Low-frequency Oscillations In Heart Rate Research Articles

Synchronization of the Processes of Autonomic Control of Blood Circulation in Humans Is Different in the Awake State and in Sleep Stages.

The influence of higher nervous activity on the processes of autonomic control of the cardiovascular system and baroreflex regulation is of considerable interest, both for understanding the fundamental laws of the functioning of the human body and for developing methods for diagnostics and treatment of pathologies. The complexity of the analyzed systems limits the possibilities of research in this area and requires the development of new tools. Earlier we propose a method for studying the collective dynamics of the processes of autonomic control of blood circulation in the awake state and in different stages of sleep. The method is based on estimating a quantitative measure representing the total percentage of phase synchronization between the low-frequency oscillations in heart rate and blood pressure. Analysis of electrocardiogram and invasive blood pressure signals in apnea patients in the awake state and in different sleep stages showed a high sensitivity of the proposed measure. It is shown that in slow-wave sleep the degree of synchronization of the studied rhythms is higher than in the awake state and lower than in sleep with rapid eye movement. The results reflect the modulation of the processes of autonomic control of blood circulation by higher nervous activity and can be used for the quantitative assessment of this modulation.

Mathematical modeling of the cardiovascular autonomic control in healthy subjects during a passive head-up tilt test

A mathematical model is proposed for the autonomic control of cardiovascular system, which takes into account two separated self-exciting sympathetic control loops of heart rate and peripheral vascular tone. The control loops are represented by self-exciting time-delay systems and their tone depends on activity of the aortic, carotid, and lower-body baroreceptors. The model is used to study the dynamics of the adaptive processes that manifest in a healthy cardiovascular system during the passive head-up tilt test. Computer simulation provides continuous observation of the dynamics of the indexes and variables that cannot be measured in the direct experiment, including the noradrenaline concentration in vessel wall and heart muscle, tone of the sympathetic and parasympathetic control, peripheral vascular resistance, and blood pressure. In the supine and upright positions, we estimated the spectral characteristics of the model variables, especially in the low-frequency band, and the original index of total percent of phase synchronization between the low-frequency oscillations in heart rate and blood pressure signals. The model demonstrates good quantitative agreement with the dynamics of the experimentally observed indexes of cardiovascular system that were averaged for 50 healthy subjects.

Mobile Device for Monitoring of Cardiovascular System State Based on Assessment of Synchronization of its Low-Frequency Rhythms

We develop an autonomous mobile device for continuous monitoring of cardiovascular system functional state, which is based on the assessment of synchronization between the low-frequency oscillations in heart rate and blood flow having a basic frequency close to 0.1 Hz.

Synchronization of low-frequency oscillations in the human cardiovascular system

We investigate synchronization between the low-frequency oscillations of heart rate and blood pressure having in humans a basic frequency close to 0.1 Hz. A method is proposed for quantitative estimation of synchronization between these oscillating processes based on calculation of relative time of phase synchronization of oscillations. It is shown that healthy subjects exhibit on average substantially longer epochs of internal synchronization between the low-frequency oscillations in heart rate and blood pressure than patients after acute myocardial infarction.

Letter Regarding Article by Wichterle et al, “Prevalent Low-Frequency Oscillation of Heart Rate: Novel Predictor of Mortality After Myocardial Infarction”

To the Editor: Wichterle et al recently presented in this journal a novel parameter of heart rate variability called prevalent low-frequency oscillation of heart rate (PLF).1 Using 2 groups of postinfarction patients derived from the EMIAT (European Myocardial Infarction Amiodarone Trial) and ATRAMI (Autonomic Tone and Reflexes After Myocardial Infarction) studies, they specifically compared and showed a predictive value for PLF that was stronger than that for heart rate turbulence (HRT) parameters using univariate analysis. They further showed that with Cox’s multivariate regression model, the relative risk for PLF remained high (4.6 and 3.6 in EMIAT and ATRAMI, respectively), whereas HRT parameters turbulence slope and turbulence onset lost their independence. Their study is noteworthy because in previous comparisons of measures of HRT and heart rate variability in large studies, HRT has consistently outperformed heart rate variability.2–4 We would like to point out that the prognostic ability of risk factors is changing significantly with declining mortality from acute ischemic events as a …

