Variations in breathing patterns increase low frequency contents in HRV spectra

Altered Relationship Between Heart Rate Variability and fMRI-Based Functional Connectivity in People With Epilepsy

Background: Disruptions in central autonomic processes in people with epilepsy have been studied through evaluation of heart rate variability (HRV). Decreased HRV appears in epilepsy compared to healthy controls, suggesting a shift in autonomic balance toward sympathetic dominance; recent studies have associated HRV changes with seizure severity and outcome of interventions. However, the processes underlying these autonomic changes remain unclear. We examined the nature of these changes by assessing alterations in whole-brain functional connectivity, and relating those alterations to HRV. Methods: We examined regional brain activity and functional organization in 28 drug-resistant epilepsy patients and 16 healthy controls using resting-state functional magnetic resonance imaging (fMRI). We employed an HRV state-dependent functional connectivity (FC) framework with low and high HRV states derived from the following four cardiac-related variables: 1. RR interval, 2. root mean square of successive differences (RMSSD), 4. low-frequency HRV (0.04-0.15 Hz; LF-HRV) and high-frequency HRV (0.15-0.40 Hz; HF-HRV). The effect of group (epilepsy vs. controls), HRV state (low vs. high) and the interactions of group and state were assessed using a mixed analysis of variance (ANOVA). We assessed FC within and between 7 large-scale functional networks consisting of cortical regions and 4 subcortical networks, the amygdala, hippocampus, basal ganglia and thalamus networks. Results: Consistent with previous studies, decreased RR interval (increased heart rate) and decreased HF-HRV appeared in people with epilepsy compared to healthy controls. For both groups, fluctuations in heart rate were positively correlated with BOLD activity in bilateral thalamus and regions of the cerebellum, and negatively correlated with BOLD activity in the insula, putamen, superior temporal gyrus and inferior frontal gyrus. Connectivity strength in patients between right thalamus and ventral attention network (mainly insula) increased in the high LF-HRV state compared to low LF-HRV; the opposite trend appeared in healthy controls. A similar pattern emerged for connectivity between the thalamus and basal ganglia. Conclusion: The findings suggest that resting connectivity patterns between the thalamus and other structures underlying HRV expression are modified in people with drug-resistant epilepsy compared to healthy controls.

Cardiohemodynamics and gas analysis rearrangements in response to re-breathing in young males of Russia’s Fareast

The objective of this study was to examine the changes occurred in the heart rate variability, cardiovascular system and gas analysis in response to the test with return breathing in young Caucasian and Native men residing in Magadan region and Chukotka Autonomous District. Methods — Total 345 young men were examined; of them 65 were Native people from Chukotka Autonomous District (ChAD) and 35 Natives from Magadan Region (MR) as well as Caucasians (48 from ChAD and 197 from MR, respectively). Results — Studies have shown that in response to the hypoxic-hypercapnic effect, there were changes in the cardiovascular system, heart rate and gas analysis, with a number of differences depending on ethnicity and the region of residence. Region-related features of cardiohemodynamics were manifested by a more pronounced increase in the systolic blood pressure and heart rate in response to the re-breathing test in the two ethnic groups living in ChAD, which was observed against the background of higher values of the difference “baseline-test” in carbon dioxide levels in the exhaled air. Ethnic differences in our studies were seen due to the pronounced increase in response to the test for the activity of the parasympathetic link of the autonomic nervous system (increased TP and HF), at the background of a decrease in VLF observed only among Caucasians, which was associated with the lowest oxygen concentration in the exhaled air at the peak of the test. It was found that the significant differences in gas analysis identified at rest and at the peak of the test as well as rearrangements of the heart rate and cardiovascular system characteristics in response to the re-breathing in the young subjects residing in different regions of northeast Russia and belonging to different ethnic groups can serve as informative criteria reflecting the region caused ethnic characteristics of the organism. Conclusion — It was found, the most visible and informative parameters for the differences in dynamics of the studied systems demonstrated by the subjects of the two ethnic groups in the two observed regions of the Far East in response to a hypoxic-hypercapnic test with return breathing have been the spectral characteristics of the heart rate (TP, HF, VLF) and gas analysis with the calculation of the difference between the baseline and the peak values (difference in the CO2 and O2 concentration of the test-baseline).

