Shimizu J, Takaki M, Kohno K, Araki J, Matsubara H, Suga H
Department of Physiology II, Okayama University Medical School, Japan.
Jpn J Physiol. 1995;45(5):837-48. doi: 10.2170/jjphysiol.45.837.
We have recently reported that the postextrasystolic contractile potentiation decays in alternans after a compensatory pause in canine left ventricles even under normal coronary and contractile conditions. The transient alternans appears to consist primarily of a small-magnitude exponential decay and a large-magnitude sinusoidal decay. We, therefore, hypothesized that the contractility (y) of the postextrasystolic alternans beats (beat number x) could be expressed as y = a x exp[-(x-1)/b] + c x exp[-(x-1)/d] x sin[pi(x-0.5)] + yo, where a and c are the normalized magnitudes (relative to the preceding regular beat) of the two exponential terms in the first postextrasystolic beat, b and d are their time constants, and yo is the normalized magnitude of the post-alternans regular beat (approximately 1). The first exponential term represents the monotonic decay. The sine term multiplied by the second exponential term represents the alternating decay. Mathematical curve-fitting indicated: 1) the above equation very closely fitted the alternans data with a squared correlation coefficient of 0.9996 on average, 2) c was 7 times on average greater than a, indicating dominance of the sine component, 3) b and d were 2.5 and 1.0 beats on average, indicating a faster decay of the sine component, and 4) this b was comparable to the time constant of the exponential decay of the postextrasystolic potentiation after no compensatory pause. This study suggests that myocardium has a mechanism to switch the postextrasystolic potentiation between the exponential and alternans decays depending on the first postextrasystolic interval.
我们最近报道，即使在正常冠状动脉和收缩条件下，犬左心室代偿间歇后早搏后收缩性增强在交替变化中也会衰减。短暂交替变化似乎主要由小幅度指数衰减和大幅度正弦衰减组成。因此，我们假设早搏后交替变化搏动（搏动次数x）的收缩性（y）可以表示为y = a x exp[-(x - 1)/b] + c x exp[-(x - 1)/d] x sin[π(x - 0.5)] + yo，其中a和c是早搏后第一个搏动中两个指数项的归一化幅度（相对于前一个正常搏动），b和d是它们的时间常数，yo是交替变化后正常搏动的归一化幅度（约为1）。第一个指数项代表单调衰减。乘以第二个指数项的正弦项代表交替衰减。数学曲线拟合表明：1）上述方程与交替变化数据拟合得非常紧密，平均平方相关系数为0.9996；2）c平均比a大7倍，表明正弦成分占主导；3）b和d平均分别为2.5次和1.0次搏动，表明正弦成分衰减更快；4）这个b与无代偿间歇时早搏后增强的指数衰减时间常数相当。本研究表明，心肌有一种机制，可根据早搏后的第一个间期在指数衰减和交替变化衰减之间切换早搏后增强。
