等容收缩期的透壁心肌力学
Transmural myocardial mechanics during isovolumic contraction.
作者信息
Ashikaga Hiroshi, van der Spoel Tycho I G, Coppola Benjamin A, Omens Jeffrey H
机构信息
Department of Medicine and Bioengineering, University of California, San Diego, CA, USA.
出版信息
JACC Cardiovasc Imaging. 2009 Feb;2(2):202-11. doi: 10.1016/j.jcmg.2008.11.009.
OBJECTIVES
We sought to resolve the 3-dimensional transmural heterogeneity in myocardial mechanics observed during the isovolumic contraction (IC) phase.
BACKGROUND
Although myocardial deformation during IC is expected to be little, recent tissue Doppler imaging studies suggest dynamic myocardial motions during this phase with biphasic longitudinal tissue velocities in left ventricular (LV) long-axis views. A unifying understanding of myocardial mechanics that would account for these dynamic aspects of IC is lacking.
METHODS
We determined the time course of 3-dimensional finite strains in the anterior LV of 14 adult mongrel dogs in vivo during IC and ejection with biplane cineradiography of implanted transmural markers. Transmural fiber orientations were histologically measured in the heart tissue postmortem. The strain time course was determined in the subepicardial, midwall, and subendocardial layers referenced to the end-diastolic configuration.
RESULTS
During IC, there was circumferential stretch in the subepicardial layer, whereas circumferential shortening was observed in the midwall and the subendocardial layer. There was significant longitudinal shortening and wall thickening across the wall. Although longitudinal tissue velocity showed a biphasic profile; tissue deformation in the longitudinal as well as other directions was almost linear during IC. Subendocardial fibers shortened, whereas subepicardial fibers lengthened. During ejection, all strain components showed a significant change over time that was greater in magnitude than that of IC. Significant transmural gradient was observed in all normal strains.
CONCLUSIONS
IC is a dynamic phase characterized by deformation in circumferential, longitudinal, and radial directions. Tissue mechanics during IC, including fiber shortening, appear uninterrupted by rapid longitudinal motion created by mitral valve closure. This study is the first to report layer-dependent deformation of circumferential strain, which results from layer-dependent deformation of myofibers during IC. Complex myofiber mechanics provide the mechanism of brief clockwise LV rotation (untwisting) and significant wall thickening during IC within the isovolumic constraint.
目的
我们试图解决等容收缩（IC）期观察到的心肌力学三维透壁异质性问题。
背景
尽管预计IC期心肌变形很小，但最近的组织多普勒成像研究表明，在此阶段心肌存在动态运动，左心室（LV）长轴视图中纵向组织速度呈双相变化。目前缺乏对IC这些动态方面的心肌力学的统一认识。
方法
我们通过植入透壁标记物的双平面电影造影术，在体内测定了14只成年杂种犬在IC期和射血期左心室前壁的三维有限应变随时间的变化过程。在死后的心脏组织中进行组织学测量透壁纤维方向。应变随时间的变化过程是参照舒张末期构型在心外膜下、中层和心内膜下层测定的。
结果
在IC期，心外膜下层出现圆周拉伸，而中层和心内膜下层出现圆周缩短。整个心室壁存在显著的纵向缩短和壁增厚。尽管纵向组织速度呈双相变化；但在IC期纵向以及其他方向的组织变形几乎是线性的。心内膜下纤维缩短，而心外膜下纤维延长。在射血期，所有应变分量随时间均有显著变化，其幅度大于IC期。在所有正常应变中均观察到显著的透壁梯度。
结论
IC期是一个动态阶段，其特征是在圆周、纵向和径向方向上的变形。IC期的组织力学，包括纤维缩短，似乎不受二尖瓣关闭产生的快速纵向运动的干扰。本研究首次报道了圆周应变的层依赖性变形，这是由于IC期肌纤维的层依赖性变形所致。复杂的肌纤维力学提供了在等容约束下IC期左心室短暂顺时针旋转（解旋）和显著壁增厚的机制。
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