The biochemical characteristics of the middle ear system measured by a new method. I: Instrumentation.

A frequent finding in patients with earlier otitis media is the sequelae of tympanic membrane atrophy and sclerosis. A major number of these patients nevertheless present with normal audiometric and tympanometric findings. In search of an objective and quantitative description of these pathological changes a new instrument has been developed to measure pressure changes in the ear canal as a function of dynamic tympanic membrane volume displacement. This pressure-volume relationship of the middle ear system expresses non-linear behaviour and hysteresis, which is due to loss of energy under dynamic conditions. Hysteresis can be measured and is here introduced as a new mechanical variable of the middle ear system along with dynamic compliance. Hysteresis is expressed in microJ and compliance in microliter/cmH2O. Analytical measurements of the instrument were found to be small compared with clinical values (< 2.8%). This paper will be succeeded by another study presenting the clinical application of the method and a normal material.