Gas absorption in the middle ear.

The middle ear (ME) pressure of alert and anesthetized rhesus monkeys was monitored by serial tympanograms in order to determine the gas absorption process in the ME cavity. During the four-hour observation period the ME pressure showed small, random fluctuations around zero pressure in the alert animals, whereas in the anesthetized animals, following an initial positive pressure phase, the ME pressure reached a plateau at an average pressure of -60 mm H2O. The ME gas composition was changed by air or oxygen gas politzerization in anesthetized animals to determine the effect of different initial gas compositions on the rate of absorption of the gas and on the magnitude of ME pressure. Politzerization with air and with oxygen gas resulted in average maximum ME pressures of -400 and -730 mm H2O, respectively. The experimental evidence suggested that the physiological composition of ME gases is nearly that of the surrounding environment and that the rate of gas absorption is low. When the gas composition of the ME is changed, the ME pressure decreases considerably. Based on these findings, a possible mechanism for the development of negative ME pressure is proposed.