Compound effects of inhaling pure oxygen and lifting height on ear baric function in a hypobaric chamber / 解放军医学杂志

ABSTRACT

Objective To compare the ear baric function between 4000m altitude chamber test with inhaling air and 6900m altitude chamber test with inhaling pure oxygen.Methods Eleven healthy male volunteers attended two tests as two groups by self-comparison. As the air group the volunteers inhaled air at 4000m, while as the pure oxygen group they inhaled pure oxygen at 6900m altitude, and the time interval between the two tests was more than two weeks. During the test, the volunteers breathed air or pure oxygen at random for 1h, and then were exposed at a speed of 20m/s to the target altitude for 5min. Hereafter they were sent back to the ground at the same speed. The changes of subjective symptoms, degree of tympanic congestion, acoustic immitance index and pure-tone auditory threshold were recorded before and after the test. The acoustic impedance index and pure-tone threshold were statistically analyzed.ResultsFour volunteers (4 ears) in air group and 7 volunteers (7 ears) in pure oxygen group reported ear pain in altitude chamber exposures, respectively. The pain-triggering altitude was higher in the pure oxygen group. Immediately after tests, there were 3 (3 ears) and 5 volunteers (5 ears) with Ⅲ degree congestion of the tympanic membrane in the two groups respectively. Four volunteers (6 ears) developed gradually aggravated hemorrhages after altitude exposure. And the tympanic membrane congestion difference between groups was statistically significant at 3 and 24h after tests (P<0.01). The type A tympanogram appeared in 11 (15 ears) and 11 (14 ears) volunteers respectively immediately after tests. The increase of static compliance value was significantly greater in pure oxygen group than in air group immediately after tests (P<0.05), the decrease of middle ear pressure was more significant in pure oxygen group than in air group at 3 and 24h after tests (P<0.05). Both the two altitude exposure tests resulted in eustachian tube dysfunction. At 3 and 24h after the tests, the increase of individual frequency pure-tone threshold was significantly higher in pure oxygen group than in air group (P<0.05).Conclusion Breathing pure oxygen and lifting height could increase the screening degree of ear baric function test in hypobaric chamber, and have greater influence on degree of tympanic congestion, acoustic immittance and pure-tone auditory threshold in 24 hours.