Clinical comparison of two electronic spirometers with a water-sealed spirometer

Evaluation of the turbine pocket spirometer

A compact electronic spirometer, the turbine pocket spirometer, which measures the FEV1, forced vital capacity (FVC), and peak expiratory flow (PEF) in a single expiration, was compared with the Vitalograph and the Wright peak flow meter in 99 subjects (FEV1 range 0.40-5.50 litres; FVC 0.58-6.48 l; PEF 40-650 l min-1). The mean differences between the machines were small--0.05 l for FEV1, 0.05 l for FVC, and 11.6 l min-1 for PEF, with the limits of agreement at +/- 0.25 l, +/- 0.48 l, and +/- 52.2 l min-1 respectively. The wide limits of agreement for the PEF comparison were probably because of the difference in the technique of blowing: a fast, long blow was used for the pocket spirometer and a short, sharp one for the Wright peak flow meter. The FEV1 and FVC showed a proportional bias of around 4-5% in favour of the Vitalograph. The repeatability coefficient for the pocket spirometer FEV1 was 0.18 l, for FVC 0.22 l, and for PEF 31 l min-1. These compared well with the repeatability coefficients of the Vitalograph and the Wright peak flow meter, which gave values of 0.18 l, 0.28 l, and 27 l min-1 respectively. At flow rates of over 600 l min-1 the resistance of the pocket spirometer marginally exceeded the American Thoracic Society recommendations. The machine is easy to operate and portable, and less expensive than the Vitalograph and Wright peak flow meter combined. It can be recommended for general use.

Computer analysis of slow vital capacity spirograms

We have developed a digital computer program which evaluates the vital capacity and its subdivisions, expiratory reserve volume and inspiratory capacity. The algorithm examines the multibreath spirogram, a continuous record of quiet breathing interspersed among repeated slow, large volume maneuvers. Quiet breaths are recognized by comparing features of each breath to the respective average and variation of these features for all breaths. A self-scaling, iterative procedure is used to identify those end-tidal points that most likely represent the subject's functional residual capacity. A least-squared error baseline is then fit through these points to partition the vital capacity. Twenty-three spirograms from patients with documented pulmonary disease were independently analyzed by the computer, a pulmonary function technician, and the laboratory supervisor. No practical differences were found among the results. However, the computer's values, in contrast to those of the technician, were reproducible on repeated trials and free of computational and transcriptional errors.

Clinical validation of automated spirometry used in surveys of large occupational groups: comparison with conventional water spirometry

An accurate, rugged automated spirometer which provides immediate data is useful both clinically and for screening large groups with various environmental exposures. Because the need for such surveys has been increasing, we compared a computerized mass flow-meter with a conventional water spirometer. The same forced expiration was measured by both instruments in the laboratory and during an occupational survey. Mean values for forced vital capacity (FVC) were 96 cc greater by the automated technique in the laboratory (this equals 2.2% of the value by the conventional method, with a correlation, r, of 0.998) and 97 cc greater in the field (2.3% of the conventional method; r = 0.995). Differences between the two methods in the laboratory and field for forced expiratory volume in one second (FEV 1.0) were +24 cc (0.68%; r = 0.996) and +47 cc (1.6%; r = 0.996) and for forced expiratory flow (FEF)25-75--179cc/sec (4.18%; r = 0.968) and -63 cc/sec (2.1%; r = 0.992), respectively. For FVC and FEV1.0, the differences between paired values were less than or equal to 10% of the value by water spirometry in all instances and less than or equal to 5% in 95.5% and 96% of comparisons, respectively. For FEF 25-75 the differences between paired values were less than or equal to 20% in 97.2% and less than or equal to 10% in 84.7% of comparisons. These findings confirm the validity of the measurements provided by the automated spirometer.

A comparison of the Jones and Stead-Wells spirometers

A comparison was made between the noncounterweighted Jones and Stead-Wells spirometers, and "conversion factors" were determined for the forced expiratory volume in one second (FEV1) and the forced vital capacity (FVC). A cross-sectional study produced a high correlation between the instruments for these two measurements, yielding quadratic and linear regression equations ("conversion factors") for FEV1 and FVC, respectively. Standard deviations of measurements were similar for both spirometers. Results from a longitudinal study agreed with the "conversion factors" predicted from the cross-sectional study; however, significant day-to-day variability was observed by both spirometers. Neither spirometer met all of the technical recommendations proposed by the Committees on Environmental Health and Respiratory Physiology of the American College of Chest Physicians; however, the Stead-Wells water-sealed spirometer complied more often than the Jones waterless spirometer (Pulmonor). In addition, the open-circuit procedure used for the Jones spirometer required more corrdination in the subject than did the closed-circuit procedure employed in this study for the Stead-Wells spirometer; however, with application of the "conversion factors," both instruments, yield comparable data and prove adequate for spirometric studies.