[A comparison of respiratory muscle strength, pulmonary function tests and endurance in patients with early and late stage ankylosing spodylitis].

BACKGROUND: Ankylosing spondylitis (AS) is a multisystemic disease in which pulmonary function is altered owing mainly to the restriction of chest wall involvement. A restrictive ventilatory defect has been extensively reported. This has been suggested to be a consequence of reduced mobility of the thoracic cage. Respiratory function in AS shows a typical restrictive pattern but pulmonary compliance, diffusion capacity, and arterial blood gases are normal.

OBJECTIVE: The objective of the present study was to compare pulmonary function tests (PFT), respiratory muscle strength (MIP, MEP) and endurance (MVV) in early and late AS.

METHODS: A total of 35 patients (30 males, 5 females) took part, all of whom met the New York criteria for AS. Patients were divided into two groups for the comparison of early (disease duration <10 years, 20 patients) and late (disease duration >10 years, 15 patients) manifestations in pulmonary function tests, respiratory muscle strength and endurance, dyspnea score, chest expansion, and BASFI score. In addition, 21 healthy controls were compared with the AS patients. Measurement of chest expansion was performed in all subjects. Pulmonary function tests were performed by spirometry. Respiratory muscle strength was evaluated by a mouth pressure meter (MPM). Functional status was assessed by BASFI in all AS patients.

RESULTS: There was no significant difference in body mass index between the groups. The FVC and FEV(1) were significantly lower in late AS (p=0.003, p=0.03, restrictive ventilatory defect ). Chest expansion was significantly lower in late AS (p<0.05). There was no significant difference for MIP or MEP values between late AS, early AS and the controls (p>0.05). Endurance (MVV) was significantly lower in late AS patients (p=0.05). Although the BASFI and dyspnea scores were higher in late AS, they did not reach significant levels. In addition, age was negatively correlated with MIP and MEP in late AS (r=-0.733; p=0.02, r=-0.667; p=0.05).

CONCLUSION: This study demonstrates that FVC and FEV(1) (hallmarks of a restrictive pattern), MVV (endurance) and chest expansion are especially involved in long-standing AS. Therefore, improvement of the thoracic cage should be taken into consideration, especially in early AS. These patients should be encouraged to make regular respiratory exercises for preventing the limitation of chest expansion and also improving cardiopulmonary fitness and respiratory endurance.