Studying middle ear gas variations needs nonporous materials

Abstract

Problem: Experimental studies that investigate middle ear (ME) gas exchange, by using either pressure or volume measurements, are conducted using various tubing connections between the ME and a measuring device. The purpose of the present study was to highlight experimental problems encountered when measuring small gas volume or pressure changes, or more specifically, error introduced by the gas permeability of the connecting tube. Methods: Several types of plastic tubes were tested for their gas permeability. Various plastic tubes including pediatric folley probe (Porgès S. A., France) were connected to a syringe filled with pure or 50% CO 2 through a gas-tight valve placed horizontally. The end of the plastic tube was plunged into colored water (Coomassie Brilliant Blue R-250 5%; Sigma®). The tube was purged with the gas until gas bubbles were seen leaving it, the valve was then closed, and the movement of water in the tube was followed with time. The same procedure was repeated with glass tubes. Results: No water movement was observed with glass tubes. In contrast, the colored solution advanced in the plastic tube at a rate twice as fast with 100% CO 2 than with 50% CO 2, a rate that changed according to the different plastic species. In contrast to the gas-tightness of glass tubes, plastic tubes exhibited significant gas permeability. The same experiments were repeated for O 2 with similar results. Conclusion: This study demonstrates the significant influence of the tubing used for connection. Significance: When studying ME gas variations, materials with no permeability such as glass must be used to overcome the loss or gain of gas through the tubing used. Support: No support