of heart rate dynamics derived from nonlinear dynamical systems theory are moderately heritable and may be more sensitive than traditional indices of HRV to reveal subtle sex differences with important implications for health and disease.

Blood pressure regulation in diabetic patients with and without peripheral neuropathy

Cardiac and vascular dysfunctions resulting from autonomic neuropathy (AN) are complications of diabetes, often undiagnosed. Our objectives were to: 1) determine sympathetic and parasympathetic components of compromised blood pressure (BP) regulation in patients with peripheral neuropathy and 2) rank noninvasive indexes for their sensitivity in diagnosing AN. We continuously measured electrocardiogram, arterial BP, and respiration during supine rest and 70° head-up tilt in 12 able-bodied subjects, 7 diabetics without, 7 diabetics with possible, and 8 diabetics with definite, sensory, and/or motor neuropathy (D2). During the first 3 min of tilt, systolic BP (SBP) of D2 decreased [-10.9 ± 4.5 (SE) mmHg] but increased in able-bodied (+4.8 ± 5.4 mmHg). Compared with able-bodied, D2 had smaller low-frequency (0.04-0.15 Hz) spectral power of diastolic BP, lower baroreflex effectiveness index (BEI), and more SBP ramps. Except for low-frequency power of SBP, D2 had greater SBP and smaller RR interval harmonic and nonharmonic components at rest across the 0.003- to 0.45-Hz region. In addition, our results support previous findings of smaller HF RR interval power, smaller numbers of baroreflex sequences, and lower baroreflex sensitivity in D2. We conclude that diabetic peripheral neuropathy is accompanied by diminished parasympathetic and sympathetic control of heart rate and peripheral vasomotion and diminished baroreflex regulation. A novel finding of this study lies in the sensitivity of BEI to detect AN, presumably because of its combination of parameters that measure reductions in both sympathetic control of vasomotion and parasympathetic control of heart rate.

Heart rate variability and diastolic dysfunction in patients with type 2 diabetes mellitus

Cardiovascular autonomic neuropathy is a common form of autonomic dysfunction in diabetes mellitus (DM) and associates abnormalities in heart rate control and in vascular dynamics. This study evaluates the impact of diabetes mellitus on left ventricular diastolic dysfunction (LVDD) and heart rate variability in a group of type 2 diabetes mellitus without signs of cardiovascular disease. The study group consisted of 58 patients, aged 61 ± 8 years, diagnosed with type 2 DM. The subjects were selected from a series of 104 consecutive diabetic patients. All the subjects were on oral therapy or on diet for DM, and ECG was normal for all the subjects. The control group consisted of 45 healthy subjects, matched for age and sex. Heart rate variability was measured using a 24-h ECG monitoring system, and standard 2D and Doppler echocardiography was performed in all the subjects. There are significant differences between groups regarding disease duration, longer in patients with impaired relaxation (11.22 ± 9.17 vs. 8.31 ± 8.95 years), and disease control, worse in impaired relaxation group. Heart rate in impaired relaxation group is significantly higher than in controls, and higher, but not significantly, when compared with normal group (91 ± 10, vs. 88 ± 11 and 71 ± 11, respectively). Cardiac autonomic neuropathy was associated with LVDD in patients with type 2 DM, but without clinically manifest heart disease. Twenty-four-hour ECG monitoring and echocardiography can detect diabetic cardiomyopathy in early stages and should be performed in all subjects.

Preoperative heart rate variability predicts atrial fibrillation after coronary bypass grafting

BACKGROUND

The purpose of the present study was to investigate the association between preoperative heart rate variability and atrial fibrillation after off-pump coronary artery bypass graft surgery.

METHODS

Of 524 consecutive patients undergoing isolated coronary artery bypass surgery, 390 were retrospectively analyzed after excluding the following 134 cases: on-pump surgery (n = 6), emergency (n = 106), chronic atrial fibrillation (n = 17), and pacemaker rhythm (n = 5). The following time-domain factors of heart rate variability were calculated: standard deviation of all normal-to-normal QRS (SDNN) and square root of mean of sum of squares of differences between adjacent normal-to-normal QRS (RMSSD).

