Effective Computational Framework for Pre-Interventional Planning of Peripheral Arteriovenous Malformations with In Vivo and In Vitro Validation

Purpose: Peripheral arteriovenous malformations (pAVMs) are congenital lesions characterised by abnormal high-flow, low-resistance vascular connections - constituting the so-called nidus - between arteries and veins. The mainstay treatment typically involves the embolisation of the nidus with embolic and sclerosant agents, however the complexity of AVMs often leads to uncertain outcomes. This study aims at developing a simple, yet effective computational framework to aid the clinical decision making around the treatment of pAVMs. Methods: A computational model was developed to simulate the pre-, intra-, and post-intervention haemodynamics of an AVM. A porous medium of varying permeability was used to simulate the effect that the sclerosant has on the blood flow through the nidus. The computational model was informed by computed tomography (CT) scans and digital subtraction angiography (DSA) images, and the results were compared against clinical data and experimental results. Results: The computational model was able to simulate the blood flow through the AVM throughout the intervention and predict (direct and indirect) haemodynamic changes due to the embolisation. The simulated transport of the dye in the AVM was compared against DSA time-series obtained at different intervention stages, providing confidence in the results. Moreover, experimental data obtained via a mock circulatory system involving a patient specific 3D printed phantom of the same AVM provided further validation of the simulation results. Conclusion: We developed a simple computational framework to simulate AVM haemodynamics and predict the effects of the embolisation procedure. The developed model lays the foundation of a new, computationally driven treatment planning tool for AVM embolisation procedures.

Piezoelectric Photoacoustic System for Fluid Flow Monitoring

The aim of this study is to investigate the feasibility of using a laboratory assembled piezoelectric based photoacoustic (PA) system for noncontact monitoring fluid flow. This is to overcome the drawbacks of some existing fluid flow detection systems, which include expensive equipment and their maintenance cost, limited sensitivity and specificity in detecting signals from restricted regions or at low flow velocity. The produced PA signal waves detected by a piezoelectric transducer used in this study was processed to determine the required phase value (Ф), which value was found to correlate linearly with fluid flow status. The fluid pressure difference of 1.16 pascals (Pa) and 11.90 Pa applied to the developed mock circulatory system was observed to produce changes in phase value with mean ± standard deviation (SD) ΔФ of 0.79 ± 0.07 rad and 2.17 ± 0.07 rad, respectively, suggesting a linear response of the developed system with changes in circulation system. This trend was supported with the relatively low absolute difference of 0.07 ± 0.01 rad in the predicted values as compared to that of the ground truth. This work concluded that the capabilities and simplicity of the proposed PA system renders it feasible for cost effective, non-destructive assessment of fluid flow in future studies.

Three-dimensional printing for cardiovascular diseases: from anatomical modeling to dynamic functionality

Three-dimensional (3D) printing is widely used in medicine. Most research remains focused on forming rigid anatomical models, but moving from static models to dynamic functionality could greatly aid preoperative surgical planning. This work reviews literature on dynamic 3D heart models made of flexible materials for use with a mock circulatory system. Such models allow simulation of surgical procedures under mock physiological conditions, and are; therefore, potentially very useful to clinical practice. For example, anatomical models of mitral regurgitation could provide a better display of lesion area, while dynamic 3D models could further simulate in vitro hemodynamics. Dynamic 3D models could also be used in setting standards for certain parameters for function evaluation, such as flow reserve fraction in coronary heart disease. As a bridge between medical image and clinical aid, 3D printing is now gradually changing the traditional pattern of diagnosis and treatment.

In vitro study of trileaflet polytetrafluoroethylene conduit and its valve-in-valve transformation

