CLINICAL USEFULNESS OF SINGLE-BREATH PULMONARY DIFFUSING CAPACITY TEST

Abstract

The breath-holding pulmonary diffusing capacity (DL) was found to be dependent upon body size and age in a group of 135 patients without significant cardiopulmonary disease. Regression formulas for predicting pulmonary diffusing capacity have been determined: [image] The concept of a characteristic pulmonary diffusing capacity/lung volume (DL /VL) ratio for a given age is suggested, and a regression formula applicable to both sexes has been determined: [image] Even when age, sex, and body size are taken into account, there is very marked variability in pulmonary diffusing capacity and pulmonary diffusing capacity/lung volume from subject to subject. This variability could not be accounted for by any parameter studied. The diffusing capacity results in 555 patients are reported. The pulmonary diffusing capacity was decreased in all cardiopulmonary disorders studied when accompanied by a fall in lung volume, and it was reduced in pulmonary emphysema. However, the pulmonary diffusing capacity was not appreciably altered in asthma or bronchitis without associated emphysema. Because of wide variability of data, the usefulness of the breath-holding pulmonary diffusing capacity test is extremely limited in determining the presence of disease or in differential diagnosis. It may have some usefulness in distinguishing emphysema from asthma or bronchitis, especially if the pulmonary diffusing capacity/lung volume is considered, although a low breath-holding diffusing capacity certainly cannot be considered a necessary criterion for the diagnosis of emphysema. A high pulmonary blood flow in a young person was found to be associated with some increase in pulmonary diffusing capacity/lung volume, and this test may have a limited usefulness in the diagnosis of left-to-right shunt in congenital heart disease. The specificity of the "alveolar-capillary block" syndrome for any particular group of diseases is questioned, as is the aptness- of the term "block" for many of the subjects in whom this syndrome is diagnosed. The term "inadequately functioning pulmonary parenchyma" would seem more generally applicable. The excellent reproducibility of the breath-holding pulmonary diffusing capacity determination on successive tests is confirmed. A definite correlation between the pulmonary diffusing capacity and arterial unsaturation on exertion was noted, but many individual discrepancies occurred. A significant fall in oxygen saturation on exertion generally occurred with diffusing capacities of less than 8 cc. of carbon monoxide per minute per mm. of mercury. The expense and inconvenience of the single-breath diffusing capacity test do not seem justified solely on the basis of its clinical usefulness, and caution must be exercised in the interpretation of breath-holding pulmonary diffusing capacity values in the presence of extensive pulmonary disease.