L’utilizzo di un software per l’analisi nella ricerca qualitativa. Potenziali e limiti di NVivo in un progetto fenomenologico-ermeneutico

Il contributo presenterà una riflessione critica relativa all’utilizzo del software NVivo all’interno progetto di ricerca qualitativa, finalizzata a indagare l’incontro nella pratica professionale tra il sapere pedagogico e quello medico/sanitario. Riferendosi a un approccio qualitativo, il progetto si è basato sul metodo fenomenologico-ermeneutico e sulla strategia dello studio di caso. Per raccogliere i dati sono stati utilizzati l’osservazione etnografica, l’intervista semi-strutturata, la pratica del collage-making, il diario di ricerca. L’analisi del materiale, effettuata seguendo il modello fenomenologico-ermeneutico, è stata supportata da NVivo. La conoscenza del software, approfondita prima del suo impiego, ha permesso di utilizzarlo come ausilio per accompagnare il lavoro di analisi, non in sostituzione all’interpretazione della ricercatrice. Riprendendo questa esperienza, il contributo presenterà aspetti positivi e difficoltà incontrati nell’utilizzo di NVivo, evidenziando come l’uso di un software per l’analisi qualitativa, e nello specifico nell’approccio fenomenologico-ermeneutico, passi inevitabilmente attraverso l’insostituibile pensiero del ricercatore

Numerical model of a valvuloplasty balloon: in vitro validation in a rapid‑prototyped phantom

Background Patient-specific simulations can provide insight into the mechanics of cardiovascular procedures. Amongst cardiovascular devices, non-compliant balloons are used in several minimally invasive procedures, such as balloon aortic valvuloplasty. Although these balloons are often included in the computer simulations of these procedures, validation of the balloon behaviour is often lacking. We therefore aim to create and validate a computational model of a valvuloplasty balloon. Methods A finite element (FE) model of a valvuloplasty balloon (Edwards 9350BC23) was designed, including balloon geometry and material properties from tensile testing. Young’s Modulus and distensibility of different rapid prototyping (RP) rubber-like materials were evaluated to identify the most suitable compound to reproduce the mechanical properties of calcified arteries in which such balloons are likely to be employed clinically. A cylindrical, simplified implantation site was 3D printed using the selected material and the balloon was inflated inside it. The FE model of balloon inflation alone and its interaction with the cylinder were validated by comparison with experimental Pressure–Volume (P–V) and diameter–Volume (d–V) curves. Results Root mean square errors (RMSE) of pressure and diameter were RMSE P = 161.98 mmHg (3.8 % of the maximum pressure) and RMSE d = 0.12 mm (<0.5 mm, within the acquisition system resolution) for the balloon alone, and RMSE P = 94.87 mmHg (1.9 % of the maximum pressure) and RMSE d = 0.49 mm for the balloon inflated inside the simplified implantation site, respectively. Conclusions This validated computational model could be used to virtually simulate more realistic valvuloplasty interventions

Numerical model of a valvuloplasty balloon:in vitro validation in a rapid-prototyped phantom

BACKGROUND: Patient-specific simulations can provide insight into the mechanics of cardiovascular procedures. Amongst cardiovascular devices, non-compliant balloons are used in several minimally invasive procedures, such as balloon aortic valvuloplasty. Although these balloons are often included in the computer simulations of these procedures, validation of the balloon behaviour is often lacking. We therefore aim to create and validate a computational model of a valvuloplasty balloon. METHODS: A finite element (FE) model of a valvuloplasty balloon (Edwards 9350BC23) was designed, including balloon geometry and material properties from tensile testing. Young’s Modulus and distensibility of different rapid prototyping (RP) rubber-like materials were evaluated to identify the most suitable compound to reproduce the mechanical properties of calcified arteries in which such balloons are likely to be employed clinically. A cylindrical, simplified implantation site was 3D printed using the selected material and the balloon was inflated inside it. The FE model of balloon inflation alone and its interaction with the cylinder were validated by comparison with experimental Pressure–Volume (P–V) and diameter–Volume (d–V) curves. RESULTS: Root mean square errors (RMSE) of pressure and diameter were RMSE(P) = 161.98 mmHg (3.8 % of the maximum pressure) and RMSE(d) = 0.12 mm (<0.5 mm, within the acquisition system resolution) for the balloon alone, and RMSE(P) = 94.87 mmHg (1.9 % of the maximum pressure) and RMSE(d) = 0.49 mm for the balloon inflated inside the simplified implantation site, respectively. CONCLUSIONS: This validated computational model could be used to virtually simulate more realistic valvuloplasty interventions

Current and future applications of 3D printing in congenital cardiology and cardiac surgery

Three-dimensional (3D) printing technology in congenital cardiology and cardiac surgery has experienced a rapid development over the last decade. In presence of complex cardiac and extra-cardiac anatomies, the creation of a physical, patient-specific model is attractive to most clinicians. However, at the present time, there is still a lack of strong scientific evidence of the benefit of 3D models in clinical practice and only qualitative evaluation of the models has been used to investigate their clinical use. 3D models can be printed in rigid or flexible materials, and the original size can be augmented depending on the application the models are needed for. The most common applications of 3D models at present include procedural planning of complex surgical or interventional cases, in vitro simulation for research purposes, training and communication with patients and families. The aim of this pictorial review is to describe the basic principles of this technology and present its current and future applications

Can finite element models of ballooning procedures yield mechanical response of the cardiovascular site to overexpansion?

