Acquired hydrocephalus IV. Determination of the absorption rate of albumin from the cerebrospinal fluid

Quantitative isotope ventriculography (QIV) has been suggested as a method for diagnosing hydrocephalus and predicting the results of CSF shunt insertion. However, the physiological significance of this and other tracer clearance studies is questionable. Using a simplified mathematical model for tracer clearance following ventricular injection, a series of isotope retention curves were generated by an IBM 360-40 computer. The author shows that the tracer clearance from the CSF is just as dependent on the volume of the CSF compartment as it is on the rate of CSF absorption. This means, for example, that doubling the CSF volume without diminishing absorption (cerebral atrophy) yields the same results as halving the absorption rate in patient with normal CSF volume (early hydrocephalus). In order for tracer clearance studies to measure CSF absorption, to determine the presence of hydrocephalus, and to predict the results of shunting, an accurate measure of CSF volume must be obtained.

supporting

confidence: 39%

Tracer clearance studies in hydrocephalus: A critique

Stein

1981

Acquired hydrocephalus III

Jensen

1979

Self Cite

On the basis of the laws of Pascal and Laplace, it is shown that the ventricular dilatation in acquired hydrocephalus is due to a primary increase in the intraventricular pressure (IVP), and that a new steady state can be reached, whether the IVP is increased or normal. The pressure increase is due to a disproportion between the production and reabsorption of cerebrospinal fluid (CSF). As water and salts pass freely across the ependyma and the choroid plexus in hydrocephalus, the pressure increase is caused by an increased protein concentration in the ventricular CSF, leading to increased fluid contents according to the Gibbs-Donnan equilibrium. During the ventricular dilatation, the ependyma is destroyed, and the protein molecules penetrate into the subependymal part of the white matter. This results in a reduction in the colloid osmotic pressure of the ventricular CSF, and a new steady state can be reached, with a normal protein concentration in an increased volume. The attendant microscopic changes in the ventricular wall were demonstrated in a patient with acquired hydrocephalus, and the observations made were in conformity with the results of a number of animal experiments. The symptomatology of acquired hydrocephalus is in agreement with a primary affection of the axons running in the juxtaventricular part of the white matter.

Acquired hydrocephalus IV. Determination of the absorption rate of albumin from the cerebrospinal fluid

Jensen

Olsen

1979

Self Cite

By quantitative isotope ventriculography (QIV), the absorption rate (lambda 2) of albumin in the cerebrospinal fluid (CSF) was determined. Regard was paid to the rate constants for the exchange of the albumin molecule between the serum and extravascular phase. The rate constant lambda 2 and mean biological transit time Tmb-2 were determined in 22 patients suspected of acquired hydrocephalus. QIV revealed that 8 patients were hydrocephalic, while 13 were non-hydrocephalic, and the findings were uncertain in one. In the patients with acquired hydrocephalus, it was demonstrated that lambda 2 and Tmb-2 were significantly reduced as compared with the non-hydrocephalic patients. By means of QIV, a curve was calculated and plotted for the biological decay from the head--the retention curve. From the initial slope of this curve (0--24 hours), the rate constant lambda 2 was calculated. A comparison of lambda 4 and lambd 2 revealed a highly significant correlation, which means that the retention curve gives an acceptable measure of the absorption rate of CSF-albumin.