Microspheres based detoxification system: in vitro study and mathematical estimation of filter performance

Because of the closed plasma (secondary) circuit in the Microspheres based Detoxification System (MDS), a convective blood purification system, the sa me amount of filtrated plasma is backfiltrated into the blood circuit. Ther efore, there is no direct way to determine the ultrafiltrate production rat e, which is an important factor of efficiency. The only possible way to est imate the filtration properties of the filter is to consider pressure value s. In this study the pressure distribution in the filter was investigated i n vitro. To explain the results and to calculate inaccessible parameters, a mathematical model was established which also considered the asymmetric be haviour of the filter membrane. The result was a linear pressure gradient, agreement with the measurements was reasonably good (calculated primary pre ssure loss differes <13% from measured value when using mean measured filte r resistance as model parameter). Linear pressure distribution offers the p ossibility of easily calculating the filtration length, a parameter which c an be used to estimate the filter condition. The comparison between calcula ted filtration and backfiltration rates offers an instrument of control for these values.