1,721,287 research outputs found
How to check steady-state condition from cardiovascular time series
No full textIn this study we propose a procedure to automatically check the hypothesis of steady state from the dynamics of the cardiovascular signals, based on the 'run test'. The total number of runs r(tot) is computed from the series of systolic and diastolic blood pressures and R-R intervals. If r(tot) is lower than a given threshold, the steady-state hypothesis is rejected. Because of long-term correlations affecting the cardiovascular series, the thresholds at the 5% significance level were estimated calculating the rtot distributions from a public database of cardiovascular signals collected in steady-state conditions. The procedure was applied to quantify the steadiness of baseline recordings, and to identify sub-periods of steady state during a sequence of physical activities. Results showed the capability of the procedure to automatically detect steady-state conditions, and to identify when the steadiness is lost because of disturbing factors or transients occurring during the recording
On the evaluation of heart rate spectra: the Lomb periodogram
No full textThe Lomb periodogram is a method for the spectral analysis of randomly sampled data. For this property and for the ability to estimate spectral peaks beyond the mean Nyquist frequency, the Lomb approach was proposed for the spectral analysis of heart rate (HR). The features of the Lomb periodogram, however hold for a random sampling while the sampling frequencies of the HR series are equal to the same HR values and thus include systematic oscillations and 1/f noise typical of HR variability. The aim of this study is to investigate whether the rhythmic oscillations and the 1/f noise may influence the performances of the Lomb method. This is done by applying the Lomb procedure to simulated HR series and to real HR data. Results indicate that the valuable features of the Lomb periodogram are in part nullified by the specific characteristics of the HR signal
Gender related differences in scaling structure of heart-rate and blood-pressure variability as assessed by detrended fluctuation analysis
No full textWomen, which have lower risks of cardiovascular events, are characterized by higher heart rate entropy. Aim of this study is to evaluate whether also the fractal structure of heart rate and blood pressure, as quantified by DFA, differs between men and women. In 33 male and 23 female volunteers, we recorded R-R intervals (RRI) and systolic (S) and diastolic (D) blood pressure (BP) for 10' in 3 conditions: supine rest, sitting at rest and sitting during exercise. We calculated a spectrum of scale exponent α(t) as function of the time scale t, by DFA. We also calculated traditional spectral indexes for assessing cardiac and vascular autonomic tone. We found gender related differences in α(t) only during supine rest. Women had significantly lower α(t) of RRI at scales ;60s. Results may in part be explained by gender differences in cardiac autonomic tone at rest
How the threshold #x201C;r #x201D; influences approximate entropy analysis of heart-rate variability
No full textCalculation of approximate entropy (ApEn) requires to select the correct threshold ldquorrdquo. Previous studies recommended r to be between 0.1 and 0.25 times the signal standard deviation, and now r=0.2 is used in almost all HRV studies. Recently it has been claimed that for fast signal dynamics, r=0.2 may lead to erroneous conclusions, while r maximizing ApEn, rMAX, correctly assesses entropy. We verified 1) if rMAX differs from r=0.2 also for HR; and 2) if all r values in the 0.1-0.25 range provide similar ApEn measures. For this aim, we recorded R-R intervals in 10 young subjects for 10psila, in supine and sitting positions, and calculated ApEn(r) for r between 0.02 and 1.20, identifying rMAX and ApEn(rMAX). rMAX felt into the recommended range, but it significantly differed from 0.2. At the extremes of the range, the effects of posture change on ApEn were even opposite: ApEn(0.25) decreased while ApEn(0.1) increased. Therefore the choice of r is critical even in HRV studies
Dynamic adaptation of cardiac baroreflex sensitivity to prolonged exposure to microgravity: data from a 16-day spaceflight
No full textDi Rienzo M, Castiglioni P, Iellamo F, Volterrani M, Pagani M, Mancia G, Karemaker JM, Parati G. Dynamic adaptation of cardiac baroreflex sensitivity to prolonged exposure to microgravity: data from a 16-day spaceflight. J Appl Physiol 105: 1569-1575, 2008. First published August 28, 2008; doi:10.1152/japplphysiol.90625.2008.-This study explored the process of arterial baroreflex adaptation to microgravity, starting from the first day of flight, during the 16-day STS-107 Columbia Space Shuttle mission. Continuous blood pressure (BP), ECG, and respiratory frequency were collected in four astronauts on ground (baseline) and during flight at days 0-1, 6-7, and 12-13, both at rest and during moderate exercise (75 W) on a cycle ergometer. Sensitivity of the baroreflex heart rate control (BRS) was assessed by sequence and spectral alpha methods. Baroreflex effectiveness index (BEI); low-frequency (LF) power and high-frequency (HF) power of systolic BP (SBP), diastolic BP (DBP), and R-R interval (RRI); the RRI LF/HF ratio; and the RRI root mean square of successive differences (RMSSD) index were also estimated. We found that, at rest, BRS increased in early flight phase, compared with baseline (means +/- SE: 18.3 +/- 3.4 vs. 10.4 +/- 1.2 ms/mmHg; P < 0.05), and it tended to return to baseline in subsequent days. During exercise, BRS was lower than at rest, without differences between preflight and in-flight values. At rest, in the early flight phase, RMSSD and RRI HF power increased (P < 0.05) compared with baseline, whereas LF powers of SBP and DBP decreased. No statistical difference was found in these parameters during exercise before vs. during flight. These findings demonstrate that heart rate baroreflex sensitivity and markers of cardiac vagal modulation are enhanced during early exposure to microgravity, likely because of the blood centralization, and return to baseline values in subsequent flight phases, possibly because of the fluid loss. No deconditioning seems to occur in the baroreflex control of the heart
