Comparison of dynamic lung function indices during forced and quiet breathing in upper airway obstruction, asthma,...

We compared the dynamic lung function indices in patients with asthma (n = 27), emphysema (n = 20), and UAO (n = 18), with the purpose being to examine whether different patterns of abnormalities could be found and which tests were most discriminative among the three groups. Forced expiratory indices were measured (FEV1; PEF; MEF50%), as well as indices obtained during quiet breathing (Raw; Gaw; Gaw/VL). The three groups were comparable as far as PEF was concerned (about 60 +/- 20 percent of predicted, yet the group with UAO showed significantly larger FEV1 (84 percent of predicted vs 55 percent and 57 percent of predicted in asthma and emphysema respectively), and larger MEF50% (71 percent of predicted vs 25 percent and 23 percent of predicted in the other groups), and the group with asthma had the largest Raw (0.37 +/- 0.18 kPa.s.L-1 vs 0.24 +/- 0.13 in UAO and 0.22 +/- 0.10 in emphysema). From these functional tests, several ratios were derived which were discriminative among the three groups. Upper airway obstruction could be recognized by a significantly lower PEF/MEF50% ratio and higher FEV1/PEF ratio than in the other conditions. Furthermore, a distinction between asthma and emphysema could be made by comparing airway patency during forced and quiet breathing, ie, the MEF50%/Gaw ratio. This ratio was, in fact, significantly different for all three groups, having the lowest value in emphysema (0.19 +/- 0.08 kPa vs 0.44 +/- 0.23 kPa and 0.63 +/- 0.34 kPa in asthma and UAO, respectively). Within the group with UAO, those with variable intrathoracic obstruction showed the least difference from asthma and emphysema for the measured indices.