Evaluation of a new piston-type spirometer.

A new dry spirometer (DS) incorporating a microcomputer for automatic calculation and direct read-out of spirometric parameters was compared to a calibrated Fleisch pneumotachograph (PT). Twenty-eight volunteers, including healthy subjects, obstructive and non-obstructive patients, performed a total of 48 spirometric tests with the two apparatuses randomly alternated. DS values for FVC were lower than those of the PT with a mean difference of 0.177 1 +/- 0.171 SD (p less than 0.0001). Mean FEV1 values were very similar in both apparatuses with a non significant difference of 0.003 1 +/- 0.182 FEF25-75 values were higher with the DS, showing a mean difference with the PT of 0.407 1 . s-1 +/- 0.324 (p less than 0.00001). The DS also gave slightly higher PEFR values than the PT, with a mean difference of 0.310 1 . s-1 +/- 0.830 (p less than 0.02). Differences in FVC readings between DS and PT were greater in severely obstructed patients (0.350 1 +/- 0.084, p less than 0.0001) than among healthy subjects (0.120 1 +/- 0.051, p less than 0.0002). On the contrary, in absolute figures DS values for FEF25-75 showed a greater difference with those of the PT in normals (0.547 1 . s-1 +/- 0.320, p less than 0.001) than in obstructed patients (0.288 1 . s-1 +/- 0.244, p less than 0.05). DS flow resistance was 2.67 cmH2). s. 1-1 for a flow of 8.8 1. s-1. Based on the spirometric differences observed, and on the high flow resistance and volume limitation imposed by its 6 1 capacity, we concluded that the apparatus tested cannot be recommended for clinical spirometry.