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.