The effects of slow-paced versus mechanically assisted breathing on autonomic function in fibromyalgia patients

Paced breathing has shown efficacy in fibromyalgia (FM), but the mechanisms associated with symptom change are largely unknown. We investigated whether changes in respiratory rate (RR) alone resulted in autonomic changes during normal, paced, and mechanically assisted breathing in untrained FM patients and controls. Participants included 20 FM patients and 14 controls matched for age and body mass index. During a single visit, participants completed three 15-minute breathing sessions: 1) normal breathing, 2) slow-paced breathing, and 3) mechanically assisted breathing (continuous positive airway pressure) while supine. Continuous blood pressure and electrocardiogram were recorded, and measures of heart rate variability (HRV) and spontaneous baroreceptor sensitivity (sBRS) were calculated. During normal breathing, FM patients had higher heart rate (HR), but lower HRV and sBRS variables compared to controls with no difference in RR. Compared to the paced breathing condition, FM patients had significantly lower HR with higher HRV and sBRS variables during mechanically assisted breathing, despite no significant change in RR. Mechanically assisted breathing provided greater benefits in autonomic function than paced breathing in untrained FM patients. Future research will be needed to elucidate the central pathways involved in these autonomic changes and whether training in paced breathing can eventually replicate the results seen in mechanically assisted patients.

The effect of continuous positive airway pressure on heart rate variability during the night in patients with chronic heart failure and central sleep apnoea

Continuous positive airway pressure (CPAP) improves autonomic activity in patients with chronic heart failure (CHF) and central sleep apnoea (CSA), but its effect on heart rate variability (HRV) during therapy has not been reported. We hypothesized that CPAP may decrease HRV, despite its beneficial effects on sympathetic overactivation, due to the expected stabilization of breathing. Sixty-seven CHF patients underwent polysomnography (PSG). Ten of them presented with CSA (age 66.1±8.5 years, apnoea-hypopnea index [AHI]=57.6±23.3, central AHI [cAHI]=41.6±24.6 [mean±SD]) and were subjected to a second PSG with manual CPAP titration. Beat-to-beat heart intervals for a 6-hour period of sleep were extracted from each recording and HRV was analysed. CPAP significantly reduced AHI (AHI=23.1±18.3 P=.004). Standard deviation of normal-normal interbeat interval (SDNN) (61.5±29.0 vs 49.5±19.3 ms, P=.021), root mean square of successive differences (RMSSD) (21.8±9.2 vs 16.4±7.1 ms, P=.042), total power (lnTP=7.8±1.1 vs 7.4±0.8 ms² , P=.037), low frequency power (lnLF=5.5±1.5 vs 5.0±1.4 ms² , P=.003) and high frequency power (lnHF=4.6±1.0 vs 4.0±1.0 ms² , P=.024) were decreased. There was a strong correlation between the decrease in AHI and the decrease in lnHF (Spearman's ρ=.782). CPAP leads to a decrease in spectral and time domain parameters of HRV during therapy in CHF patients with CSA. These changes are best explained by the effect which CPAP-influenced breathing pattern and lowered AHI exert on HRV.

The Ornstein-Uhlenbeck third-order Gaussian process (OUGP) applied directly to the un-resampled heart rate variability (HRV) tachogram for detrending and low-pass filtering

The heart rate variability signal derived from the ECG is a beat-to-beat record of RR-intervals and is, as a time series, irregularly sampled. It is common engineering practice to resample this record, typically at 4 Hz, onto a regular time axis for conventional analysis using IIR and FIR filters, and power spectral estimators, in the time and frequency domain, respectively. However, such interpolative resampling introduces noise into the signal and the information quality is compromised. Here, the Ornstein-Uhlenbeck third-order band-pass filter is presented which operates on data sampled at arbitrary time and preserves fidelity. The algorithm is available as open source code for MATLAB(®) (MathWorks™ Inc.) and supported by an interactive website at http://clinengnhs.liv.ac.uk/OUGP.htm.

Estimation of the Uncertainty in Time Domain Indices of RR Time Series

A method for estimating the uncertainty in time-domain indices of RR time series is described. The method relies on the central limit theorem that states that the distribution of a sample average of independent samples has an uncertainty that asymptotically approaches to the sample standard deviation divided by the square root of the number of samples. Because RR time series cannot be characterized by a set of independent samples, we propose to estimate the uncertainty of indices by computing them in blocks that satisfy that the obtained partial indices are independent. We propose a methodology to search sets of independent partial indices and apply this methodology to the estimation of the uncertainty in the mean RR, SDRR, and r-msDD indices. The results show that the uncertainty can be higher than the 10% of the index for the SDRR and even higher for the r-msDD. Moreover, a statistical test for the difference of two indices is proposed.