Heart rate dynamics during three forms of meditation

Objective: This study was designed to quantify and compare the instantaneous heart rate dynamics and cardiopulmonary interactions during sequential performance of three meditation protocols with different breathing patterns. Background: We analyzed beat-to-beat heart rate and continuous breathing signals from 10 experienced meditators (4 females; 6 males; mean age 42 years; range 29–55 years) during three traditional interventions: relaxation response, breath of fire, and segmented breathing. Results: Heart rate and respiratory dynamics were generally similar during the relaxation response and segmented breathing. We observed high amplitude, low frequency (∼0.05–0.1 Hz) oscillations due to respiratory sinus arrhythmia during both the relaxation response and segmented breathing, along with a significantly ( p<0.05) increased coherence between heart rate and breathing during these two maneuvers when compared to baseline. The third technique, breath of fire, was associated with a different pattern of response, marked by a significant increase in mean heart rate with respect to baseline ( p<0.01), and a significant decrease in coherence between heart rate and breathing ( p<0.05). Conclusions: These findings suggest that different meditative/breathing protocols may evoke common heart rate effects, as well as specific responses. The results support the concept of a “meditation paradox,” since a variety of relaxation and meditative techniques may produce active rather than quiescent cardiac dynamics, associated with prominent low frequency heart rate oscillations or increases in mean resting heart rate. These findings also underscore the need to critically assess traditional frequency domain heart rate variability parameters in making inferences about autonomic alterations during meditation with slow breathing.

Influence of Cheyne-Stokes respiration on cardiovascular oscillations in heart failure.

In patients with congestive heart failure, Cheyne-Stokes respiration is accompanied by oscillations in blood pressure and heart rate at a very low frequency. It is not known whether these cardiovascular oscillations are primarily related to oscillations in ventilation or oxyhemoglobin saturation. We hypothesized that abolition of the ventilatory oscillations of Cheyne-Stokes respiration by CO2 inhalation would eliminate accompanying oscillations in blood pressure and heart rate but that elimination of hypoxic dips by supplemental O2 would not. We studied 10 subjects with heart failure and Cheyne-Stokes respiration during sleep using frequency spectral analysis. During Cheyne-Stokes respiration, heart rate and blood pressure oscillated in association with respiratory oscillations at very low frequency. Inhalation of CO2 abolished Cheyne-Stokes respiration and associated oscillations in both blood pressure and heart rate. In contrast, inhalation of O2 sufficient to eliminate hypoxic dips had no significant effect on Cheyne-Stokes respiration, blood pressure (n = 6), or heart rate (n = 5). We conclude that ventilatory oscillations during Cheyne-Stokes respiration rather than oscillations in oxygenation per se powerfully induce heart rate and blood pressure oscillations. Cheyne-Stokes respiration is therefore one of the mechanisms that contributes to the very low-frequency oscillations in heart rate and blood pressure observed in patients with heart failure.

Prevalent low-frequency oscillation of heart rate is a powerful predictor of postinfarction mortality: Comparison of two computational methods

Prevalent low-frequency oscillation of heart rate is a powerful predictor of postinfarction mortality: Comparison of two computational methods

Prevalent low-frequency oscillation of heart rate is the strongest risk stratifier independent of all available mortality predictors in the placebo population of EMIAT trial

Prevalent low-frequency oscillation of heart rate is the strongest risk stratifier independent of all available mortality predictors in the placebo population of EMIAT trial

P3285 Composite index consisting of prevalent low-frequency oscillation of heart rate and turbulence slope is an optimum predictor of mortality in the placebo arm of EMIAT trial

P3285 Composite index consisting of prevalent low-frequency oscillation of heart rate and turbulence slope is an optimum predictor of mortality in the placebo arm of EMIAT trial

2694 Prevalent low-frequency oscillation of heart rate was validated as a strong risk stratifier in the population of ATRAMI trial

2694 Prevalent low-frequency oscillation of heart rate was validated as a strong risk stratifier in the population of ATRAMI trial

P946 Prevalent low-frequency oscillation of heart rate probably reflects fractal properties of heart rate variability

P946 Prevalent low-frequency oscillation of heart rate probably reflects fractal properties of heart rate variability

