Visser K R, Lamberts R, Zijlstra W G
Department of Physiology, University of Groningen, The Netherlands.
Cardiovasc Res. 1987 Sep;21(9):637-45. doi: 10.1093/cvr/21.9.637.
To test one of the assumptions underlying the calculation of stroke volume--namely, that the transthoracic impedance consists of a parallel connection of a tissue impedance and a blood resistance--experiments were carried out on four dogs in which blood was gradually replaced by a stroma free haemoglobin solution, with the purpose of changing the blood resistance while leaving the tissue impedance unchanged. This was accomplished by exchange transfusion in such a way that the volume of the circulating fluid remained constant and the distribution of fluid volume between the fluid compartments was not altered. During the exchange transfusions the mean decrease in resistivity of the circulating fluid was 54%. The packed cell volume and resistivity of every volume of removed circulating fluid were measured. Just before each exchange the real and imaginary parts of the transthoracic impedance were measured. The packed cell volume decreased exponentially with the number of exchanges. This indicates that the circulating fluid volume remained constant during the exchange transfusion. From the packed cell volumes an estimate of the circulating fluid volume was made. Because of the parallel connection all calculations were based on the use of admittance, which is the reciprocal value of impedance. The real and imaginary parts of the transthoracic admittance were calculated from the measured values of the real and imaginary parts of the transthoracic impedance.(ABSTRACT TRUNCATED AT 250 WORDS)
为了验证心搏量计算所依据的一个假设，即经胸阻抗由组织阻抗和血液电阻的并联组成，对四只狗进行了实验。在实验中，血液逐渐被无基质血红蛋白溶液替代，目的是在保持组织阻抗不变的情况下改变血液电阻。这通过换血来实现，换血方式使得循环流体的体积保持恒定，且流体腔室间的流体体积分布未改变。在换血过程中，循环流体电阻率的平均降低为54%。测量了每次移除的循环流体的血细胞比容和电阻率。每次换血前测量经胸阻抗的实部和虚部。血细胞比容随换血次数呈指数下降。这表明在换血过程中循环流体体积保持恒定。根据血细胞比容估算了循环流体体积。由于是并联关系，所有计算均基于导纳的使用，导纳是阻抗的倒数。经胸导纳的实部和虚部由经胸阻抗实部和虚部的测量值计算得出。（摘要截选于250词）
