Between-technician variation in the measurement of spirometry with air and helium

A study using a two-period cross-over design was conducted to determine the between-technician variation in the measurement of variables derived from spirograms with subjects breathing room air and also breathing a mixture of 80% helium and 20% oxygen (He-O2). Twenty-four subjects were allocated systematically into three 2-period cross-over studies (blocks) of 8 subjects each (4 in each sequence in each block). There were 3 technicians in the study, and the subjects in each block were tested by a pair of technicians. The following variables derived from the tracings were analyzed statistically: forced expiratory volume in one second (FEV1), forced vital capacity (FVC) while breathing room air and also while breathing He-O2, maximal mid-expiratory flow rate (MMRF), FEV1/FVC %, and the per cent decrease in time between 60% VC and 40% VC for the spirograms comparing He-O2 with air (delta t). Analyses were performed to assess the presence of residual effects in the cross-over design, the between-technician difference in the administration of the tests, and in the interpretation of tracings. The results indicated that: (1) significant differences were observed between technicians in the administration of the tests to obtain FVC while the subjects breathed room air and while they breathed He-O2, (2) there were significant differences between the 3 technicians in the interpretation of MMFR, and (3) the between-technician variation in the administration of the tests with respect to delta t and with He-O2 in general were not significantly different from that of the other spirometric variables studied.