Heart rate variability in obesity and the effect of weight loss

To investigate the effects of obesity and weight loss on cardiovascular autonomic function, we examined 28 obese patients referred for weight-reducing gastroplasty, 24 obese patients who received dietary recommendations, and 28 lean subjects. Body weight, blood pressure, and 24-hour urinary norepinephrine excretion were measured, and time and frequency domain indexes of heart rate variability (HRV) were obtained from 24-hour Holter recordings. A measure of long-term HRV, the SD of all normal RR intervals (SDANN), was used as an index of sympathetic activity and the high-frequency (HF) component of the frequency domain, reflecting short-term HRV, as an estimate of vagal activity. All 3 study groups were investigated at baseline, and the 2 obese groups were reexamined at 1-year follow-up. Obese patients had higher blood pressure, higher urinary norepinephrine excretion, and attenuated SDANN and HF values than lean subjects (p <0.01). Obese patients treated with surgery had a mean weight loss of 32 kg (28%), whereas the obese group treated with dietary recommendations remained weight stable (p <0.001). At follow-up the weight-loss group displayed decreases in blood pressure and norepinephrine excretion and showed increments in SDANN and HF values. These changes were significantly greater than those observed in the obese control group (p <0.05). Our findings suggest that obese patients have increased sympathetic activity and a withdrawal of vagal activity and that these autonomic disturbances improve after weight loss.     

Impact of bariatric surgery--induced weight loss on heart rate variability

Obesity is associated with an increased risk of sudden death that may be due to abnormal cardiac vagal modulation reflected by reduced heart rate variability (HRV). Few studies have been conducted analyzing the effect of bariatric surgery-induced weight loss on HRV assessed by 24-hour Holter monitoring. The aim of this study was to assess weight loss effect after bariatric surgery on HRV and ventricular size and function. Ten morbidly obese patients, 6 women and 4 men aged 24 to 47 years, underwent bariatric surgery. Seven morbidly obese patients without active obesity treatment were used as controls. Twenty-four-hour Holter monitoring and echocardiogram were obtained before and at 6 to 12 months after surgery or at follow-up in control patients. Changes in minimal, maximal, and mean heart rate along with HRV during daytime and nighttime were compared before and after surgery. Baseline characteristics in the control group did not differ significantly from the treatment group. Average weight in the treatment group was 141 +/- 31 kg (mean +/- SD) at baseline and decreased to 101 +/- 18 kg at follow-up, corresponding to a body mass index of 52.3 +/- 7.6 kg/m(2) at baseline and 37.7 +/- 5.3 kg/m(2) at follow-up. There was a decrease in minimal heart rate (48 +/- 10 vs 40 +/- 6 beats per minute, P = .021) and mean heart rate (82 +/- 7 vs 66 +/- 10 beats per minute, P < .001) during the Holter monitoring. Spectral analysis showed a significant enhancement in HRV parameters (high- and low-frequency power) because there was an increase in the standard deviation of normal to normal R-R intervals (116 +/- 25 vs 174 +/- 56 milliseconds, P < .001), the standard deviation of the mean R-R intervals calculated over a 5-minute period (104 +/- 25 vs 148 +/- 45 milliseconds, P < .001), the square root of the mean of the squared differences between adjacent normal R-R intervals (25 +/- 8 vs 50 +/- 20 milliseconds, P < .001), and the percentage of differences between adjacent normal R-R intervals exceeding 50 milliseconds (5% +/- 5% vs 22% +/- 13%, P < .001). Echocardiographic measures remained unchanged when comparing the groups. Weight loss after bariatric surgery enhances HRV and decreases mean and minimal heart rate during Holter monitoring through a better cardiac parasympathetic modulation.     

