Department of Cardiac Surgery, Cardiovascular Center, University of Michigan, Ann Arbor, Michigan, United States of America.
PLoS One. 2013 Apr 8;8(4):e60580. doi: 10.1371/journal.pone.0060580. Print 2013.
Diastolic dysfunction is the hemodynamic hallmark of hypertensive heart disease. Tau (τ) has been used to describe left ventricle relaxation. The relationship between τ and afterload has been controversial. Our goal was to demonstrate this relationship in mice, because genetically-modified mouse models have been used extensively for studies in cardiovascular diseases.
Increased arterial load was produced by phenylephrine administration (50 µg/kg iv) (n = 10). A series of pressure-volume loops was recorded with a Millar conductance catheter in vivo as the left ventricle pressure reached the maximum. The arterial load was expressed as Ea (effective arterial elastance). Tau values were computed using three mathematical methods: τWeiss, τGlantz, and τLogistic.
A correlation plot between τ and Ea showed a biphasic relationship a flat phase I and an inclined phase II. The existence of an inflection point was proved mathematically with biphasic linear regression. Pressure-volume area (PVA), a parameter linearly related to myocardial O2 consumption (MVO2), was found to be directly proportional to Ea. The plot of τ versus PVA was also biphasic.
We concluded that a small increase of the arterial load by phenylephrine increased PVA (index of MVO2) but had little effect on τ. However, after an inflection point, further increase of arterial load and PVA resulted in the linear increase of τ.
舒张功能障碍是高血压性心脏病的血流动力学特征。τ（tau）被用来描述左心室舒张。τ与后负荷之间的关系一直存在争议。我们的目的是在小鼠中证明这种关系，因为遗传修饰的小鼠模型已被广泛用于心血管疾病的研究。
通过静脉注射苯肾上腺素（50μg/kg）（n=10）来增加动脉负荷。在体内用 Millar 传导导管记录一系列压力-容积环，当左心室压力达到最大值时。动脉负荷表示为 Ea（有效动脉弹性）。τ值使用三种数学方法计算：τWeiss、τGlantz 和 τLogistic。
τ 与 Ea 的相关图显示出双相关系，即平坦的 I 相和倾斜的 II 相。通过双相线性回归证明了存在拐点的数学存在。压力-容积面积（PVA）是与心肌耗氧量（MVO2）线性相关的参数，与 Ea 呈正比。τ 与 PVA 的关系图也是双相的。
我们得出结论，苯肾上腺素引起的动脉负荷的小幅度增加会增加 PVA（MVO2 的指标），但对 τ 影响不大。然而，在拐点之后，动脉负荷和 PVA 的进一步增加导致 τ 的线性增加。
