[The measurement of pulmonary diffusing capacity for carbon monoxide].

The pulmonary diffusing capacity for oxygen (DLo,) is of great physiological and clinical significance (1). Its measurement, however, is relatively complex (2). Pulmonary diffusing capacity for carbon monoxide (DLco) which, it is usually assumed,' can be converted to DL02 from the known solubilities and molecular weights of the two gases, is, in general, more readily measured. Further, since the rate of reaction of carbon monoxide with hemoglobin has been measured (4) in vitro while that of oxygen has not, determination of DLco at two or more alveolar oxygen tensions makes possible the computation of pulmonary capillary blood volume and pulmonary membrane diffusing capacity (5-7). The methods used for measuring DLco are the single breath technique of Krogh (8) as modified by Ogilvie, Forster, Blakemore and Morton (9), the steady state technique using an independent measurement of the physiological dead space (10), the steady state technique using an alveolar sample (11) and a rebreathing technique using C'40 (12). The present paper presents a modification of the rebreathing method utilizing stable CO and continuous analysis.