Insulin resistance and circadian rhythm of cardiac autonomic modulation

Transcutaneous auricular vagus nerve stimulation as a novel therapy connecting the central and peripheral systems: a review

Currently, clinical practice and scientific research mostly revolve around a single disease or system, but the single disease-oriented diagnostic and therapeutic paradigm needs to be revised. This review describes how transcutaneous auricular vagus nerve stimulation (taVNS), a novel non-invasive neuromodulation approach, connects the central and peripheral systems of the body. Through stimulation of the widely distributed vagus nerve from the head to the abdominal cavity, this therapy can improve and treat central system disorders, peripheral system disorders, and central-peripheral comorbidities caused by autonomic dysfunction. In the past, research on taVNS has focused on the treatment of central system disorders by modulating this brain nerve. As the vagus nerve innervates the heart, lungs, liver, pancreas, gastrointestinal tract, spleen and other peripheral organs, taVNS could have an overall modulatory effect on the region of the body where the vagus nerve is widespread. Based on this physiological basis, the authors summarize the existing evidence of the taVNS ability to regulate cardiac function, adiposity, glucose levels, gastrointestinal function, and immune function, among others, to treat peripheral system diseases, and complex diseases with central and peripheral comorbidities. This review shows the successful examples and research progress of taVNS using peripheral neuromodulation mechanisms from more perspectives, demonstrating the expanded scope and value of taVNS to provide new ideas and approaches for holistic therapy from both central and peripheral perspectives.

Correlation of Circadian Rhythms of Heart Rate Variability Indices with Stress, Mood, and Sleep Status in Female Medical Workers with Night Shifts

PURPOSE

Heart rate variability (HRV) indices have been used as stress indicators. Rare studies investigated the associations of circadian rhythms of the HRV indices with the stress, mood, and sleep conditions in populations under stress.

METHODS

In total 257 female participants (203 shift workers and 54 non-shift workers) were included. All the participants completed a structured questionnaire to assess the stress, mood, and sleep conditions and performed 24-hour Holter electrocardiogram monitoring on the day away from shifts. Using epochs of 1-min or 5-min beat-to-beat intervals, the HRV indices (SDNN, RMSSD, LF, HF, LF/HF, and LFnu, SD1, SD2, SD1/SD2) were plotted as a function of time and fitted into cosine periodic curves, respectively. Three mathematical parameters based on the cosine periodic curves were extracted, MESOR (M, overall averages of the cosine curve), amplitude (A, amplitude of the peak of the cosine curve), and acrophase (θ, latency to the peak) to quantify the circadian rhythms of the HRV indices. Multivariable linear regression models were used to reveal the associations of these parameters with the clinical assessments of stress, mood, or sleep conditions, as well as with the 24-h averages of the HRV indices.

RESULTS

The parameters M and A of SDNN, RMSSD, LF, and HF, and θ of LF/HF and LFnu significantly differ between shift and non-shift workers. The parameter θ of LF/HF positively correlates with the severity of stress and anxiety. The parameter A of LF/HF and LFnu also positively correlates with daytime sleepiness and sleep fragmentation. In addition, the parameters M and A instead of θ of SDNN, RMSSD, LF, LF/HF, and LFnu significantly correlate with the 24-h averages of HRV indices.

CONCLUSION

The circadian rhythms of the HRV indices over 24 hours can, to some extent, predict the severity of stress, emotion and sleep conditions in female populations under stress.

Insulin resistance and reduced cardiac autonomic function in older adults: the Atherosclerosis Risk in Communities study

Background

Prior studies have shown insulin resistance is associated with reduced cardiac autonomic function measured at rest, but few studies have determined whether insulin resistance is associated with reduced cardiac autonomic function measured during daily activities.

