MEASUREMENT OF RESPIRATORY TIMES IN FREELY MOVING RATS

A catheter was threaded beneath the skin from the trachea to an openin g on the top of the skull. It conducted a small fraction of the ventil atory Bow to an external miniaturized transducer, which was composed o f a heating element surrounded by two thermocouples. During inspiratio n, the heating element heated the inner thermocouple, whereas during e xpiration it heated the outer one. A square signal synchronous with br eathing was obtained from the difference in temperature at the two pro bing sites. Inspiratory and expiratory times were calculated from this signal. This device has been tested with calibrated flows, and compar ed with head-out plethysmography. It may be easily adapted for ventila tory measurements in any small mammal.