Several parameters assessing nonlinear properties of heart rate variability (HRV) from short-term (<10 min) laboratory recordings have been proposed so far, but their reliability is unknown. In this study, we addressed this issue analysing a comprehensive set of these indices. In 42 healthy subjects (mean age (min-max): 38 (26-56) years, 21 men) we recorded 5 min of supine ECG in two consecutive days. From RR intervals we computed 11 nonlinear HRV indices, representative of symbolic dynamics, entropy, fractality, predictability, empirical mode decomposition and Poincaré plot families. Absolute reliability was assessed by the 95% limits of random variation and relative reliability was assessed computing the intraclass correlation coefficient (ICC). We found marked differences in the reliability of short-term nonlinear indices of HRV. In the majority of indices, changes in test-retest measurements ranged between about -30% and +50%, indicating good absolute reliability while in the others the change was <-60% and >140%. Relative reliability was substantial (0.6 < ICC < 0.8) in half of the indices, moderate in one and poor in the remaining. Compared to classical linear indices, nonlinear HRV parameters seem more suitable for individual test-retest evaluations but, due to a reduced ICC, they need increased sample size in comparative studies involving two groups of subjects.

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BackgroundPulse wave velocity (PWV) is a biomarker for arterial stiffness, clinically assessed by applanation tonometry (AT). Increased use of phase-contrast cardiac magnetic resonance (CMR) imaging allows for PWV assessment with minor routine protocol additions. The aims were to investigate the acquired temporal resolution needed for accurate and precise measurements of CMR-PWV, and develop a tool for CMR-PWV measurements.MethodsComputer phantoms were generated for PWV = 2–20 m/s based on human CMR-PWV data. The PWV measurements were performed in 13 healthy young subjects and 13 patients at risk for cardiovascular disease. The CMR-PWV was measured by through-plane phase-contrast CMR in the ascending aorta and at the diaphragm level. Centre-line aortic distance was determined between flow planes. The AT-PWV was assessed within 2 h after CMR. Three observers (CMR experience: 15, 4, and <1 year) determined CMR-PWV. The developed tool was based on the flow-curve foot transit time for PWV quantification.ResultsComputer phantoms showed bias 0.27 ± 0.32 m/s for a temporal resolution of at least 30 ms. Intraobserver variability for CMR-PWV were: 0 ± 0.03 m/s (15 years), -0.04 ± 0.33 m/s (4 years), and -0.02 ± 0.30 m/s (<1 year). Interobserver variability for CMR-PWV was below 0.02 ± 0.38 m/s. The AT-PWV overestimated CMR-PWV by 1.1 ± 0.7 m/s in healthy young subjects and 1.6 ± 2.7 m/s in patients.ConclusionsAn acquired temporal resolution of at least 30 ms should be used to obtain accurate and precise thoracic aortic phase-contrast CMR-PWV. A new freely available research tool was used to measure PWV in healthy young subjects and in patients, showing low intra- and interobserver variability also for less experienced CMR observers.

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IntroductionThe Public Access to Defibrillation (PAD) program was designed to raise the awareness of sudden cardiac death (SCA) pre-hospital management among the community. The goal of the following research was to confirm the final impact of the Polish PAD program on various resident groups that differ by age, training and education level.Material and methodsThe trial total number of participants reached 404 people from three cities divided into two groups. In group one (n = 295) were randomly selected people inside the trial area and in group two (n = 109) we had individuals who were theoretically trained in basic life support (BLS) algorithms, including the use of an automatic external defibrillator (AED). The research method was based on two different questionnaires completed by participants from each group.ResultsThe greatest knowledge of SCA, as well as the use of AED, and the best practical skills, were possessed by the residents of cities with a population over 100 000, aged between 18 and 30 years, who completed secondary or higher education (31.7%). The group with the smallest knowledge about SCA lived in the country (10.7%). The second group with little knowledge of the subject consisted mostly of individuals with primary education (4.19%) or professional abilities and over 50 years old (2.16%).ConclusionsThere must be some actions taken in order to increase the community awareness concerning automatic defibrillation. Training on AED and the possibility of practical exercise needs to be organized and should be conducted especially among residents of the countryside and people under 30 or over 50 years old.