Technical pitfalls in middle ear gas studies: Errors introduced by the gas permeability of tubing and additional dead space
Conclusions We demonstrated errors introduced by the gas permeability of the tubing and additional dead space. Materials with practically no permeability, such as glass, must be used to overcome the loss or gain of gas through the walls of tubes used for studying ME gas variations. Experiments conducted at a constant volume (variable pressure) require the smallest possible tubing volume in order to obtain good sensitivity and improve the accuracy of the results. Objectives Experimental studies that investigate middle ear (ME) gas exchanges, using either pressure measurements or volume changes, are conducted using various tubing connections between the ME and a measuring device. The aims of this study were to highlight experimental problems due to the errors introduced by (i) the gas permeability of the tubing used and (ii) additional dead space in experiments conducted at constant volume. Material and methods The problem of the gas permeability of the tubing was addressed by comparing three types of tube (silicone, polyethylene, PVC) with a glass tube. Horizontally placed tubes were connected to a syringe filled with pure CO2 via a gas-tight valve. The end of each tube tested was plunged into colored water (5% Coomassie Brilliant Blue R-250). The tube was washed out with CO2 until gas bubbles were seen leaving it. The valve was then closed and the movement of water in the tube was observed. The same experiments were repeated for pure O2. The problem of the error introduced by the additional dead space volume was addressed at a theoretical level using the well-known gas laws. Two conditions were studied: condition A, in which the experiment was conducted at constant pressure and the volume was measured; and condition B, in which the experiment was conducted at constant volume and the pressure was measured. The main outcome measure of each condition was the calculated variation in the final number of moles of gas involved. Results No water movement was observed in glass tubes. In contrast, plastic tubes exhibited significant gas permeability effects for both CO2 and O2. The colored solution advanced at a faster rate with CO2 than O2 but differently for each type of tubing. For condition A, gas transfer was independent of the volume of the external tubing and was accurately measured by the displacement of the droplet in the lumen. In contrast, for condition B, the pressure variations were influenced by the volume of the tubing.
Pressure changes in tracheal tube cuffs
The pressure changes in tracheal tube cuffs can be explained by classical permeation theory. The transport of all gases contributes to pressure changes which may be negative or positive, depending upon the conditions. In vitro experiments were carried out to determine the applicability of this approach and the efjcacy of the methods for minimising the rise in cuff pressure.
Tourism in the Amazon: identifying challenges and finding solutions
Purpose – The purpose of this paper is to provide an overview of the tourism sector in the Amazon regions of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Suriname and then discuss the manner in which tourism activity assists the protection of the Amazon rainforests. The paper also describes the manner in which the first World Hospitality and Tourism Themes Roundtable on Tourism in the Amazon is organized in 2009.Design/methodology/approach – Teams of researchers from the Ministries of Tourism, the private sector and academia in the Member Countries of Treaty for Amazon Cooperation collaborated to address, in ten‐page papers, the question “Does sustainable tourism offer solutions for the protection of the Amazon rainforest?”Findings – The paper provides valuable information on the current state of tourism policy and practice in the Amazon Member Countries. It also articulates the challenges that attend the development of sustainable tourism as a mechanism for the protection of the Amazon.Practical...