Taking the Pressure Off Bone Conduction Hearing Aid Users

The long-term use of headband-worn bone vibrators has been associated with skin ulceration and, in severe cases, physical depression at the point of contact. The cause for this problem has been poorly understood and a mechanism is suggested for the skin condition. When the pressure applied at the bone vibrator contact area exceeds the capillary closure pressure, blood supply is cut off. This affects skin and underlying tissue. Eleven subjects were tested to measure bone-vibrator pressure on the head. Bone conduction hearing aid fittings result in pressure on the head that greatly exceeds capillary closure pressure. It is recommended that bone vibrator contact area and headband force be chosen to avoid exceeding a maximum contact pressure of 3.7 kPa over an extended period of time, measured in hours. If the headband force holding the bone vibrator against the head cannot be measured, then the bone vibrator should be fitted with only enough force to hold it in place against the mastoid process without excessive movement.