RESULTS

Atrial fibrillation occurred in 98 patients (25%) after surgery. Patients not having atrial fibrillation had significantly lower heart rate variability than did patients having atrial fibrillation, with median values of 91 versus 121 for SDNN and 19 versus 25 for RMSSD. Reduced heart rate variability was significantly associated with a lower risk of postoperative atrial fibrillation: the adjusted hazard ratio (95% confidence interval) was 0.29 (0.17 to 0.49) for SDNN 99 ms or less and 0.47 (0.30 to 0.74) for RMSSD 20 ms or less. The area under the receiver operating characteristic curves for SDNN and RMSSD as a predictor of postoperative atrial fibrillation was 0.764 and 0.696, respectively.

CONCLUSIONS

Reduced time-domain factors in preoperative 24-hour heart rate variability are independently associated with a lower risk of atrial fibrillation after off-pump coronary artery bypass surgery.

Variability--the drama of the circulation

The two most common vital signs, ie, pulse and blood pressure (BP), are obtained to seek guidance in clinical management of patients in virtually all primary care practices. Even a cursory glance at their values, whether it is within a person over time or between patients on a particular day, reflects an amazing degree of variability. In this brief editorial we provide a focused review of the assessment and the importance of variability in within-patient heart rate and BP and conclude with a few thoughts about the discordance in significance attached to these ubiquitous clinical measures.

Differential effects of statins (pravastatin or simvastatin) on ventricular ectopic complexes: Galpha(i2), a possible molecular marker for ventricular irritability

Retrospective studies suggest that statins might exert an antiarrhythmic effect on the heart. The mechanism of this effect is unclear. Parasympathetic stimulation of the heart has been shown to protect against ventricular arrhythmias. The goal of this study was to determine the effect of statins on ventricular arrhythmias and its correlation with changes in parasympathetic responsiveness and Galpha(i2) expression. Patients were randomized to pravastatin and simvastatin in a double-blind crossover design. Ventricular arrhythmias were determined by analysis of 24-hour Holter recordings. Spectral RR interval analysis of Holter studies determined peak high-frequency power fraction, which reflects parasympathetic modulation of heart rate. Expression of Galpha(i2), a molecular component of the parasympathetic response pathway, was determined by Western blots of patients' lymphocytes. Pravastatin treatment decreased the incidence of ventricular premature complexes by 22.5 + or - 3.4% (n = 20, p <0.05), couplets, and runs of 3 to 6 beats of nonsustained ventricular tachycardia from 9.8 + or - 2.67 to 3.9 + or - 1.25 events/patient/24 hours (n = 12, p <0.05). Pravastatin increased peak high-frequency fraction by 29.8 + or - 4.3% (n = 33, p <0.001), while Galpha(i2) expression increased by 51.3 + or - 22.5% (n = 21, p <0.05). Effects of simvastatin on ventricular premature complexes and nonsustained ventricular tachycardia were not significant. Relative changes in couplets and nonsustained ventricular tachycardia in pravastatin-treated patients correlated negatively with changes in Galpha(i2) and high-frequency fraction (rho = -0.588 and rho = -0.763, respectively, n = 12, p <0.05). In conclusion, these data suggest that pravastatin might decrease cardiac irritability via an increase in parasympathetic responsiveness and that changes in Galpha(i2) expression might serve as a molecular marker for this effect, which might play a role in the molecular mechanism of the antiarrhythmic effect of statins.