窦性心率震荡技术的新标准、新应用、新评价

窦性心率震荡(heart rateturbulence,HRT)最早由德国慕尼黑流行病和医学技术学院以及英国圣乔治医学院的学者对室性早搏后心率的双相变时性变化开展临床试验研究后提出,并认为这是一项心肌梗死后猝死高危患者可靠的预测方法。     

Heart rate variability biofeedback: effects of age on heart rate variability, baroreflex gain, and asthma

OBJECTIVES: To present additional analysis of data from a previously published study showing that biofeedback training to increase heart rate variability (HRV) can be an effective component in asthma treatment. HRV and intervention-related changes in HRV are negatively correlated with age. Here we assess the effects of age on biofeedback effects for asthma. DESIGN: Ten sessions of HRV biofeedback were administered to 45 adults with asthma. Medication was prescribed by blinded physicians according to National Heart, Lung, and Blood Institute criteria. Medication needs were reassessed biweekly. RESULTS: Decreases in need for controller medication were independent of age. There were larger acute decreases in forced oscillation frequency dependence in the older group but larger increases in HRV variables in the younger group. Differences between age groups were smaller among subjects trained in pursed-lips abdominal breathing as well as biofeedback, than among those receiving only biofeedback. CONCLUSIONS: Age-related attenuation of biofeedback effects on cardiovascular variability does not diminish the usefulness of the method for treating asthma among older patients. Additional training in pursed-lips abdominal breathing obliterates the effects of age on HRV changes during biofeedback.     

Heart rate and heart rate variability, a pharmacological target

Summary Heart rate varies with respiration, blood pressure, emotion, etc., and heart rate variability (HRV) is presently one of the best indices to predict fatal issues in cardiac failure and after myocardial infarction. HRV depends on various reflexes. In addition, parallel studies of HRV and the myocardial adrenergic and muscarinic transduction system in experimental models of cardiac hypertrophy (CH) have suggested that the myocardial phenotype at the sinus-node level may also play a role. A transgenic strain of mice with atrial overexpression of the 677-1 receptors was generated with attenuated HRV, which demonstrates that the phenotype itself is a determinant of HRV. HRV is explored by noninvasive techniques, including simple determination of the standard error of the mean, time-domain analysis, and Fourier transformation. We recently developed a time and frequency domain method of analysis, the smoothed pseudo-Wigner-Ville transformation, which allows better exploration of nonstationarity. Nonlinear methods have also been applied due to the extreme complexity of the biological determinants, and have provided evidence of a chaotic attractor in certain conditions. It is proposed that in steady state a very simple process, which is not completely deterministic, could better explain intermit interval regulations than chaotic behavior. In contrast, under extreme circumstances the regulation proceeds using chaotic behavior. Arrhythmias and HRV can be quantitated in 16-month-old unanesthetized spontaneously hypertensive rats (SHR). Ventricular premature beats are more frequent in SHR than in age-matched controls; they disappear after converting enzyme inhibition (CEI) relative to the reduction of both cardiac hypertrophy and ventricular fibrosis. HRV is attenuated in SHR, as it is in compensatory CH in humans. When CH is prevented, HRV returns to normal. CEI is therefore antiarrhythmic. Another pharmacological application of this concept concerns the bradycardic agents that may improve HRV.     

Gallstones in obesity and weight loss

The prevalence of cholesterol gallstones is increased in obese persons. The risk is especially high in those with the highest body mass index (relative risk 5-6). Weight loss further increases the risk of gallstones: the prevalence of new gallstones reaches 10-12% after 8-16 weeks of low-calorie diet and more than 30% within 12-18 months after gastric by-pass surgery. About one-third of the stones are symptomatic. The increased prevalence of stones is mostly due to supersaturation of bile with cholesterol, because of an increased synthesis by the liver and secretion into bile. Saturation is further increased during weight loss. It returns toward normal after weight stabilization at a lower level, allowing spontaneous stone dissolution in some cases. Identified risk factors for gallstones during weight loss are a relative loss of weight greater than 24% of initial body weight, a rate of weight loss greater than 1.5 kg per week, a very low calorie diet with no fat, a long overnight fast period and a high serum triglyceride level. Ursodeoxycholic acid decreases cholesterol saturation of bile and gallstone incidence during weight loss. Other preventive measures include a control of weight loss rate, a reduction of the length of overnight fast, and maintenance of a small amount of fat in the diet.     

