Noninvasive monitoring of tidal volume with an extensometer: laboratory and clinical studies.

The extensometer or "rubbery ruler" (RR) is a new torso transducer with potential application in the field of respiratory pattern analysis. This paper determines whether the RR can measure tidal volume over a clinically useful time frame following spirometric calibration. Laboratory testing identified no error or baseline drift during 774,000 controlled stretches. Clinical testing in a variety of patients demonstrated that 96.6% of derived spirometric values were contained within an error range of +15.2% to -16.9% of spirometrically measured tidal volume and that accuracy did not change over a period of one hour. These results are encouraging and suggest that this device merits further investigation.