Autonomic nervous system function in infants and adolescents: impact of autonomic tests on heart rate variability

Measurement of heart rate variability (HRV) shows information on the functional state of the autonomic nervous system (ANS). In adults there are standardized autonomic tests and well-established ranges of normal values, which is not the case in children. The aim of the present study was (1) to introduce an ANS test battery, especially for children and adolescents; (2) to establish normative HRV parameters; and (3) to determine the impact of ANS tests on HRV parameters compared with baseline measurements. We investigated 100 healthy children and adolescents between 6 and 15 years old. We subdivided the investigated group into a group of children (5-11 years old) and adolescents (12-15 years old) and measured HRV by time and frequency domain parameters during baseline, rhythmic breathing, Valsalva test, active standing, tilt-table testing, and handgrip test. The normative HRV data are presented by means, SDs, medians, and percentiles. The results described refer to baseline values for each HRV parameter separately to demonstrate the influence of age on HRV parameters. The study results present not only first normative HRV data for an autonomic test battery especially adapted to children and adolescents, but they also quantify the autonomic changes induced by test procedures compared with baseline measurements.

Fast and low-cost analysis of heart rate variability reveals vegetative alterations in noncomplicated diabetic patients

The aim of the present preliminary study was to describe a simple protocol for the analysis of the heart rate variability (HRV) that can reveal the different autonomic control between noncomplicated diabetic patients and normal subjects within 15 min. The power spectrum of the HRV was evaluated on 5-min-long electrocardiographic recordings in both the supine and the seated positions in 30 noncomplicated non-insulin-dependent diabetic (NIDDM) patients and in 30 healthy volunteers. In healthy subjects the low-frequency (LF) value was higher in seated position than in supine position, while in diabetic patients the LF value in seated position did not differ from that in supine position and did not differ from that in healthy subjects in supine position. The present work demonstrates that the protocol described reveals a different autonomic regulation of the heart rate in healthy subjects and in NIDDM patients even if there is no clinically evident autonomic neuropathy.

Effects of strenuous exercise on autonomic nervous system activity in sickle cell trait carriers

This study compared the nocturnal autonomic nervous system (ANS) activity in seven sickle cell trait (SCT) carriers and six subjects with normal hemoglobin in response to exercise Sympathetic and parasympathetic indices of nocturnal ANS were measured in the two groups before and 24 and 48 h after a strenuous exercise consisting of the repetition of three maximal exercise bouts. Global ANS activity decreased 24 h after exercise in both groups and was lower before as well as after exercise in SCT carriers. Indices of parasympathetic activity were lower in SCT carriers at all times, indicating a persistent sympatho-vagal imbalance. Exercise did not cause a rebound in parasympathetic activity in either group, but a rebound was noted for sympathetic index values two days after exercise in SCT group only. The ANS activity was generally lower, and the sympatho-vagal imbalance greater, in SCT carriers compared with control subjects irrespective of exercise and could increase the risk for medical complications in this population.

Recognition and management of diabetic neuropathy

Pain and disability associated with diabetic neuropathy have economic, social, and emotional consequences. Because these complications impact patients during the prime of their lives, physicians should screen and manage patients at risk. Improvement in glycemic and lipid management, glycemic variability, and lifestyle interventions such as smoking cessation should limit disease progression. Patients who have symptomatic disease should be treated, targeting a 50% improvement in pain within 4 weeks. Physicians should also strive to improve function and comorbidities such as sleep disorders, depression, and anxiety. Patient education is critical for treatment adherence and prevention of serious complications. Consequences associated with diabetic neuropathy include nontraumatic amputations and silent ischemia; thus proper foot care and education regarding "warning signs" of silent ischemia are necessary.

Epidemiological evidence of altered cardiac autonomic function in overweight but not underweight subjects

BACKGROUND

Little is known about the altered cardiac autonomic function (CAF) across different levels of body mass index (BMI), including underweight, normal weight, overweight and obesity. This study provides a thorough analysis to clarify the CAF change in subjects with underweight, overweight and obesity.

