Negative middle ear pressure induced by sniffing. A tympanometric study in persons with healthy ears

In routine clinical tympanometry the finding of negative middle ear pressure is not uncommon. The traditional explanation of the negative pressure is that passive gas resorption takes place when the Eustachian tube is blocked. However, recent investigations in patients with middle ear disease have shown that a high negative intratympanic pressure can be actively induced by sniffing. In the present study 100 subjects with healthy ears were investigated by tympanometry in order to evaluate their ability to evacuate the middle ear by sniffing. Fourteen per cent were able to evacuate the middle ear to stable negative pressures ranging from -1.0 to -3.5 kPa, mean value -1.9 kPa (1 kPa corresponds approximately to 100 mm water). The present findings indicate that a sniff-induced negative pressure is not pathological per se. A temporary negative middle ear pressure induced by sniffing can explain the presence of a type C tympanogram in patients with healthy ears. This findings also emphasizes the difficulty in determining the borderline between normal and pathological tympanograms.