Nevo E, Lanir Y
Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa.
J Biomech. 1994 Dec;27(12):1433-46. doi: 10.1016/0021-9290(94)90193-7.
The unloaded heart is not stress-free. It is subjected to residual stress and strain. Their extent and influence on the global performance of the left ventricle and on local phenomena in the ventricular wall are studied by model simulation. The analysis focuses on the equatorial region of the ventricle, with an approximate thick-walled cylindrical geometry. The in vivo myocardium is considered to be incompressible, consisting of fibers embedded in a fluid matrix, with transmurally varying anisotropic microstructure in accordance with morphological characteristics. The results show that residual strain is transmurally distributed with a pattern and magnitude which agree well with measurements. The calculated residual strains are within mean +/- one standard deviation of the measured ones. Their magnitude was found to increase with increasing opening angle and with increasing wall thickness. The residual strain was found to have several effects on ventricular function: At volumes higher than the reference one it gives rise to more uniform transmural distributions of stress and intramyocardial pressure; it causes about 50% increase in the ventricular compliance at high volumes and doubles the suction of atrial blood at low volumes, thus facilitating the diastolic filling. In addition, residual strains cause bias of in vivo measured strains from their true values. This may significantly affect physiological interpretation of measured ventricular deformations. In conclusion, the present structural analysis predicts that residual strain has favorable effect on left-ventricular diastolic performance, and gives rise to more uniform ventricular stress distribution.
无负荷的心脏并非没有应力。它会受到残余应力和应变的影响。通过模型模拟研究了它们的程度以及对左心室整体性能和心室壁局部现象的影响。分析聚焦于心室的赤道区域，其具有近似厚壁圆柱的几何形状。活体心肌被认为是不可压缩的，由嵌入流体基质中的纤维组成，其透壁各向异性微观结构根据形态特征而变化。结果表明，残余应变呈透壁分布，其模式和大小与测量结果吻合良好。计算得到的残余应变在测量值的均值±一个标准差范围内。发现其大小随开口角度的增加和壁厚的增加而增大。发现残余应变对心室功能有多种影响：在高于参考容积时，它会使应力和心肌内压力的透壁分布更加均匀；在高容积时，它会使心室顺应性增加约50%，在低容积时会使心房血液的抽吸量翻倍，从而促进舒张期充盈。此外，残余应变会导致活体测量应变偏离其真实值。这可能会显著影响对测量到的心室变形的生理学解释。总之，目前的结构分析预测残余应变对左心室舒张性能有有利影响，并会使心室应力分布更加均匀。
