Biomechanical Measurement and Modeling of Human Eardrum Injury in Relation to Blast Wave Direction

Rupture of the eardrum or tympanic membrane (TM) is one of the most frequent injuries of the ear after blast exposure. To understand how the TM damage is related to blast wave direction, human cadaver ears were exposed to blast waves along three directions: vertical, horizontal, and front with respect to the head. Blast overpressure waveforms were recorded at the ear canal entrance (P0), near the TM (P1), and inside the middle ear (P2). Thirteen to fourteen cadaver ears were tested in each wave direction and the TM rupture thresholds were identified. Results show that blast wave direction affected the peak P1/P0 ratio, TM rupture threshold, and energy flux distribution over frequencies. The front wave resulted in lowest TM rupture threshold and the horizontal wave resulted in highest P1/P0 ratio. To investigate the mechanisms of TM injury in relation to blast wave direction, the recorded P1 waveforms were applied onto the surface of the TM in a three-dimensional finite element model of the human ear and distributions of the stress in TM were calculated. Modeling results indicate that the sensitivity of TM stress change with respect to P1 pressure (dσ/dP1) may characterize mechanical damage of the TM in relation to blast waves.