Short-term variations in oscillatory and spirometric lung function indices among school children

Abstract

The aim of this study was to compare immediate, daily and weekly variation in respiratory resistance measured by means of the forced oscillation technique (R(rs,FOT)) to spirometric indices in 7-12 year old children with chronic respiratory symptoms. The lung function measurements were performed in 19 children on 4 days, i.e. two consecutive days during two consecutive weeks. On each day, the measurements were carried out at the same time of day and always repeated three times. In addition, R(rs,FOT) and spirometric lung function indices were compared with an exercise challenge test in 12 children. Intrasubject coefficients of variation (CoVs) for R(rs,FOT) were larger than those for spirometric indices. Only in the immediately repeated measurements was the CoV of maximal expiratory flow at 25% vital capacity larger than that of R(rs,FOT) (16.6 vs 14.9%). At all time intervals, the smallest CoVs were observed in forced vital capacity (FVC) or in the ratio of forced expiratory volume in one second to FVC (2.0-2.6%). When excluding R(rs,FOT) values which were not within 2 SD (0.11 kPa · L-1 · s) of the differences between the immediately repeated measurements, the CoV of the immediately repeated measurements of R(rs,FOT) was reduced to 9.1%, being smaller than that of maximal mid-expiratory flow (10.1%). However, even then the day-to-day variation in R(rs,FOT), was clearly larger (16.0%) than those of the airflow indices at specified lung volumes (7.2-8.3%). This was also true for the weekly variation. In the exercise challenge test, there were larger changes in R(rs,FOT) values than in the spirometric indices, but R(rs,FOT) was the most sensitive index to detect changes in the respiratory system. In conclusion, the variation in R(rs,FOT) values was larger than that of most spirometric indices. When a reliability index was applied, the immediate variation in R(rs,FOT) values was comparable to those of the airflow indices at specified lung volumes. R(rs,FOT) was also the most sensitive index in the exercise challenge test, and therefore it seems to be suitable for detection of short-term functional changes in the respiratory system. However, the relatively low repeatability of R(rs,FOT) over days and weeks limit its applicability to longer-term follow-ups.