Airway responsiveness following wheezy bronchitis in infants.

The study was undertaken to assess the airway function and its response to carbachol and salbutamol in infants recovering from wheezy bronchitis. In 82 children aged 3-33 mths, free from wheeze at the time of testing, and in 14 healthy infants, airway resistance (Raw) and thoracic gas volume (TGV) were measured using a body plethysmograph. Specific airway resistance (sRaw = Raw x TGV) was calculated. Increasing doses of nebulized carbachol were applied to challenge the airways. After a positive reaction had been achieved, 0.1 mg of nebulized salbutamol was administered. Raw was monitored during the whole procedure. In 23 of the 82 children the study was repeated after nine months on average. Within this period Raw remained elevated, whereas TGV and sRaw fell considerably (TGV from 37.9 to 28.2 ml.kg-1, p less than 0.01; sRaw from 0.78 to 0.63 kPa.s-1, p less than 0.01). Airway responsiveness also dropped during the observation period (mean log provocation dose producing 50% fall (PD50) 0.026 and 0.358, p less than 0.01). In comparison with controls the study infants responded to lower doses of carbachol (mean log PD50 0.610 and 0.031, respectively, p less than 0.01). Airway responsiveness was not related to baseline airway calibre or to signs of atopy. sRaw returned to baseline 2-5 min following salbutamol. The results suggest that airways of children in a symptom-free period following wheezy bronchitis have reduced patency and reveal hyperresponsiveness to carbachol.