Comparison of peak expiratory flows and FEV1 in assessing immediate asthmatic reactions due to occupational agents.

Abstract

FEV1 is more sensitive than PEF in assessing late asthmatic responses (LAR) after specific inhalation challenges (SIC) with occupational agents. As immediate asthmatic reactions (IAR) mainly involve proximal airways, PEF may, however, be as valid as FEV1. Thirty-seven subjects who experienced an immediate fall in FEV1 of > or =20% during SIC with occupational agents and 20 subjects with fall of < or =10% in FEV1 were included. Both FEV1 and PEF were measured in a random order every 10 min for 1 h after exposure. We corrected PEF (PEFc) for inaccuracies of the mini-Wright meters by the Miller equation. Maximum changes in PEFc (30+/-11%) were not significantly different from changes in FEV1 (27+/-5%) (P=0.13). Their timings after exposure were 14+/-11 min and 17+/-17 min, respectively (P=0.4). High sensitivity (92%), specificity (95%), accuracy (93%), and positive predictive value (97%) were found for a 20% fall in PEFc to detect a significant IAR. Results were better and not influenced by meter inaccuracies with a cutoff point of 15% change in noncorrected PEF (PEFnc). An absolute decrease in PEF of 70 l/min gave a good discrimination between reactions with and without an asthmatic response. PEF is as satisfactory as FEV1 for detecting a significant IAR after exposure to an occupational agent if one considers a cutoff point of 1) 15% fall in PEF 2) 20% fall in PEFc 3) 20% fall and/or 70 l/min decrease in PEFnc.