Simultaneous measurement of pulmonary diffusing capacity for CO and cardiac output by a rebreathing method in patients with pulmonary diseases.

Pulmonary diffusing capacity for CO (DLCO) and cardiac output (Q) were simultaneously measured by a noninvasive rebreathing method (RB) in 15 normal subjects and in 60 patients, including cardiac diseases (CD), bronchial asthma (BA), chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (PF). DLCO and Q were tested by the single breath method (SB) and the dye-dilution method (Dye), respectively. DLCO (RB) correlated well with DLCO (SB) (r = 0.890, p < 0.001). Q(RB) also correlated well with Q(Dye) (r = 0.909, p < 0.001). Factors affecting DLCO (RB) were age, height, body surface area, O2 consumption, Q, hematocrit (Het) and Q.Hct, among which Q.Hct was the prominent influential determinant. DLCO per lung volume was smaller in COPD and PF than in BA or healthy subjects, while, the ratio of DLCO/(Q.Hct) was significantly higher in COPD than in PF. Simultaneous measurements of DLCO and Q offer comprehensive characterization for functional changes in lung parenchyma.