Absence of deep inspiration-induced bronchoprotection against inhaled allergen.

Deep inspiration-induced bronchoprotection appears to be a major mechanism through which airway obstruction by spasmogens is avoided. Loss of bronchoprotection is associated with airway hyper-responsiveness. Individuals with allergic rhinitis and no airway hyperresponsiveness develop obstruction after allergen inhalation. To test the hypothesis that deep inspiration-induced bronchoprotection is not active against allergic reactions, we performed four single-dose bronchial challenges, two with methacholine and two with allergen, on 10 subjects with allergic rhinitis. Without deep inspirations, the methacholine-induced reduction in FEV1 from baseline was 36.9 +/- 3.6% (mean +/- SEM); this was attenuated to 15.0 +/- 2.0 when five deep inspirations preceded methacholine inhalation (p = 0.0001). When allergen was inhaled, the reduction in FEV1 was 24.7 +/- 2.9% and 28.8 +/- 6.4% without and with deep inspirations, respectively. We conclude that bronchoprotection by deep inspirations is absent against allergic reactions. Understanding the cause of this phenomenon may shed light into the pathogenesis of airway hyperresponsiveness in allergic asthma.