OBJECTIVES

1. Longitudinal Comparison of Measures of Lung Diffusing Capacity of Carbon Monoxide in Systemic Sclerosis Melissa Caron, Russell Steele, Rébecca G. Taillefer, Solène Tatibouet, Murray Baron, Marie Hudson, and Canadian Scleroderma Research Group OBJECTIVES RESULTS • Systemic sclerosis (SSc) is an autoimmune disease characterized by widespread fibrosis and vascular abnormalities in the skin and internal organs including the lungs, heart, oesophagus, gastrointestinal tract and kidneys. Interstitial lung disease (ILD) and pulmonary arterial hypertension (PAH) are leading causes of death in SSc patients. • Lung function is measured, among other things, using the lung diffusion capacity of carbon monoxide (DLCO). DLCO measures the degree to which oxygen and carbon monoxide can travel in and out of the lungs and the blood stream. DLCO is an important measure of lung function in SSc since it correlates well with ILD and PAH. There exist many different measures of DLCO that can be used to evaluate lung function. • In order to best help SSc patients, we wanted to determine which DLCO measure(s) captured lung function best in SSc patients. METHODS • We evaluated the following DLCO measures: DLCO single breath (DLCOsb), DLCOsb corrected for hemoglobin (DLCOsbcorr), DLCOsb corrected for alveolar volume (DLCOsb/VAsb), DLCOsbcorr corrected for alveolar volume (DLCOsbcorr/VAsb), DLCO rebreathable (DLCOrb), DLCOrb corrected for hemoglobin (DLCOrbcorr), DLCOrb corrected for alveolar volume (DLCOrb/VArb) and DLCOrbcorr corrected for alveolar volume (DLCOrbcorr/VArb). • We examined correlations between the various DLCO measures and clinical variables, including patient self-reported shortness of breath on a scale of 0-10, fatigue measured using the Vitality subscale of the SF-36, extent of skin involvement measured using the modified Rodnan skin score, function measured with the Health Assessment Questionnaire HAQ, range 0-3), physician-reported New York Heart Association class (I-IV), presence of interstitial lung disease (ILD) and presence of pulmonary hypertension (defined as a systolic pulmonary artery pressure > 45 on cardiac echocardiography). CONCLUSIONS • The next step in our research is to determine which DLCO measure predicts outcomes in SSc best. We will examine how various DLCO measures are associated with incident ILD and PAH, and with survival. • In the end, we hope to make a recommendation as to which measure of DLCO should be used in studies of SSc. ACKNOWLEDGEMENTS • This research project was made possible by the CSRG 2011 Summer Studentship program. SUMMARY OF RESULTS • We have found that percent predicted DLCOsb and DLCOrb differed quite a bit (74.59% and 82.97%, respectively). However, once we adjusted these values for alveolar volume, DLCOsb and DLCOrb became quite similar (92.69% and 93.16%, respectively). • In cross-sectional analyses, DLCOsb had the strongest and most consistent correlations with clinical outcomes among the various DLCO measures.