Quail A W, Traugott F M, Porges W L, White S W
J Appl Physiol Respir Environ Exerc Physiol. 1981 Jan;50(1):191-5. doi: 10.1152/jappl.1981.50.1.191.
Blood resistivity (rho) values used in the Kubicek formula for stroke volume (SV) calculation by impedance cardiography are bench derived and do not take into account complex blood velocity movements and dynamic hematocrit changes in systole. In this study, the relevance of rho has been questioned. Thoracic resistivity (rho tau) has been calculated in dogs from the rearranged Kubicek formula: rho tau = (SV . ZO2)/(L2 dZ/dtmax.T), where SV was measured by the electromagnetic flowmeter (EM). Hematocrit (Hct) in the dog was varied by hemorrhage and infusion. In contrast to the direct and exponential bench rho-Hct relationship, rho tau varies inversely with Hct, but by no more than +6.3 omega . cm (at Hct 26%) and -11.8 omega . cm (at Hct 66%) about a mean rho tau of 135 +/- 1.0 omega . cm (at Hct 40%). Impedance SV calculated using rho tau over a wide range of SV bears a linear relationship to EM values with a 95% prediction limit for a single SV estimate of +/- 0.84 about a mean value of 26.9 ml. The findings suggest that rho tau is virtually constant during a variety of physiological disturbances.
用于通过阻抗心动描记法计算每搏输出量（SV）的Kubicek公式中的血液电阻率（ρ）值是在实验台上得出的，未考虑心脏收缩期复杂的血流速度变化和动态血细胞比容变化。在本研究中，ρ的相关性受到了质疑。已根据重新排列的Kubicek公式在犬类中计算出胸段电阻率（ρτ）：ρτ = （SV·ZO2）/（L2 dZ/dtmax·T），其中SV通过电磁流量计（EM）测量。通过放血和输液改变犬类的血细胞比容（Hct）。与直接且呈指数关系的实验台ρ-Hct关系不同，ρτ与Hct呈反比，但在平均ρτ为135±1.0Ω·cm（Hct为40%时）的情况下，变化不超过+6.3Ω·cm（Hct为26%时）和-11.8Ω·cm（Hct为66%时）。在很宽的SV范围内使用ρτ计算出的阻抗SV与EM值呈线性关系，对于单个SV估计值，其95%的预测极限为±0.84，围绕平均值26.9ml。研究结果表明，在各种生理干扰期间，ρτ实际上是恒定的。
