Claessens T E, Georgakopoulos D, Afanasyeva M, Vermeersch S J, Millar H D, Stergiopulos N, Westerhof N, Verdonck P R, Segers P
Institute of Biomedical Technology, Ghent University, Sint-Pietersnieuwstr. 41, Gent B-9000, Belgium.
Am J Physiol Heart Circ Physiol. 2006 Apr;290(4):H1474-83. doi: 10.1152/ajpheart.00663.2005. Epub 2005 Nov 11.
The linear time-varying elastance theory is frequently used to describe the change in ventricular stiffness during the cardiac cycle. The concept assumes that all isochrones (i.e., curves that connect pressure-volume data occurring at the same time) are linear and have a common volume intercept. Of specific interest is the steepest isochrone, the end-systolic pressure-volume relationship (ESPVR), of which the slope serves as an index for cardiac contractile function. Pressure-volume measurements, achieved with a combined pressure-conductance catheter in the left ventricle of 13 open-chest anesthetized mice, showed a marked curvilinearity of the isochrones. We therefore analyzed the shape of the isochrones by using six regression algorithms (two linear, two quadratic, and two logarithmic, each with a fixed or time-varying intercept) and discussed the consequences for the elastance concept. Our main observations were 1) the volume intercept varies considerably with time; 2) isochrones are equally well described by using quadratic or logarithmic regression; 3) linear regression with a fixed intercept shows poor correlation (R(2) < 0.75) during isovolumic relaxation and early filling; and 4) logarithmic regression is superior in estimating the fixed volume intercept of the ESPVR. In conclusion, the linear time-varying elastance fails to provide a sufficiently robust model to account for changes in pressure and volume during the cardiac cycle in the mouse ventricle. A new framework accounting for the nonlinear shape of the isochrones needs to be developed.
线性时变弹性理论常被用于描述心动周期中心室僵硬度的变化。该概念假定所有等容线（即连接同时出现的压力-容积数据的曲线）都是线性的，且有一个共同的容积截距。特别值得关注的是最陡的等容线，即收缩末期压力-容积关系（ESPVR），其斜率可作为心脏收缩功能的指标。在13只开胸麻醉小鼠的左心室中，使用压力-电导联合导管进行压力-容积测量，结果显示等容线明显呈曲线形。因此，我们使用六种回归算法（两种线性、两种二次和两种对数算法，每种算法都有固定或时变截距）分析了等容线的形状，并讨论了其对弹性概念的影响。我们的主要观察结果如下：1）容积截距随时间变化很大；2）使用二次或对数回归对等容线的描述效果相当；3）固定截距的线性回归在等容舒张期和早期充盈期显示出较差的相关性（R(2) < 0.75）；4）对数回归在估计ESPVR的固定容积截距方面更具优势。总之，线性时变弹性未能提供一个足够稳健的模型来解释小鼠心室心动周期中压力和容积的变化。需要开发一个新的框架来解释等容线的非线性形状。
