1,720,962 research outputs found
Evaluation of T-wave alternans activity under stress conditions after 5 d and 21 d of sedentary head-down bed rest
Full text linkIt is well known that prolonged microgravity leads to cardiovascular deconditioning, inducing significant changes in autonomic control of the cardiovascular system. This may adversely influence cardiac repolarization, and provoke cardiac rhythm disturbances. T-wave alternans (TWA), reflecting temporal and spatial repolarization heterogeneity, could be affected. The aim of this work was to test the hypothesis that 5 d and 21 d head-down (-6°) bed rest (HDBR) increases TWA, thus suggesting a higher underlying electrical instability and related arrhythmogenic risk.Forty-four healthy male volunteers were enrolled in the experiments as part of the European Space Agency's HDBR studies. High-fidelity ECG was recorded during orthostatic tolerance (OT) and aerobic power (AP) tests, before (PRE) and after HDBR (POST). A multilead scheme for TWA amplitude estimation was used, where non-normalized and T-wave amplitude normalized TWA indices were computed. In addition, spectral analysis of heart rate variability during OT was assessed.Both 5 d and 21 d HDBR induced a reduction in orthostatic tolerance time (OTT), as well as a decrease in maximal oxygen uptake and reserve capacity, thus suggesting cardiovascular deconditioning. However, TWA indices were found not to increase. Interestingly, subjects with lower OTT after 5 d HDBR also showed higher TWA during recovery after OT testing, associated with unbalanced sympathovagal response, even before the HDBR. In contrast with previous observations, augmented ventricular heterogeneity related to 5 d and 21 d HDBR was not sufficient to increase TWA under stress conditions
Ventricular repolarization changes driven by deconditioning after 21-days of head-down bed-rest
Full text linkT-wave alternans and autonomic nervous system activity during orthostatic stress after 5 days of head-down bed-rest
Full text link
Sviluppo di un algoritmo per l'estrazione dei punti fiduciari da segnale ballistocardiografico acquisito con piattaforma di forza
No full textLAUREA MAGISTRALENegli ultimi anni, inoltre, sono state effettuate acquisizioni del segnale BCG in assenza di gravità in modo da valutare le sole accelerazioni del corpo dovute allo spostamento della massa di sangue sotto condizioni isotrope e per studiare la modifica delle proprietà fisiologiche del cuore sottoposto alla assenza di gravità. Questo lavoro di tesi fa parte di una ricerca ben più vasta che è volta a studiare in modo completamente non invasivo gli effetti della microgravità sulla meccanica cardiaca tramite l'analisi del segnale BCG. Questo lavoro ha l'obiettivo di caratterizzare il segnale BCG registrato a terra, in modo da valutare le informazioni che effettivamente si possono ricavare e di creare una base di dati fruibili per il confronto con i dati acquisiti in microgravità.
A tale fine è stato predisposto un opportuno protocollo sperimentale per poter acquisire contemporaneamente il segnale BCG, tramite pedana di forza, ed il segnale ECG, utilizzato come riferimento.In the last years, BCG was also acquired under zero gravity (0G) in order to evaluate the acceleration of the body under isotropic conditions and to investigate the physiological changes of the heart under sustained 0G. This master’s thesis is part of a research project aimed at the evaluation of microgravity effects on cardiac mechanics through a non-invasive analysis of the BCG signal. We have performed a previous on-ground characterization of the BCG signal, with the aim of better understanding the 3D signal content and having available a new on-ground database, useful for comparing results with those obtained under microgravity conditions.
In order to do that, an appropriate experimental protocol to simultaneously acquire the BCG signal, using a force platform, and the electrocardiogram (ECG) signal (used as a reference) has been proposed
Weightlessness and Cardiac Rhythm Disorders: Current Knowledge from Space Flight and Bed-Rest Studies
Full text linkIsolatedepisodesofheartrhythmdisordershavebeenreportedduring40yearsofspaceflight,triggeringresearchtoevaluatetheriskofdevelopinglife-threateningarrhythmiasinducedbyprolongedexposuretoweightlessness.Infact,theseeventscouldcompromiseastronautperformanceduringexploratorymissions,aswellasposeatrisktheastronauthealth,duetolimitedoptionsofcareonboardtheInternationalSpaceStation.Startingfromoriginalobservations,thisminireviewwillexplorethelatestresearchinthisfield,consideringresultsobtainedbothduringspaceflightandonEarth,thelatterbysimulatinglong-termexposuretomicrogravitybyhead-downbedrestmaneuverinordertoelicitcardiovasculardeconditioningonnormalvolunteers
Circadian modulation on T-wave alternans activity in chronic heart failure patients
Full text linkConference paper: Computing in Cardiology 2015; 42:845-848. Alba Martín-Yebra, Enrico G Caiani, Pablo Laguna, Violeta Monasterio, Juan Pablo Martíne
Assessment of ventricular repolarization instability and cardiac risk stratification in different pathological and abnormal conditions
No full textLe malattie cardiovascolari sono la principale causa di morte al mondo. Queste condizioni patologiche sono normalmente caratterizzate da difetti cardiaci a livello strutturale, e rendono perciò il cuore una struttura vulnerabile, incline alla generazione e/o propagazione anomala di impulsi elettrici che determinano l’instaurarsi di aritmie ventricolari. In questo contesto, è stato mostrato come la misura della ripolarizzazione ventricolare a partire dall’elettrocardiogramma (ECG) fornisca informazioni importanti per una stratificazione del rischio, per la quale sono stati proposti diversi indici elettrocardiografici.
