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

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 categories of shunt valves are available today, the differential-pressure valve (with or without antisiphon device) and the flow-control valve. We have previously shown that the relationship between the position of the valve body and the inlet catheter tip can have profound effects on the outflow rate of differential pressure valves with antigravity devices. The current study was conducted to evaluate the importance of this relationship for the pressure/flow characteristics of the flow-control shunt valve.

We bench-tested flow-control valves from two manufacturers in the system we devised for testing differential-pressure valves. Valves were connected to an "infinite" reservoir, and the starting head pressure was determined from product inserts. The inlet catheter tip was fixed at this position and the valve 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.

All flow-control valves utilized in this study showed nearly constant outflow rate as the valve body was moved incrementally with respect to the level of the inlet catheter tip. As previously tested, differential-pressure valves exhibit significant increases in outflow rate as the valve body is moved below the inlet catheter tip. The outflow rate for the flow-control shunt valves does not change over the range of effective head pressures used in this study.