Reduced vital capacity leads to exercise intolerance in patients with ankylosing spondylitis

Background. It is well-known that pulmonary function is altered in patients with ankylosing spondilitis (AS) owing mainly to the restriction of chest expansion. In addition to musculoskeletal factors, development of pulmonary function abnormalities may also deteriorate exercise tolerance of the patients. Aim. The aim of this study was to examine the pulmonary function and exercise tolerance of AS patients. Design. A case controlled study. Setting. Outpatient clinic of an university hospital. Population and Methods. Twenty-two men with the diagnosis of definite AS and 20 healthy controls matched according to age, sex, smoking habits and physical activity level were enrolled in this study. After a detailed physical examination, pulmonary function and exercise tolerance were assessed by "Sensormedics-Vmax 229" ergospirometry system. Maximal exercise testing was performed on a cycle ergometer using "10 watt ramp" protocol. Results. Patients with AS had lower chest expansion, vital capacity and exercise tolerance than healthy subjects. Exercise tolerance strongly correlated with the patients' age, disease duration, chest expansion, modified Schober test, and vital capacity. In stepwise regression analysis, the best regression model for explaining the total variation of exercise tolerance selected only vital capacity as an independent variable (R-2=54.9%). Conclusion. Rather than musculoskeletal manifestations, exercise intolerance was mainly explained by pulmonary function impairment in AS patients. Clinical Rehabilitation Impact. These results suggest that efforts should be directed not only towards improving spinal mobility but also towards increasing cardiopulmonary fitness in AS patients.