Regional lung ventilation in ankylosing spondylitis.

Patients with ankylosing spondylitis (AS) sometimes develop apical lung fibrosis and cavitation. It has been suggested that one causative factor is reduced apical ventilation due to rigidity of the thoracic cage. We measured regional ventilation in 27 patients with AS and 18 normal volunteers. Twelve patients (Group A) had chest expansion greater than 2 cm, twelve (Group B) had chest expansion of 2 cm or less and three (Group C) had apical lung lesions on chest radiographs; patients in Groups A and B had no radiographic lung lesions. Ventilation per unit volume (VE/VA min-1) was calculated from 81Krm washout curves. The ratio of upper zone to lower zone ventilation (VR) was calculated. VR in Group A (0.74 +/- 0.11) and group B (0.75 +/- 0.12) was not significantly different from VR in controls (0.76 +/- 0.08). There was no significant correlation between VR and FVC, FEV1 or maximal chest expansion. In patients with apical fibrosis only the radiographically abnormal areas had reduced ventilation. Patients with AS do not underventilate the upper zones of the lungs except in the presence of radiographically visible fibrosis.