DIURNAL-VARIATIONS AND REPRODUCIBILITY OF N-2 CLOSING VOLUME TEST IN HEALTHY SUBJECTS

  • 1 January 1976
    • journal article
    • research article
    • Vol. 12  (6) , 757-770
Abstract
To assess the diurnal variation of closing volume measurements, 11 non-smokers and 10 smokers, all healthy, were tested with the single-breath N2 test. In each subject, 3 satisfactory tracings were recorded at 9 a.m., 11 a.m., 1 p.m., 3 p.m. and 5 p.m. on each of 2 consecutive days. Duplicate copies of the tracings were read in random order by 2 independent observers. The best and the mean values of closing volume to tidal capacity ratio (CV/VC or phase 4/VC) and of the slope of phase 3 were calculated. The time of the day may be a source of variation of the closing volume measurements. Meals and cigarette smoke did not appear to be responsible for this diurnal variation. Values obtained with the best tracing method can, at least in some readers, give systematic differences with the mean of several traces. Individual variations in CV/VC and in the slope of phase 3 are the highest with the best trace analysis, and the values obtained by 2 independent readers may significantly differ. The differences observed between hours, although significant, were nevertheless small in magnitude and did not explain most of the variation of the measurements. Variations in trace aspect were small in some subjects. The reproducibility of the test was remarkable in them, at least when the junction of phase 4 with phase 3 was well defined. In other subjects, the coefficient of variation was high, mainly because of varying curve shape and/or poorly defined departure of phase 4. This explains the intra-and inter-reader variations observed in this study.