[The intraoperative monitoring of the gas pressure in the middle ear]

The objective of the present work was to elucidate the patterns and mechanisms underlying the changes of gas pressure in the middle ear during the operation of stapedoplasty with a view to the application of the data obtained for objective recording of the stapedial reflex at the time of surgical intervention. Ten subjects with the unaffected hearing function were recruited for the study. Tympanometry was carried out at one-minute intervals starting from the onset of feeding nitrogen monooxide till the completion of septoplasty. It was shown that the surgical intervention under inhalation anesthesia is associated with periodic rises and drops in the gas pressure in the middle ear within a range from 500 dPA to 88 dPA with a period from 5.7 to 22 minutes. It is argued that these changes can be attributed to the periodic opening of the Eustachian tube when the gas pressure reaches a certain level due to continuous diffusion of nitrogen monooxide into the middle ear (the "preventive" release of pressure) followed by the passive closure of the auditory tube. The authors propose based on the results of the study recommendations on the performance of stapedial reflexometry during the surgical intervention with the use of impedancometry.