Paolo Peruzzo

Diffusion of floating particles in flow through emergent vegetation: Further experimental investigation

[1] In this paper we present the results of a new laboratory investigation aimed at providing a better understanding of the transport and diffusion processes of floating particles (e.g., buoyant seeds) in open channel flow with emergent vegetation. The experiments are designed primarily to study the influence of vegetation density and flow velocity on the relevant interaction mechanisms between particles and vegetation. The aim is also to ascertain the validity of a stochastic model recently proposed by Defina and Peruzzo (2010). We find that (1) the proper definition of plant spacing is given as 1/npdp, with dp being the plant diameter and np being the number of plants per unit area, (2) the particle retention time distribution can be satisfactorily approximated by a weighted combination of two exponential distributions, (3) flow velocity has a significant influence on the retention time and on the efficiency of the different trapping mechanisms, and (4) vegetation pattern and density have a minor influence on the probability of capture and on the retention time of particles. Indeed, the comparison between model predictions and experimental results is satisfactory and suggests that the observed relevant aspects of the particle-vegetation interaction processes are properly described by the model.

In vitro hemodynamic testing of Amplatzer plugs for paravalvular leak occlusion after transcatheter aortic valve implantation.

OBJECTIVE We aimed to in-vitro test Amplatzer devices (Amplatzer Vascular Plug II and Amplatzer Vascular Plug III, SJM, St. Paul, MN) in closing PVL generated by transcatheter balloon expandable aortic valve prosthesis in order to quantify the effective treatment of PVL. BACKGROUND Transcatheter aortic valve implantation (TAVI) procedures represent the treatment of choice for high risk patients. Despite evolving technologies paravalvular leak (PVL) is still a major unaddressed issue. This severe complication significantly impairs long-term survival. Percutaneous treatment of this complication is usually performed with the implantation of not specifically designed and not approved vascular devices. METHODS A 26 mm Sapien XT (Edwards Lifesciences, Irvine, CA) was implanted in a rubber aortic root and a semi-elliptical shape PVL was created. The vascular occluder devices were implanted in the PVL and hemodynamic performance was tested in a pulse duplicator according to international standard ISO 5840-3:2013. Different type of comparison tests together with high speed camera recording allowed us to define the global efficiency of the occluders and their interaction with the transcatheter prosthesis. RESULTS The results revealed that the use of vascular plugs was not per se sufficient to produce an effective or substantial reduction of PVL with a maximum efficiency of less than 50%. Recorded video showed clearly that the vascular plug always interfered with the leaflet of the prosthetic valve. CONCLUSIONS Currently used devices do not guarantee effective treatment of PVL and may otherwise compromise the structural integrity of the prosthetic valve implanted. Specifically designed devices are required. CONDENSED ABSTRACT Despite evolving technologies, paravalvular leak (PVL) is still a major unaddressed issue after transcatheter aortic valve implantation. Percutaneous treatment of this complication is usually performed with the implantation of Amplatzer devices not specifically designed and not approved for this specific use. We tested Amplatzer devices in a pulse duplicator to occlude PVL generated after implantation of a 26 mm SAPIENT XT prosthesis. The results revealed that the use of vascular plugs was not per se sufficient to produce an effective or substantial reduction of PVL. The video showed clearly that the vascular plug always interfered with the leaflet of the prosthetic valve.