gms | German Medical Science

Objective: By working on the hypothesis that cerebrospinal elastance determines the course of intracranial pressure (ICP) during constant rate infusion a non-linear mathematical approach was chosen to fit ICP under volume loading. The influence of elastance on ICP is assumed in the transient behaviour. This is described by coefficients that control the dynamic properties of the function to fit. There were hints of a sexual dimorphism in the pressure responses observed. This was considered during hypothesis testing introducing gender as a factor.

Methods: Patients with suspected cerebrospinal fluid (CSF) circulatory disorders and signs of hydrocephalus were assessed. All patients underwent a standardised intrathecal volume-pressure testing procedure consisting of a bolus and infusion test. In two subgroups matched for mean age (24 male, 23 female, grand mean 61±14 years) a four coefficient sigmoidal function was applied to approximate infusion test ICP data. Weighted least mean squares regression analysis was used for computation of the coefficients‘ relationship to a robust elastance estimate, namely the pressure difference due to a bolus of 8 ml test volume.

Results: In male and female patients the working hypothesis could be rejected for all four and two coefficients, respectively, meaning that a constant elastance is present throughout the coefficients‘ ranges. In females, however, two of the four coefficients depicted marked linear relationships that outline dependence from infusion induced pressure elevation (max; slope: 1.21±0.29 mmHg/min, n=22, p=0.00048) and unstressed volume (xhalf; slope: -5.06±1.50 mmHg/min, n=20, p=0.00343).

Conclusions: Statistical results indicate that there is no information about the elastic cerebrospinal properties to derive from coefficients in male patients. In females elastance is noticeably associated with coefficients approximating CSF outflow resistance (max) and CSF volume reserve (xhalf). These inconsistent results are more likely due to the choice of bolus volume and the well-known gender differences in CSF volume: testing elastance in small, mainly female patients with an equivalent volume would produce a more pronounced pressure response than in tall males normally having both a higher baseline CSF volume and larger CNS measures. As far as these results were understood test settings have to be corrected for at least body height avoiding insufficient diagnostic results in (male) patients.