VARIABILITY OF FORCED OSCILLATION (SIEMENS SIREGNOST FD-5) MEASUREMENTS OF TOTAL RESPIRATORY RESISTANCE IN PATIENTS AND HEALTHY-SUBJECTS

The reproducibility of total respiratory resistance (R(rs)) measured w ith a simplified forced oscillatory method (Siemens Siregnost FD 5) wa s measured and compared with that of slow inspiratory vital capacity ( IVC) and forced expiratory volume in one second (FEV1). The former tec hnique has the advantage that assessment of bronchial obstruction can be made without a forced maneuver, which may be difficult in patients with chronic obstructive pulmonary disease (COPD). We used the criteri a proposed by the American Thoracic Society for the diagnosis of COPD. Pulmonary function tests (IVC, FEV1 and R(rs)) were measured in seven healthy subjects and in two groups of patients with COPD. First one t echnician performed six measurements of IVC, FEV1 and R(rs) in all sub jects during a period of 90 minutes on the same day. Second to evaluat e intraindividual variability the measurements were performed on ten s ubsequent days. The median interval (range) between the first and last measurements in days was 38 (20-186). The mean +/- SD coefficient of variation (CV) R(rs) in patients was 15.7% +/- 5.0% and in normals, 10 .8% +/- 3.2%. There was less variation in the FEV1 value of 11.0% +/- 6.2% and normals, 2.2% +/- 1.0%; and IVC, 6.9% +/- 5.0% and normals, 2 .4% +/- 0.7%. There is no correlation between age and CV. It is conclu ded from the study that oscillatory R(rs) has a larger coefficient of variation within one patient than FEV1 or IVC. If R(rs) is used for lo ngitudinal follow-up in COPD patients, we suggest that variations less than 26% (mean +/- 2 SD) can be considered the result of ''spontaneou s'' variation in lung function.