METHODS

According to the World Health Organization (WHO) Asia-Pacific BMI cutoffs, a total of 1437 participants were classified as underweight (n=74), normal weight (n=588), overweight (n=313), obesity I (n=390) and obesity II (n=72). CAF was determined by standard deviation of normal-to-normal (SDNN) intervals or RR intervals, power spectrum in low (LF) and high frequency (HF) (LF, 0.04-0.15 Hz; HF, 0.15-0.40 Hz), and LF/HF ratio at supine for 5 min, the ratio between the 30th and the 15th RR interval after standing from the supine position (30/15 ratio) and the average heart-rate change while taking six deep breaths in 1 min (HR(DB)).

RESULTS

There were significant differences in age, gender, socioeconomic status, blood pressure, HOMA insulin resistance index, fasting glucose, cholesterol, triglyceride and high-density lipoprotein (HDL)-C, and the prevalence of hypertension, ischemic/left bundle branch block (LBBB) electrocardiography (EKG) pattern, current smoking and alcohol use among subjects with underweight, normal weight, overweight, obesity I and II. Univariate analysis showed that SDNN, HR(DB), HF power and the square root of the LF/HF ratio differed among these five groups. Multivariate analysis showed that obesity I and II were inverse correlates of HR(DB) and HF power. Overweight, obesity I and II were positively associated with the square root of the LF/HF ratio. No BMI status was related to SDNN, 30/15 ratio or LF power. Underweight was not the independent correlate of any CAF indices.

CONCLUSIONS

The risk for altered CAF is significant in overweight and obese subjects, independent of cardiovascular risk factors. Underweight is not apparently associated with CAF change.

Selective quantification of the cardiac sympathetic and parasympathetic nervous systems by multisignal analysis of cardiorespiratory variability

Heart rate (HR) power spectral indexes are limited as measures of the cardiac autonomic nervous systems (CANS) in that they neither offer an effective marker of the β-sympathetic nervous system (SNS) due to its overlap with the parasympathetic nervous system (PNS) in the low-frequency (LF) band nor afford specific measures of the CANS due to input contributions to HR [e.g., arterial blood pressure (ABP) and instantaneous lung volume (ILV)]. We derived new PNS and SNS indexes by multisignal analysis of cardiorespiratory variability. The basic idea was to identify the autonomically mediated transfer functions relating fluctuations in ILV to HR (ILV→HR) and fluctuations in ABP to HR (ABP→HR) so as to eliminate the input contributions to HR and then separate each estimated transfer function in the time domain into PNS and SNS indexes using physiological knowledge. We evaluated these indexes with respect to selective pharmacological autonomic nervous blockade in 14 humans. Our results showed that the PNS index derived from the ABP→HR transfer function was correctly decreased after vagal and double (vagal + β-sympathetic) blockade ( P < 0.01) and did not change after β-sympathetic blockade, whereas the SNS index derived from the same transfer function was correctly reduced after β-sympathetic blockade in the standing posture and double blockade ( P < 0.05) and remained the same after vagal blockade. However, this SNS index did not significantly decrease after β-sympathetic blockade in the supine posture. Overall, these predictions were better than those provided by the traditional high-frequency (HF) power, LF-to-HF ratio, and normalized LF power of HR variability.

