Nellis S H, Liedtke A J
Am J Physiol. 1979 Apr;236(4):H657-63. doi: 10.1152/ajpheart.1979.236.4.H657.
A low mechanical impedance strain gauge that imposed insignificant preload to the myocardial fibers was tested in vitro and in vivo. The dynamic response of the gauge to an abrupt change in length (step response) and to sinusoidal perturbation was determined. The electrical output reached 95% of maximum steady-state response within 3-5 ms after a step displacement. Frequency analysis indicated a flat response up to 80 oscillations/s. The in vivo testings of the gauges were performed on intact, working swine hearts during control and ischemic flows in a regionally perfused preparation. During control perfusion the gauges demonstrated epicardial shortening in systole and early-to-mid diastole. Relaxation was confined to late diastole. With ischemic perfusion there was a progressive loss of systolic shortening, but minimal disruption in global hemodynamics. Correlative measurements were also made with sonomicrometers positioned in subepicardial myocardium. Patterns of motion, shortening, and changes in strain were similar between the two types of gauges.
一种对心肌纤维施加极小预负荷的低机械阻抗应变计在体外和体内进行了测试。测定了该应变计对长度突然变化（阶跃响应）和正弦扰动的动态响应。在阶跃位移后3 - 5毫秒内，电输出达到最大稳态响应的95%。频率分析表明，在高达80次振荡/秒时响应平坦。应变计的体内测试是在完整的、工作的猪心脏上进行的，在局部灌注制剂中控制血流和缺血血流期间。在控制灌注期间，应变计显示收缩期和舒张早期至中期的心外膜缩短。舒张仅限于舒张晚期。在缺血灌注时，收缩期缩短逐渐丧失，但整体血流动力学的破坏最小。还使用置于心外膜下心肌的超声微测仪进行了相关测量。两种类型的应变计之间的运动、缩短和应变变化模式相似。
