Measurement of tympanic membrane displacement arising from aural cardiovascular activity, swallowing, and intra-aural muscle reflex.

A new technique based on constant pressure metrology has been developed to measure displacement of the tympanic membrane. Known as the Tympanic Membrane Displacement Measurement System (TMD system), this device is designed to be suitable for application in the audiology clinic. The TMD system resolves volume displacements as small as a nanolitre. Measurements are absolute--being independent of volume and compliance of the external auditory meatus, have a wide dynamic range, and are essentially made under free-field conditions. It employs closed volume metrology which allows the meatal pressure to be varied independently of the ambient pressure. The principle of constant pressure metrology using a standard TDH-39 headphone cone is discussed. Details are provided on the electronics, mechanical hardware, and software used for evaluating aural cardiovascular activity, stapedial muscle reflex, swallowing and Eustachian tube function.