A TRIM32-AMBRA1-ULK1 complex initiates the autophagy response in atrophic muscle cells
No full textThe Ser/Thr protein kinase ULK1 is an upstream macroautophagy/autophagy regulator that is rapidly activated to ensure a proper adaptive response to stress conditions. Signaling pathways modulating ULK1 activity have been extensively characterized in response to nutrient/energy shortage, which mainly act by mediating ULK1 post-translational modifications, such as phosphorylation, acetylation and ubiquitination. Less characterized is how tissue-specific stress signals are able to activate ULK1 to induce autophagy. Our recent study has uncovered the E3 ubiquitin ligase TRIM32 as a novel ULK1 activator that regulates autophagy in muscle cells upon atrophy induction. TRIM32 is conveyed to ULK1 by the autophagy cofactor AMBRA1 to stimulate its kinase activity through unanchored K63-linked polyubiquitin chains. Notably, mutations in TRIM32 responsible for limb-girdle muscular dystrophy 2H disrupt its ability to bind ULK1 and to induce autophagy in muscle cells, resulting in a dysregulated activation of the atrophic process. In conclusion, we have identified a novel molecular mechanism by which autophagy is regulated in muscles, whose alteration is associated with the development of muscular dystrophy
Reply to Dr. Cysarz's comment on Point : Counterpoint "Cardiovascular variability is/is not an index of autonomic control of circulation"
No full textInterpolation technique for extracting features from ECG signals sampled at low sampling rates
No full textThe occurrence of the R peak (tR), and the area of the QRS complex (AQRS) are among the features estimated from each ECG wave. To estimate these parameters ECG is traditionally sampled at a high sampling rate (250-500 Hz). However, since tR and AQRS are identified by the selective analysis of the QRS complex and since the QRS maximal frequency component is about 25 Hz, we propose a new procedure to identify tR and AQRS from ECG sampled at the relatively low rate dictated by the frequency content of the QRS complex. The procedure identifies each QRS complex from the sampled ECG, and estimates tR and AQRS after interpolation of the QRS complex. The interpolation is obtained as the inverse discrete Fourier transform (IDFT) of the zero-padded DFT of the QRS. The technique was tested on a public database of ECG. Results showed that by this technique tR and AQRS can be accurately derived from ECG sampled at frequency as low as 70 Hz
Spectral and fractal structures of heart rate variability in coronary artery disease patients without myocardial infarction
No full textHeart rate variability (HRV) allows risk stratification in coronary artery disease (CAD) patients, but only few works evaluated HRV in CAD patients with preserved ejection fraction. Aim of this work is to describe spectral and fractal structures of HRV in CAD patients with normal ejection fraction. We recorded R-R intervals for 15 minutes in 10 CAD patients and in 10 matched controls with the same ejection fraction, estimating broadband power spectra, PSD(f), and the recently proposed temporal spectrum of scale coefficients, α(τ). In CAD patients, PSD(f) was significantly (p<;0.05) lower over a low-frequency band (0.047-0.240 Hz) and over a very-low frequency band (0.007-0.022 Hz); α(τ) was significantly higher between 9 and 25 s (corresponding to low frequencies) but did not difer from controls at scales τ corresponding to very-low frequencies. Therefore, in CAD patients, even when the ejection fraction is preserved, a low frequency spectral component with its own fractal signature is absent. In addition, fluctuations at lower frequencies are reduced but, in this case, the power reduction is not associated with an altered fractal dynamics
Assessment of latency in baroreflex control of heart rate during spontaneous behavior
No full textThis study proposes a new simplified approach for estimating the latency in the baroreflex control of heart rate by the analysis of systolic blood pressure (SBP) and RR interval (RRI) spontaneous variability. Application of this technique on SBP and RRI 24-h recordings, allowed us to identify a large fluctuation of the baroreflex latency over time with a circadian pattern characterised by a reduction of the latency at night. Since our approach provides a quantification of the latency in terms of heart beats, there was the possibility that the results would be influenced by the RRI. The observed absence of any significant correlation between latency and RRI excluded this adverse possibility. These results encourage the use of the proposed procedure for obtaining a simple and noninvasive measure of the baroreflex latency in daily life condition
- …
