Comparison of histologically-measured endolymph cross-sectional area with that measured in vivo using an ionic volume marker .

Salt, A.N., DeMott, J.E. and Kimura, R.S.

Abstract

In order to establish how endolymph volume is regulated, it is essential to be able to measure endolymph volume or cross-sectional area in vivo. We have developed methods to accomplish this by injecting the volume marker ion arsenic hexafluoride (AsF) into endolymph by iontophoresis. For an injection at a constant rate, the endolymph tracer concentration is inversely dependent on the cross-sectional area of the scala into which injection occurred. Tracer concentrations were monitored by inserting ion-selective microelectrodes into endolymph near the injection site. In a previous study we quantified the degree of hydrops in animals following ablation of the endolymphatic sac. In the present study we have validated the technique by comparing the endolymphatic cross-sectional area measured in vivo with AsF with that measured by established histological procedures. The correlation between the two measures was good, with a coefficient of 0.903, although the area measured histologically was a little lower than that measured in vivo.

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