Problem of power spectra estimation in application to the analysis of heart rate variability

We investigated how the parameters of the spectral analysis affect standard deviation and error of the estimation of well-known indices for the heart rate variability. We compared the nonparametric Fourier transform to the parametric approach based on autoregressive models. We also investigated how the precision of the indices estimation depends on the choice of the window function, parameterization of the Bartlett’s method, and the lengths of time series. For each set of parameters, we calculated the sensitivity and specificity of the resulting indices when diagnosing arterial hypertension. To isolate and investigate the errors caused by inaccuracy of the spectral analysis itself, we conducted our study using the mathematical models of heart rate variability for healthy subjects and arterial hypertension patients, for which the correct values of the spectral indices are known. The obtained results suggest that the analysis of 20-min signals, comparing to 5-min signals, significantly decreases the standard deviation of the estimations and increases both their sensitivity and specificity. We found no advantages of using the parametric approach over the Fourier transform. We have shown that application of the Hann’s window function and normalization of the spectral indices decreases the sensitivity and specificity of the medical diagnostics

Dynamics of 0.1 Hz Oscillations Synchronization in Cardiovascular System during the Treatment of Acute Myocardial Infarction Patients

Aim: The aim was the studying of synchronization between 0.1 Hz oscillations in heart rate (HR) and plethysmographic peripheral microcirculation (PM) in acute myocardial infarction (AMI) patients and in healthy subjects. Material and Method: 12 healthy volunteers aged 26±5 years and 125 patients with AMI aged 65±9 years were involved in the study. Simultaneous registration of electrocardiogram and photoplethysmogram were performed during 10 min. In AMI patients the signals were recorded twice: the first record was done during 3-5 days after AMI, the second record was done during the third week after AMI. Phase differences between HR and PM oscillations were used to measure the degree of synchronization (S). Data are submitted as medians with inter-quartile ranges (25%, 75%). Results: S was 65.8% (50.5%; 79.5%) in healthy subjects whereas in AMI patients at the first week after AMI S was 16.3% (9.4%; 24.6%) (p<0.001). In records made at the third week after AMI index S was 18.4% (11.2%; 28.2%). Two groups of AMI patients were identified on the basis of individual S dynamics. In 100 AMI patients no dynamics of S was observed during the observation period and in 25 AMI patients the increase of S was observed. The group of AMI patients with increase of S had greater HR values during the first week after AMI. Conclusion: The index S of synchronization of 0.1 Hz oscillations in HR and PM appears to be a sensitive indicator of autonomic control dynamic disturbances in AMI patients

Statistical properties of the phase synchronization index of cardiovascular autonomic control contours

Objective ― The purpose of this paper is to study statistical and dynamic properties of the low-frequency (LF) oscillation synchronization in the heart rate variability (HRV) and the finger photoplethysmographic waveform variability (PPGV) in time. Material and Methods ― Our study included 42 healthy men aged 19-21 years. The HRV and the finger PPGV were simultaneously recorded in all subjects during 7,200 seconds at rest. We extracted the LF oscillations in the HRV and the PPGV. To estimate this synchronization we used the method we suggested earlier. Index S was calculated as the relative time of synchronization between the considered LF oscillations. Results ― The sequence of the synchronization intervals between the LF oscillations behaves as a weakly correlated random process, demonstrating the 1/f distribution. However, the distribution of the index S, estimated even for 10-minute records, is close to normal. The results of estimating the S value from realizations of increasing length indicate that S tends to a fixed value with the increase of time series length. Conclusion ― For practical studies we recommend using the experimental records of ECG and PPG with the length of 10 minutes or more, which will provide a standard deviation of the S estimate less than 10%

Uncovering interaction between the loops of autonomic regulation of blood circulation from long time series

The purpose of this work is to study the interaction between the autonomic regulatory loops of blood circulation from long time series. Methods ― We simultaneously recorded four-hour signals of electrocardiogram and photoplethysmogram from the ear and finger of ten healthy adults. We determined the intervals of phase synchronization of the studied regulatory loops and analyzed the dependence of their length on the recording time. The deviations of the total percentage of phase synchronization (index S) from its mean value were estimated in moving non-overlapping windows. Results ― For studied signals we found no significant correlation between the length of synchronization epoch and the time of its beginning. A sharp increase in the deviation of the index S from its mean was shown at the end of the experiment. Conclusion ― The increase in the deviation from the mean at the end of our records is most likely associated more with psychosomatic influences than with hormonal regulation or immobilization stress

Method of estimation of synchronization strength between low-frequency oscillations in heart rate variability and photoplethysmographic waveform variability

This paper describes in detail a new method proposed by authors for quantitative estimation of the strength of synchronization between the low-frequency oscillations (with the main frequency of about 0.1 Hz) in the heart rate variability (HRV) and photoplethysmogram (PPG). Calculation of index value is followed by statistical significance control. The proposed method is applied for the analysis of 1056 pairs of HRV and PPG signals obtained from patients having different clinical status. Methodological recommendations are developed for method application in clinical studies

Λ(1405) photoproduction at the BGO-OD experiment

Since the discovery of the Λ(1405), it remains poorly described by conventional constituent quark models, and it is a candidate for having an “exotic” meson-baryon or “penta-quark” structure, similar to states recently reported in the hidden charm sector. The Λ(1405) can be produced in the reaction γp K+Λ(1405). The pure I=0 decay mode into Σ0π0 is prohibited for the mass-overlapping Σ(1385). Combining a large aperture forward magnetic spectrometer and a central BGO crystal calorimeter, the BGO-OD experiment is ideally suited to measure this decay with the K+ in the forward direction. Preliminary results are presented. *Supported by DFG (PN 388979758, 405882627

Σ

The BGO-OD experiment at the ELSA accelerator facility uses an energy tagged bremsstrahlung photon beam to investigate the excitation structure of the nucleon via meson photoproduction. The setup with a BGO calorimeter surrounding the target and an open dipole spectrometer covering the for ward region is ideally suited for investigating low momentum transfer processes, in particular in strangeness photoproduction. The associated photoproduction of K0S and hyperons is essential to understand the role of K* exchange mech anisms. A cusp-like structure observed in the yp → K0SΣ+ reaction at the K* threshold is described by models including dynamically generated resonances from vector meson-baryon interactions. Such interactions are pre dicted to give a peak like structure in K0SΣ0 photoproduction off the neutron. A very preliminary cross section is determined and compared to the prediction, the results appear to support the mode