Effects of auricular hematoma on propagation components of cartilage conduction

Cartilage conduction (CC) is a method of perceiving sound via biological tissues by presenting a transducer to the auricular cartilage. Unlike conventional bone conduction through the bony section of the skull, conduction through lightweight auricular cartilage requires a weak force, thus resulting in less pain. CC has potential for hearing in clinical conditions such as ear canal atresia and auricular hematoma. Auricular hematoma, also known as cauliflower ear, is a swelling and deformation of the pinna due to internal bleeding. The bump makes it difficult to use ordinary earphones, and CC is thought to be a suitable alternative solution. However, the impact of hematoma on CC hearing varied with frequency, location within the pinna, and so on, and the underlying mechanism remained unclear. This study aimed to examine the effect of the changes in the auricular hardness on CC propagation by measuring the pinna/head vibration, ear canal sound pressure, and hearing threshold. Our result indicated that hard pinnae, due to hematoma, increase pinna/head vibrations by CC, however, the effect of pinna hardness varied depending on frequency and position on the pinna.