Pulmonary physiology in interstitial lung disease: recent developments in diagnostic and prognostic implications.

Pulmonary function changes in interstitial lung disease are characterized by loss of lung volume, increase in ratio of forced expiratory volume in 1 second to forced vital capacity, and decrease in carbon monoxide diffusion capacity. Recent developments in the assessment of respiratory mechanics in infiltrative lung disease have elucidated volume and flow dependence of lung and total respiratory resistance and elastance related to the viscoelastic properties of the respiratory system. A new, simple test of applying negative expiratory pressure at the mouth during tidal expiration can be used to generate expiratory flow-volume curves to detect flow limitation in patients with restrictive as well as obstructive disorders. This method is useful in patients who are weak, uncoordinated, or who cough during forced maneuvers. Poor prognostic signs in interstitial lung disease include male gender, paucity of lymphocytes on bronchoalveolar lavage, extensive radiographic infiltration, absence of cellular histologic findings on lung biopsy, presence of right-axis deviation, persistent or progressive decrease in lung volumes, and diffusion capacity of carbon monoxide.