Tympanometry:between ear symmetry and normative values.

Marked asymmetry of auditory function between left and right ears would normally be indicative of some abnormality. This study was designed to investigate the limits of tympanometric symmetry in normal individuals. A limiting ratio of 4/3 between left and right ear compliances is suggested. Applying this criterion and strict criteria for normality of middle ear pressure and reflex thresholds, a value for middle ear compliance was obtained with a considerably smaller range for "normality" than from previous studies. A marked difference between middle ear compliances of male and female subjects was observed, and evidence was adduced to suggest that this was due to differences in size of the ear canal and tympanic membrane.