SHORT-TERM VARIATIONS IN OSCILLATORY AND SPIROMETRIC LUNG-FUNCTION INDEXES AMONG SCHOOL-CHILDREN

The aim of this study was to compare immediate, daily and weekly varia tion in respiratory resistance measured by means of the forced oscilla tion technique (Rrs,FOT) to spirometric indices in 7-12 year old child ren with chronic respiratory symptoms. The lung function measurements were performed in 19 children on 4 days, i.e. two consecutive days dur ing two consecutive weeks. On each day, the measurements were carried oat at the same time of day and always repeated three times. In additi on, Rrs,FOT and spirometric lung function indices were compared with a n exercise challenge test in 12 children. Intrasubject coefficients of variation (CoVs) for Rrs,FOT were larger than those for spirometric i ndices. Only in the immediately repeated measurements was the CoV of m aximal expiratory flow at 25% vital capacity larger than that of Rrs,F OT (16.6 vs 14.9%). At all time intervals, the smallest CoVs were obse rved in forced vital capacity (FVC) or in the ratio of forced expirato ry volume in one second to FVC (2.0-2.6%). When excluding Rrs,FOT valu es which were not within 2 SD (0.11 kPa . L(-1). s) of the differences between the immediately repeated measurements, the CoV of the immedia tely repeated measurements of Rrs,FOT was reduced to 9.1%, being small er than that of maximal mid-expiratory flow (10.1%). However, even the n the day-to-day variation in Rrs,FOT was clearly larger (16.0%) than those of the airflow indices at specified lung volumes (7.2-8.3%). Thi s was also true for the weekly variation, In the exercise challenge te st, there were larger changes in Rrs,FOT values than in the spirometri c indices, but Rrs,FOT was the most sensitive index to detect changes in the respiratory system. In conclusion, the variation in Rrs,FOT val ues was larger than that of most spiro metric indices. When a reliabil ity index was applied, the immediate variation in Rrs,FOT values was c omparable to those of the airflow indices at specified lung volumes. R rs,FOT was also the most sensitive index in the exercise challenge tes t, and therefore it seems to be suitable for detection of short-term f unctional changes in the respiratory system. However, the relatively l ow repeatability of Rrs,FOT over days and weeks may limit its applicab ility to longer-term follow-ups. (C)ERS Journals Ltd 1997.