Exercise alveolar-arterial oxygen pressure difference in interstitial lung disease

Our plain-English summary of Exercise alveolar-arterial oxygen pressure difference in interstitial lung disease, by C. Risk, G.R. Epler, E.A. Gaensler (Chest, 1984).

The study

• Authors: C. Risk, G.R. Epler, E.A. Gaensler
• Journal: Chest
• Published: 1984;85(1):69-74
• Cited by: 93 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000569).

Abstract

Abnormality of gas exchange is best evaluated by the exercise alveolar-arterial oxygen pressure difference, P(A-a)O2. We studied the P(A-a)O2 in 168 patients with sarcoidosis, desquamative interstitial pneumonia (DIP), usual interstitial pneumonia (UIP), berylliosis, and asbestosis who were seen for clinical and disability consultations. The increase of P(A-a)O2 with exercise was greatest in UIP (mean 16 mm Hg), least in sarcoidosis (mean 1 mm Hg), and intermediate in DIP, berylliosis, and asbestosis (means 9, 9, and 7 mm Hg, respectively). The increase was best predicted by the single breath diffusing capacity (Dsb), and it occurred in patients with sarcoidosis and DIP if the Dsb was less than 50 percent predicted and in patients with the other diseases if the Dsb was less than 70 percent predicted. However, the magnitude of the increase could not be predicted from resting tests, even when multilinear regression equations were used. We conclude that for clinical evaluation of patients with interstitial lung disease, the exercise test with arterial blood gas measurement adds important information if the Dsb is less than 70 percent predicted. For disability evaluation, the invasive exercise study may be helpful when there is a wide discrepancy between clinical findings and resting physiologic studies.

In plain English

The authors reviewed records of 800 patients seen from 1955 to 1981 with five interstitial lung diseases. Of these, 168 met the study's conditions, including 18 with asbestosis. The authors compared resting lung tests with the alveolar-arterial oxygen pressure difference during treadmill exercise. This measure of how well lungs pass oxygen into blood combined arterial blood drawn by catheter with a calculated alveolar value. With exercise, this difference rose most in usual interstitial pneumonia (mean 16 mm Hg), least in sarcoidosis (mean 1 mm Hg), and by a mean of 7 mm Hg in asbestosis. In asbestosis, the rise was marked not statistically significant at each level of resting diffusing capacity, a test of gas transfer. Across all patients, severity graded by diffusing capacity and by the exercise test disagreed in about 40 percent of studies. The authors described the asbestosis patients as tending not to be severely ill. They concluded the exercise test adds important information when diffusing capacity is below 70 percent predicted, and may help disability evaluation when clinical findings and resting tests disagree widely.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective review of patient records comparing resting lung function tests with arterial blood gas measurements taken during exercise
• Who was studied: 168 patients seen at the Thoracic Services, Boston University School of Medicine, between 1955 and 1981, selected from 800 records. They had usual interstitial pneumonia (UIP, 32), desquamative interstitial pneumonia (DIP, 28), asbestosis (18), berylliosis (29) or sarcoidosis (61). Diagnosis was confirmed by open lung biopsy, except that node biopsy was accepted for sarcoidosis and epidemiologic and biochemical criteria for berylliosis. In Table 1, the asbestosis patients had a mean age of 54 and were 95% male.
• Exposure: This was not a study of asbestos exposure, and no fiber types, jobs or doses are reported. What the study compared was two kinds of testing: resting lung function tests, and steady-state treadmill exercise at a moderate level (oxygen uptake about 1.0 L/min). During exercise, arterial blood was drawn through a catheter and alveolar oxygen pressure was calculated. The authors state that the asbestosis patients frequently came to their attention during industrial surveys.
• Main results:
  • The mean rise in alveolar-arterial oxygen pressure difference with exercise was greatest in UIP (16 mm Hg) and least in sarcoidosis (1 mm Hg). It was intermediate in DIP (9), berylliosis (9) and asbestosis (7 mm Hg).
  • For the asbestosis patients, the exercise-minus-rest change was reported for three diffusing-capacity groups. It was 4 plus or minus 15 mm Hg in 8 patients with diffusing capacity above 70% predicted, 7 plus or minus 13 in 6 patients at 50 to 70%, and 10 plus or minus 11 in 4 patients at 50% or less. All three were marked not significant (NS).
  • Diffusing capacity (percent predicted) correlated with exercise alveolar-arterial oxygen pressure difference at p less than 0.001 in all the disorders except asbestosis.
  • The authors reported that the exercise value became larger than the resting value when diffusing capacity was below 50% predicted in sarcoidosis and DIP, and below 70% predicted in berylliosis, asbestosis and UIP.
  • Across all patient studies, severity was graded both by diffusing capacity and by the exercise test. The two gradings were discordant in about 40 percent of studies.
  • Regression equations using resting tests predicted the exercise value only approximately. The standard errors were about 10 mm Hg overall, and for asbestosis r was 0.68 with a standard error of the estimate of 9.5.
• The authors' conclusion: The authors concluded that, for clinical evaluation of interstitial lung disease, the exercise test with arterial blood gas measurement adds important information if diffusing capacity is less than 70 percent predicted. For disability evaluation, they wrote that the invasive exercise test may be helpful when there is a wide discrepancy between clinical findings and resting physiologic studies.
• Limitations the authors state:
  • The authors note that their patients were a heterogeneous referral population, and that differences between diseases may partly reflect who was referred. For example, the asbestosis patients came largely from industrial surveys and tended not to be severely ill. The authors stratified patients by diffusing capacity to account for this.

Topics

Medical terms in this study, explained in our Lexicon: Interstitial Lung Disease, Interstitial, Diffusing Capacity (DLCO).

Related studies

• Lung function impairment as a guide to exercise limitation in work-related lung disorders — J.E. Cotes, J. Zejda, et al. (1988)
• Relation between lung function, exercise capacity, and exposure to asbestos cement — P. Wollmer, L. Eriksson, et al. (1987)
• Evidence supporting a role for active oxygen species in asbestos-induced toxicity and lung disease — B.T. Mossman, J.P. Marsh (1989)
• Crackles (rales) in the interstitial pulmonary diseases — G.R. Epler, C.B. Carrington, et al. (1978)
• Asbestos-induced pleural fibrosis and impaired exercise physiology — J.F. Shih, J.S. Wilson, et al. (1994)
• Lung function and exercise performance in smoking and nonsmoking asbestos-exposed workers — D.Y. Sue, A. Oren, et al. (1985)

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