The obesity paradox and weight loss

Background

An “obesity paradox,” in which overweight and obese individuals with established cardiovascular disease have a better prognosis than normal weight subjects, has been reported in a number of clinical cohorts, but little is known about the effects of weight loss on the obesity paradox and its association with health outcomes.

Methods

Weight was determined in 3834 men at the time of a clinically referred exercise test and again during a clinical evaluation a mean of 7 years later. The associations among weight changes, baseline fitness, and other risk markers with cardiovascular and all-cause mortality were determined by Cox proportional hazards analysis.

Results

During the follow-up period, 314 subjects died (72 of cardiovascular causes). In a multivariate analysis (including baseline weight, weight change, exercise capacity, and cardiovascular disease), weight gain was associated with lower mortality and weight loss was associated with higher mortality (4% higher per pound lost per year, P < .001) compared with stable weight. For all-cause mortality, the relative risks for the no change, weight gain, and weight loss groups were 1.0 (referent), 0.64 (95% confidence interval, 0.50-0.83), and 1.49 (95% confidence interval, 1.17-1.89), respectively (P < .001). Those who died and exhibited weight loss had a significantly higher prevalence of deaths due to cancer and cardiovascular causes.

Conclusion

Weight loss was related to higher mortality and weight gain was related to lower mortality when compared with stable weight. The obesity paradox in our sample is explained in part by a combination of non-volitional weight loss related to occult disease and a protective effect of weight gain.     

Los function and obesity: the impact of untreated obesity, weight loss, and chronic gastric balloon distension

BACKGROUND/AIMS: In obesity, many gastro-oesophageal reflux promoting factors are present. Weight reduction is advised to symptomatic overweight subjects. The aim of the present study was to investigate the influences of untreated obesity, weight loss, and chronic gastric balloon distension on the lower oesophageal sphincter (LOS) function. METHODS: Patients entering a randomized, double-blind, sham-controlled study of balloon treatment, consisting of 4 months of either sham balloon or balloon treatment followed by 4 months of balloon treatment. Manometry and 24-hour pH measurements were performed at the start of the study and after 13 and 26 weeks. RESULTS: Before treatment, LOS dysfunction was present in 7 of 32 patients (21.9%). Increased upright and supine reflux was present in 8 patients (25%). Sham treatment resulted in a weight loss of 9.7% with improved LOS function (a significant 0.6-cm increase in LOS length and a non-significant 2.6 mm Hg higher LOS pressure) and in a significantly decreased upright reflux (acid reflux time decreasing from 8.0 to 5.5% and number of meal-related and postprandial reflux episodes decreasing from 49 to 32). These improved values deteriorated after 4 months of balloon placement, with significantly increasing total, upright, and supine reflux to 7.5, 7.6, and 6.7% of the time, respectively, with oesophageal lesions after an overall 17.8% weight loss. Four months of balloon treatment induced a similar weight loss (9.9%) with significantly increased supine reflux from 1.6 to 6.7% of the time. After a second 4-month balloon period and an overall 13.8% weight loss, LOS and reflux values returned towards baseline values. A comparison of both groups demonstrated the adverse effects of balloon positioning after a period of substantial sham-induced weight loss. CONCLUSIONS: Impaired LOS function and increased gastro-oesophageal reflux were observed in one quarter of the untreated obese subjects. Weight loss ameliorated manometry and pH values, but subsequent balloon positioning tended to counteract these beneficial changes. In patients on balloon treatment from the start, adverse effects seemed to wear off with prolonged treatment.     

