Bronchial challenge tests in patients with asthma sensitized to cats: the importance of large particles in the immediate response.

Our aim was to compare bronchial responses to major cat allergen (Fel d 1) in individuals with intermittent asthma sensitized to cats (19 subjects) according to the droplet particle size. We used three nebulizers, which delivered particles with mass median aerodynamic diameters of 1.4, 4.8, and 10.3 microm. A dosimeter nebulizer was used. The cat allergen was diluted to obtain the same amount of Fel d 1 per puff with each nebulizer. Each patient underwent three methacholine bronchial challenge tests (BCT), each followed 24 hours later by a cat allergen BCT, each performed with a different nebulizer (randomly selected each time, with patient and tester always blinded). Subjects did not differ for methacholine responsiveness, FEV1, mean forced expiratory flow during the middle half of the FVC (FEF25-75), PEF, or dyspnea (Borg scale) before any of the three cat BCTs. Cat allergen PD20 was 271 ng of Fel d 1 with the 1.4 microm nebulizer, 46 ng with the 4.8 microm nebulizer, and 13.5 ng with the 10.3 microm nebulizer (p = 0.00001). Inhalation of small particles (1.4 microm) resulted in significantly lower FEF25-75 24 hours after provocation than large particles did. In conclusion, immediate bronchial response appears to be localized in large airways, and the use of large particles is more appropriate for cat allergen BCTs.