Comparison of FEV1 and specific airway conductance in assessing airway response to occupational agents

There is theoretical evidence that specific airway conductance (SGaw) could be more reliable than forced expiratory volume in 1 s (FEV1) for assessing changes in airway calibre. We investigated the changes in FEV1 and SGaw when assessing bronchial responses to occupational agents.

SGaw and FEV1 were measured during inhalation challenges with various occupational agents in 174 consecutive subjects investigated for possible occupational asthma.

A decline in SGaw of 50% or greater was documented in 77 of 90 subjects (86%) who showed a >/=20% fall in FEV1 and in 11 of 84 subjects (13%) who failed to demonstrate such a fall in FEV1. Among subjects who developed a >/=20% fall in FEV1, those who failed to develop a >/=50% decline in SGaw had a lower baseline SGaw than those who did. Among the group without a >/=20% fall in FEV1, a >/=50% decrease in SGaw was associated with either an 'intermediate' fall in FEV1 (between 15 and 17% from baseline value) (n = 4), a significant postchallenge increase in nonspecific bronchial hyper-responsiveness to histamine (n = 2), or both features (n = 3).

A decline in SGaw of 50% or greater may provide useful complementary evidence of a bronchial response during challenges that produce equivocal results in FEV1.