心臓代用弁の構造的工夫による動脈弁の弁機能向上の試み

抄録

Novel artificial heart valves have been fabricated using tissue-regeneration techniques or the latest biocompatible materials. We investigated prototypes of such valves and experimentally measured how the valve size and shape influence the performance. A previous study reported that the hemodynamic performance during valve opening and closing was completely co-dependent. Combining the two performances was difficult using our fabricated semilunar valve made of a uniform thin membrane. Nevertheless, modifying the mechanical property of deformation balanced the opening and closing effectively for higher valve performance. This was achieved by adding mechanical anisotropy to the valvular cusp. This study aimed to establish how changes in mechanical property influence artificial heart-valve performance, particularly for semilunar valves whose shape is employed for atrioventricular valves as well. To add mechanical anisotropy to the valve cusp, we fabricated valvular-cusp models, with spatially periodic surface asperities using a polyurethane sheet. Its mechanical properties were identical to those of a porcine aortic valve. Further, to determine the optimal anisotropic properties of the valve cusps, sheet thickness and orientation direction of surface asperities were varied as experimental parameters. Subsequently, isotropic and fabricated anisotropic models were compared. The experiment was conducted using our fabricated in-vitro simulator under the physiological conditions of a healthy adult. Valve function was evaluated based on the international standards ISO 5840-1 and ISO 5840-2 for artificial valves. The results indicated that the functions of the valve model with anisotropic mechanical properties improved remarkably. The effective orifice area in particular, indicating valve-opening performance, was 1.5-2.0 times higher than the isotropic model with the same maximum cusp-sheet thickness. Additionally, the regurgitant fraction decreased remarkably; however, the anisotropic property did not affect its trend when cusp thickness increased. However, the thinner cusp had a lower leakage regurgitant fraction during diastole. Therefore, a combination of the anisotropic orientation on each valvular cusp and sheet-thickness distribution is effective for balancing both opening and closing performances of the valve.