The diagnosis of idiopathic interstitial pneumonia (IIP) is based on computed tomography (CT) imaging, whereas lung function studies are used for staging and follow up. Lung diffusing capacity for carbon monoxide (DLCO) is generally reduced but weakly correlated with the severity of CT-determined fibrotic process. A possible explanation of this finding is that DLCO is relatively insensitive to changes in alveolar membrane diffusive conductance (DMCO). Lung diffusion capacity for nitric oxide (DLNO) was strongly correlated with CT-determined amount of fibrosis/honeycombing in both usual and non-specific interstitial pneumonias. Moreover. Both DLNO and DMCO were below the lower limit of normality even in patients with small amount of fibrosis. Measurement of DLNO may provide a more reliable assessment of fibrotic changes than DLCO because it better reflects DMCO.

Rationale: Lung diffusing capacity for carbon monoxide (DLCO) is decreased in both usual interstitial pneumonia-idiopathic pulmonary fibrosis (UIP-IPF) and nonspecific interstitial pneumonia (NSIP), but is weakly related to computed tomography (CT)-determined fibrotic changes.

Objectives: To determine whether measurement of lung diffusing capacity for nitric oxide (DLNO) better reflects fibrotic changes than DLCO.

Methods: DLNO and DLCO were measured simultaneously in 30 patients with UIP-IPF and 30 with NSIP. The amount of pulmonary fibrosis was estimated by volumetric analysis of visually bounded areas showing reticular opacities and honeycombing. Alveolar membrane conductance (DMCO) and pulmonary capillary volume (Vc) were calculated.

Inclusion Criteria:

• Chest computed tomography (CT) scan diagnosis of either usual interstitial pneumonia-idiopathic pulmonary fibrosis (UIP-IPF) or idiopathic nonspecific interstitial pneumonia (NSIP)

Exclusion Criteria:

• Symptoms/signs or specific serum markers of an underlying autoimmune process
• Previous environmental/occupational exposure to fibrogenic dusts
• Use of fibrogenic medications

The investigators used retrospectively collected data of 60 Caucasian patients with clinical and radiological features of Idiopathic Interstitial Pneumonias referred to Respiratory Pathophysiology Unit for a complete pulmonary function evaluation.