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

Abstract

. Role of nitrogen in transmucosal gas exchange rate in the rat middle ear. J Appl Physiol 101: [1281][1282][1283][1284][1285][1286][1287] 2006. First published July 13, 2006; doi:10.1152/japplphysiol.00113.2006.-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 Ϫ0.128 l/min (SD 0.023) in the air group (n ϭ 10) and Ϫ0.105 l/min (SD 0.032) in the N 2 group (n ϭ 10), but the difference was not significant (P ϭ 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 N2 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 N2 exchange between the ME gas and its mucosal blood circulation. rat model

Improving the visualization of fluorescently tagged nanoparticles and fluorophore-labeled molecular probes by treatment with CuSO4 to quench autofluorescence in the rat inner ear

“…The PEG-PCL polymersomes were either applied to the inner ear by osmotic pumps (1003D, Alzet, Canada) for 3 days (6 cochleae) or by transtympanic injection (40 ml) for 3 days (4 cochleae) or 5 days (2 cochleae). The injection volume was defined according to the literature report that an average volume of SD rat middle ear cavity is 42 ml (Kania et al, 2006). All experimental procedures were performed under general anesthesia, induced and maintained by intraperitoneal injections of a mixture of Domitor (1 mg/ml, Domitor, Orion, Finland) and Ketalar (50 mg/ml, Pfizer, UK) (0.6 ml for induction and 0.3 ml for maintenance) (Domitor:Ketalar ¼ 1:2).…”

Pressure changes in the human middle ear without opening the eustachian tube

“…We can assume that there was almost an equilibrium between pCO 2 in ME gas and venous blood, as has been described in the literature for the CO 2 and O 2 in the steady-state ME gas composition [11Á13]. Only the partial pressure of N 2 (and also Ar, mostly measured together with N 2 ) is higher in ME gas than in venous or arterial blood, with a gradient of 17 Torr (according to Kania et al [9]). If we assume an opening of the ET just before the onset of each of our test sessions, ME gas may contain a little less CO 2 and a little more O 2 because of an influx of air from the nasopharynx.…”

“…Kania et al gave a convincing explanation of the three phases, summarizing the relevant literature [9]. According to them phase I is governed by CO 2 diffusing from the mucosa blood vessels into the ME gas.…”

Comparison of the distribution pattern of PEG-b-PCL polymersomes delivered into the rat inner ear via different methods

“…For transtympanic membrane injection, 40 ml of PMs were injected into the middle ear cavity using 28-gauge needles. The injection volume was defined according to the literature report that the average volume of an adult rat middle ear cavity is 42 ml [10]. During the procedure the animal eyes were protected by Terra-Cortril-P (Pfizer).…”