Low-frequency oscillation of instantaneous heart rate in newly hatched chicks

Instantaneous heart rate (IHR) of chickens began to fluctuate on days 13–14 of incubation and heart rate (HR) fluctuations became augmented towards hatching and increased further after hatching. IHR fluctuations of newly hatched chicks have been categorized into three types: type I HR variability (HRV), which is high-frequency oscillation; type II HRV, which is low-frequency oscillation; and type III HR irregularities (HRI), which are irregular HR accelerations. The present experiment was carried out to investigate the origin of type II HR oscillations. Following previous evidence, we assumed that the low-frequency oscillation of HR in newly hatched chicks was related to thermoregulation and changed by environmental temperature. Eventually, type II HRV was produced or augmented by exposure of hatchlings to lowered ambient temperature and was abolished by exposure to elevated environmental temperature. The hatchlings that were exposed to large temperature decreases tended to increase their HR more than those exposed to small temperature decreases, and vice versa. The HR oscillation accompanied by an elevation of HR baseline in response to cooling may be a phenomenon related to thermoregulation in chick hatchlings.

Deglutition-induced tachycardia and spectral analysis of the heart rate

In healthy subjects at rest, swallowing is accompanied by a tachycardiac or tachycardiac-bradycardiac reaction, during which the heart rate can be accelerated by as much as 20 beats/min. The duration of these reactions is comparable to the period of regular low-frequency heart rate oscillations, thereby their occurrence during ECG recordings for heart rate spectral analysis leads to overestimation of low-frequency oscillation power. Using a special method of smoothing of single tachycardia waves, we found that in young healthy subjects the mean contribution of deglutition-induced tachycardia waves to the power of low-frequency heart rate oscillations is 42%.

Effect of periodic thermal stimulus on heart rate in term newborn infant

We studied heart rate changes in 25 term infants aged 1-7 days in quiet sleep during periodic thermal stimulation of one foot to widen the range of frequencies previously studied by others and to develop spectral analysis methods to quantify responses to thermal and other periodic sensory stimuli. The stimulation frequency was 0.10 Hz in all babies and ranged from 0.05 to 0.15 Hz in some. At 0.10 Hz, there was 1) an increase in spectral power at the frequency of stimulation (P < 0.001), 2) a tendency for overall low-frequency power to increase, 3) a reduction in respiratory sinus arrhythmia (P < 0.025), and 4) attenuation in the response between the first and second minute of stimulation (P < 0.01). At other frequencies of stimulation, essentially similar results were obtained. Respiration and other types of periodic sensory stimulation may also entrain the heart rate; we raise the question of whether low-frequency oscillations in heart rate are in fact related to thermoregulation or are a nonspecific feature of integrative processes in the brain stem.

Rapid Development of Nitrate Tolerance in Healthy Volunteers

Summary: Nitrate tolerance is characterized by a loss of nitroglycerin (NTG) vasodilating and hypotensive effects during continuous administration, but is difficult to detect clinically. We hypothesized that the decrease in arterial blood pressure (BP) and the reflex sympathetic activation and tachycardia due to baroreflex deactivation associated with rapid intravenous (i.v.) infusion of NTG would be decreased during continuous NTG patch therapy as a result of tolerance to transdermal NTG. Sympathetic activation was measured as the change in amplitude of lowfrequency (66-129 mHz) oscillations in BP and heart rate (HR) recorded by a noninvasive method. Eleven healthy male volunteers received rapid i.v. infusion of 0.45 mg NTG in 1 min on 3 consecutive days: before NTG patch, after 22.5 h of patch therapy, and 22.5 h after patch removal. The maximum decrease in systolic BP (SBP) and maximum reflex tachycardia as well as the sympathetic activation produced by i.v. NTG were compared during each of the three study periods. The maximum decrease in SBP was 38 ± 8 mm Hg before NTG patch and 27 ± 15 mm Hg during NTG patch (p < 0.05), with return to baseline values (37 ± 13 mm Hg) after patch removal. There was no significant change in amplitude of reflex tachycardia among study periods. However, low-frequency oscillations in SBP increased by 40 ± 31% in the absence of NTG patch and by only 9 ± 35% after 22.5 h of patch therapy (p < 0.05). Patch removal resulted in a significant rebound increase in these oscillations (70 ± 51%; p < 0.05 vs. baseline). Similar results were noted when sympathetic activation was assessed as the change in lowfrequency oscillations in HR. We conclude that nitrate tolerance develops rapidly and can be assessed by the change in BP and HR oscillations produced by i.v. NTG administration.

Cerebral autoregulation of preterm neonates--a non-linear control system?

