Is the indicator dilution theory really the adequate base of many blood flow measurement techniques?
The indicator dilution theory is the underlying model of many blood flow measurement techniques used daily in hospitals, for instance in cardiac catheterization laboratories. The basic version of this theory applies to a “stationary” flow system with one inlet and one outlet, into which a small amount M of indicator is injected “suddenly” at time t = 0 at the inlet. The quintessence of the theory consists in three equations, which themselves result from some apparently simple assumptions about the considered flow systems. The first equation states that the (constant) flow Q through the system can be calculated by use of the known amount of indicator, M, and of the indicator concentration-time curve c(t) recorded at the outlet. The second one allows the calculation of the “mean transit time” t* of fluid and indicator particles through the system from the curve c(t). The third equation, V = Qt*, yields the system volume V. It is generally believed that these three equations would be abso
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