Negative middle ear pressure induced by excretory function of eustachian tube was measured using fifteen cats. Under general anesthesia, a tube was connected to the bulla, whole space including middle ear and the tube was filled with physiological saline and the pressure of the space was measured with micro-tip pressure transducer (Miller PC-330 3F) which was hermetically connected to the tube.
By the ciliary function, negative pressure of-25-233 (mean-134.8) mmH₂O developed in 1-6 hours in nine ear, ., By the muscular pumping function (electril stimulation of tensor veli palatini muscle), negative pressure of-10-60 (mean-35) mmH₂O developed with 10-20 times of stimulation within a few minutes in 6 ears.
It is concluded that negative pressure in the middle ear develops in a short time merely by the excretory function of the eustachian tube when middle ear was filled with fluid.