The Physical Volume Test in impedance audiometry.

Impedance audiometry offers a clinically practical method for measuring the physical volume in cc of air space medial to the hermetically sealed probe tip. Knowledge of the air space volume is meaningful when average norms are known, either when the TM is intact or, more significantly, when the TM is perforated. With the latter, the temporally dynamic space changes during external, middle ear and/or mastoid disease, the size of the total air space measured offers objective information when determined over time. The resultant volume can offer an indirect mirror readout of progression or regression of a disease process. Likewise, historically there may be a close relationship between eustachian tube function and the overall air cell space within the petrotympanomastoid bone. In such conditions, the smaller the air cell space, the poorer the eustachian tube function. The PVT offers a more expedient clinical tool over roentgenography for measuring the viable air space of the middle ear and petromastoid air cell system. Since the PVT is used primarily with an open system (i.e. with a perforated TM) electroacoustic volumetric determinations with a 220 Hz acoustic input more reliably represents the actual volume present.