The altered autonomic nervous system activity in iron deficiency anemia

Autonomic function is impaired in anemic patients with various etiologies such as vitamin B12 deficiency, sickle cell trait, and thalassemia major. However, there are insufficient data about autonomic functions in patients with iron deficiency anemia, the leading cause for anemia in the general population. In the present study we aimed to investigate the autonomic status in iron deficiency anemia by analyzing the heart rate variability (HRV). Age- and gender-matched 43 patients with iron deficiency anemia and 39 healthy subjects were undertaken into 24-hr Holter monitoring for assessing the HRV. We used serum levels of iron, iron binding capacity, C-reactive protein, vitamin B12, and folate to exclude other causes of anemia. While age, gender, vitamin B12 and folate levels were not different between the groups, HRV values were lower in patients with iron deficiency anemia compared to control group, which reflects parasympathetic withdrawal. Blood hemorheological factors such as decreased viscosity and/or altered red cell deformability may be responsible for this decreased parasympathetic activity. However, these components do not display remarkable contribution in iron deficiency anemia. Therefore, we speculated a probable link between anemia and the accentuated sympathetic activity that may be triggered by hypoxia sensed through carotid bodies. Despite lacking adequate convincing evidence concerning exact mechanism of carotid body activation, it is assumed as due either to hypoxia-related mitochondrial respiratory chain inhibition or potassium channel suppression that leads to intracellular calcium accumulation. In conclusion, the present study demonstrates an altered autonomic balance in patients with true iron deficiency anemia.

A point process adaptive filter for time-variant analysis of heart rate variability

Estimating time-variant heart variability indices from R-R interval beat series has been widely investigated by current research involving cardiovascular control. Most of the currently accepted approaches in time-variant heart rate analysis ignore the underlying discrete structure of human heart beats, and usually require minutes of data. We derive an adaptive point process Bayes' filter based on a statistical model which considers the stochastic structure of heart beat intervals as a point process. From the explicit inverse Gaussian probability density describing heart rate and heart rate variability we are able to extract and recursively update, at any time resolution, a set of indices related to the first and second moments of this probability density. We apply our algorithm in an analysis of human heart beat intervals from a tilt-table experiment. Our results describe real instantaneous estimates of heart rate variability and may have important implications for research studies of cardiovascular and autonomic regulation. Our algorithm is easy to implement for on-line analysis of heart rate variability in the intensive care unit, operating room or labor and delivery suits.

Incipient cardiovascular autonomic imbalance revealed by wavelet analysis of heart rate variability in Type 2 diabetic patients

AIM

Incipient cardiovascular autonomic imbalance is not readily diagnosed by conventional methods. Spectral analysis of heart rate variability (HRV) by wavelet transform (WT) was used to measure cardiovascular autonomic function in patients with Type 2 diabetes.

METHODS

Thirty-two diabetic patients without (D), 26 with cardiovascular autonomic neuropathy (DAN) and 72 control subjects (C) participated. A 30-min HRV time series was analysed by wavelet transformation and four characteristic frequency intervals were defined: I (0.0095-0.021 Hz), II (0.021-0.052 Hz), III (0.052-0.145 Hz) and IV (0.145-0.6 Hz).

RESULTS

When compared with C, in both D and DAN the normalized power and amplitude of interval II were increased and of interval IV decreased, resulting in a significantly higher II/IV ratio. Furthermore, in DAN the normalized power and amplitude of interval I were increased and of interval III decreased when compared with the D and C groups. The diabetic patients were divided in two equal subgroups according to HbA(1c) < 8.0% and >or= 8.0%. In the subgroup with HbA(1c) >or= 8.0%, normalized power in interval II was significantly higher and in interval IV significantly lower than in the subgroup with HbA(1c) < 8.0%. In D, but not in DAN patients prescribed ACE inhibitors, the absolute amplitude and power of oscillations were significantly higher than in patients not taking ACE inhibitor therapy.

CONCLUSIONS

Patients with diabetes have increased sympathetic and decreased parasympathetic cardiac activity regardless of the presence of autonomic neuropathy. Glycaemic control and treatment with ACE inhibitors may favourably influence HRV in diabetic patients without autonomic neuropathy.

Cardiovascular autonomic neuropathy: diagnosis and management

Cardiovascular autonomic neuropathy increases morbidity and mortality, and reduces quality of life and activities of daily living of the patients with diabetes. The reduced cardiovascular autonomic function as measured by heart rate variability is strongly associated with an increased risk of silent myocardial ischemia and mortality. Currently, no specific therapeutic strategies can be recommended for cardiac autonomic neuropathy, but management of hyperglycemia and the use of angiotensin-converting enzyme inhibitors and beta blockers should be instituted.

