A new transducer for respiratory monitoring. A description of a hot-wire anemometer and a test procedure for general use.

A respiratory transducer based on the constant temperature anemometry principle has been developed for respiratory monitoring, and as a tool for bedside evaluation of pulmonary function. The transducer is characterized by a dynamic range from 0-2.5 1/s and an upper limiting frequency of 50 Hz. It is designed with a view to a low pressure drop of 2.5 mbar/1/s and a minimum dead space of 5 ml. The transducer has been tested using a generally applicable procedure which includes both static and dynamic test set-ups. The influence of variation in gas composition, temperature and pressure, together with variations in tidal volume and respiration rate, have been investigated. The results show that the transducer registers the immediate value of gas flow-rate with a mean error less than 5-10% in all situations which are predictable in clinical use. The mean error can be reduced to less than 5% when systematic errors are eliminated.