Effects of high-carbohydrate and high-fat dietary treatments on measures of heart rate variability and sympathovagal balance

Fat intake impairs the recovery of endothelial function following mental stress in young healthy adults

Introduction

Mental stress has been identified as a trigger of cardiovascular events. A single episode of stress can induce acute impairments in endothelial function in healthy adults. Importantly, during stressful periods, individuals often resort to unhealthy behaviors, such as increased consumption of high-fat foods, which is also known to negatively impact endothelial function. Therefore, this study examined whether consumption of a high-fat meal would further exacerbate the negative effect of mental stress on vascular function.

Methods

In a randomized, counterbalanced, cross- over, postprandial intervention study, 21 healthy males and females ingested a high-fat (56.5 g fat) or a low-fat (11.4 g fat) meal 1.5 h before an 8-min mental stress task (Paced-Auditory-Serial-Addition-Task, PASAT). Plasma triglyceride (TAG) concentration was assessed pre-and post-meal. Forearm blood flow (FBF), blood pressure (BP), and cardiovascular activity were assessed pre-meal at rest and post-meal at rest and during stress. Endothelial function, measured by brachial flow-mediated dilatation (FMD) was assessed pre-meal and 30 and 90 min following mental stress.

Results

Plasma TAG concentration was significantly increased following the high-fat meal compared to the low-fat condition. Mental stress induced similar increases in peripheral vasodilation, BP, and cardiovascular activity, and impaired FMD 30 min post-stress, in both conditions. FMD remained significantly impaired 90 min following stress in the high-fat condition only, suggesting that consumption of fat attenuates the recovery of endothelial function following mental stress.

Discussion

Given the prevalence of fat consumption during stressful periods among young adults, these findings have important implications for dietary choices to protect the vasculature during periods of stress.

Nonlinear Conte-Zbilut-Federici (CZF) Method of Computing LF/HF Ratio: A More Reliable Index of Changes in Heart Rate Variability

Objectives:

Acupuncture treatments are safe and effective for a wide variety of diseases involving autonomic dysregulation. Heart rate variability (HRV) is a noninvasive method for assessing sympathovagal balance. The low frequency/high frequency (LF/HF) spectral power ratio is an index of sympathovagal influence on heart rate and of cardiovascular health. This study tests the hypothesis that from rest to 30% to 50% of peak oxygen consumption, the nonlinear Conte-Zbilut-Federici (CZF) method of computing the LF/HF ratio is a more reliable index of changes in the HRV than linear methods are.

Methods:

The subjects of this study were 10 healthy young adults. Electrocardiogram RR intervals were measured during 6-minute periods of rest and aerobic exercise on a cycle ergometer at 30% and 50% of peak oxygen consumption (VO_2peak).

Results:

The frequency domain CZF computations of the LF/HF ratio and the time domain computations of the standard deviation of normal-to-normal intervals (SDNN) decreased sequentially from rest to 30% VO_2peak (P < 0.001) to 50% VO_2peak (P < 0.05). The SDNN and the CZF computations of the LF/HF ratio were positively correlated (Pearson’s r = 0.75, P < 0.001). fast Fourier transform (FFT), autoregressive (AR) and Lomb periodogram computations of the LF/HF ratio increased only from rest to 50% VO_2peak.

Conclusion:

Computations of the LF/HF ratio by using the nonlinear CZF method appear to be more sensitive to changes in physical activity than computations of the LF/HF ratio by using linear methods. Future studies should determine whether the CZF computation of the LF/HF ratio improves evaluations of pharmacopuncture and other treatment modalities.

Differentiation of Overweight from Normal Weight Young Adults by Postprandial Heart Rate Variability and Systolic Blood Pressure

INTRODUCTION

Obesity and cardiovascular disease are inextricably linked and the health community's response to the current epidemic of adolescent obesity may be improved by the ability to target adolescents at highest risk for developing cardiovascular disease in the future. Overweight manifests early as autonomic dysregulation and current methods do not permit differentiation of overweight adolescents or young adults at highest risk for developing cardiovascular disease.

