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Effects of various densities of middle ear fluids on acoustic immittance: experimental study.

OBJECTIVE
To study the effects of various densities of middle ear fluids on acoustic immittance and elucidate the characteristics of this study that might be beneficial for clinical use in otitis media with effusion.


STUDY DESIGN
Experimental, in vivo model.


MATERIALS AND METHODS
The study was performed on 12 ears of six white Vienna rabbits. Rabbits were placed in six positions: normal resting position (group 1); after drilling a hole into the tympanic bulla (group 2); filling the bulla with distilled water (group 3; density = 1000 g/cm(3)); filling the bulla with 8.4% bicarbonate solution (group 4; density = 1005 g/cm(3)); filling the bulla with Tonimer gel (group 5; density = 1035 g/cm(3)); and filling the bulla with glycerine (group 6; density > 1050 g/cm(3)). Acoustic immittance measurements were then made in vivo. During each measurement, volume, compliance, pressure, and gradient values were recorded. Analysis of variance, Student t-test, and Pearson correlation coefficient and multiple regression analyses were used for statistical evaluations of the data.


RESULTS
Volume, compliance, and pressure values were obtained in all of the six measurements. A significant difference in volume was found between groups 1 and 2 (p < .001) and between the other four groups in this study (p < .001). With regard to compliance, group 2 was significantly different from groups 3, 4, 5, and 6 (p < .001). With regard to pressure, there was no intergroup (1 and 2) difference (p = .639); however, a significant difference (p < .001) was found between groups 1 and 2 and the other four groups. A significant difference was found between groups 3 and 6 (p = .006). A gradient value was obtained in all of the six measurements only for groups 1 and 2. In group 2, a significant rise in gradient was observed (p = .001).


CONCLUSION
Generally, volume, compliance, and pressure values declined significantly in rabbits in which the bulla had been filled with fluid when compared with rabbits with empty bullae. Drilling a hole into the bulla increased volumetric values under normal conditions but had no effect on compliance and pressure values. The significant difference between groups 3 and 6 regarding pressure demonstrates that the density of fluid in the middle ear plays a role in pressure values when measured with tympanometry. We conclude that the correlation between density and pressure values of middle ear fluids may be useful in the clinical decision-making process when treating disorders such as otitis media.