Lung function tests in patients with idiopathic pulmonary fibrosis. Are they helpful for predicting outcome?

Idiopathic pulmonary fibrosis (IPF) varies widely in its course. To evaluate predictive parameters at presentation to the hospital, we investigated 99 patients with IPF (47 women), focusing on extensive lung function tests.

Standard tests of lung volumes, arterial oxygen tension, and gas exchange at rest and during bicycle exercise were performed. Survival rates in relation to functional parameters were calculated using the actuarial method. Differences in survival proportions were summarized as hazard ratios, and significance levels were determined by log-rank test.

At presentation, most patients showed a reduced total lung capacity (TLC) of 79.2 +/- 21.1%, an arterial oxygen tension (PaO2) considered pathologic in 63%, when related to age, a significant decrease of PaO2 with 11.8 +/- 12.1 mm Hg and an increase of the alveolar-arterial oxygen pressure difference with 46.4 +/- 16.4 (12.2 to 76.8) mm Hg during bicycle exercise. Diminished survival was associated with an age older than 50 years, a reduced value to more than 2 SDs below the predicted values of both, TLC alone, or in combination with a reduced vital capacity. Factors not influencing survival were gender, parameters of gas exchange at rest, and PaO2 at rest and during bicycle exercise.

We conclude that standard lung function tests make it possible to assess the prognosis of patients with IPF, while extensive tests like gas exchange measurements at rest and during bicycle exercise do not contribute additional information to make the prognostic estimations more precise.