SFTPB and chronic obstructive pulmonary disease: The pro-SP-B concentrations in lung of COPD patients are positively associated with severity of airflow limitation as measured by FEV1 % of predicted and FEV1/FVC ratio [24].SP-D levels in BALF are decreased in smokers and patients with COPD and are positively correlated with FEV1/FVC [25].