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D Rassi

Publications and source records attributed to D Rassi.

7 recordsLinked to original sources
PubMed2006

Analysis of the QT interval and its variability in healthy adults during rest and exercise.

The aim of the present study was to quantify the variability of electrocardiographic QT and RR intervals during rest and dynamic physical exercise, and to interpret these variabilities in terms of relative autonomic modulation of the atrial and ventricular myocardium. We also sought to characterize the relationships between QT, heart rate-corrected QT (QT(c)) and RR intervals, and to consider their associations with differential autonomic regulation. Nine males and eight females of similar age (22.8 +/- 4.7 years), mass (75.5 +/- 13.0 kg) and aerobic fitness (43.6 +/- 7.7 ml kg(-1) min(-1)) (mean +/- SD) undertook progressive bicycle exercise. A three-lead Holter ECG was recorded continuously during pre-exercise, exercise and recovery, and mean values of RR, QT, QT(c), QT variability index (QTVI) and mean-normalized QT variance (QTVN) were determined. At the onset of exercise QTVI increased rapidly compared with rest and remained significantly elevated throughout exercise and recovery. There were significant differences between QT(a)VI and QT(e)VI (QT measured from Q wave onset to T wave apex (QT(a)) and T wave end (QT(e)), respectively) throughout the experimental protocol. QTVI was significantly reduced in males compared with females prior to exercise but was similar thereafter. We suggest that physical exercise perturbs the resting QT-RR relationship owing to the onset of differential parasympathetic modulation of the atrial and ventricular myocardium. QTVI can be used to quantify the relative autonomic influence on the atrial and ventricular myocardium during rest and exercise, and might be related to HR-dependent and HR-independent influences on the QT interval.

Adult↗
PubMed2004

Time domain correlation analysis of heart rate variability in preterm neonates.

BACKGROUND AND AIM: A fuller understanding of the neural control mechanisms of heart rate during the early stages of human development would be of great value to obstetric and neonatal management. In this paper, we investigate the correlation between heart rate variability (HRV) and other physiological parameters such as blood pressure and respiration in preterm neonates with the aim of developing a numerical model to explain and predict heart rate variability. STUDY DESIGN AND SUBJECTS: All the required data are readily available for premature babies who are routinely monitored while being nursed in intensive care, and we have collected large data sets for a random group of such neonates. For the quantitative analysis of the data, we have developed a time domain correlation method, which has a number of advantages over the more commonly used power spectral analysis. We have been able to study the dynamics of the different frequency components of HRV by this method. RESULTS: Highly correlated behaviour of the different HRV components, previously observed in our work on fetal HRV, is also present in the neonate, with similar characteristic time constants. Furthermore, the correlation of high-frequency (HF) oscillations of HRV with respiration and that of low-frequency (LF) oscillations of HRV with blood pressure are demonstrated on timescales of a single oscillation. In neonates receiving artificial ventilation, the correlation between HRV and respiration depends on the type of ventilation involved and assumes opposite polarities for the two main types of equipment currently in use. CONCLUSION: We demonstrate that it is possible to analyse HRV quantitatively by calculating the relative gains and characteristic time constants for the correlated parameters and components.

Blood Pressure↗
PubMed1995

Sequential recording of the abdominal fetal electrocardiogram and magnetocardiogram.

The aim of this study was to demonstrate the acquisition of both the fetal magnetocardiogram (FMCG) and fetal electrocardiogram (FECG) from the abdomen of the same subject. This contrasts with previous reported studies which have generally recorded one or other of these signals but not the two together. Both signals were successfully recorded and averaged to produce a typical complex, thus allowing their direct comparison.

Electrocardiography↗
PubMed1995

Power spectral analysis of the foetal magnetocardiogram.

The results of power spectral analysis of foetal magnetocardiographic (FMCG) data, acquired using a DC-SQUID-based system, are reported. Similar analyses have been previously reported using foetal electrocardiographic data, but it is believed that our work represents one of the first attempts to analyse, in the frequency domain, the magnetic fields produced by foetal cardiac activity. Analysis of the data in this way may enable the integrity of the foetal nervous system, and thus the status of the foetus as a whole, to be monitored and evaluated during a significant part of the antenatal period. The results obtained are discussed with reference to the probable underlying physiological mechanisms. This preliminary study highlights some of the advantages of FMCG as a novel, non-invasive technique for obtaining clinically useful information. Fourier analysis of the FMCG data is likely to yield new information, not only about cardiac function but also about the foetal central nervous system.

Algorithms↗
PubMedDate not supplied

Magnetic susceptibility mapping of the human thorax using a SQUID biomagnetometer.

Biomagnetism is essentially the study of the weak magnetic fields generated by biological organisms, in particular the human body. The human thorax is composed of a variety of tissues and organs of slightly different magnetic susceptibility. In an applied magnetic field (of the order of milliTeslas) these small differences in susceptibility lead to measurable field variations (of the order of nanoTeslas) at the body surface which may be of diagnostic value. Physiological processes such as cardiac activity, cardiac output, blood flow and respiratory related lung volume changes also contribute to the observed signal. In this study susceptibility 'maps' were obtained by measuring the magnetic field at several hundred points over the thorax. Results indicate that magnetic susceptibility mapping produces low-resolution images of internal body structures from which is should be possible to detect pathologies that cause alterations in tissue susceptibility.

Biomedical Engineering↗