Haemodynamic alterations after percutaneous valve implantation

Many patients who suffer from aortic valve dysfunction are too weak to be eligible for valve replacement via surgery, due to co-morbidities and old age. Transcatheter aortic valve (TAV) implantation has been developed as an alternative to surgery, enabling replacement of the dysfunctional valve percutaneously. However, the inability to remove the native leaflets leads to the bioprosthetic being held in place inside a pseudo-cylindrical structure. The passive nature of heart valves means the surrounding fluid environment’s dynamics are critical in producing optimum performance, and would ideally be returned to the healthy, physiological state. The association of TAVs with thrombotic events, such as strokes, has not yet been fully explained. A pulse duplicator and particle image velocimetry were used to model and characterise the flow fields of a healthy, physiological aortic root and valve, which was then compared to those resulting from a number of typical post- surgical outcomes, identifying the fluid mechanisms promoted by the root geometry to optimise the ejection and closing phases of the cardiac cycle, and revealing the importance of an optimal integration of valve and root architecture, and characterising common post-surgical environments. The same techniques were then used to examine the flow dynamics of the region following TAV implantation, revealing the effect of TAV alignment with its hosts’ commissures, and how the presence of native leaflets, commonly omitted from in vitro TAV testing, affect the valve performance. Slow and stagnant flow was observed within the sinuses due to the native leaflets, whilst global valve performance was broadly unaffected, and omission of the native leaflets resulted in improved haemodynamic performance. A model of coronary arteries was incorporated into the benchtop simulation, revealing increase of flow in the upper coronary sinuses, but flow at the base of all sinuses remained very slow following TAV implantation. The elucidation of this stagnation, associated with thrombotic events, provides an explanation for the increased levels of thrombotic-associated pathologies following TAV implantation

Use of portable air purifiers to reduce aerosols in hospital settings and cut down the clinical backlog

SARS-CoV-2 has severely affected capacity in the NHS, and waiting lists are markedly increasing due to downtime of up to 50 minutes between patient consultations/procedures, to reduce the risk of infection. Ventilation accelerates this air cleaning, but retroactively installing built-in mechanical ventilation is often cost-prohibitive. We investigated the effect of using portable air cleaners (PAC), a low-energy and low-cost alternative, to reduce the concentration of aerosols in typical patient consultation/procedure environments. The experimental setup consisted of an aerosol generator, which mimicked the subject affected by SARS-CoV-19, and an aerosol detector, representing a subject who could potentially contract SARS-CoV-19. Experiments of aerosol dispersion and clearing were undertaken in situ in a variety of rooms with 2 different types of PAC in various combinations and positions. Correct use of PAC can reduce the clearance half-life of aerosols by 82% compared to the same indoor-environment without any ventilation, and at a broadly equivalent rate to built-in mechanical ventilation. In addition, the highest level of aerosol concentration measured when using PAC remains at least 46% lower than that when no mitigation is used, even if the PAC’s operation is impeded due to placement under a table. The use of PAC leads to significant reductions in the level of aerosol concentration, associated with transmission of droplet-based airborne diseases. This could enable NHS departments to reduce the downtime between consultations/procedures

Valvulogenesis of a living, innervated pulmonary root induced by an acellular scaffold

Heart valve disease is a major cause of mortality and morbidity worldwide with no effective medical therapy and no ideal valve substitute emulating the extremely sophisticated functions of a living heart valve. These functions influence survival and quality of life. This has stimulated extensive attempts at tissue engineering “living” heart valves. These attempts utilised combinations of allogeneic/ autologous cells and biological scaffolds with practical, regulatory, and ethical issues. In situ regeneration depends on scaffolds that attract, house and instruct cells and promote connective tissue formation. We describe a surgical, tissue-engineered, anatomically precise, novel off-the-shelf, acellular, synthetic scaffold inducing a rapid process of morphogenesis involving relevant cell types, extracellular matrix, regulatory elements including nerves and humoral components. This process relies on specific material characteristics, design and “morphodynamism”.</p

Finite element and fluid-structure interaction modelling of a balloon catheter

Intervention treatments for aortic stenosis strongly rely on the use of a medical balloon catheter which is utilized for dilating the narrowed aortic valve or the deployment of the implanted devices. However, the complete inflation of the balloon will block the blood outflow and cause instability. This paper demonstrates a computational analysis method to examine the influence of the amount of balloon inflation volume on balloon movement within a pulsating fluid environment. A tri-folded typical shape of the balloon model was inflated by pressurization. The balloon’s front projection area changes during both simulation and experiment were recorded. To address the interaction between the balloon model with varying inflation levels and the introduction of fluid into the arched aorta, a Fluid-Structure Interaction (FSI) model was developed. Compared with the experimental data, the front projection area in the simulation showed a similar increment, which can be used to validate the balloon model. For FSI simulation, the balloon catheter’s maximum displacement rises with the inflation level, with a slight rise at about 10 ml and a substantial rise at 20 ml volume. This work showed a significant advancement in the ability to replicate balloon movement during valvuloplasty using an FSI model