Methods

We examined older adults without diabetes with 48-h ambulatory electrocardiography (n = 759) in an ancillary study of the Atherosclerosis Risk in Communities Study. Insulin resistance, the exposure, was defined by quartiles for three indexes: 1) the homeostatic model assessment of insulin resistance (HOMA-IR), 2) the triglyceride and glucose index (TyG), and 3) the triglyceride to high-density lipoprotein cholesterol ratio (TG/HDL-C). Low heart rate variability, the outcome, was defined by <25th percentile for four measures: 1) standard deviation of normal-to-normal R-R intervals (SDNN), a measure of total variability; 2) root mean square of successive differences in normal-to-normal R-R intervals (RMSSD), a measure of vagal activity; 3) low frequency spectral component (LF), a measure of sympathetic and vagal activity; and 4) high frequency spectral component (HF), a measure of vagal activity. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals weighted for sampling/non-response, adjusted for age at ancillary visit, sex, and race/study-site. Insulin resistance quartiles 4, 3, and 2 were compared to quartile 1; high indexes refer to quartile 4 versus quartile 1.

Results

The average age was 78 years, 66% (n = 497) were women, and 58% (n = 438) were African American. Estimates of association were not robust at all levels of HOMA-IR, TyG, and TG/HDL-C, but suggest that high indexes were associated consistently with indicators of vagal activity. High HOMA-IR, high TyG, and high TG/HDL-C were consistently associated with low RMSSD (OR: 1.68 (1.00, 2.81), OR: 2.03 (1.21, 3.39), and OR: 1.73 (1.01, 2.91), respectively). High HOMA-IR, high TyG, and high TG/HDL-C were consistently associated with low HF (OR: 1.90 (1.14, 3.18), OR: 1.98 (1.21, 3.25), and OR: 1.76 (1.07, 2.90), respectively).

Conclusions

In older adults without diabetes, insulin resistance was associated with reduced cardiac autonomic function – specifically and consistently for indicators of vagal activity – measured during daily activities. Primary prevention of insulin resistance may reduce the related risk of cardiac autonomic dysfunction.

Enhancing the Robustness of Smartphone Photoplethysmography: A Signal Quality Index Approach

Heart rate variability (HRV) provides essential health information such as the risks of heart attacks and mental disorders. However, inconvenience related to the accurate detection of HRV limits its potential applications. The ubiquitous use of smartphones makes them an excellent choice for regular and portable health monitoring. Following this trend, smartphone photoplethysmography (PPG) has recently garnered prominence; however, the lack of robustness has prevented both researchers and practitioners from embracing this technology. This study aimed to bridge the gap in the literature by developing a novel smartphone PPG quality index (SPQI) that can filter corrupted data. A total of 226 participants joined the study, and results from 1343 samples were used to validate the proposed sinusoidal function-based model. In both the correlation coefficient and Bland–Altman analyses, the agreement between HRV measurements generated by both the smartphone PPG and the reference electrocardiogram improved when data were filtered through the SPQI. Our results support not only the proposed approach but also the general value of using smartphone PPG in HRV analysis.

Metabolic syndrome is associated with decreased heart rate variability in a sex-dependent manner: a comparison between 252 men and 249 women

Impaired heart rate variability (HRV) is associated with increased risk of cardiovascular disease, but evidence regarding alterations of HRV in metabolic syndrome (MetS) remains elusive. In order to examine HRV in MetS, we subjected 501 volunteers without atherosclerosis, diabetes or antihypertensive medication, mean age 48 years, to passive head-up tilt. The subjects were divided to control men (n = 131), men with MetS (n = 121), control women (n = 191) and women with MetS (n = 58) according to the criteria by Alberti et al. (Circulation, 2009, 120, 1640). In unadjusted analyses (i) men and women with MetS had lower total power and high-frequency (HF) power of HRV than controls whether supine or upright (P<0·05 for all). (ii) Supine low-frequency (LF) power of HRV was lower in men (P = 0·012) but not in women (P = 0·064) with MetS than in controls, while men and women with MetS had lower upright LF power of HRV than controls (P <0·01 for both). (iii) The LF:HF ratio did not differ between subjects with and without MetS. After adjustment for age, smoking habits, alcohol intake, height, heart rate and breathing frequency, only the differences in upright total power and HF power of HRV between women with MetS and control women remained significant (P<0·05). In conclusion, reduced total and HF power of HRV in the upright position may partially explain why the relative increase in cardiovascular risk associated with MetS is greater in women than in men. Additionally, the present results emphasize that the confounding factors must be carefully taken into consideration when evaluating HRV.