Relationships between pulse wave velocity and heart rate variability in healthy men with a range of moderate-to-vigorous physical activity levels

Pulse wave velocity (PWV) is associated with heart rate variability (HRV) in 24-39-year-old men. This study of 40-65-year-old men ranging in moderate-to-vigorous physical activity levels investigated whether (a) PWV is related to spectral HRV, (b) using normalised units for HRV influences that relationship, and (c) HRV predicts PWV when other factors, including age and blood pressure, are accounted for. Subjects were healthy men (N=115), mean (SD) age 50.8 (7.1) years. Carotid-femoral PWV was measured using Complior. HRV was derived from a 5 min ECG for total, high-frequency, and low-frequency power (TP, HF, and LF, respectively), the LF/HF ratio, and normalised units for HF (HFnu) and LF (LFnu). Non-parametric data were natural log-transformed. PWV was 8.5 (1.4) m s-1. TP, HF, LF, LF/HF, HFnu and LFnu were 1908 (2195) m s2, 577 (1034) m s2, 457 (514) m s2, 1.5 (1.3), 46.8 (17.9), and 49.4 (19.4), respectively. PWV was inversely associated with TP (R2=0.061, p=0.008), HF (R2=0.095, p=0.001), LF (R2=0.086, p=0.002) and HFnu (R2=0.040, p=0.031), but was not associated with LF/HF (R2=0.020, p=0.136) or LFnu (R2=0.028 p=0.076). Only age and systolic blood pressure (adjusted R2=0.306, p<0.001) predicted PWV in multivariate analysis. This study has shown that PWV was weakly associated with TP and HF. The use of normalised units only influenced the relationship between PWV and LF. Finally, relationships between PWV and HRV are mediated through age and systolic blood pressure in this population of men ranging in moderate-to-vigorous physical activity level.

Can brain dysfunction be a predisposing factor for metabolic syndrome?

The various mechanisms that may explain the association between brain dysfunction and the pathogenesis of metabolic syndrome (MS) leading to cardiovascular disease and type 2 diabetes have been reviewed. A Medline search was conducted until September 2003, and articles published in various national and international journals were reviewed. Experts working in the field were also consulted. Compelling evidence was found that saturated and total fat and low dietary n-3 fatty acids and other long-chain polyunsaturated fatty acids (PUFAs) in conjunction with sedentary behavior and mental stress combined with various personality traits can enhance sympathetic activity and increase the secretion of catecholamine, cortisol and serotonin, all of which appear to be underlying mechanisms involved in MS. Excess secretion of these neurotransmitters in conjunction with underlying long-chain PUFA deficiency may damage the neurons in the ventromedial hypothalamus and insulin receptors in the brain, in particular during fetal life, infancy and childhood, and lead to their dysfunction. Since 30-50% of the fatty acids in the brain are long-chain PUFAs, especially omega-3 fatty acids which are incorporated in the cell membrane phospholipids, it is possible that their supplementation may have a protective effect. Omega-3 fatty acids are also known to enhance parasympathetic activity and to increase the secretion of anti-inflammatory cytokines as well as acetylecholine in the hippocampus. It is possible that a marginal deficiency of long-chain PUFAs, especially n-3 fatty acids, due to poor dietary intake during the critical period of brain growth and development in the fetus, and later in the infant and also possibly in the child, adolescent and adult may enhance the release of tumor necrosis factor-alpha (TNF-alpha) interleukin (IL)-1, 2 and 6 and cause neuronal dysfunction. Experimental studies indicate that ventromedial hypothalamic lesions in rats induce hyperphagia, resulting in glucose intolerance and insulin resistance. Treatment with neuropeptide Y abolished hyperphagia and ob mRNA (leptin mRNA) in this animal model. Long-term infusion of norepinephrine and serotonin into the ventromedial hypothalamus impaired pancreatic islet function inasmuch as ventromedial hypothalamic norepinephrine and serotonin levels were elevated in hyperinsulinemic and insulin-resistant animals. Treatment with insulin was associated with restoration of hypothalamic neurotransmitter abnormalities, indicating that ventromedial hypothalamus dysfunction can impair pancreatic beta cells resulting in metabolic abnormalities consistent with MS. Treatment with omega-3 fatty acids, beta blockers, ACE inhibitors, estrogen, and meditation may have a beneficial effect on insulin receptors and ventromedial hypothalamic dysfunction. However, no definite or precise insight into the pathophysiological link between MS, brain function and nutrition is available. Despite this, epidemiological studies and intervention trials indicate that treatment with n-3 fatty acids may be adopted in clinical practice and used to direct therapy for prevention of type 2 diabetes, hypertension, coronary artery disease (CAD), and atherosclerosis, thereby indicating that MS may also respond to this treatment.

