Chest
Volume 85, Issue 1, January 1984, Pages 69-74
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Exercise Alveolar-Arterial Oxygen Pressure Difference in Interstitial Lung Disease

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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.

Section snippets

Respiratory Function Tests

The forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and maximum minute ventilation (MW) were measured with a Stead-Wells spirometer. The single breath diffusing capacity (Dsb) was determined by the method of Ogilvie and associates1 with an automated system.2 Normal values for the FVC are those of Morris et al.3 Normal values for the Dsb are those of Gaensler and Wright4 with a modification for the alveolar volume in terms of height and age; specifically, predicted

RESULTS

There were 168 patients that satisfied the conditions of our study (Table 1). The mean age was lowest for sarcoidosis, and except for this disease, there was a preponderance of males. Patients with UIP had the most abnormal roentgenographic score and the most abnormal FVC and Dsb, while patients with sarcoidosis tended to have the least abnormality. The mean FEV1/FVC was normal for the most part, but was slightly reduced in berylliosis. Steady state studies at rest showed an elevated V˙EV˙O

DISCUSSION

The concept of an alveolar arterial oxygen pressure difference plays a central role in our understanding of oxygenation in health and disease. Using the original equation for calculation of the P(A-a)O2, a value of about 10 mm Hg in normal persons at rest was attributed largely to V˙/Q˙ discrepancies and perhaps to small venous shunts.6, 7, 8,18, 19, 20, 21, 22 Exercise was variously reported to cause an increase, a decrease, or no change in P(A-a)O2.22, 23, 24 This confusion was resolved

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  • Cited by (0)

    This study was supported in part by a Training Grant (HL 07035), a Program Grant (HL 19717) and a Research Career Award (HL1173) all from the National Heart, Lung and Blood Institute, USPHS.

    Manuscript received April 19; revision accepted June 29.

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