Prognostic value of cardiac I-123 metaiodobenzylguanidine imaging in patients with non-insulin-dependent diabetes mellitus

BACKGROUND

123I-metaiodobenzylguanidine (MIBG) myocardial scintigraphy is a useful tool for diagnosing cardiac autonomic neuropathy (CAN) in non-insulin-dependent diabetes mellitus (NIDDM). However, the long-term prognostic value for cardiac events or mortality in NIDDM has not been clarified.

METHODS AND RESULTS

We investigated the long-term prognostic value of cardiac MIBG imaging for both cardiac event and mortality owing to a variety of causes of death in NIDDM. 144 NIDDM patients were analyzed retrospectively with the end-points of a cardiac event and various causes of mortality. The heart-to-mediastinum uptake ratio on the delayed image (H/M [d]) was obtained from anterior planar imaging. The mean follow-up period was 7.2+/-3.2 years. Seventeen patients had a cardiac event onset and 7 patients died during observation. During the same observation course, 16 patients died, including some who died of cardiac event. Both multivariate and univariate analyses revealed that decreased H/M (d) (<1.7) was the independent predictor of long-term mortality for a variety of causes of death. Although the value of H/M (d) was not a significant prognostic factor for predicting a cardiac event, CAN, diagnosed by a combination of H/M (d) and coefficient variance of RR interval, was an independent predictor for the cardiac event in NIDDM.

CONCLUSION

MIBG myocardial scintigraphy was useful for predicting cardiac events and long-term mortality in NIDDM.

Estimation of arterial and cardiopulmonary total peripheral resistance baroreflex gain values: validation by chronic arterial baroreceptor denervation

Feedback control of total peripheral resistance (TPR) by the arterial and cardiopulmonary baroreflex systems is an important mechanism for short-term blood pressure regulation. Existing methods for measuring this TPR baroreflex mechanism typically aim to quantify only the gain value of one baroreflex system as it operates in open-loop conditions. As a result, the normal, integrated functioning of the arterial and cardiopulmonary baroreflex control of TPR remains to be fully elucidated. To this end, the laboratory of Mukkamala et al. (Mukkamala R, Toska K, and Cohen RJ. Am J Physiol Heart Circ Physiol 284: H947–H959, 2003) previously proposed a potentially noninvasive technique for estimating the closed-loop (dimensionless) gain values of the arterial TPR baroreflex (GA) and the cardiopulmonary TPR baroreflex (GC) by mathematical analysis of the subtle, beat-to-beat fluctuations in arterial blood pressure, cardiac output, and stroke volume. Here, we review the technique with additional details and describe its experimental evaluation with respect to spontaneous hemodynamic variability measured from seven conscious dogs, before and after chronic arterial baroreceptor denervation. The technique was able to correctly predict the group-average changes in GA and GC that have previously been shown to occur following chronic arterial baroreceptor denervation. That is, reflex control by the arterial TPR baroreflex was virtually abolished (GA = −2.1 ± 0.6 to 0.3 ± 0.2; P < 0.05), while reflex control by the cardiopulmonary TPR baroreflex more than doubled (GC = −0.7 ± 0.4 to −1.8 ± 0.2; P < 0.05). With further successful experimental testing, the technique may ultimately be employed to advance the basic understanding of TPR baroreflex functioning in both humans and animals in health and disease.

Baroreceptor sensitivity is impaired in elderly subjects with metabolic syndrome and insulin resistance

OBJECTIVE

Metabolic syndrome consists of a collection of cardiovascular risk factors and is considered to increase the risk of cardiovascular morbidity and mortality. This study aimed to investigate whether altered baroreflex sensitivity (BRS), a measure of cardiovascular autonomic control, is related to metabolic syndrome and insulin resistance.

