Submitted on January 28, 2006
Accepted on June 29, 2006
Role of Nitrogen in Transmucosal Gas Exchange Rate in the Rate in the Rat Middle Ear
Romain Kania1*, Philippe Herman1, Patrice Tran Ba Huy1, and Amos Ar2
1 LNRS, CNRS 70-60, University Paris VII, 10 avenue de Verdun, 75010 Paris, FRANCE, Paris, France; Department of Oto-Rhino-Laryngology, Head & Neck Surgery, APHP, Lariboisiere Hospital, 2, rue Ambroise Pare, 75010 Paris, FRANC, Paris, France
2 Department of Zoology, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, ISRAEL, Tel-Aviv, Israel; LNRS, CNRS 70-60, University Paris VII, 10 avenue de Verdun, 75010 Paris, FRANCE, Paris, France
* To whom correspondence should be addressed. E-mail: romain.kania{at}lrb.ap-hop-paris.fr.
This study investigates the role of nitrogen (N2) in transmucosal gas exchange of the middle ear (ME). We used an experimental rat model to measure gas volume variations in the ME cavity at constant pressure. We disturbed the steady state gas composition with either air or N2 to measure resulting changes in volume at ambient pressure. Changes in gas volume over time could be characterized by 3 phases: a primary transient increase with time (phase I), followed by a linear decrease (phase II), then a gradual decrease (phase III). The mean slope of phase II was -0.128 µL.min-1 ± 0.023SD in the air group (n=10) and -0.105 µL.min-1 ± 0.032SD in the N2 group (n=10), but the difference was not significant (p=0.13), which suggests that the rate of gas loss can be attributed mainly to the same steady state partial pressure gradient of N2 reached in this phase. Further, a mathematical model analyzing the transmucosal N2 exchange in phase II was developed. The model takes gas diffusion into account, predicting that, in the absence of change in mucosal blood flow rate, gas volume in the middle ear should show a linear decrease with time after steady state conditions and gas composition are established. In accordance with the experimental results, the mathematical model also suggested that transmucosal gas absorption of the rat middle ear during steady state conditions is governed mainly by diffusive N2 exchange between the ME gas and its mucosal blood circulation.
