Role of nitrogen in transmucosal gas exchange rate in the rat middle ear

• Published in: Journal of applied physiology (1985) 2006-11, Vol.101 (5), p.1281-1287
• Main Authors: Kania, Romain E, Herman, Philippe, Huy, Patrice Tran Ba, Ar, Amos
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Ear, Middle - metabolism; Fundamental and applied biological sciences. Psychology; Gases; Male; Mathematical models; Models, Animal; Models, Biological; Mucous Membrane - metabolism; Nitrogen; Nitrogen - metabolism; Pressure; Rats; Rats, Sprague-Dawley; Rodents; Volume
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00113.2006

1 Laboratoire de Neurobiologie des Réseaux Sensorimoteurs, Centre National de la Recherche Scientifique 70–60, Faculté de Médecine Lariboisière Saint-Louis, Université de Paris VII; 2 Department of Oto-Rhino-Laryngology, Head and Neck Surgery, Assistance Publique-Hôpitaux de Paris, Hôpital Lariboisière, Paris, France; and 3 Department of Zoology, Tel Aviv University, Tel Aviv, Israel Submitted 30 January 2006 ; accepted in final form 29 June 2006 This study investigates the role of nitrogen (N 2 ) 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 N 2 to measure resulting changes in volume at ambient pressure. Changes in gas volume over time could be characterized by three phases: a primary transient increase with time (phase I), followed by a linear decrease (phase II), and then a gradual decrease (phase III). The mean slope of phase II was –0.128 µl/min (SD 0.023) in the air group ( n = 10) and –0.105 µl/min (SD 0.032) in the N 2 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 N 2 reached in this phase. Furthermore, a mathematical model was developed analyzing the transmucosal N 2 exchange in phase II. The model takes gas diffusion into account, predicting that, in the absence of change in mucosal blood flow rate, gas volume in the ME 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 ME during steady-state conditions is governed mainly by diffusive N 2 exchange between the ME gas and its mucosal blood circulation. rat model Address for reprint requests and other correspondence: R. E. Kania, Service d'Oto-Rhino-Laryngologie et de Chirurgie de la Face et du Cou, Hôpital Lariboisière, 2, rue Ambroise Paré, 75010 Paris, France (e-mail: romain.kania{at}lrb.ap-hop-paris.fr )