Figure 1

The test system. Proximal pressure of the shunt was controlled by air pressurizing the sealed bottle with the computer controlled air pump. Flow through the shunt was estimated from the pressure drop over the glass constriction using the calibrated resistance. Both the pressure drop over the constriction and the proximal shunt pressure were measured with differential pressure transducers from Druck (LPM8000). Outflow from the shunt was led into an overflow container with a constant water level at the zero pressure level. The set-up was placed in an incubator set at 37°C. Computer–controlled solenoid cocks were used to automatically perform the protocol, including pressure recalibrations.