Heart rate variability in restless legs syndrome and periodic limb movements of Sleep

INTRODUCTION

The relationship between the autonomic nervous system and restless legs syndrome (RLS) and periodic limb movements of sleep (PLMS) consists of varied and somewhat conflicting reports. In order to further elucidate these complexities, a retrospective analysis of polysomnography (PSG) records and clinical data was performed.

METHODS

Records from 233 adult subjects were randomly selected and organized into one of four groups ("non-RLS/PLMS" [n=61], "RLS" [n=60], "PLMS" [n=58], and "RLS/PLMS" [n=54]). Heart rate variability (HRV) analysis was based on 5-minute samples of 2-lead electrocardiogram data isolated from PSG recordings during wakefulness and NREM sleep, and included mean RR interval (labeled "NN") and standard deviation of the RR intervals (labeled "SDNN"), and HRV power, very low frequency (VLF), low frequency (LF), and high frequency (HF) spectral bands.

RESULTS

A significant reduction in the VLF band in the PLMS group as compared to the non-RLS/PLMS group (542±674 vs. 969±1025 ms², p=0.038) was found in wakefulness. Statistically significant differences were seen in the PLMS group as compared to the non-RLS/PLMS group with a reduction in SDNN (p=0.001) and the HF (p=0.001) band, and an increase in HRV power (p=0.001), and the VLF (p=0.005) and LF (p=0.001) bands in NREM sleep.

CONCLUSIONS

The PLMS group exhibited reduced basal sympathetic activity in wakefulness, but basal sympathetic predominance during NREM sleep, distinguishing this group from the RLS and RLS/PLMS groups.

Time-restricted feeding for prevention and treatment of cardiometabolic disorders

The soaring prevalence of obesity and diabetes is associated with an increase in comorbidities, including elevated risk for cardiovascular diseases (CVDs). CVDs continue to be among the leading causes of death and disability in the United States. While increased nutritional intake from an energy-dense diet is known to disrupt metabolic homeostasis and contributes to the disease risk, circadian rhythm disruption is emerging as a new risk factor for CVD. Circadian rhythms coordinate cardiovascular health via temporal control of organismal metabolism and physiology. Thus, interventions that improve circadian rhythms are prospective entry points to mitigate cardiometabolic disease risk. Although light is a strong modulator of the neural circadian clock, time of food intake is emerging as a dominant agent that affects circadian clocks in metabolic organs. We discovered that imposing a time-restricted feeding (TRF) regimen in which all caloric intakes occur consistently within ≤ 12 h every day exerts many cardiometabolic benefits. TRF prevents excessive body weight gain, improves sleep, and attenuates age- and diet-induced deterioration in cardiac performance. Using an integrative approach that combines Drosophila melanogaster (fruit fly) genetics with transcriptome analyses it was found that the beneficial effects of TRF are mediated by circadian clock, ATP-dependent TCP/TRiC/CCT chaperonin and mitochondrial electron transport chain components. Parallel studies in rodents have shown TRF reduces metabolic disease risks by maintaining metabolic homeostasis. As modern humans continue to live under extended periods of wakefulness and ingestion events, daily eating pattern offers a new potential target for lifestyle intervention to reduce CVD risk.

Heart rate variability in normal-weight patients with polycystic ovary syndrome

Objective:

Polycystic ovary syndrome (PCOS) is an endocrine disease closely related to several risk factors of cardiovascular disease. Obese women with PCOS show altered autonomic modulation. The results of studies investigating cardiac autonomic functions of normal-weight women with PCOS are conflicting. The aim of the study was to assess the reactivity of cardiac sympathovagal balance in normal-weight women with PCOS by heart rate variability analysis.

