Respiratory muscle strength but not BASFI score relates to diminished chest expansion in ankylosing spondylitis

Pulmonary function is altered in ankylosing spondylitis (AS) owing mainly to the restriction of chest wall involvement (limited chest expansion). The objective of this study was to investigate the relationship between chest expansion, respiratory muscle strength (MIP, MEP) maximum voluntary ventilation (MVV), and BASFI score in patients with AS. Twenty-three male patients with definite AS and 21 age-matched healthy male controls were recruited for the study. Patients with AS were assessed for functional status by BASFI. Measurement of chest expansion and lumbar spinal flexion (modified Schober) method was performed in all subjects. Pulmonary function tests were performed by spirometry. Respiratory muscle strength was evaluated by a mouth-pressure meter (MPM). Body mass index (kg/m2) was recorded in all individuals. Chest expansion and modified Schober measurement were significantly lower in AS patients (p