The low frequency cerebral blood flow velocity (CBFV) oscillations in neonates are commonly attributed to an under-dampened immature linear type cerebral autoregulation, and the 'instability' is regarded as causative for peri-intraventricular haemorrhage/periventricular leukomalacia. In contrast, oscillations susceptible to frequency entrainment are a fundamental part of the stable function of non-linear control systems. To classify the autoregulation an observational study was done on the relationship between CBFV oscillations, heart rate variability, and artificial ventilation. In 10 preterm neonates (gestational age 26 to 35 weeks) we serially Doppler traced arterial CBFV continuously for 12 minutes between days 1 and 49 of life. The individual time series of CBFV and heart rate were subjected to spectral analysis. Forty six of 47 tracings showed significant low frequency CBFV oscillations. Low frequency heart rate oscillations were not a prerequisite thereof. All patients with < 30% of total power in the low frequency band of CBFV oscillations were on the ventilator. Three of them demonstrated a shift of spectral power from low frequency to a frequency equal or harmonic to the ventilator rate indicating entrainment. The findings of CBFV oscillations combined with entrainment classify the autoregulation as a non-linear system. It is suggested that entrainment by periodic high amplitude stimuli might challenge the regulatory capacity to its limits thus increasing the risk for cerebral damage.

Heart rate response to hemorrhage-induced 0.05-Hz oscillations in arterial pressure in conscious dogs

We have previously reported that oscillations at 0.05 Hz can be generated by a simple computer model incorporating a negative-feedback reflex mechanism and an effector mechanism with a time delay. Computer simulations by inhibiting the vagal effector mechanism and activating the adrenergic effector mechanism elicited low-frequency oscillations at a frequency of 0.05 Hz in heart rate. We have observed that the cardiovascular system of the conscious dog, when stressed by the loss of blood, generates oscillations in arterial pressure and heart rate at a frequency of 0.05 Hz. We investigated in six conscious dogs the role of the sympathetic and parasympathetic nervous systems in generating these heart rate oscillations. During baseline conditions, the predominant peak in the arterial pressure and heart rate power spectra was located at the respiratory frequency, while the low-frequency oscillations were small. After a 30-ml/kg hemorrhage or after an 8-, 15-, or 30-ml/kg hemorrhage with glycopyrrolate, a muscarinic-blocking agent, low-frequency oscillations at a frequency of 0.05 Hz predominated, while the respiratory frequency oscillations were negligible. Since respiratory frequency oscillations have been reported to reflect vagal activity, and since the low-frequency oscillations were present after vagal blockade, these hemorrhage-induced low-frequency oscillations in heart rate may be primarily mediated by the cardiac sympathetic nerves. Also cross-correlation analysis between arterial pressure and heart rate showed that a change in arterial pressure caused an opposite change in heart rate with a delay of 2-5 s. We conclude that hemorrhage-induced oscillations in heart rate at 0.05 Hz represent the arterial baroreceptor-beta-sympathetic reflex response to underlying arterial pressure oscillations.

Effect of posture on spontaneous and thermally stimulated cardiovascular oscillations

The aim of the study was to investigate the effect of posture on thermally stimulated cardiovascular oscillations. The effect of increased gravitational stress (rising from sitting to standing position) on the thermally stimulated cardiovascular oscillations was measured in young male volunteers. Extensive cardiovascular function data were obtained using a cardiovascular investigation protocol. The volunteers were five fit young men, aged 20-21 years. EXPERIMENTS AND MAIN RESULTS: Cardiovascular changes from sitting to standing indicated increased sympathetic and decreased parasympathetic influence on heart and skin blood vessels; mean heart rate increased, beat to beat heart rate variability diminished, high frequency periodic heart rate variability decreased, low frequency heart rate oscillations and ratio of low frequency to high frequency heart rate variability increased, mean skin blood flow and oscillations of skin blood flow decreased (all p less than 0.05). Thermal skin stimulation at 0.01-0.10 Hz frequency increased both sitting and standing 0.10 Hz periodic heart rate variability (p less than 0.05), and 0.10 Hz thermal stimulation entrained the heart rate oscillations in sitting and standing subjects (p less than 0.05). In contrast, skin blood flow oscillations in sitting subjects decreased, while in standing subjects it increased during 0.10 Hz thermal stimulation compared to the corresponding prestimulus values (p less than 0.04). On the basis of previous physiological experiments, these results suggest coupling between thermoregulatory and 0.10 Hz reflex activities.