RESISTANCE TO AIRFLOW IN ANAESTHETIC BREATHING SYSTEMS

The resistance to airflow of the components of breathing systems have been examined pre-viously. Tracheal tubes and their connectors have been studied by a number of authors [1,2] and expiratory valves by others [3,4]. Smith [5] examined the resistance of the Magill system for both separate and assembled components. Shandro [6] studied the Ayre's T-piece, Bain and several circle systems. Several new breathing systems have been developed in recent years, and changes have been introduced, into both the design of their compo-nents and the materials used. These changes may have affected the resistance to gas flow. The aim of this study was to investigate the resistance to airflow in some of the commonly used anaesthetic breathing systems under stand-ardized conditions. METHODS The apparatus used to measure resistance to airflow was described by Gaensler and colleagues [7] and is shown in figure 1. Air was supplied from a cylinder through a variable pressure regulator (Murex Saffire BS 5741). The airflow rate was controlled by a needle valve and measured by a flowmeter (Platon Gap Meter type GTLK laboratory flow meter). The air was passed into a 10-litre glass bottle, which was used to avoid any Venturi effect [8]. The outlet of this bottle was fitted with a standard 22-mm male connector, to which apparatus under investigation was connected either directly or vi