O'Brien P D, O'Brien W D, Rhyne T L, Warltier D C, Sagar K B
Medical College of Wisconsin, Division of Cardiology, Milwaukee 53226.
Circulation. 1995 Jan 1;91(1):171-5. doi: 10.1161/01.cir.91.1.171.
Ultrasonic backscatter demonstrates a cardiac cycle-dependent modulation. The exact mechanism of the modulation is under debate. The objective of the present study was to test the hypothesis that a change in size and configuration of myofilaments from systole to diastole alters acoustic propagation properties and backscatter.
In vivo measurements were made of integrated backscatter at 5 MHz (IBR5), followed by in vitro measurements of ultrasonic attenuation, speed, and heterogeneity index using a scanning laser acoustic microscope at 100 MHz. Studies were performed in canine hearts (16) arrested in systole (8) with calcium chloride or arrested in diastole (8) with potassium chloride. Sarcomere length was measured with a calibrated eyepiece on a Ziess microscope. Wall thickness was measured with calipers. The attenuation coefficient of 220 +/- 34 dB/cm during systole was significantly higher than the coefficient of 189 +/- 24 dB/cm during diastole (P < .01); the IBR5 of -44.7 +/- 1.2 dB during systole was significantly greater than the IBR5 of -47.0 +/- 1.0 dB during diastole (P < .01); the ultrasonic speed of 1591 +/- 11 m/s during systole was higher than the speed of 1575 +/- 4.2 m/s during diastole (P < .01); and the heterogeneity index of 7.4 +/- 1.8 m/s during systole was significantly lower than the index of 9.0 +/- 2.0 m/s during diastole (P < .02). The sarcomere length of 1.804 +/- 0.142 microns during diastole was significantly higher than the length of 1.075 +/- 0.177 micron during systole (P < .01). Wall thickness was significantly greater during systole than during diastole (20 +/- 3 versus 9 +/- 3 mm, P < .01).
Ultrasonic backscatter and propagation properties are directly related to sarcomere length and myocardial thickness and may be responsible for cardiac cycle-dependent variation in backscatter.
超声背向散射表现出与心动周期相关的调制。该调制的确切机制仍在争论中。本研究的目的是检验以下假设：从收缩期到舒张期肌丝大小和构型的变化会改变声传播特性和背向散射。
在体内以5兆赫测量积分背向散射（IBR5），随后在体外使用100兆赫的扫描激光声学显微镜测量超声衰减、速度和异质性指数。研究在犬心脏（16个）中进行，其中8个用氯化钙使其停搏于收缩期，8个用氯化钾使其停搏于舒张期。用校准目镜在蔡司显微镜上测量肌节长度。用卡尺测量壁厚度。收缩期的衰减系数为220±34分贝/厘米，显著高于舒张期的189±24分贝/厘米（P<.01）；收缩期的IBR5为-44.7±1.2分贝，显著大于舒张期的-47.0±1.0分贝（P<.01）；收缩期的超声速度为1591±11米/秒，高于舒张期的1575±4.2米/秒（P<.01）；收缩期的异质性指数为7.4±1.8米/秒，显著低于舒张期的9.0±2.0米/秒（P<.02）。舒张期的肌节长度为1.804±0.142微米，显著高于收缩期的1.075±0.177微米（P<.01）。收缩期的壁厚度显著大于舒张期（20±3对9±3毫米，P<.01）。
超声背向散射和传播特性与肌节长度和心肌厚度直接相关，可能是背向散射中与心动周期相关变化的原因。
