Pressure-absorption responses to the infusion of fluid into the spinal cord central canal of kaolin-hydrocephalic cats

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Abstract
The resistance to cerebrospinal fluid (CSF) absorption through the alternative CSF absorption pathway in kaolin-induced hydrocephalic cats was measured by the constant infusion-manometric test. The cerebral ventricles were bypassed, and artificial CSF was infused directly into the central canal of the spinal cord. The infusion rates were increased stepwise from 0.022 to 0.168 ml/min when the capacity to absorb CSF was exceeded. There was an initial increase in resistance which was associated with the emergence of infusion fluid through a slit-like opening in the dorsal columns of the lower lumbar spinal cord. The resistance to flow decreased when the infusion rate was greater than 0.086 ml/min. Fluid accumulated in the spinal subarachnoid space when the ability to absorb was exceeded. The diversion of this fluid caused the pressure in the spinal cord central canal to fall rapidly. The results suggest that the CSF absorption deficit in chronic kaolin-induced hydrocephalic cats is probably caused by the restriction of CSF flow from the central canal through the spinal cord and into the spinal subarachnoid space. As a result of kaolin, the central canal is sufficiently dilated to permit, during infusion, the flow of at least five times as much CSF as the hydrocephalic cats produce. It is not clear whether the overloading of the CSF absorption mechanism is due to the restrictions imposed by the size of the subarachnoid space, or to the structures in this space involved with the return of CSF to the blood.