What is Comprehensible from the Infusion Test?

Abstract

The purpose of this report is to clarify the origin of the pressure-response (p-r) curve after a bolus normal saline injection into the subarachnoid space. Eighteen adult mongrel dogs weighing 9-13 kg were intubated and ventilated artificially. A bolus normal saline injection (0.8 ml-sec) was performed and the changes in intracranial pressure, superior sagittal sinus pressure, and systemic arterial pressure were monitored and recorded continuously for 30 minutes. The following results were elicited: 1) The shape of the p-r curve was determined by three resistances: resistance to the cerebrospinal fluid (CSF) absorption (r), blood inflow resistance into the sinus (Ri), and blood outflow resistance from the sinus to the extracranial venous system (Ro). A new intracranial volume-pressure model was proposed for detailed analysis of the volume-pressure relationship. 2) Changes in the CSF pressure after a bolus injection were characterized by two components. The steep decay of the p-r curve was thought to occur because of the CSF absorption, and the gentle decay should be the result of sinus outflow resistance which might be equivalent to the CSF absorption resistance, since the CSF absorption resistance should be rapidly changeable and pressure dependent. Patterns of the p-r curve were divided into three groups, namely “normal, ” “borderline, ” and “delayed” patterns. The last one could result either from high r state or from high Ro conditions. The borderline group contained dogs in which the intracranial cavity was tight. The CSF absorption resistance could be obtained by careful analysis of the p-r curve, but it might be modified by the spatial compensation of the venous system. It is thought to be important for the reasonable analysis of the p-r curve that the shape consideration, the baseline-peak pressure gradient (pressure increment), and the recovery time to the baseline pressure should all be included in a single analytical theory.