Wu Z J, Gao B Z, Slonin J H, Hwang N H
Department of Biomedical Engineering, University of Miami, Coral Gables, Florida 33124, USA.
ASAIO J. 1996 Sep-Oct;42(5):M747-9. doi: 10.1097/00002480-199609000-00088.
Several earlier studies have indicated that bileaflet mechanical heart valves behave irregularly at low cardiac output and low pulse rate conditions, and that their hydrodynamic performances are generally inadequate. The authors conducted in vitro experiments in a pulsatile mock circulatory loop to compare the performance of the St. Jude Medical (SJM) valve and a long body bileaflet prosthesis recently introduced by Medical Carbon Research Institute (MCRI) (Austin, TX). The new MCRI mechanical heart valve model was designed with emphasis on improved hydrodynamic efficacy by introducing a long body with parallel leaflets and by leaflets increasing the flow area. Experimental studies were conducted on five test valves (MCRI 19 mm, MCRI 25 mm, SJM 19 mm, SJM 23 mm, and SJM 29 mm) with cardiac outputs of 2.0, 2.5, 3.0, and 3.5 L/min at a pulse rate of 40 beats/min, and 3.5, 4.0, 4.5, and 5.0 L/min at a pulse rate of 70 beats/min. Transvalvular pressure drop and closure volume were assessed by measuring the instantaneous ventricular and aortic pressures and aortic flow. The leaflet motions of the tested valves were observed by direct video recording using a charge coupled device camera while the flow measurements were being conducted. Testing under simulated physiologic ventricular and aortic pressure waveforms, the results of this study show that the MCRI bileaflets remained fully open during the entire ejection phase, even at very low cardiac output conditions (2.0 L/min). The closure volume (defined as percentage of forward flow volume) increased with decreasing cardiac output, as reported earlier by others. Comparative results also indicate that the MCRI design has nearly a two size pressure drop advantage over the SJM, with significantly smaller closure volume.
多项早期研究表明，双叶机械心脏瓣膜在低心输出量和低脉率条件下表现异常，其流体动力学性能总体不足。作者在脉动模拟循环回路中进行了体外实验，以比较圣犹达医疗公司（SJM）瓣膜和医学碳研究所（MCRI，得克萨斯州奥斯汀）最近推出的长体双叶人工心脏瓣膜的性能。新的MCRI机械心脏瓣膜模型的设计重点是通过引入带有平行瓣叶的长体以及增加瓣叶的流动面积来提高流体动力学效率。对五个测试瓣膜（MCRI 19毫米、MCRI 25毫米、SJM 19毫米、SJM 23毫米和SJM 29毫米）进行了实验研究，心输出量分别为2.0、2.5、3.0和3.5升/分钟，脉率为40次/分钟，以及心输出量为3.5、4.0、4.5和5.0升/分钟，脉率为70次/分钟。通过测量瞬时心室和主动脉压力以及主动脉流量来评估跨瓣压差和关闭容积。在进行流量测量时，使用电荷耦合器件相机通过直接视频记录观察测试瓣膜的瓣叶运动。在模拟生理心室和主动脉压力波形下进行测试，本研究结果表明，即使在非常低的心输出量条件下（2.0升/分钟），MCRI双叶瓣膜在整个射血期仍保持完全打开。如其他人之前所报道的，关闭容积（定义为正向流量容积的百分比）随心输出量的降低而增加。比较结果还表明，MCRI设计在跨瓣压差方面比SJM有近两个尺寸的优势，关闭容积明显更小。
