EXCHANGE-RATES OF GASES ACROSS THE TYMPANIC MEMBRANE IN RHESUS-MONKEYS

The exchange rates of CO, and He across the tympanic membrane were est imated in 5 monkeys. For these experiments, the monkey was anesthetize d and one arm of a polyethylene ''T'' tube was introduced into the ext ernal canal of the test ear and sealed to the ambient environment with wax. One arm of the T tube was attached to a pressure transducer and the other to an argon gas source via a valve. Silica tubing sealed wit hin the probe provided periodic gas samples for composition analysis b y an online mass spectrometer. Prior to each experiment, the probe was washed with Argon. In 5 experiments the probe was sealed within the e xternal canal of animals with physiological middle ear gas composition s, and in 5 experiments the probe was sealed within the external canal of animals whose middle ears were partially washed with He. The gas i n the probe was sampled and analyzed at 10-min intervals for up to 4 h . The results documented a significant increase in the percentage comp osition of CO, but not He in the experiments conducted with physiologi cal middle ear gas compositions, and increases in both He and CO, in t he experiments conducted after the middle ear was washed with He. Esti mated, average exchange constants for He and CO2 were 0.0005 mu l/min/ mmHg and 0.0103 mu l/min/mmHg. respectively. Using data from previous experiments, the relative trans-mucosal to trans-tympanic membrane gas exchange rates in monkeys are estimated to be in the order of 10 : 1 for inert gases and 180 : 1 for chemically active gases.