Peripheral airway involvement in asthma assessed by single-breath SF6and He washout

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Abstract
The aim of the study was to assess how deep into the acinar region the airway response to cold dry-air hyperventilation challenge (CACh) reaches in subjects with asthma of different severity.Peripheral airway function was measured using a single-breath sulphur hexafluoride (SF6) and helium (He) washout test and overall airway function by forced expiratory volume in one second (FEV1) at rest, after CACh and β2-therapy in 55 adults with a history of asthma. The normalised phase-III slopes (SnIII) for SF6and He were used to assess peripheral airway obstruction and the (SF6-He) SnIIIdifference to indicate where obstruction occurred. While a greater HeversusSF6slope increase indicates a response close to the acinar entrance, the reverse indicates a response deeper into the acinar airspaces.Twelve subjects had a major fall in FEV1(≥20%) after CACh, 16 a minor fall (10–19%), and 27 did not react. Resting He and SF6SnIIIwere significantly greater in major responders with respect to minor and nonresponders, while resting FEV1did not differ between the three groups. The major responders showed marked increases of He and SF6SnIIIafter CACh, with greater increase for He resulting in a negative (SF6-He) SnIIIdifference.To conclude, airways close to the acinar entrance participate in the overall airway response to cold-air challenge in asthmatic adults with marked airway hyperresponsiveness to cold, dry air.