Changes in Pressure-Flow Control Characteristics of Shunt Valvesby Intracranial Pressure Pulsation: an In Vitro Study

Abstract

Shunt valves used to treat patients with hydrocephalus were tested to investigate influence of intracranial pressure pulsation on their flow control characteristics. Five commercial shunt valves were tested in the flow loop that simulates pulsed flow under pressure pulsation. As 20cc/hr of flow rate was adjusted at a constant pressure, application of 40mmH2O of pressure pulse increased the flow rate by 67.9%. As a 90cm length catheter was connected to the valve outlet, increase in the flow rate was substantially reduced to 17.5%. As the flow rate was adjusted to 40cc/hr at a constant pressure, increase in the flow rate was 51.1% with the same pressure pulsation of 40mmH2O. The results indicated that pressure-flow control characteristics of shunt valves implanted above human brain ventricle is quite different from those obtained by syringe pump test at constant pressures right after manufacture. The influence of pressure pulsation was observed to be more significant at low flow rate and the flexibility of the outlet silicone catheter was estimated to significantly reduce flow increase due to pressure pulsation.