Methods:

We examined the heart rate variability in 60 normal-weight women with PCOS and compared them with that in 60 age-matched healthy women having a similar metabolic profile. Time and frequency domain parameters of heart rate variability were analyzed based on 5-min-long continuous electrocardiography recordings for the following 3 periods: (1) during rest in supine position, (2) during controlled breathing, and (3) during isometric handgrip exercise.

Results:

Time and frequency domain parameters of heart rate variability for the 3 periods assessed were similar in the two groups. Although modified Ferriman–Gallwey score and serum testosterone and luteinizing hormone levels were significantly higher in women with PCOS, homeostatic model assessment-insulin resistance (HOMA-IR) was not different the between the PCOS and control groups. There were no significant correlations between serum testosterone levels and heart rate variability parameters among the study population.

Conclusion:

The findings of this study suggest that the reactivity of cardiac sympathovagal balance is not altered in normal-weight women with PCOS having a normal HOMA-IR.

Association Between Heart Rate Variability Measures and Blood Glucose Levels: Implications for Noninvasive Glucose Monitoring for Diabetes

BACKGROUND

Diabetes mellitus (DM) is a global metabolic epidemic associated with numerous adverse complications. Invasive finger prick tests or invasive monitors are currently the most common means of monitoring and controlling blood glucose levels (BGLs). Heart rate variability (HRV) is a noninvasive measure of the autonomic nervous system, and its dynamic physiological nature may provide an alternative means of blood glucose monitoring. However, the relationship between BGL and HRV parameters remains relatively unknown.

MATERIALS AND METHODS

Thirty-two participants with diabetes (39.97 ± 17.21 years of age) and 31 without diabetes (27.87 ± 10.55 years of age) participated in the current study. Fasting preceded a 10-min three-lead electrocardiogram (ECG), which was followed by a finger prick blood glucose assessment. Following this, a regular meal was consumed, and 30 min after ingestion, a second postprandial 10-min ECG was obtained, and blood glucose assessment was conducted.

RESULTS

Low-frequency (LF) power, high-frequency (HF) power, and total power (TP) of HRV were negatively associated with BGL in participants with DM. Additionally, the ratio of LF to HF was positively correlated with BGL. Duration of DM was also associated with multiple HRV parameters, with negative associations to both LF and HF parameters as well as TP.

CONCLUSIONS

This study demonstrates links between specific HRV variables and BGL. In the future the dynamic nature of HRV could provide a unique and real-time method for monitoring BGL, for continuous noninvasive prediction and/or management of DM.

The circadian pattern of cardiac autonomic modulation and obesity in adolescents

PURPOSE

To assess the impact of obesity and population attributes on the circadian pattern of cardiac autonomic modulation (CAM) in a population-based sample of adolescents.

METHODS

We used data from 421 adolescents who completed the follow-up exam in the Penn State Children Cohort study. CAM was assessed by heart rate variability (HRV) analysis of beat-to-beat, normal R-R intervals from a 24-hour ECG, on a 30-minute basis. The HRV indices included frequency-domain (HF, LF, and LF/HF ratio) and time-domain (SDNN, RMSSD, and HR) variables. Nonlinear mixed-effect models were used to calculate a cosine periodic curve, each having three parameters quantifying its circadian period: M (mean levels of the HRV variables), Â (amplitude of the oscillation), and θ (the time of the highest oscillation).

RESULTS

The mean (SD) age was 16.9 (2.2) years, with 54 % male and 77 % white. The mean BMI percentile was 66, with 16 % obese (BMI percentile ≥ 95). Overall, HF (a marker of parasympathetic modulation) gradually increased from the late afternoon, reached peak amplitude around 3 a.m., and then decreased throughout the daytime until late afternoon. In contrast, obesity had adverse effects on all circadian parameters. The age, sex and race showed varying differences on the CAM circadian parameters. The adjusted means (95 %Cls) of M, Â, and θ for HF were 5.99 (5.79-6.19), 0.77 (0.66-0.89), 3:15 (2:15-4:15) a.m., and 6.21 (6.13-6.29), 0.66 (0.61-0.70), 2:45 (2:30-3:15) a.m. for obese and non-obese subjects, respectively.

