Mechanics of the middle ear system: computerized measurements of its pressure–volume relationship

A new method is described measuring the pressure–volume relationship of the middle ear system (MES). These measurements express the dynamic mechanical properties of the MES. Ear canal pressure changes are measured in response to tympanic membrane (TM) volume displacements in a material of 39 younger normal adults. During one recording procedure several displacements curves are obtained from which one curve is isolated representing the neutral position of the TM. From this curve the following variables are determined: hysteresis (μJ) describing the viscoelastic properties of the MES, compliance (mm3/kPa) describing its elasticity, Prange (kPa) describing the pressure range of the curve, and Pec0 (kPa) describing the ear canal pressure for the neutral position of the TM. Normative data are presented and compared with tympanometric measurements. Compliance correlates significantly to static admittance (P<0.001), while Pec0 correlates significantly to middle ear pressure (P<0.001). Further, data on repeatability and sources of measurement errors are reported, which support a high reliability of the method. Compared with tympanometry the method is more detailed and has several advantages, which are discussed, and it has been found valuable for future mechanical studies of the MES. These studies include possibilities for diagnostics of middle ear disorders and derivation of pressure–volume equations useful in modeling of the MES.