A Simple Test of Abnormal Ventilation-Perfusion Relationships

¹ Director, Cardio-Pulmonary Laboratory, University of Louisville School of Medicine

A simple test of ventilation-perfusion relationships has been described. This consists in the determination of end expiratory-end tidal pCO₂ difference by means of an infrared CO₂ analyzer. This difference did not exceed 5 mm.Hg in the control group with a residual volume of less than 40 per cent of the total lung capacity. A difference greater than 5 mm.Hg was found in 92 per cent of patients with chronic bronchitis and/or emphysema, in three patients with bronchiectasis and four with category 3 occupational pneumoconiosis. The increased end expiratory-end tidal pCO₂ difference was found to correlate reasonably well with increasing residual volume and decreasing maximum breathing capacity in the bronchitis-emphysema group. Correlation with vital capacity was not as good. It is suggested that the deterimnation of end expiratory-end tidal pCO₂ difference could serve as a rapid screening test for abnormal ventilation-perfusion relationships.