TYMPANOMETER

Abstract: Intratympanic pressures were measured by tympanometer in forty ears free from disease. In the recumbent position, the first tympanogram was obtained in the morning at awakening, before swallowing. The second pressure measurement was performed in the upright position after swallowing and chewing. Twenty-two ears showed positive pressure in the middle ear before swallowing and decreased pressure after swallowing. The present results revealed no evidence of continuous gas absorption from the middle ear during sleep. The other experiment demonstrated that raising of the PCO2 level by hypoventilation increased the pressure in the middle ear. The results suggested indirectly a diffusion of carbon dioxide to the middle ear cavity from its surrounding tissue. The intratympanic pressure seems limited in part to the partial pressure gradient of gases between the middle ear cavity and its surrounding tissue when ventilation through the Eustachian tube is impaired.

Abstract: The gas exchange function through the middle ear (ME) mucosa was investigated by comparing normal and inflamed ears in an animal model. Piglets were examined (n = 15) because their tympanic bulla closely resembles the human mastoid air cell system. Four untreated ears served as controls. Eleven ears were injected with glycerin into the tympanic bulla to induce inflammation and were studied as inflamed ears. Two respiratory conditions, spontaneous respiration and hyperventilation by a ventilator, were alternated repeatedly. ME pressure was measured intermittently by a tympanometer and blood gas was measured simultaneously. In all four normal ears, both ME pressure and carbon dioxide (CO2) partial pressure in the blood decreased in parallel following alternation of the respiratory conditions from spontaneous respiration to hyperventilation, while both pressure levels increased in parallel when respiration was changed from hyperventilation to spontaneous respiration. This result indicates that there is a gas exchange between the ME and the blood through the mucosa. However, ME pressure change in inflamed ears was limited, though the change in CO2 partial pressure in the blood was the same as that in normal ears. There was a significant difference in the degree of ME pressure change occurring in normal ears compared to that in inflamed ears, suggesting that inflammation of the mucosa reduced gas exchange function in the ME.