OBJECTIVES Handmade trileaflet expanded polytetrafluoroethylene valved conduit developed using the flip-over method has been tailored for pulmonary valve reconstruction with satisfactory outcomes. We investigated the in vitro performance of the valve design in a mock circulatory system with various conduit sizes. In our study, the design was transformed into a transcatheter stent graft system which could fit in original valved conduits in a valve-in-valve fashion. METHODS Five different sizes of valved polytetrafluoroethylene vascular grafts (16, 18, 20, 22 and 24 mm) were mounted onto a mock circulatory system with a prism window for direct leaflets motion observation. Transvalvular pressure gradients were recorded using pressure transducers. Mean and instant flows were determined via a rotameter and a flowmeter. Similar flip-over trileaflet valve design was then carried out in 3 available stent graft sizes (23, 26 and 28.5 mm, Gore aortic extender), which were deployed inside the valved conduits. RESULTS Peak pressure gradient across 5 different sized graft valves, in their appropriate flow setting (2.0, 2.5 and 5.0 l/min), ranged from 4.7 to 13.2 mmHg. No significant valve regurgitation was noted (regurgitant fraction: 1.6–4.9%) in all valve sizes and combinations. Three sizes of the trileaflet-valved stent grafts were implanted in the 4 sizes of valved conduits except for the 16-mm conduit. Peak pressure gradient increase after valved-stent graft-in-valved-conduit setting was <10 mmHg in all 4 conduits. CONCLUSIONS The study showed excellent in vitro performance of trileaflet polytetrafluoroethylene valved conduits. Its valved stent graft transformation provided data which may serve as a reference for transcatheter valve-in-valve research in the future.

An Original Valveless Artificial Heart Providing Pulsatile Flow Tested in Mock Circulatory Loops

Purpose We present the test bench results of a valveless total artificial heart that is potentially compatible with the pediatric population. Methods The RollingHeart is a valveless volumetric pump generating pulsatile flow. It consists of a single spherical cavity divided into 4 chambers by 2 rotating disks. The combined rotations of both disks produce changes in the volumes of the 4 cavities (suction and ejection). The blood enters/exits the spherical cavity through 4 openings that are symmetrical to the fixed rotation axis of the first disk. Mock circulatory system: The device pumps a 37% glycerin solution through 2 parallel circuits, simulating the pulmonary and systemic circulations. Flow rates are acquired with a magnetic inductive flowmeter, while pressure sensors collect pressure in the left and right outflow and inflow tracts. In vitro test protocol: The pump is run at speeds ranging from 20 to 180 ejections per minute. The waveform of the pressure generated at the inflow and outflow of the 4 chambers and the flow rate in the systemic circulation are measured. Results At an ejection rate of 178 min−1, the Rolling Heart pumps 5.3 L/min for a systemic maximal pressure gradient of 174 mmHg and a pulmonary maximal pressure gradient of 75 mmHg. The power input was 14 W, corresponding to an efficiency of 21%. Conclusions The Rolling Heart represents a new approach in the domain of total artificial heart. This preliminary study endorses the feasibility of a single valveless device acting as a total artificial heart.

Hemolysis research of implantable axial flow pump for two -step heart transplantation in children

Introduction.One of the main indicators characterizing mechanical circulatory support devices (artificial valve, implantable pumps, etc.) is trauma of blood cells. Therefore, while developing new pumps, one of the key studies in vitro is to evaluate blood hemolysis. For an objective hemolysis analysis of pump it is required to create a standardized methodology of hemolysis studies. The object of the study in this paper is implantable axial pump DON for two-step heart transplantation in children.The aimof study is to develop a standardized methodology of hemolysis studies of blood pumps and to conduct research of pediatric axial pump DON.Materials and methods.To conduct hemolysis research we created a mock circulatory system consisting of a reservoir placed in water bath maintaining a constant working fluid (blood) temperature, hydrodynamic resistance, connecting tubes, ports for blood sampling and pressure and flow measurement systems, and research pump. Test method is to estimate levels of free hemoglobin pHb obtained by blood samples during pump working in operating mode (for pediatric pump: blood flow 2.5 l/min, pressure difference 80 mmHg). Using the data obtained the standardized indices of hemolysis NIH and MIH are calculated based on pHb values, hematocrit, total hemoglobin, blood flow and working pump time.Results.We developed and realized a standardized methodology of hemolysis research by which we evaluated hemolysis of pediatric axial pump. The results of hemolysis tests allowed us to optimize the design of DON. Obtained values of hemolysis of the latest version of pediatric pump DON-3 have shown that they do conform to the requirements of minimum blood injury and it allows us to proceed to the next step of pediatric pump research – animal experiments.Conclusion.Developed methods and evaluation tools of hemolysis allow us to provide objective information on one of the most important indicators of developing implantable pediatric axial pump and they could be recommended for hemolysis research of others pumps.