AIM

This study was designed to test the hypothesis that scaling exponents motivated by nonlinear fractal analyses of Heart Rate Variability (HRV) differentiate overweight, otherwise healthy adolescent/young adult subjects at risk for developing prehypertension, the primary forerunner of cardiovascular disease.

MATERIALS AND METHODS

The subjects were 18-20year old males with Body Mass Index (BMI) 20.1-42.5kg/m(2). Electrocardiographic inter-beat (RR) intervals were measured during 3h periods of bed rest after overnight fasting and ingestion of 900Cal high-carbohydrate and high-fat test beverages on separate days. Detrended Fluctuation Analysis (DFA), k-means cluster and ANOVA analyses of scaling coefficients α, α(1), and α(2), showed dependencies on hourly measurements of systolic blood pressure and on premeasured BMI.

RESULTS

It was observed that α value increased during the caloric challenge, appears to represent metabolically-induced changes in HRV across the participants. An ancillary analysis was performed to determine the dependency on BMI without BMI as a parameter. Cluster analysis of the high-carbohydrate test beverage treatment and the high-fat treatment produced grouping with very little overlap. ANOVA on both clusters demonstrated significance at p<0.001. We were able to demonstrate increased sympathetic modulation of our study group during ingestion and metabolism of isocaloric high-carbohydrate and high-fat test beverages.

CONCLUSION

These findings demonstrate significantly different clustering of α, α1, and α2 and Systolic Blood Pressure (SBP) with respect to normal, overweight and obese BMI.

Effects of Nitrate Supplementation on Cardiovascular and Autonomic Reactivity in African-American Females

Previous studies have shown that beetroot juice (BJ) decreases systolic blood pressure (SBP) and oxygen demand. This study tests the hypothesis that a beetroot juice (BJ) treatment increases heart rate variability (HRV) measured by the average standard deviation of normal-normal electrocardiogram RR intervals (SDNN) and the low frequency (LF), mainly sympathetic, fast Fourier transform spectral index of HRV. The subjects were 13 healthy young adult African-American females. Placebo control orange juice (OJ) and BJ treatments were given on separate days. Blood nitric oxide [NO], SBP and RR intervals were measured at rest and at constant workloads set to 40% and 80% of the predetermined VO_2peak. Two hours after ingestion the BJ treatment increased [NO] and decreased SBP. BJ also increased SDNN at rest and at the 40% VO_2peak workload, without significant effects on LF. SDNN was significantly greater after the BJ than after the OJ treatment, across the two physical activity conditions and SDNN was (negatively) correlated with SBP. These results suggest that BJ decreases SBP and increases HRV at rest and during aerobic exercise. Similar results in subjects with prehypertension or hypertension could translate to a dietary nitrate treatment for hypertension.

Metabolic energy correlates of heart rate variability spectral power associated with a 900-calorie challenge

We studied healthy males challenged with a 900 Cal test beverage and correlated EE with the raw (ms²) and normalized units (nu) of total power (TP), low frequency/high frequency (LF/HF) and VLF spectral power of heart rate variability (HRV). The correlations were evaluated during 20 min of normal breathing (NB, control) and 20 min of paced breathing (PB) at 12 breaths·min⁻¹ (0.2 Hz). EE was not significantly correlated with any of the HRV variables before the metabolic challenge. After the challenge, EE was positively correlated with LF/HF and with VLF; VLF was also positively correlated with LF/HF during both NB and PB. These findings suggest that EE may be a correlate of LF/HF and of VLF spectral power of HRV in healthy adolescent/young adult males. The association of lower resting energy expenditure with lower amounts of VLF spectral power may occur in individuals with predilections for obese phenotypes.

