Respiratory disease and respiratory physiology: putting lung function into perspective interstitial lung disease.

The interstitial lung diseases pathologically involve the pulmonary interstitium but may also involve the airways, pleura and pulmonary circulation. They may be idiopathic, be part of other conditions, or be related to drug or environmental exposures. This review will focus on diagnostic and prognostic information provided by lung function tests in the idiopathic interstitial pneumonias, particularly idiopathic pulmonary fibrosis and non-specific interstitial pneumonia. These disorders are characterized by small stiff lungs with impaired gas exchange. Lung function tests, particularly lung volumes and gas transfer, used initially on patient presentation and then repeatedly on follow up, together with high-resolution computed tomography scans, can generate predictive formulae which are superior to single tests and can be used to provide useful information to assess the natural history of the disease or guide therapy. The concomitant presence of emphysema may mask the degree of restriction and may have adverse prognostic implications when accompanied by pulmonary hypertension.