Maximal expiratory flow and airway resistance during induced bronchoconstriction in patients with asthma due to Western red cedar (Thuja plicata).

Eleven patients with asthma due to occupational exposure to western red cedar were studied before and during bronchoconstriction induced by the inhalation of an extract of western red cedar or plicatic acid. The latter has been shown to be the compound in red cedar extract causing bronchoconstriction. Serial measurements of forced expiratory volume in 1 second, vital capacity, functional residual capacity, total lung capacity, airway conductance, and maximal expiratory flows from flow-volume curves were made. During the asymptomatic period, the mean maximal expiratory flows at 50 per cent of vital capacity and 60 per cent of total lung capacity were markedly reduced, whereas other parameters were within normal limits. In 19 provocation tests, late asthmatic reactions were induced in 4 tests and “dual” asthmatic reactions were induced in 15. At the height of both immediate and late reactions, the forced expiratory volume in 1 second and the vital capacity decreased, and the residual volume increased; maxim...