Comparative airway response to high- versus low-molecular weight agents in occupational asthma

Airway responses to occupational agents in sensitised workers may vary clinically and physiologically. The patterns of change in airway responsiveness, type of response and fall in expiratory flows following laboratory exposure to high- or low-molecular weight agents (HMW and LMW agents, respectively) were compared in sensitised workers. Data on workers who underwent specific inhalation challenges with occupational sensitisers (117 exposed to HMW agents and 130 to LMW agents) were collected from their medical charts. Maximum falls in forced expiratory volume in one second (FEV(1)) were of similar magnitude for both types of agents. Compared with HMW agents, LMW agents induced more frequently late or dual responses and higher increases in airway responsiveness. After exposure to HMW agents, there was a mean+/-sd reduction in doubling concentrations of methacholine of 0.5+/-1.7 for early responses, compared with 2.8+/-1.2 and 1.4+/-2.0 for late and dual responses, respectively. Isolated early responses were more frequently found in females, smokers, workers with a higher % predicted FEV(1) and higher provocation concentration causing a 20% fall in FEV(1), and in those with longer asthma duration. Workers' characteristics, as well as the type of agent they are sensitised to, may help to predict the type of response after specific inhalation challenge.