Lumens Joost, Delhaas Tammo, Arts Theo, Cowan Brett R, Young Alistair A
Dept. of Biophysics, Cardiovascular Research Institute Maastricht, Maastricht Univ., PO Box 616, 6200 MD Maastricht, The Netherlands.
Am J Physiol Heart Circ Physiol. 2006 Oct;291(4):H1573-9. doi: 10.1152/ajpheart.00074.2006. Epub 2006 May 5.
With aging, structural and functional changes occur in the myocardium without obvious impairment of systolic left ventricular (LV) function. Transmural differences in myocardial vulnerability for these changes may result in increase of transmural inhomogeneity in contractile myofiber function. Subendocardial fibrosis and impairment of subendocardial perfusion due to hypertension might change the transmural distribution of contractile myofiber function. The ratio of LV torsion to endocardial circumferential shortening (torsion-to-shortening ratio; TSR) during systole reflects the transmural distribution of contractile myofiber function. We investigated whether the transmural distribution of systolic contractile myofiber function changes with age. Magnetic resonance tissue tagging was performed to derive LV torsion and endocardial circumferential shortening. TSR was quantified in asymptomatic young [age 23.2 (SD 2.6) yr, n = 15] and aged volunteers [age 68.8 (SD 4.4) yr, n = 16]. TSR and its standard deviation were significantly elevated in the aged group [0.47 (SD 0.12) aged vs. 0.34 (SD 0.05) young; P = 0.0004]. In the aged group, blood pressure and the ratio of LV wall mass to end-diastolic volume were mildly elevated but could not be correlated to the increase in TSR. There were no significant differences in other indexes of systolic LV function such as end-systolic volume and ejection fraction. The elevated systolic TSR in the asymptomatic aged subjects suggests that aging is associated with local loss of contractile myofiber function in the subendocardium relative to the subepicardium potentially caused by subclinical pathological incidents.
随着年龄增长，心肌会发生结构和功能变化，但左心室（LV）收缩功能无明显受损。这些变化在心肌易损性方面的透壁差异可能导致收缩性肌纤维功能的透壁不均一性增加。高血压导致的心内膜下纤维化和心内膜下灌注受损可能会改变收缩性肌纤维功能的透壁分布。收缩期左心室扭转与心内膜圆周缩短的比值（扭转-缩短比值；TSR）反映了收缩性肌纤维功能的透壁分布。我们研究了收缩期收缩性肌纤维功能的透壁分布是否随年龄变化。采用磁共振组织标记技术来获取左心室扭转和心内膜圆周缩短数据。对无症状年轻志愿者[年龄23.2（标准差2.6）岁，n = 15]和老年志愿者[年龄68.8（标准差4.4）岁，n = 16]的TSR进行了量化。老年组的TSR及其标准差显著升高[老年组为0.47（标准差0.12），年轻组为0.34（标准差0.05）；P = 0.0004]。在老年组中，血压和左心室壁质量与舒张末期容积的比值略有升高，但与TSR的增加无相关性。左心室收缩功能的其他指标，如收缩末期容积和射血分数，无显著差异。无症状老年受试者收缩期TSR升高表明，衰老与心内膜下相对于心外膜下收缩性肌纤维功能的局部丧失有关，这可能是由亚临床病理事件引起的。
