PULMONARY FUNCTION STUDIES AS AN AID IN DIFFERENTIAL DIAGNOSIS OF PULMONARY HYPERTENSION

Pulmonary function studies in patients with pulmonary hypertension secondary to interstitial fibrosis reveal reduced lung volumes, and the carbon monoxide diffusing capacity, measured by the single breath method, is one third or less of predicted. In patients with pulmonary hypertension secondary to primary pulmonary vascular disease the lung volumes were found to be generally normal and the diffusing capacity averaged 55 per cent of predicted. The relative preservation of the carbon monoxide diffusing capacity in the presence of severe obstruction to the pulmonary arterial system contrasts with the severe impairment of oxygen diffusion which may occur in this situation. To illustrate the diagnostic usefulness of pulmonary function studies in this connection, a patient is cited who presented with symptoms of pulmonary hypertension initially diagnosed as primary pulmonary hypertension. However, severe impairment of carbon monoxide diffusing capacity led to the correct diagnosis of interstitial pulmonary fibrosis, despite a normal x-ray film of the chest; this was confirmed by open lung biopsy. © 1969.