Use of static lung mechanics to identify early pulmonary involvement in patients with ankylosing spondylitis

Aim: To assess if a detailed analysis of lung mechanics could help in early recognition of pulmonary abnormalities in patients with ankylosing spondylitis. Methods: Static pulmonary mechanics were studied in 17 patients (16 men and one woman) of ankylosing spondylitis with no obvious clinical or radiological evidence of pulmonary involvement. Lung pressure-volume relationship was generated using a whole body plethysmograph, and a monoexponential equation fitted to this data. Results: Total lung capacity (TLC) was reduced in one (5.9%) and static lung compliance (C_st) in nine (52.9%) patients. Four (23.5%) patients had normal TLC, yet C_st and shape constant (K) were reduced. Five (29.4%) patients had reduced TLC and C_st; four of them had low K. One (5.9%) patient had normal TLC but elevated C_st and K. Conclusions: Pulmonary involvement in patients with ankylosing spondylitis is probably diffuse and begins much earlier than generally presumed. Evaluation of static lung mechanics can identify pulmonary involvement early in the course of disease in several of these patients.