A nonlinear finite-element model of the newborn middle ear

Abstract

A three-dimensional static nonlinear finite-element model of a 22-day-old newborn middle ear is presented. The model includes the tympanic membrane ͑TM͒, malleus, incus, and two ligaments. The effects of the middle-ear cavity are taken into account indirectly. The geometry is based on a computed-tomography scan and on the published literature, supplemented by histology. A nonlinear hyperelastic constitutive law is applied to model large deformations. The middle-ear cavity and the Young's modulus of the TM have significant effects on TM volume displacements. The TM volume displacement and its nonlinearity and asymmetry increase as the middle-ear cavity volume increases. The effects of the Young's moduli of the ligaments and ossicles are found to be small. The simulated TM volume changes do not reach a plateau when the pressure is varied to either −3 kPa or +3 kPa, which is consistent with the nonflat tails often found in tympanograms in newborns. The simulated TM volume displacements, by themselves and also together with previous ear-canal model results, are compared with equivalent-volume differences derived from tympanometric measurements in newborns. The results suggest that the canal-wall volume displacement makes a major contribution to the total canal volume change, and may be larger than the TM volume displacement.

Effects of ear canal static pressure on the dynamic behaviour of outer and middle ear in newborns

“…This finding suggests that positive (+200 daPa) static pressure produced a smaller effect than negative pressure (-200 daPa) on the mobility of the middle ear. This observation is consistent with the findings of Qi et al study using a nonlinear finite element model of the newborn middle ear [33]. Qi and colleagues [33] reported larger displacement of the TM for negative pressures than positive pressures.…”

“…This finding suggests that positive (+200 daPa) static pressure produced a greater impact than negative pressure (-200 daPa) on the mobility of the outer ear. This observation is supported by a three-dimensional nonlinear finiteelement model study of a 22-day-old neonate [22]. In this study, Qi et.…”

“…On pressurization, the A c c e p t e d M a n u s c r i p t 5 cartilaginous ear canal diameter increases by an average of 18.3% under positive pressure or decreases by an average of 28.2% of its original value under negative ear canal pressure [23]. Furthermore, ear canal volume changes from 27 to 75% over a range of ± 300 daPa in newborns [22]. In view of these characteristics, the dynamic behaviour of the outer and middle ear of newborns will undoubtedly change in response to pressurization of the ear canal [15,16,24].…”

“…In this study, Qi et. al [22], reported that displacements of ear canal wall are slightly larger under positive pressures than under negative pressures.…”

“…The middle ear and mastoid cavities are small (452 mm 3 ) compared to adult tympanic cavity (640 mm 3 ) [14,16,21]. Newborns also have loose ossicular joints [14,22] which become more stiff with age.…”