Visceral obesity and the metabolic syndrome: effects of weight loss

A large body of experimental and epidemiological evidence has established an association between visceral obesity and the metabolic syndrome, which retains its power throughout the spectrum of adiposity and is still clinically meaningful in severe obesity. The association may be due to an overload of liver free fatty acids (FFA) produced by the high lipolytic activity of omental fat. A substantial improvement in all aspects of the metabolic syndrome with only a moderate degree of weight loss has been observed in a large number of randomised controlled studies and can also be obtained in severe obesity, despite the fact that the patients remain obese. The reasons for this apparent dissociation between weight loss and metabolic improvement are not yet clearly understood, but may involve the relationship between visceral fat and metabolic alterations. The results of some studies suggest that the favourable metabolic changes observed in obese patients with weight loss may be directly attributable to a reduction in visceral fat, and other studies have recently shown that a rapid and preferential reduction in visceral fat mass occurs during the first phase of weight loss in morbidly obese patients possibly as a result of sympathetic nervous system activation. It is therefore possible that the apparent dissociation between weight loss and metabolic improvement is partially due to a difference in the responsiveness of visceral and subcutaneous adipose tissue to energy restriction: i.e. the fact that the metabolic profile of patients with visceral obesity may substantially improve after the loss of only a few kilograms of body weight could be related to a greater relative reduction in the amount of visceral rather than other fat. In this respect, the characteristically high rate of visceral fat mobilisation can also be seen as a good target for interventions aimed at reducing cardiovascular risk factors.     

Orlistat for obesity: benefits beyond weight loss

Orlistat lowers lipids and improves insulin sensitivity, but its effect on other metabolic syndrome related parameters is not known. To assess its influence on adiponectin, high sensitive C-reactive protein (hs-CRP) and other metabolic syndrome related parameters, this study enrolled 106 participants in a weight-reduction program and categorized them into a group of 51 who had been treated with orlistat 360 mg/day for one year and a group of 55 age and sex and body mass index (BMI) matched controls. The orlistat group had greater changes in BMI, % body fat (% BF), waist circumference, and insulin resistance, hs-CRP, leptin and adiponectin levels after one year on the program than the controls. After adjusting for % BF and waist circumference, change of serum leptin and adiponectin levels remained significantly different. It was found that orlistat could effectively manage obesity related co-morbidities, especially insulin resistance and atherosclerosis risk. It decreases leptin and increases adiponectin independent of % BF and waist circumference. Therefore, orlistat appears to have anti-diabetic and anti-atherogenic properties and may help prevent metabolic syndrome in the overweight people.     

Heart rate variability and vasovagal syncope

OBJECTIVE: Tilt Table testing is widely used for the diagnosis and evaluation of vasovagal syncope. By evaluating the fluctuations of the autonomic nervous system that play an important role in syncope genesis, heart rate variability (HRV) can be considered as a tool of added value. METHODS: We evaluated prospectively 123 patients admitted for recurrent syncope with a positive tilt Table testing. A time domain analysis of a 24 hours ambulatory electrocardiography was used in all patients to asses the particularities of their autonomic function. We compared their results with those obtained from a group of 82 healthy volunteers. RESULTS: Statistical analysis of the results showed a significant increase of all HRV parameters in the group of vasovagal syncope compared to the healthy volunteers. SDNNidx (58 vs 42; p < 0.001), rMSSD (40 vs 27; p < 0.001), SDNN (102 vs 83; p < 0.001), SDANN (79 vs 67; p< 0.001), pNN50 (11 vs 4.9; p <0.001). CONCLUSION: Time domain analysis of heart rate variability reveals increased values in patients with vasovagal syncope. It seems to be an interesting, easy and complementary test in the evaluation of syncope of unknown etiology.     

Heart rate variability and familial amyloidosis

A 32-year-old man with family history of amyloidosis was admitted to the hospital because of orthostatic hypotension. An echocardiogram was suggestive for cardiac amyloidosis. Heart rate variability analysis, performed on 24-h Holter monitoring, showed markedly low values in both frequency and time domain, reflecting a severe autonomic nervous system dysfunction.     

Heart rate variability and cardiovascular mortality

The autonomic nervous system plays a major role in affecting the cardiac milieu and promoting malignant ventricular activity. The measurement of heart rate variability (HRV) is a noninvasive tool for assessing the status of the autonomic nervous system. A depressed HRV among post-myocardial infarction patients is a well-established risk factor for arrhythmic death. A reduced HRV has also been used to identify diabetic patients with autonomic neuropathy. This paper presents recent developments in the use of HRV, focusing on further refinement and validation of the use of both linear and nonlinear dynamics for sudden death prognostication, evaluation of the effect of specific pharmacologic agents on HRV, and assessment of HRV in health and in specific disease states that have been associated with an increased mortality risk.