This study was designed to test the hypothesis that, irrespective of the degree of interstiaI lung disease and/or pulmonary arterial hypertension, the combined measurement of lung diffusing capacity for nitric oxide and carbon monoxide, might be useful to provide a mechanistic interpretation of changes of diffusion subcomponents in systemic sclerosis (SSc).

In systemic sclerosis (SSc) the impairment of lung function is generally inferred from measurements of forced vital capacity (FVC) and standard lung diffusing capacity for carbon monoxide (DLCO). However, FVC measurement does not provide an accurate estimate of lung restriction and DLCO does not allow separate the alveolar membrane (DMCO) from erythrocyte (DeCO) diffusive conductance for CO. Previous studies have shown that DMCO and DeCO may change irrespective of overt intersitial lung disease (ILD) and/or pulmonary arterial hypertension (PAH). These changes may be consistent with a limitation of alveolar-capillary erythrocyte recruitment which impairs DM.This study was designed to test the hypothesis that, irrespective of the degree of ILD and/or PAH, combined DLNO-DLCO measurement might be useful to provide a mechanistic interpretation of DM and De changes in SSc.

Inclusion Criteria:

• patients fulfilling the 2013 American College of Rheumatology/European League Against Rheumatism criteria for a definite diagnosis of SSc with a total score ≥9

Exclusion Criteria:

• unstable subjects and/or who have suffered from respiratory exacerbations in the previous 4-wk

SSc patients