CONCLUSION

The circadian pattern of CAM can be quantified by the three cosine parameters. Obesity is associated with lower HRV even in young individuals like children/adolescents.

Childhood obesity and autonomic dysfunction: risk for cardiac morbidity and mortality

OPINION STATEMENT

The epidemic of childhood obesity is becoming a major predictor for risk of cardiovascular diseases (CVD) and mortality during adulthood. Alterations in the morphology of the heart due to obesity could be a predictor for the dysfunction of cardiac autonomic modulation (CAM). A number of epidemiologic studies have evaluated the effect of obesity and CAM in children, finding that obesity impaired the balance of CAM toward a sympathetic overflow and reduced parasympathetic modulation, a significant predictor of CVD morbidity and mortality in adults. Lifestyle modifications, for example long-term exercise programs, have been shown to improve CAM in the obese. This review discusses the recent evidence on childhood and adolescent obesity and its impact on CAM, as well as how early lifestyle changes could help improve CAM, which may in turn reduce the burden of CVD in adults.

Hypoglycemic effects and mechanisms of electroacupuncture on insulin resistance

The aim of this study was to investigate effects and mechanisms of electroacupuncture (EA) on blood glucose and insulin sensitivity in mice fed a high-fat diet. Both wild-type (WT) and adipose ectonucleotide pyrophosphate phosphodiesterase (ENPP1) transgenic (TG) mice were fed a high-fat diet for 12 wk; for each mouse, an intraperitoneal glucose tolerance test (IPGTT) and insulin tolerance test (ITT) were performed with or without EA at abdomen or auricular areas. A high-fat diet-induced insulin resistance in both WT and TG mice. In the WT mice, EA at 3 Hz and 15 Hz, but not at 1 Hz or 100 Hz, via CV4+CV12 significantly reduced postprandial glucose levels; EA at 3 Hz was most potent. The glucose level was reduced by 61.7% at 60 min and 74.5% at 120 min with EA at 3 Hz (all P < 0.001 vs. control). Similar hypoglycemic effect was noted in the TG mice. On the contrary, EA at auricular points increased postprandial glucose level (P < 0.03). 4). EA at 3 Hz via CV4+CV12 significantly enhanced the decrease of blood glucose after insulin injection, suggesting improvement of insulin sensitivity. Plasma free fatty acid was significantly suppressed by 42.5% at 15 min and 50.8% at 30 min with EA (P < 0.01) in both WT and TG mice. EA improves glucose tolerance in both WT and TG mice fed a high-fat diet, and the effect is associated with stimulation parameters and acupoints and is probably attributed to the reduction of free fatty acid.

Effects of induced hyperinsulinaemia with and without hyperglycaemia on measures of cardiac vagal control

AIMS/HYPOTHESIS

We examined the effects of serum insulin levels on vagal control over the heart and tested the hypothesis that higher fasting insulin levels are associated with lower vagal control. We also examined whether experimentally induced increases in insulin by beta cell secretagogues, including glucagon-like peptide-1 (GLP-1), will decrease vagal control.

METHODS

Respiration and ECGs were recorded for 130 healthy participants undergoing clamps. Three variables of cardiac vagal effects (the root mean square of successive differences [rMSSD] in the interbeat interval of the heart rate [IBI], heart-rate variability [HRV] caused by peak-valley respiratory sinus arrhythmia [pvRSA], and high-frequency power [HF]) and heart rate (HR) were obtained at seven time points during the clamps, characterised by increasing levels of insulin (achieved by administering insulin plus glucose, glucose only, glucose and GLP-1, and glucose and GLP-1 combined with arginine).

RESULTS

Serum insulin level was positively associated with HR at all time points during the clamps except the first-phase hyperglycaemic clamp. Insulin levels were negatively correlated with variables of vagal control, reaching significance for rMSSD and log10HF, but not for pvRSA, during the last four phases of the hyperglycaemic clamp (hyperglycaemic second phase, GLP-1 first and second phases, and arginine). These associations disappeared when adjusted for age, BMI and insulin sensitivity. Administration of the beta cell secretagogues GLP-1 and arginine led to a significant increase in HR, but this was not paired with a significant reduction in HRV measures.

