健康比格犬左心室壁生物力学特征的超声速度向量成像研究

目的应用超声速度向量成像（VVI）技术评价健康雌性比格犬左心室壁短轴切面不同节段心内、外膜下心肌生物力学特征，探讨其跨壁差异与左心室壁厚度变化的关系。方法以经心外膜超声心动图分别采集25只健康开胸比格犬二尖瓣、乳头肌和心尖水平标准左心室短轴切面3个完整心动周期实时声像图。应用VVI软件提取一个完整心动周期左心室壁3个标准短轴切面整体及其短轴切面18个节段心、内外膜下心肌的径向位移、周向应变和旋转角时间序列参数，计算并比较一个完整心动周期内左心室壁不同节段和不同短轴水平心、内外膜下心肌的最大径向位移（RDmax）、最大周向应变（CSmax）、最大旋转角（RAmax）。计算并比较一个完整心动周期内左心室不同节段和不同水平的室壁最大净增厚值（△Tmax），心内、外膜下心肌最大应变差（△CSmax），心内、外膜下心肌最大旋转角差（△RAmax）。相关分析3个不同短轴水平左心室壁的△Tmax与△CSmax、△RAmax。结果①左心室壁心内膜下心肌RDmax、CSmax和RAmax均大于心外膜下心肌（P〈0.05）；②左心室壁△Tmax为心尖〈二尖瓣〈乳头肌水平，△CSmax于乳头肌水平最大，△RAmax于心尖水平最大（P〈0.05）；③3个标准短轴切面左心室壁△CSmax和△RAmax均与△Tmax呈直线相关（r=0.705-0.802，P〈0.001；r=0.697-0.736，P〈0.001）。结论健康犬左心室壁心肌力学状态存在不同水平的跨壁差异；左心室壁心、内外膜下心肌间的周向应变差异和相对周向剪切运动与左心室壁厚度变化密切有关；超声VVI技术有助于揭示犬左心室壁生物力学基本特征。

Biomechanical characteristics of left ventricular wall using ultrasonic velocity vector imaging:a healthy canine mode

Objective To evaluate biomechanical characteristics of sub-endocardial and sub-epicardial myocardium at circumferential left ventricular segments on healthy canine model using ultrasonic velocity vector imaging（VVI） and to demonstrate the spatial difference of transmural biomechanical characteristics within left ventricular wall and the mechanical mechanism of left ventricular wall thickening. Methods The standard two-dimensional dynamic gray-scale short-axis images at the levels of mitral valve, papillary muscle arid apex in 3 complete cardiac cycles in 25 healthy open-chest beagles were acquired separately using epi- cardial echocardiography. The time sequential paralneters of left ventricular sub-endocardium and sub-epicar- dium at 18 circumferential myocardial segments and 3 standard short-axis levels in a completed cardiac cycle were extracted respectively via a dedicated VVI workstation for radial displacement, circumferential strain and rotation angle. The myocardial maximal radial displacement （RDmax）, maximal circumferential strain （CSmax） and maximal rotation angle（RAmax） at sub-endocardium and sub-epicardium of 18 segments and 3 short-axis levels of left ventricular wall in a completed cardiac cycle were calculated and compared. The maximal net incrassate values（△Tmax） , maximal rotation angle difference（△RAmax） and maximal strain difference（△CSmax） between sub-endocardium and sub-epicardium at different myocardial segments and levels of left ventricular wall were calculated and compared. The correlation were performed among △Tmax and △CSmax, and ARAmax at 3 short-axis levels, respectively. Results ①RDmax, CSmax and RAmax of sub-endocardium were higher than those of sub-epicardium （P 〈 0.05）.②The distribution of left ventricular △Tmax at different levels were：apex 〈 mitral valve 〈 papillary muscle （P 〈 0.05）. △RAmax was highest at apex level （P 〈 0.05） ;△ CSmax was highest at papillary muscle level （ P 〈 0.05）.③Linear correlationships were estab- lished between △Tmax and △CSmax （r=-0.705-0.802, P 〈 0.001） and between △Tmax and △RAmax （ r=0.697-0.736,P 〈 0.001） at 3 short-axis levels of left ventricle. Conclusions There is a spatial discrepancy distribution of left ventricular mechanics at different short-axis circumferential levels and segments in healthy beagles. The co-relationship for left ventricular wall thickness and the circumferential shear movement existed between left ventrieular sub-endocardium and sub-epicardium has been explored and the basic transmural myocardial mechanics could be demonstrated using ultrasonic VVI techniques.