MEASUREMENTS OF MEMBRANE DIFFUSING-CAPACITY AND PULMONARY CAPILLARY BLOOD-VOLUME IN NORMAL SUBJECTS AND PATIENTS WITH MILD EMPHYSEMA

Objective. To establish predicted values of membrane diffusing capacit y (Dm) and pulmonary capacity blood volume (Vc), to compare the predic ted values from our equations with those for Caucasians, to determine whether there are changes initially in Dm or Vc in patients with mild emphysema. Patients and Methods. Diffusing capacity for carbon monoxid e (DLco), Dm and Vc were determined in 86 normal subjects and 16 patie nts using the single-breath diffusing capacity for carbon monoxide (DL cosB) with two different alveolar concentrations of oxygen. Results. T he predicted equations are as follows: For males, DLco (ml/min/mm Hg)= 0.37H-0.19A-27.8; Dm (ml/min/mm Hg)=0.65H-0.24A-53.7; Vc(ml)=0.88H-78. 9. For females, DLco=0.28H-22.7; Dm=0.59H-53.6; Vc=66.6-0.36A. DLco an d Vc are lower in Chinese than Caucasians while Dm is similar in Chine se and Caucasians. Eleven of 16 patients had a low DLco (<80% predicte d value), 12 had a low Dm and 5 had a low Vc. Eight of 12 patients wit h a low Dm also had a low DLco, but in 4 the DLco was normal. Nine of 12 with low Dm had a normal Vc. Conclusions. This study provides predi ction equations of Dm and Vc. Chinese have a low DLco because their Vc is lower than Caucasians. The DLco and Dm are abnormal in a comparabl e percentage of patients. In patients with mild emphysema, the Dm beco mes abnormal before the Vc.