Mediterranean dietary pattern is associated with improved cardiac autonomic function among middle-aged men: a twin study

BACKGROUND

Reduced heart rate variability (HRV), a measure of cardiac autonomic dysfunction, is a risk factor for coronary artery disease. Diet can influence HRV, but this association may be confounded by genetic and environmental factors.

METHODS AND RESULTS

We administered the Willett Food Frequency Questionnaire to 276 middle-aged male twins. We derived a score measuring the extent to which an individual's diet conformed to the Mediterranean diet following a published algorithm. The higher the score, the greater the similarity to the Mediterranean diet. All twins underwent 24-hour ambulatory ECG recording. Time and frequency domain measures of HRV were calculated. Mixed-effects regression was used to partition the association into between- and within-twin pair differences. After adjusting for energy intake, other nutritional factors, shared genes, and common environment, a 1-unit higher score was significantly associated with 3.9% to 13% higher time and frequency domain HRV parameters. Further controlling for known cardiovascular risk factors and use of fish oil supplements and medications did not substantially change the estimates.

CONCLUSIONS

The Mediterranean dietary pattern is associated with higher HRV.

Mechanism of impaired baroreflex sensitivity in Wistar rats fed a high-fat and -carbohydrate diet

Both high-fat and high-carbohydrate diets have been considered in association with the impairment of baroreflex sensitivity. However, the mechanisms are unclear. In the present study, the effects of a complex high-fat and high-carbohydrate diet (HFCD) on baroreflex circuitry were investigated. A HFCD emulsion was formulated and orally administered to rats for 30 d. Rats were then anaesthetised and baroreflex sensitivity was measured following intravenous injection of phenylephrine (PE) and sodium nitroprusside (SNP) at various doses. Morphological changes of the brainstem were detected by transmission electron microscopy. Baroreflex sensitivity-associated gene and protein expression was determined by quantitative RT-PCR and Western blot analysis. We found that: (1) the HFCD significantly attenuated heart rate responses to arterial blood pressure (ABP) increases induced by PE, but had no effect on heart rate responses to ABP decreases induced by SNP; (2) the HFCD induced medullary sheath thickening, myelinated nerve atrophy and hyaloplasm dissolving; (3) protein levels of substance P, calcitonin gene-related peptide, GlutR2 and γ-aminobutyric acid A receptors were all markedly decreased in the brainstems of rats administered with the HFCD. These findings conclude that a HFCD could impair the baroreflex sensitivity of rats. Remodelled morphology and decreased neurotransmitters and receptors in the domains of the nucleus tractus solitarii and nucleus ambiguus are participating in this process.

Association of body fat percentage and heart rate variability measures of sympathovagal balance

AIMS

We tested the hypothesis that body fat percentage determines cardiac sympathovagal balance in healthy subjects.

MAIN METHODS

Heart rate variability (HRV) measurements were made of the standard deviation of the normal-normal RR intervals (SDNN) and the low frequency/high frequency (LF/HF) ratio, from time domain and fast Fourier transform spectral analysis of electrocardiogram RR intervals during trials of uncontrolled and controlled (paced) breathing at 0.2Hz. Body fat percentage was measured by dual energy x-ray absorptiometric (DEXA) scanning. Significance of differences between uncontrolled and controlled (paced) breathing was determined by analysis of variance and correlations between body fat percentage and HRV measurements by Pearson's coefficient at P<0.05.

KEY FINDINGS

Percent body fat was negatively correlated with LF/HF during the uncontrolled breathing (r=-0.56, two-tailed P<0.05, one-tailed P<0.01) but not during the paced breathing trial (r=-0.34, (P>0.1).

SIGNIFICANCE

We conclude that sympathetic activity produced by paced breathing at 0.2Hz can obscure the relationship between body fat percentage and sympathovagal balance and that high body fat percentage may be associated with low sympathetic modulation of the heart rate in healthy adolescent/young adult males.