Objective: To assess the relationship between thoracoabdominal motion during quiet breathing and standardized indices of disease severity in Ankylosing spondylitis (AS) patients; also to evaluate whether thoracoabdominal motion improves following institution of biological agents in these patients.
Methods: The displacements of the rib cage (RC) and abdomen (Abd) during quiet breathing in the sitting, standing, and supine position were recorded with impedance plethysmography in 60 AS patients (41±10 years, 56 men) and 21 healthy men (36±7 years). X-Y plots of RC versus Abd displacements during quiet breathing were constructed and the angle of the slope of the RC-Abd loop was calculated and averaged for 5 consecutive breaths. In 13 patients treated with anti-TNFa, measurements were made prior to therapy and at 3, 6 and 12 months post-therapy initiation.
Results In the entire AS group, the angle of the slope of the RC-Abd loop correlated with BASFI in the sitting (R=-0.50, P<0.0001), standing (R=-0.36, P=0.004) and supine position (R=-0.47, P=0.0001) but not with BASDAI, BASMI or the modified Schober’s test. In 13 patients treated with anti-TNFa, the angle of the RC-Abd slope improved significantly (35%–69% over baseline at three months) in all body positions and in a nearly parallel fashion with the improvements of standardized clinical measurements.
Conclusion The pattern of thoraco-abdominal motion during quiet breathing correlates with BASFI and responds highly to anti-TNFa therapy. This parameter might be an appropriate target for evaluation of its potential usefulness in monitoring thoracic spine involvement and response to therapy in AS.
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Web only appendix 68:6;966-971
Web only appendix 68;6:966-971