The effect of alignment on the pressure/flow characteristics of flow control shunt valves

Object: The proper functioning of shunt valves in vivo is dependent on many factors, including the valve itself, the antisiphon device (if included), patency of inlet and outlet tubing and location of the valve. Two general c ategories of shunt valves are available today, the differential-pressure va lve (with or without antisiphon device) and the flow-control valve. We have previously shown that the relationship between the position of the valve b ody and the inlet catheter tip can have profound effects on the outflow rat e of differential pressure valves with antigravity devices. The current stu dy was conducted to evaluate the importance of this relationship for the pr essure/flow characteristics of the flow-control shunt valve. Methods: We be nch-tested flow-control valves from two manufacturers in the system we devi sed for testing differential-pressure valves. Valves were connected to an " infinite" reservoir, and the starting head pressure was determined from pro duct inserts. The inlet catheter tip was fixed at this position and the val ve body was moved in relation to the inlet catheter tip. Outflow rates were determined gravimetrically for positions +4 to -8 cm relative to the inlet catheter tip. Conclusions: All flow-control valves utilized in this study showed nearly constant outflow rate as the valve body was moved incremental ly with respect to the level of the inlet catheter tip. As previously teste d, differential-pressure valves exhibit significant increases in out-flow r ate as the valve body is moved below the inlet catheter tip. The outflow ra te for the flow-control shunt valves does not change over the range of effe ctive head pressures used in this study.