2000 OPEN FORUM Abstracts
ACCURACY OF THE MICRO PLUS HANDHELD SPIROMETER FOR THE MEASUREMENT OF FVC, FEV1 AND PEFR
David C. Shelledy, PhD, RRT, Terry S. LeGrand, PhD, RRT, Stefani Stevenson, CRT, and Robert Evans, CRT. The University of Texas Health Science Center at San Antonio, San Antonio, Texas
INTRODUCTION: The Micro Plus (MP) [Micro Direct Inc., Lewiston, ME] is a compact, battery operated, handheld spirometer for the measurement of FEV1, FVC and PEFR. We compared the MP to the SensorMedics 2450 (SM) to determine the accuracy of the MP. METHOD: Prior to data collection, the MP and SM were calibrated according to factory recommendations. We then compared inline and separate measures at 1, 1.5, 2.0, 2.5 and 3.0 L using a calibration syringe to verify that placing the MP inline with the SM did not affect the volume readings. Fifteen normal subjects, aged 18 to 60, then performed 3 FVC maneuvers with the MP and SM inline. Mean values were compared using the t-test for dependent samples. Pearson-product moment correlations were calculated and regression equations were evaluated to determine the slope and intercept of the regression line. Means (SD) and ranges were calculated for the differences between paired results between instruments to provide measures of bias and imprecision. Limits of agreement were then calculated as the mean difference ± 2 SD.
Results: Mean (SD) values for FVC, FEV1 and PEFR were:
|Micro Plus||3.99 (1.0)||3.19 (.83)||5.98 (2.25)|
|SensorMedics 2450||4.17 (1.13)||3.42 (.91)||6.23 (2.19)|
There were significant differences (p< 0.0001) between the MP and SM for FVC, FEV1 and PEFR. Correlation coefficients for FVC, FEV1 and PEFR were r=0.979, r=0.9996, and r=0.9888 (p<0.0001). Regression equations were: FVC MP = 0.344 + 0.873 SM; FEV1 MP = 0.044 + 0.920 SM; PEFR MP = 0.359 + 1.017 SM. The mean (SD) difference for the paired results (bias) for FVC was 0.19 (0.25) with a range of -0.89 to 0.51; FEV1 was 0.23 (0.08), range: 0.12 to 0.08; and PEFR was 0.25 (0.34), range: -1.66 to .53. The limits of agreement between the SM and MP were -0.313 to +0.687 for FVC; 0.077 to 0.382 for FEV1 and -0.424 to +0.926 for PEFR.
Conclusions: FEV1, FVC and PEFR values obtained via the MP correlated significantly with SM values. There were small, but statistically significant differences between mean MP and SM values and the MP tended to underestimate FVC, FEV1 and PEFR. We believe the MP can be useful for monitoring and bedside evaluation, however, it may not be suitable as a diagnostic spirometer.