Pulmonary function tester

Claim 1

A pulmonary function tester for measurement of a patient's pulmonary function, comprising: a mouthpiece for placement in the patient's mouth; transducer means for sensing a pressure level and means for connecting said mouthpiece to said transducer means, said transducer means, connected to and in fluid communication with said mouthpiece through said means for connecting said mouthpiece to said transducer means, said transducer means sensing a pressure level in said means for connecting, said transducer means producing an output signal indicative of the sensed pressure level, said sensed pressure level being indicative of a rate of airflow in said mouthpiece; valve means, connected with said means for connecting said mouthpiece to said transducer means, for venting said transducer means to ambient atmosphere; and dynamic calibration means for (a) opening said valve means to the ambient atmosphere for a time interval sufficient for said transducer means to accurately sense an initial pressure level, when said valve means is open; (b) storing an initial zero level signal indicative of the initial sensed pressure level; (c) detecting a decrease in the sensed pressure level, after beginning the pulmonary function measurement, below a selected pressure level, the selected pressure level being greater than the initial sensed pressure level; (d) opening said valve means to the ambient atmosphere for a time interval sufficient for said transducer means to accurately sense a second pressure level when said valve means is open; (d) storing a second zero level signal indicative of the second sensed pressure level; and (e) calibrating sensed pressure levels of said transducer means, previously obtained during the pulmonary function measurement, in view of a difference between the initial zero level signal and the second zero level signal.