L’obiettivo principale di questa tesi è proporre sviluppi metodologici per la valutazione della ripolarizzazione ventricolare in condizioni patologiche e non fisiologiche. I contributi qui presentati sono volti al miglioramento della predizione delle aritmie ventricolari e, di conseguenza, a migliorare la diagnosi di rischio di arresto cardiaco improvviso. In particolare, il nostro approccio ha previsto lo sviluppo di metodi robusti per la valutazione dell’alternanza dell’onda T (TWA) e dell’instabilità della ripolarizzazione ventricolare, usando segnali cardiaci invasivi e non, e testando i metodi in condizioni sperimentali e cliniche. In conclusione, il lavoro qui presentato contribuisce ad una migliore identificazione di fattori che predispongono ad aritmie, passo fondamentale per l’adozione di strategie terapeutiche efficaci.Cardiovascular deseases represents the leading cause of mortality worldwide. These pathological conditions are mainly characterized by a vulnerable substrate prone to the abnormal generation and/or propagation of the electrical impulse, determining the onset of ventricular arrhythmias, which can lead to sudden cardiac death (SCD) outcome. In this context, the assessment of ventricular repolarization from the electrocardiogram (ECG) signal has been shown to provide with valuable information for risk stratification and several ECG-derived markers have been proposed in the literature.
The main objective of this thesis is to propose methodological advances for the assessment of ventricular repolarization instability in pathological and abnormal conditions. These contributions are aimed at improving SCD prediction. In particular we have addressed this objective by developing robust methodologies for the assessment of T-wave alternans (TWA) and ventricular repolarization instability, in invasive and non-invasive cardiac signals, that have been evaluated in both experimental and clinical conditions. In conclusion, the research presented in this thesis sheds some light in the identification of pro-arrhythmic factors, which plays an important role in adopting efficient therapeutic strategies.DIPARTIMENTO DI ELETTRONICA, INFORMAZIONE E BIOINGEGNERIA29RAIMONDI, MANUELA TERESAALIVERTI, ANDRE
Beat-to-beat heart rate detection by smartphone's accelerometers: Validation with ECG
Full text linkMobile phones offer the possibility to monitor and track health parameters. Our aim was to test the feasibility and accuracy of measuring beat-to-beat heart rate using smartphone accelerometers by recording the vibrations generated by the heart during its function and transmitted to the chest wall, i.e. the so-called seismocardiographic signal (SCG). Methods: 9 healthy male volunteers were studied in supine (SUP) and in standing (ST) posture. A smartphone (iPhone6, Apple) was positioned on the thorax (POS1) to acquire SCG signal. While supine, a second smartphone was positioned on the navel (POS2). The SCG signal was recorded for 3 minutes during spontaneous respiration, synchronous with 3-leads ECG. Using a fully automated algorithm based on amplitude thresholding after rectification, the characteristic peak of the SCG signal (IVC) was detected and used to compute beat-to-beat heart duration, to be compared with the corresponding RR intervals extracted from the ECG. Results: A 100% feasibility of the approach resulted for POS1 in SUP, while 89% in POS2, and 78% for POS1 in ST. In supine, for each smartphones' position, the automated algorithm correctly identified the cardiac beats with >98% accuracy. Linear correlation (r2) with RR was very high (>0.98) in each posture and position, with no bias and narrow limits of agreement. Conclusions: The obtained results proved the feasibility of the proposed approach and the robustness of the applied algorithm in measuring the beat-to-beat heart rate from smartphone-derived SCG, with high accuracy compared to conventional ECG-derived measure
Evaluation of respiratory- and postural-induced changes on the ballistocardiogram signal by time warping averaging
Full text linkThe aim of this work was to evaluate the potential changes in the ballistocardiogram (BCG) signal induced by different respiratory patterns and posture, by using the dynamic time warping (DTW) technique
- …
