Pathophysiology of activity limitation in patients with interstitial lung disease.

OBJECTIVE: To analyze the relative importance of gas exchange, ventilatory, and circulatory abnormalities in limiting exercise in patients with interstitial lung disease. DESIGN AND
SETTING: Retrospective study at a referral cardiopulmonary exercise laboratory in a university/county medical center. PATIENTS AND METHODS: A database with more than 1,300 patients with incremental cycle exercise studies was screened to find 42 patients with interstitial lung disease, but without accompanying airflow limitation, chest wall, primary heart, or systemic vascular disease, or poor motivation. All had spirometry, lung volume, and gas transfer index measures at rest and repeated gas exchange, ventilatory, and circulatory measures during exercise; 37 of the 42 patients had multiple blood gas measures during exercise. We graded the gas exchange, ventilatory and circulatory dysfunction during maximally tolerated cycle ergometry and correlated the grades of dysfunction of these three components of respiration with percent predicted peak O2 uptake (peak Vo2).
RESULTS: Peak Vo2 values were not well correlated with the grades of ventilatory impairment but were well correlated with the grades of gas exchange and circulatory dysfunction. Patients who had reduced peak Vo2 values often had a normal breathing reserve with physiologic evidence of pulmonary vascular disease.
CONCLUSIONS: The pathophysiology of the pulmonary circulation is usually more important than ventilatory mechanics in limiting exercise in patients with interstitial lung disease.