CONCLUSION/INTERPRETATION

Experimentally induced hyperinsulinaemia is not correlated with cardiac vagal control or HR when adjusting for age, BMI and insulin sensitivity index. Our findings suggest that exposure to a GLP-1 during hyperglycaemia leads to a small acute increase in HR but not to an acute decrease in cardiac vagal control.

Cardiac autonomic modulation in polycystic ovary syndrome: does the phenotype matter?

OBJECTIVE

To assess whether heart rate variability (HRV) at rest and during sympathetic stimulation is disturbed in patients with different polycystic ovary syndrome (PCOS) phenotypes in comparison to healthy controls.

DESIGN

Cross-sectional study.

SETTING

University hospital.

PATIENT(S)

Thirty women with classic, anovulatory PCOS, 16 women with ovulatory PCOS, and 23 age-paired women with regular and proven ovulatory cycles.

INTERVENTION(S)

Anthropometric and hormonal evaluation and analysis of HRV (time and frequency domain HRV indices) at rest and after a mental stress test.

MAIN OUTCOME MEASURE(S)

Difference between HRV components during rest and stress.

RESULT(S)

Mean age was 22.80 ± 5.80 years in patients with classic PCOS, 19.81 ± 6.43 years in ovulatory PCOS, and 22.65 ± 5.89 years in controls. During mental stress, patients with classic PCOS showed lower HRV response when compared with the control group, even after adjustment for body mass index (BMI) and age. When patients with classic and ovulatory PCOS were considered together, total T levels were inversely associated with the low frequency component, low frequency/high frequency ratio, and the difference between high frequency response at rest and after the stress test.

CONCLUSION(S)

Young patients with the classic PCOS phenotype have an impaired autonomic modulation in response to sympathetic stimulation that is typical of considerably older women, or of advanced age.

Ambulatory ECG-based T-wave alternans and heart rate turbulence can predict cardiac mortality in patients with myocardial infarction with or without diabetes mellitus

Background

Many patients who survive a myocardial infarction (MI) remain at risk of sudden cardiac death despite revascularization and optimal medical treatment. We used the modified moving average (MMA) method to assess the utility of T-wave alternans (TWA) and heart rate turbulence (HRT) as risk markers in MI patients with or without diabetes mellitus (DM).

Methods

We prospectively enrolled 248 consecutive patients: 96 with MI (post-MI patients); 77 MI with DM (post-MI + DM patients); 75 controls without cardiovascular disease (group control). Both TWA and HRT were measured on ambulatory electrocardiograms (AECGs). HRT was assessed by two parameters ─ turbulence onset (TO) and turbulence slope (TS). HRT was considered positive when both TO ≥0% and TS ≤2.5 ms/R-R interval were met. The endpoint was cardiac mortality.

Results

TWA values differed significantly between MI and controls. Post-MI + DM patients had higher TWA values than post-MI patients (58 ± 21 μV VS 52 ± 18 μV, P = 0.029). Impaired HRT--increased TO and decreased TS were observed in MI patients with or without DM. During follow-up of 578 ± 146 days, cardiac death occurred in ten patients and three of them suffered sudden cardiac death (SCD). Multivariate analysis determined that a HRT-positive outcome [HR (95% CI): 5.01, 1.33–18.85; P = 0.017], as well as the combination of abnormal TWA (≥47 μV) and positive HRT had significant association with the endpoint [HR (95% CI): 9.08, 2.21–37.2; P = 0.002)].

Conclusion

This study indicates that AECGs-based TWA and HRT can predict cardiac mortality in MI patients with or without DM. Combined analysis TWA and HRT may be a convenient and useful method of identifying patients at high risk for cardiovascular death.

Heart rate variability is associated with glycemic status after controlling for components of the metabolic syndrome

OBJECTIVE

To evaluate the relationship between heart rate variability (HRV) and glycemic status after controlling for metabolic syndrome (MetS) in a healthy working cohort.

