[A new modified wick catheter for measurement of the brain tissue pressure-an evaluation of static and dynamic properties of the catheter (author's transl)]

Abstract

The interstitial pressure of the brain was measured with wick catheter by Lassen in 1972. But original wick catheter inserted into the brain tissue does not always measure the real interstitial pressure as indicated by experimental results of Brodersen, because, the interstitial pressure is always affected by solid pressure such as cells in the brain tissue, in the condition of which surrounded by positive CSF pressure in the semiclosed skull box. It is not yet clarified what kinds of the pressure are measured by wick catheter method in the brain tissue. The size of wick catheter is 300-500 times as large as the width of interspace of the brain tissue and the catheter is easily obstructed by brain tissue. Therefore, a new, modified wick catheter is made for improvement of these problems which is observed by using original wick catheter. The new, modified catheter has 0.4 mm inside diameter and 10 cm length. The tip of catheter is closed and 6 small side holes(0.1 mm0)are made. Inside the catheter, several pieces of 0.04 mm diameter nylon threads are inserted as shown in figure 1, and the catheter is filled up with the cerebrospinal fluid. In this paper, the structure of the new, modified catheter is demonstrated, and the brain tissue pressure is measured, comparing with the results of the original wick catheter to test the function of the new, modified catheter. The results of measurement of the brain tissue fluid pressure with the new, modified catheter are as follows; 1) The brain tissue fluid pressure is relatively constant and shows a positive pressure of 5.2 mmHg. 2) As there are few blocking effects in the catheter, the new, modified catheter is useful for the measurement of the brain tissue fluid pressure for a long time. 3) The brain tissue fluid pressure is not altered by the number's of nylon threads in the catheter at static condition, but movement of brain tissue fluid pressure with respiration is a little dumped by the increased conductancy with the numbers of nylon threads in the catheter. 4) The tissue fluid pressure affected by the viscosity and osmolarity of the fluid in the catheter, CSF should be used for correct measurement. According to these results, it might be concluded that the new, modified wick catheter is better than the original wick catheter regarding prevention of obstruction of the catheter by brain tissue fragments, artifacts which causet by movement of wick fibers, measurement of brain tissue fluid pressure for a long time and clarify the resistance of catheter to pressure conductancy.