Carbon Monoxide Diffusing Studies in the Clinical Evaluation of Chronic Lung Diseases

Abstract

The fractional carbon monoxide uptake, pulmonary diffusing capacity, arterial pH, partial pressures of carbon dioxide and of oxygen, and complete ventilatory studies were performed on 74 patients with chronic lung disease. Of the 74 patients, 73 per cent had normal diffusing capacity at rest, and 79.7 per cent had normal diffusing capacity after correction of their heart failure or hypoventilation. The fractional uptake was normal in 93.2 per cent of the series and was normal in 95.6 per cent after treatment of congestive heart failure. There was no correlation between the diffusing capacity and any of the ventilatory studies. The diffusing capacity was lower than normal in eight of the 15 patients (53.3 per cent) whose arterial carbon dioxide partial pressure was above 45 mm Hg. This also suggested a relationship between the diffusing capacity and alveolar ventilation. The diffusing capacity is shown to increase with increase in tidal volume, and occasionally with minute volume, and can be used to help distinguish between alveolar-capillary block and hypoventilation. The test can be modified to measure the component parts of the diffusing capacity. The test presented here is a simple, accurate and rapid test of gas exchange which can be used routinely in the evaluation of patients with chronic lung disease.