Wu Z J, Hwang N H
Department of Biomedical Engineering, University of Miami, Coral Gables, Florida 33124, USA.
ASAIO J. 1995 Jul-Sep;41(3):M763-7. doi: 10.1097/00002480-199507000-00115.
The maximum left ventricular pressure slope (dP/dt) value has been used by several investigators as the criterion for studying mitral valve closure. In this article, the relationship between the ventricular pressure slope (dP/dt) and the leaflet closing behavior of bileaflet mechanical heart valves (BMV) is investigated. Two current BMVs, the St. Jude Medical 29 mm and CarboMedics 29 mm, installed in the mitral position of a mock circulatory pulsatile flow loop were used as the study model. Under simulated physiologic pressures and flow conditions, the experiment was conducted at 70, 90, and 120 beats/min with corresponding flow rates of 5.0, 6.0, and 7.5 liters/min, respectively. A laser sweeping technique was used to monitor the leaflet closing motion within the last 3 degrees excursion at valve closure. A modified dual beam laser sweeping technique system was used to register the difference of leaflet/housing impact time between the two BMV closing leaflets in asynchronous closure. Common BMV asynchronous closures were found in both BMVs at all three heart rates tested. The second closing leaflet was found to always close at higher velocity than the first. Simultaneous measurements of the ventricular pressure (Pv) and the leaflet closing time showed that Pv exhibited three stage characteristics. In the first stage, Pv gradually increased as the ventricle was filled. A sudden rise of Pv occurred immediately after closing of the first leaflet. The maximum dp/dt occurred in the third stage after closure of both BMV leaflets. The BMV closing behavior and the corresponding Pv pattern were found to depend strongly upon valve type and heart rate. The time averaged ventricular pressure slope (dp/dt) values at 70, 90, and 120 beats/min were about 40, 70, and 150 mmHg/sec for the St. Jude Medical valve and 40, 105, and 205 for the CarboMedics valve during the first closing stage. The maximum dp/dt values were 2670, 4350, and 5000 mmHg/sec for the St. Jude Medical valve and 1210, 2530, and 3210 mmHg/sec for the CarboMedics valve at the three heart rates tested, respectively. The study showed that the left ventricular pressure patterns (dP/dt) at valve closure were the result of valve operation under given driving conditions. The dp/dtmax cannot be used as the criterion for studying BMV closure.
几位研究人员已将最大左心室压力斜率（dP/dt）值用作研究二尖瓣关闭的标准。在本文中，研究了心室压力斜率（dP/dt）与双叶机械心脏瓣膜（BMV）瓣叶关闭行为之间的关系。将两个当前的BMV，即圣犹达医疗公司的29毫米瓣膜和卡博梅迪克斯公司的29毫米瓣膜，安装在模拟循环脉动流回路的二尖瓣位置，用作研究模型。在模拟生理压力和流量条件下，实验分别在70、90和120次/分钟的心率下进行，相应的流量分别为5.0、6.0和7.5升/分钟。使用激光扫描技术监测瓣膜关闭时最后3度偏移内的瓣叶关闭运动。使用改进的双光束激光扫描技术系统记录异步关闭时两个BMV关闭瓣叶之间瓣叶/外壳撞击时间的差异。在所有测试的三种心率下，两种BMV均发现常见的BMV异步关闭情况。发现第二个关闭瓣叶的关闭速度总是比第一个快。心室压力（Pv）和瓣叶关闭时间的同步测量表明，Pv呈现三个阶段特征。在第一阶段，随着心室充盈，Pv逐渐升高。第一个瓣叶关闭后，Pv立即突然升高。最大dp/dt发生在两个BMV瓣叶关闭后的第三阶段。发现BMV的关闭行为和相应的Pv模式在很大程度上取决于瓣膜类型和心率。在第一关闭阶段，圣犹达医疗瓣膜在70、90和120次/分钟时的时间平均心室压力斜率（dp/dt）值分别约为40、70和150 mmHg/秒，卡博梅迪克斯瓣膜的分别为40、105和205。在测试的三种心率下，圣犹达医疗瓣膜的最大dp/dt值分别为2670、4350和5000 mmHg/秒，卡博梅迪克斯瓣膜的分别为1210、2530和3210 mmHg/秒。研究表明，瓣膜关闭时的左心室压力模式（dP/dt）是在给定驱动条件下瓣膜运行的结果。dp/dtmax不能用作研究BMV关闭的标准。
