A noninvasive approach to quantitative measurement of flow through CSF shunts. Technical note.

A method of measuring flow rate through cerebrospinal fluid (CSF) shunts is reported. It consists of two thermistors in series applied to the skin over the shunt tubing. The thermistors respond by a drop in measured temperature following application of an ice cube placed on the skin overlying the proximal shunt tube. The time required for the thermal response to travel between the two thermistors is related to the velocity of flow through the shunt tubing. Flow rate can then be calculated using the internal diameter of the tubing. A series of animal experiments employing a constant infusion of mock CSF through subcutaneously implanted shunt tubing showed excellent correlation between calculated flow rates and actual infusion rates. The device is noninvasive and easily adapted to use in patients. The measurements are readily repeatable.