低强度超声辐照对兔左室心肌收缩力影响的实验研究

Experimental study on the effect of left ventricular myocardial contractility in rabbits by low intensity ultrasound irradiation

目的应用低强度超声辐照兔左室心肌,探讨其对兔心肌收缩力的影响。方法选取8只新西兰白兔,设置超声辐照输出功率0.75 W,最大声强0.8 W/cm^(2),从心尖区向左室长轴方向辐照25 min,间隔1周后再辐照50 min,应用M型超声于左室中间段短轴切面获取辐照前、辐照25 min和辐照50 min兔左室射血分数(LVEF),Qlab图像分析软件获取左室基底段、中间段、心尖段和整体心肌内层圆周应变,计算其绝对值,比较辐照前后上述参数的差异;计算并比较辐照前与辐照50 min各节段心肌内层圆周应变绝对值差值,比较辐照前后上述参数的差异。实验结束后处死2只兔,观察其心尖部心肌及微血管病理变化。结果与辐照前比较,辐照25 min及50 min兔LVEF均增大,且辐照50 min时LVEF大于辐照25 min,差异均有统计学意义(均P<0.05)。辐照前、辐照25 min及50 min兔左室整体心肌内层圆周应变绝对值依次增大,差异有统计学意义(P<0.05);辐照50 min兔左室基底段心肌内层圆周应变绝对值大于辐照前,辐照25 min和50 min兔左室中间段及心尖段心肌内层圆周应变绝对值均大于辐照前,差异均有统计学意义(均P<0.05)。辐照前与辐照50 min兔左室基底段、中间段、心尖段心肌内层圆周应变绝对值差值比较差异有统计学意义(F=7.95,P<0.001),心尖段心肌内层圆周应变绝对值差值与基底段、中间段比较差异均有统计学意义(t=5.62、3.23,P=0.002、0.03)。病理检测结果显示,辐照50 min后兔心肌细胞未见明显肿胀、变性及坏死,心肌微血管未见出血及破裂。结论低强度超声辐照兔左室心肌可产生明显的正性肌力作用,随着辐照时间的增加心肌收缩功能可得到改善,且靠近超声发射区的左室心尖段改善更为显著。

Objective To irradiate left ventricular myocardium in rabbits by low intensity ultrasound,and to explore the effect of the myocardial contractility.Methods Eight New Zealand white rabbits were irradiated from the apex of the heart towards the left ventricular major axis for 25 min and 50 min after 1 week by low intensity ultrasound,respectively,and the output power was 0.75 W,the maximum sound intensity was 0.8 W/cm2.The left ventricular ejection fraction(LVEF)was obtained by M-mode ultrasound at the short axis section of the middle segment of the left ventricle before irradiation and 25 min,50 min after irradition.The circumferential strain at the basal segment,the middle segment and apex segment of the left ventricle,and the global myocardium inner layer were obtained by Qlab analysis software,the absolute value were calculated,the absolute differences of the circmferential strain in the myocardium inner layer of the corresponding segment before irradiation and 50 min after irradiation were calculated and compared.2 rabbits were killed after experiment,the pathological changes of apical myocardium and microvessels were observed.Results LVEF of 25 min and 50 min after irradiation were higher than that before irradiation,and LVEF of 50 min after irradiation was higher than that of 25 min after irradiation,the differences were statistically significant(all P<0.05).The absolute value of left ventricular global circumferential strain before irradiation,25 min and 50 min after irradiation were increased successively,and the difference was statistically significant(all P<0.05).The absolute value of circumferential strain in the myocardium inner layer of the left ventricular basal segment in 50 min after irradiation was higher than that before irradiation,the absolute values of the circumferential strain of myocardium inner layer of left ventricular middle and apex in 25 min after and 50 min after irradiation were higher than those before irradiation,the differences were statistically significant(all P<0.05).There was statistical significance in the absolute difference of circumferential strain of myocardium inner layer of left ventricular basal segment,middle segment and apex segment before irradiation and 50 min after irradiation(F=7.95,P<0.001).There were statistically significant differences in the absolute difference of circumferential strain of inner myocardium between the apical segment,the basal segment and the middle myocardium(t=5.62,3.23,P=0.002,0.03).The pathological results showed that 50 min after irradiation,there was no obvious swelling,degeneration or necrosis of the rabbit myocardial cells,and there was no bleeding or rupture of the myocardial microvessels.Conclusion Low intensity ultrasound irradiation of left ventricular myocardium of rabbits can produce obvious positive inotropic effect,the increase of irradiation time can improve myocardial systolic function,and the improvement of left ventricular apical segment near the ultrasonic emission area is more significant.