Abstract
A simulation study, which analyses the relationship between the actual blood flow into the aorta, transthoracic impedance variation and the value of stroke volume measured by Kubicek's equation, was proposed on a simple vascular tube model by means of a digital computer. The effect of varying the value of such parameters as total transthoracic impedance (Z0), elasticity of the aorta (E), peripheral resistance of the vascular beds (Rs) and velocity of the pressure pulse in the aorta on SVz was also investigated. By the numerical computation of the differential equations introduced on this model, the following evidences were obtained :
(1) The amplitude (maximum flow velocity, Qmax), duration (ejection time, Ts) and rising and falling time (tr and tf) of the inflow were the most significant factors determining the SV, value.
(2) The SVz value is equal to the actual inflow (SV), only when tr=tf=0 and the flow velocity is constant during the ejection time, i. e., the inflow is a square wave.
(3) The value of SVz increases with increasing tr, whereas it takes a constant value which is proportional to the product of Ts and dZ|dt| max at any length of tf. Thus the SVz value increases with increasing tf, if Ts is constant.
(4) Z0 is a factor determining the sensitivity of this method.
(5) Evidences expressed in (1) - (4) were confirmed through experiments on the dogs.
(6) The value of SVz shows little change with the change in the value of such parameters as E, Rs and velocity of the pressure pulse.