Patient-specific numerical models could aid the decision-making process for percutaneous valve selection; in order to be fully informative, they should include patient-specific data of both anatomy and mechanics of the implantation site. This information can be derived from routine clinical imaging during the cardiac cycle, but data on the implantation site mechanical response to device expansion are not routinely available. We aim to derive the implantation site response to overexpansion by monitoring pressure/dimensional changes during balloon sizing procedures and by applying a reverse engineering approach using a validated computational balloon model. This study presents the proof of concept for such computational framework tested in-vitro. A finite element (FE) model of a PTS-X405 sizing balloon (NuMed, Inc., USA) was created and validated against bench tests carried out on an ad hoc experimental apparatus: first on the balloon alone to replicate free expansion; second on the inflation of the balloon in a rapid prototyped cylinder with material deemed suitable for replicating pulmonary arteries in order to validate balloon/implantation site interaction algorithm. Finally, the balloon was inflated inside a compliant rapid prototyped patient-specific right ventricular outflow tract to test the validity of the approach. The corresponding FE simulation was set up to iteratively infer the mechanical response of the anatomical model. The test in this simplified condition confirmed the feasibility of the proposed approach and the potential for this methodology to provide patient-specific information on mechanical response of the implantation site when overexpanded, ultimately for more realistic computational simulations in patient-specific settings

The interplay between chemical and mechanical feedback from the first generation of stars

We study cosmological simulations of early structure formation, including non-equilibrium molecular chemistry, metal pollution from stellar evolution, transition from population III (popIII) to population II (popII) star formation, regulated by a given critical metallicity, and feedback effects. We investigate the properties of early metal spreading from the different stellar populations and its interplay with primordial molecular gas. We find that, independently of the details about popIII modeling, after the onset of star formation, regions enriched below the critical level are mostly found in isolated environments, while popII star formation regions are much more clumped. Typical star forming haloes show average SN driven outflow rates of up to 10^{-4} Msun/yr in enriched gas, initially leaving the original star formation regions almost devoid of metals. The polluted material, which is gravitationally incorporated in over-dense environments on timescales of 10^7 yr, is mostly coming from external, nearby star forming sites ("gravitational enrichment"). In parallel, the pristine-gas inflow rates are between 10^{-3} - 10^{-1} Msun/yr. However, thermal feedback from SN generates turbulence and destroys molecules within the pristine gas, and only the polluted material, incorporated via gravitational enrichment, can continue to cool by atomic metal fine-structure transitions on time scales short enough to end the initial popIII regime within less than 10^8 yr.Comment: Accepted on the 31/1/201

Common variants at ABCA7, MS4A6A/MS4A4E, EPHA1, CD33 and CD2AP are associated with Alzheimer's disease

We sought to identify new susceptibility loci for Alzheimer's disease through a staged association study (GERAD+) and by testing suggestive loci reported by the Alzheimer's Disease Genetic Consortium (ADGC) in a companion paper. We undertook a combined analysis of four genome-wide association datasets (stage 1) and identified ten newly associated variants with P ≤ 1 × 10−5. We tested these variants for association in an independent sample (stage 2). Three SNPs at two loci replicated and showed evidence for association in a further sample (stage 3). Meta-analyses of all data provided compelling evidence that ABCA7 (rs3764650, meta P = 4.5 × 10−17; including ADGC data, meta P = 5.0 × 10−21) and the MS4A gene cluster (rs610932, meta P = 1.8 × 10−14; including ADGC data, meta P = 1.2 × 10−16) are new Alzheimer's disease susceptibility loci. We also found independent evidence for association for three loci reported by the ADGC, which, when combined, showed genome-wide significance: CD2AP (GERAD+, P = 8.0 × 10−4; including ADGC data, meta P = 8.6 × 10−9), CD33 (GERAD+, P = 2.2 × 10−4; including ADGC data, meta P = 1.6 × 10−9) and EPHA1 (GERAD+, P = 3.4 × 10−4; including ADGC data, meta P = 6.0 × 10−10)

A computational framework for mitral valve analysis combining multi-modality imaging, statistical shape modelling and fluid-structure simulations

In the context of cardiac disease, >300,000 people in the world are annually referred for mitral valve (MV) treatment as a consequence of MV regurgitation (MR). Current surgical strategies adopted to repair or replace the malfunctioning valve carry high risks, and considerable efforts are invested towards the development of less invasive techniques in order to reduce such risks and extend the treatment to a larger number of patients. However, the anatomy of the MV apparatus is rather complex, with several structures arranged in a non-uniform geometry interacting to guarantee the valvular function. Due to this geometrical complexity, the options for transcatheter and/or suture-less devices for MV repair or replacement on the market are limited. Given the wide variability encountered in MV anatomy and physiology, I hypothesize that patient or population- specific geometries play a relevant role in influencing the process of designing a new MV device. By exploiting clinical data acquired on relevant patient cohorts, I developed computational techniques for the automatic analysis of the MV apparatus, with the aim to provide a tool for tackling the complex problem of device optimisation via a patient or population driven approach. Specifically, I collected 3D echocardiography and cardiovascular magnetic resonance images from patients suffering from MR and who require a new valve. I processed such images with an automatic segmentation method and obtained a comprehensive virtual anatomical model of the left heart and MV. Analysed with a statistical shape modelling technique, these models allowed me to identify shape descriptors in the target patients, and to classify the full population on the basis of quantifiable anatomical 3D parameters. Finally, I used these results to generate an anatomical model of the average patient, which I combined with numerical simulations to derive mechanical and fluid-dynamics information for potential device improvements