BACKGROUND

A growing body of literature suggests that reduced HRV, a physiological marker of autonomic nervous system activity, is associated with various pathological conditions including glycemic disorders and cardiovascular diseases. The extent to which this association is confounded by other more traditional markers of cardiovascular risk, such as MetS, is unclear.

METHODS

We recruited 2441 study participants (age 17-65) employed at three sites of an airplane manufacturing plant in southern Germany. All subjects underwent medical examination, blood sampling, and 24-hour ambulatory heart rate recording while on their normal work routine. Indices of HRV were determined from readings made throughout the 24-hour examination period, those during either the day or night only as well as a night to day ratio. Pearson correlations and multivariate-adjusted partial correlation coefficients (PCCs) were calculated.

RESULTS

Pearson correlations suggested inverse associations between HRV measurements and glycemic status (e.g. High frequency r=-0.07, p<0.001; SDNN r=-0.09, p<0.001). After multivariate adjustment of all other components of MetS (triglyceride, blood pressure, waist circumference, high density lipoproteins), medical and demographic variables, these associations persisted (e.g. High frequency PCC=-0.05, p<0.001; SDNN PCC=-0.06, p<0.001).

CONCLUSIONS

We confirm a negative correlation between HRV and glycemic status that appeared to be almost linear in a large cohort of healthy workers. Importantly, we showed that this association was independent of potential confounders, especially all of the MetS components and inflammation.

Effects of surgically induced weight loss by Roux-en-Y gastric bypass on cardiovascular autonomic nerve function

BACKGROUND

Obesity is associated with autonomic imbalance. With respect to cardiovascular autonomic dysfunction, this is characterized by reduced heart rate variability (HRV). Our objective was to determine the effect of surgically induced weight loss on cardiovascular autonomic nerve fiber function in subjects with severe obesity and examine whether an association with reduced insulin resistance exists. The setting was a hospital and private practice in the United States.

METHODS

A total of 32 morbidly obese patients (body mass index 51 ± 11 kg/m(2)) underwent laparoscopic Roux-en-Y gastric bypass. Measures of HRV (e.g., power spectral analysis, RR variation during deep breathing) were used to evaluate autonomic function before and 6 months after surgery. The homeostasis model assessment of insulin resistance index (HOMA-IR) was used to assess insulin resistance.

RESULTS

At 6 months after bariatric surgery, the patients had lost 58% excess body mass index with improvement in the HOMA-IR (3.0 ± 1.4 versus 1.1 ± .7; P < .001). Measures of RR variation during deep breathing and total spectral power, low frequency (LF) power (influenced by sympathetic and parasympathetic activity), and high frequency (HF) power (parasympathetic activity) increased with weight loss. The LF/HF ratio was lower (1.5 ± 1.5 versus .9 ± .7, P < .05) with a reduction in weight. Spectral analysis of HRV combined with spectral analysis of respiratory activity generated the respiration frequency area (RFA) and low frequency area. The RFA was increased, and the LFA/RFA ratio was reduced with weight loss. HOMA-IR and HRV did not correlate.

CONCLUSION

Surgically induced weight loss has a favorable effect on autonomic function, but it does not appear to be directly attributable to reduced insulin resistance.

Relationship of autonomic imbalance and circadian disruption with obesity and type 2 diabetes in resistant hypertensive patients

Background

Hypertension, diabetes and obesity are not isolated findings, but a series of interacting interactive physiologic derangements. Taking into account genetic background and lifestyle behavior, AI (autonomic imbalance) could be a common root for RHTN (resistant hypertension) or RHTN plus type 2 diabetes (T2D) comorbidity development. Moreover, circadian disruption can lead to metabolic and vasomotor impairments such as obesity, insulin resistance and resistant hypertension. In order to better understand the triggered emergence of obesity and T2D comorbidity in resistant hypertension, we investigated the pattern of autonomic activity in the circadian rhythm in RHTN with and without type 2 diabetes (T2D), and its relationship with serum adiponectin concentration.

