Evaluation of cerebrospinal fluid flow through a Pudenz 12 mm or a standard Rickham reservoir: phantom experiments

We have investigated the assessment of fluid flow through a Pudenz and a Rickham shunt using radioactive tracer. Experimentally, the radioactivity clearance curve obtained, using either shunt, is defined by two exponents. The relationship between flow-rate (F) and clearance half-time (T1/2) of the first component is identical with the clearance formula (formula: see text) or log10(F) =-LOG10(T1/2) + LOG100.693V using the physical volume. The value of the second component in a Pudenz 12 mm and a standard Rickman reservoir is log10(F) = -1.3LOG10(T1/2) + 0.087 and log 10(F) =-1.8log10(T1/2) + 0.019 respectively. In clinical practice, the first component may not be recorded adequately because the interval between appearance of the first and second components is very short. To calculate the CSF flow, we recommend referring to the line of "radioactivity clearance half-time and flow-rate" of the second component instead of the calculation based on clearance formula using a physical volume.