A new index for the analysis of heart rate variability dynamics: characterization and application

A new index for the analysis of the heart rate variability (HRV) dynamics is presented. The proposed index (acceleration change index (ACI)) characterizes the sign of the differences of a time series. A theoretical study shows an expression that relates ACI and the autocorrelation function of the time series. This formula is tested and validated with different simulated time series (uncorrelated noise, sinusoidal and fractional Brownian motion). Next, ACI is applied to RR time series from healthy subjects showing that ACI decreases with periodic controlled breathing, increases during exercise, and it has a lower value at night than during the day. In a preliminary study, ACI has been shown to be lower in healthy subjects than in patients who had suffered a myocardial infarction one month previously. ACI can be employed as a fast and robust new marker of the HRV dynamics.

Circadian heart rate and blood pressure variability considered for research and patient care

OBJECTIVES

To review mechanisms of circadian variations in heart rate variability (HRV) and blood pressure variability (BPV) and mortality and morbidity due to cardiovascular diseases (CVD).

METHODS

Results from 7-day/24-h HRV and BPV are interpreted by gender and age-specified reference values in the context of a Medline search.

RESULTS

Abnormal HRV and BPV measured around the clock for 7 days provides information on the risk of subsequent morbid events in subjects without obvious heart disease and without abnormality outside the conventional (in the sense of chronobiologically unquantified) physiological range. Meditation, beta-blockers, ACE inhibitors, n-3 fatty acids and estrogens may have a beneficial influence on HRV, but there is no definitive outcome-validated therapy. Low HRV has been associated with a risk of arrhythmias and arrhythmic death, unstable angina, myocardial infarction, progression of heart failure and atherosclerosis. BPV may be characterized by treatable circadian-hyper-amplitude-tension (CHAT), which can be transient '24-h CHAT' or '7-day-CHAT', MESOR-hypertension and/or an unusually-timed (odd) circadian acrophase (ecphasia), all associated with an increased risk of stroke, stroke death, myocardial infarction, and kidney disease.

CONCLUSIONS

Precise insight into the patho-physiology in time of HRV and BPV is needed with development of a consensus on best measures of HRV for clinical purposes and to determine when a 7-day record interpreted chronobiologically suffices and when it does not, for detection within as well as outside the conventional normal range, for diagnostic clinical practice and to direct therapy of risk greater than that associated with hypertension, smoking or any other risk factor.

Can nutrition influence circadian rhythm and heart rate variability?

Recent studies indicate that there is an interaction between biorhythms, the biological clock and triggers, which may be important in the pathogenesis of altered heart rate variability (HRV) and blood pressure variability (BPV). Circadian rhythms are under the influence of, and physiological variables are mediated by the activation of the adrenals, sympathetic/parasympathetic, hypothalamic and pituitary activity. Emotional stress, physical exertion, sleep deprivation and large fatty meals are major triggers of myocardial ischemia, angina, infarction, sudden cardiac death (SCD) and stroke. These events have been reported to exhibit a circadian variation with increased frequency in the second quarter of the day, which has also been observed in our studies on Indians. Recent studies indicate that altered HRV and BPV are also important in the pathogenesis and progression of heart failure, atheroma and thrombosis. Mediation via beta-blockers, oestrogens, n-3 fatty acids, vitamin E and coenzyme Q10 and fasting appears to have a beneficial influence whereas progestins, nifedipine, stress and exercise may have an adverse effect on HRV and BPV. We have reported that plasma levels of vitamin E and C are lower in the second quarter of the day than at other times, indicating their role in the pathogenesis of variability and cardiac events. Prospective studies also indicate that HRV and BPV are important and independent risk factors for cardiovascular events. However, no study has yet been conducted in patients with abnormal HRV and BPV in a randomized, placebo-controlled intervention trial to find out whether improvement in variability can cause a significant reduction in cardiovascular events. There is a need to study the role of n-3 fatty acids, coenzyme Q10, the effect of regular physical training, medication and ACE inhibitors in patients with abnormal HRV and BPV to demonstrate that improving variability can modulate cardiovascular events.