Chest
Volume 109, Issue 6, June 1996, Pages 1566-1576
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Clinical Investigations: Exercise
Pathophysiology of Activity Limitation in Patients With Interstitial Lung Disease

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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 V02 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 V02 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.

Section snippets

Population

We screened the records of the last 1,300 integrated cardiopulmonary clinical exercise tests performed in our medical center, as described below and previously reported.25 The laboratory is often referred patients with uncommon disorders. We did not include or exclude patients on the basis of their referring diagnoses and believe we found all patients who might be expected to have interstitial lung disease as their primary disorder. For the diagnosis of asbestosis, patients had to have

Patient Profile

Exercise studies and associated records for 42 patients with interstitial lung disease or pulmonary alveolar proteinosis (P) were found and analyzed (Table 2). Primary left heart disease was doubtful because of the absence of murmurs, left ventricular hypertrophy on chest radiograph or ECG, ECG evidence for myocardial infarction, or ST-segment depression during maximal exercise. Musculoskeletal disease did not limit exercise because no patient stopped exercise with complaints of back, hip, or

DISCUSSION

The major finding of this study suggests that physiologic defects accounting for the reduced peak V˙o2 in our patients with interstitial lung disease were more likely circulatory than ventilatory. In fact, the dominant measure of ventilatory impairment, the exercise breathing reserve, tended to be high when peak V˙o2 values were low. The circulatory impairment appears to be primarily due to pulmonary vascular disease with accompanying gas exchange impairment.

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