BACKGROUND: Both ventilation (V) and perfusion (Q) of the lungs are altered in asthma, but their relationships with allergen-induced airway responses and gas exchange are not well described.
METHODS: The effects of aerosolized allergen provocation of V/Q abnormalities in nonsmoking, male atopic asthmatics (six dual responders and two isolated early responders) were compared with measurements of airflow limitation (forced expiratory volume in 1 s [FEV1]), gas exchange (arterial oxygen saturation, arterial oxygen partial pressure and alveolar-arterial oxygen gradient) and airway reactivity (provocative concentration of histamine causing a decrease of 20% in FEV1). V and Q lung scans at 30 min and 6 h following allergen challenge and changes in all variables were compared with prechallenge data. Digital image data were registered to baseline scans, and quantitative comparisons of changes made were supported by qualitative assessments of the images.
RESULTS: All subjects showed evidence of impaired gas exchange, as reflected by lowered arterial oxygen tension and widened alveolar arterial oxygen gradients. Baseline V/Q scans were abnormal, and there were allergen-induced changes in V and Q at 30 min, with scans at 6 h showing additional changes in Q, particularly in dual responders. Allergen-induced gas trapping was evident at 30 min and was sustained at 6 h.
CONCLUSIONS: Regional patterns of V and Q derived from lung scintigraphy showed a wider range of disturbances than were indicated by the magnitude of airflow limitation and arterial hypoxemia following allergen provocation, and they remained abnormal despite normalization of FEV1. Imaging of regional abnormalities of gas exchange may be relevant in the evaluation of patients with asthma.