Methods

Twenty five RHTN patients (15 non-T2D and 10 T2D, 15 males, 10 females; age range 34 to 70 years) were evaluated using the following parameters: BMI (body mass index), biochemical analysis, serum adiponectinemia, echocardiogram and ambulatory electrocardiograph heart rate variability (HRV) in time and frequency domains stratified into three periods: 24 hour, day time and night time.

Results

Both groups demonstrated similar characteristics despite of the laboratory analysis concerning T2D like fasting glucose, HbA1c levels and hypertriglyceridemia. Both groups also revealed disruption of the circadian rhythm: inverted sympathetic and parasympathetic tones during day (parasympathetic > sympathetic tone) and night periods (sympathetic > parasympathetic tone). T2D group had increased BMI and serum triglyceride levels (mean 33.7 ± 4.0 vs 26.6 ± 3.7 kg/m² - p = 0.00; 254.8 ± 226.4 vs 108.6 ± 48.7 mg/dL - p = 0.04), lower levels of adiponectin (6729.7 ± 3381.5 vs 10911.5 ± 5554.0 ng/mL - p = 0.04) and greater autonomic imbalance evaluated by HRV parameters in time domain compared to non-T2D RHTN patients. Total patients had HRV correlated positively with serum adiponectin (r = 0.37 [95% CI -0.04 - 1.00] p = 0.03), negatively with HbA1c levels (r = -0.58 [95% CI -1.00 - -0.3] p = 0.00) and also adiponectin correlated negatively with HbA1c levels (r = -0.40 [95% CI -1.00 - -0.07] p = 0.02).

Conclusion

Type 2 diabetes comorbidity is associated with greater autonomic imbalance, lower adiponectin levels and greater BMI in RHTN patients. Similar circadian disruption was also found in both groups indicating the importance of lifestyle behavior in the genesis of RHTN.

Association of glycemic variability and the presence and severity of coronary artery disease in patients with type 2 diabetes

BACKGROUND

Glucose variability is one of components of the dysglycemia in diabetes and may play an important role in development of diabetic vascular complications. The objective of this study was to assess the relationship between glycemic variability determined by a continuous glucose monitoring (CGM) system and the presence and severity of coronary artery disease (CAD) in patients with type 2 diabetes mellitus (T2DM).

METHODS

In 344 T2DM patients with chest pain, coronary angiography revealed CAD (coronary stenosis ≥ 50% luminal diameter narrowing) in 252 patients and 92 patients without CAD. Gensini score was used to assess the severity of CAD. All participants' CGM parameters and biochemical characteristics were measured at baseline.

RESULTS

Diabetic patients with CAD were older, and more were male and cigarette smokers compared with the controls. Levels of the mean amplitude of glycemic excursions (MAGE) (3.7 ± 1.4 mmol/L vs. 3.2 ± 1.2 mmol/L, p < 0.001), postprandial glucose excursion (PPGE) (3.9 ± 1.6 mmol/L vs. 3.6 ± 1.4 mmol/L, p = 0.036), serum high-sensitive C-reactive protein (hs-CRP) (10.7 ± 12.4 mg/L vs. 5.8 ± 6.7 mg/L, p < 0.001) and creatinine (Cr) (87 ± 23 mmol/L vs. 77 ± 14 mmol/L, p < 0.001) were significantly higher in patients with CAD than in patients without CAD. Gensini score closely correlated with age, MAGE, PPGE, hemoglobin A1c (HbA1c), hs-CRP and total cholesterol (TC). Multivariate analysis indicated that age (p < 0.001), MAGE (p < 0.001), serum levels of HbA1c (p = 0.022) and hs-CRP (p = 0.005) were independent determinants for Gensini score. Logistic regression analysis revealed that MAGE ≥ 3.4 mmol/L was an independent predictor for CAD. The area under the receiver-operating characteristic curve for MAGE (0.618, p = 0.001) was superior to that for HbA1c (0.554, p = 0.129).

CONCLUSIONS

The intraday glycemic variability is associated with the presence and severity of CAD in patients with T2DM. Effects of glycemic excursions on vascular complications should not be neglected in diabetes.