High-Resolution Measurements of Middle Ear Gas Volume Changes in the Rabbit Enables Estimation of its Mucosal CO2 Conductance

Abstract

Transmucosal CO(2) exchange in the middle ear (ME) of the New Zealand White rabbit (Oryctolagus cuniculus) was studied using an accurate novel detecting and recording system for measuring gas volume changes at constant pressure, based on a principle that was previously used by Kania et al. (Acta Otolaryngol 124:408-410, 2004). After the ME cavity was washed with ambient air, the initial diffusion rate of CO(2) (V(.-)(i)CO(2)) from the blood perfusing the ME mucosa was calculated from gas volume change measurements. In nine cases, the (V(.-)(i)CO(2))calculated after normalization due to shifts in baseline was 314+/-112 microL x h(-1) (mean +/- SD). In two cases where normalization was not needed, (V(.-)(i)CO(2)) was 409 microL x h(-1) (276 and 543 microL x h(-1)). Normalization of (V(.-)(i)CO(2)) data was also made in five additional cases where secretion of fluids from the lining of the ear canal was observed. In these cases (V(.-)(i)CO(2)) was 245 +/- 142 microL x h(-1). No differences were found between results obtained in the three groups. Thus, an overall mean value of (V(.-)(i)CO(2)) of 305 +/- 131 microL x h(-1) (n = 16) was calculated. An effective coefficient of conductance of CO(2) (G(CO(2))) between the mucosal circulation and the ME gas cavity of the New Zealand White rabbit was estimated to be approximately 0.05 microL (h x Pa)(-1) and compared to the G(CO(2)) estimated for humans in a different study.

Mechanical properties of human tympanic membrane in the quasi-static regime from in situ point indentation measurements

“…Experimental loading curves and optimal simulation output. Lim, 1970;Uebo et al, 1988;Ruah et al, 1991) only report data on small parts of the tympanic membrane. In Kuypers et al (2005), similar distribution patterns were found along specimens (a rather constant central region thickness and steep thickness increases toward the edges with the annulus and manubrium), but a large spread on absolute thickness values is reported.…”

“…For example these originate from taking an elevator, meteorologic changes and gas exchange processes in the middle ear (Gaihede et al, 2010;Marcusohn et al, 2006). They are called quasi-static since the corresponding frequencies typically fall within the range [0.001, 20] Hz.…”

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

“…As can be seen from the partial pressure differences presented in Table 2, O 2 is driven from the ME cavity to the surrounding tissues and blood, and, conversely, CO 2 moves into it from tissues and blood (34). The initial gradients of partial pressures under which gases are exchanged are between the arterial blood and the ME cavity.…”

Perfusion and diffusion limitations in middle ear gas exchange: The exchange of CO2 as a test case

“…'Maintenance', i.e. : continuous intravenous (in rabbits) or subcutaneous infusion (in rats) of a mix of ketamine, xylazine and Ringer (rabbits)/Ringer lactate (rats) using an infusion pump (Marcusohn, 2003;Marcusohn et al, 2006). After initiation of a long-term anesthesia protocol, the tympanic membranes were perforated.…”

“…We revisited this issue using data obtained from our previous studies of gas exchange in the ME of rabbits (Marcusohn et al, 2006) and rats (Marcusohn, 2003). In these experiments we used devices that allowed iso-pressure measurements of gas volume changes.…”