DESIGN AND METHODS

Spontaneously occurring fluctuations in blood pressure and heart rate were recorded during 5 min of controlled breathing in a population sample of 1016 subjects aged 70 (the Prospective Investigation of the Vasculature in Uppsala Seniors study). BRS was calculated through both sequence and frequency domain analysis in 77% of the sample.

RESULTS

BRS was reduced in those with metabolic syndrome (n = 172, median 4.3 versus 5.7; P < 0.0001 after correction for heart rate, cardiovascular diagnosis and medication) and was reduced in proportion to the number of fulfilled National Cholesterol Education Program/Adult Treatment Panel III metabolic syndrome criteria (P < 0.0001). BRS was inversely related to insulin resistance, calculated by homeostatic model assessment (HOMA index; r = -0.18, P < 0.0001).

CONCLUSIONS

Cardiovascular autonomic imbalance, measured as a reduced BRS, is present in metabolic syndrome and in subjects with insulin resistance. As BRS mainly reflects vagal activity, future prospective studies will address the possibility of vagal impairment in the pathogenesis of metabolic syndrome.

Assessment of cardiovascular autonomic function

Autonomic assessment has played an important role in elucidating the role of the autonomic nervous system in diverse clinical and research settings. The techniques most widely used in the clinical setting entail the measurement of an end-organ response to a physiological provocation. The non-invasive measures of cardiovascular parasympathetic function involve the analysis of heart rate variability while the measures of cardiovascular sympathetic function assess the blood pressure response to physiological stimuli. Prolonged tilt-table testing, with or without pharmacological provocation, has become an important tool in the investigation of a predisposition to neurally mediated (vasovagal) syncope. Frequency domain analyses of heart rate and blood pressure variability, microneurography, occlusion plethysmography, laser Doppler imaging and flowmetry, and cardiac sympathetic imaging are currently research tools but may find a place in the clinical assessment of autonomic function in the future.

Heart rate variability and outcome in acute severe stroke: role of power spectral analysis

INTRODUCTION

Heart rate variability (HRV) is a predictor of outcome in acute myocardial infarction and head trauma. Its efficacy in predicting outcome in stroke has not been well documented.

MATERIALS AND METHODS

Twenty-five patients (mean age 39 years) with acute stroke treated in a stroke intensive care unit were studied. Continuous echocardiogram recorded for a 1-hour period was digitized and stored for off-line analysis. Time and frequency domain HRV measures were derived for the filtered and rectified ECG data for each patient. Clinical and HRV profiles were compared among patients who died or survived.

RESULTS

At admission, 16 patients were comatose (Glasgow Coma score<9 at admission), 16 had focal weakness, and all had abnormal brain computed tomography. Of the 25 patients,11 died, 10 had a poor outcome, and 4 had good outcome. Two variables low-frequency (LF) spectral power and very low-frequency (VLF) spectral power correlated with mortality. After adjustment for mechanical ventilation and vasopressor administration, LF, VLF, and Triangular index of RR interval (TINN) correlated with mortality. On multiple regression analysis weighed for mechanical ventilation and vasopressor administration, the eye-opening score on Glasgow Coma Scale and LF spectral power were factors that were independently predictive of mortality.

CONCLUSION

HRV measurements are independent predictors of outcome in acute severe stroke.

Fully-integrated heart rate variability monitoring system with an efficient memory

Heart rate variability is a strong indicator of a number of medical conditions. Current HRV systems typically determine R-R intervals from pre-recorded ECG signals, which include a large amount of redundant data. In this paper we describe a more efficient HRV monitoring and assessment system on chip. By applying digital techniques to store the difference between every two adjacent R-R intervals in a single-port synchronous, high-performance SRAM, up to 24 hours of continuous ECG data can be stored on chip with a fixed resolution of 1 ms. The system has been tested for functionality, synthesized and laid out in a commercial 0.18 microm CMOS process in a 2.5 x 2.5 mm2 hardware core with less than 155 microW power consumption. Such a system can enable HRV monitoring with home based health care and implantable devices.