1,721,076 research outputs found
Electro spun bioresorbable trileaflet heart valve prosthesis for tissue engineering: In vitro functional assessment of a pulmonary cardiac valve design
No full textCurrently implanted prosthetic heart valves, both mechanical or biological ones, are used to restore the proper blood hemodynamics when the native valves fail. However, these medical devices are not free from drawbacks, such as hemolysis or calcification, also presenting the relevant disadvantage of being unable to growth, repair and remodel. An improvement could be represented by bioresorbable polymeric tissue-engineered heart valves. In this paper a poly(e-caprolactone) (PCL) heart valve prosthesis, realized by means of electrospinning, and its in vitro functional characterization in a pulse duplicator, resembling pulmonary conditions, is presented. Morphological examination revealed polymeric micrometric fibers randomly oriented with an average porosity of about 90%. Pulse duplicator testing highlighted that leaflets opened synchronously and showed a correct coaptation in the diastolic phase, even if a slight rotation of the leaflets was visualized. In silico study by numerical simulation of the closed phase predicted the stress distribution within the leaflet, showing that peak levels are reached at the commissures and sustained by the structure without failure. The present study highlighted the technical feasibility to produce polymeric bioresorbable functional heart valves by means of electrospinning. Further studies and design changes are needed in order to optimize the final scaffold to bear arterial hemodynamic conditions
Nonlinear Analysis of Heart Rate Variability to Monitor Fetal Stress During Fetal Cardiac Surgery
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Optical vibrocardiography: a novel tool for optical monitoring of cardiac activity
No full textWe present an optical non-contact method for heart beat monitoring, based on the measurement of chest wall movements induced by the pumping action of the heart, which is eligible as a surrogate of electrocardiogram (ECG) in assessing both cardiac rate and heart rate variability (HRV). The method is based on the optical recording of the movements of the chest wall by means of laser Doppler interferometry. To this aim, the ECG signal and the velocity of vibration of the chest wall, named optical vibrocardiography (VCG), were simultaneously recorded on 10 subjects. The time series built from the sequences of consecutive R waves (on ECG) and vibrocardiographic (VV) intervals were compared in terms of heart rate (HR). To evaluate the ability of VCG signals as quantitative marker of the autonomic activity, HRV descriptors were also calculated on both ECG and VCG time series. HR and HRV indices obtained from the proposed method agreed with the rate derived from ECG recordings (mean percent difference <3.1%). Our comparison concludes that optical VCG provides a reliable assessment of HR and HRV analysis, with no statistical differences in term of gender are present. Optical VCG appears promising as non-contact method to monitor the cardiac activity under specific conditions, e.g., in magnetic resonance environment, or to reduce exposure risks to workers subjected to hazardous conditions. The technique may be used also to monitor subjects, e.g., severely burned, for which contact with the skin needs to be minimized
Laser Doppler vibrometry in non contact monitoring of the heart beat
No full textOptical techniques for vibration measurements, due their non-contact nature, could be an alternative diagnostic tool to be tested in clinic fields. The purpose of this study is to present a non-contact measurement techinique to monitor the heart rate (HR) and follow vital signs
Helical flow as fluid dynamic signature for atherogenesis risk in aortocoronary bypass. A numeric study
No full textThe main purpose of the study was to verify if helical flow, widely observed in several vessels, might be a signature of the blood dynamics of vein graft anastomosis. We investigated the existence of a relationship between helical flow structures and vascular wall indexes of atherogenesis in aortocoronary bypass models with different geometric features. In particular, we checked for the existence of a relationship between the degree of helical motion and the magnitude of oscillating shear stress in conventional hand-sewn proximal anastomosis. The study is based on the numerical evaluation of four bypass geometries that are attached to a simplified computer representation of the ascending aorta with different angulations relative to aortic outflow. The finite volume technique was used to simulate realistic graft fluid dynamics, including aortic compliance and proper aortic and graft flow rates. A quantitative method was applied to evaluate the level of helicity in the flow field associated with the four bypass models under investigation.
A linear inverse relationship (R=-0.97) was found between the oscillating shear index and the helical flow index for the models under investigation. The results obtained support the hypothesis that an arrangement of the flow field in helical patterns may elicit damping in wall shear stress temporal gradients at the proximal graft. Accordingly, helical flow might play a significant role in preventing plaque deposition or in tuning the mechanotransduction pathways of cells.
Therefore, results confirm that helical flow constitutes an important flow signature in vessels, and its strength as a fluid dynamic index (for instance in combination with magnetic resonance imaging flow visualization techniques) for risk stratification, in the activation of both mechanical and biological pathways leading to fibrointimal hyperplasia
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