Two-sidearm tracheal cannula for respiratory airflow measurements in small animals.

We have investigated the possibility of using a two-sidearm tracheal cannula for measurements of respiratory airflow. Measurements of mean flow and tidal volume using four such cannulas (0.7, 1.5, 1.8, and 2.5 mm ID) are described. They have a linear response up to flows of 6, 10, 12, and 28 ml X s-1, respectively, that correspond to 100 ml X s-1 X kg-1 or more, depending on the body size of the animals (15-350 g) in which they could be used. These characteristics, coupled with small volume and flow resistance, make the use of these cannulas as pneumotachographs a suitable and very practical way of measuring mean airflow and tidal volume in anesthetized small animals, ranging in size from newborn rats to newborn puppies.