The study analyses retrospectively the characteristics of carbon monoxide diffusing capacity of the lung (DL,CO) and transfer coefficient (KCO) in relation to the spirometric parameters in patients with different pulmonary disorders. The study involved 41 patients (24 males), aged 53 yr (median, range: 19–74): 13 with chronic obstructive pulmonary disease (COPD), 17 with diffuse parenchymal lung diseases (DPLD), and 11 with noncomplicated chronic bronchitis (CB). DL,CO, KCO, vital capacity (VC), residual volume (RV), and total lung capacity (TLC) were measured with Transferscreen II (Jaeger) using the CO single breathholding method. Forced expiratory volume per second (FEV1) and forced expiratory vital capacity (FVC) were measured with a Flowscreen spirometer (Jaeger).
Patients with COPD showed a marked decline in DL,CO and had an airway obstruction. The diffusion parameters were also significantly decreased in the DPLD group, however, although present, the decline in FVC and FEV1 was far less marked than in COPD. In DPLD, DL,CO correlated significantly with FVC (ρ = 0.62, p = 0.011), VC (ρ = 0.63, p = 0.009), and TLC (ρ = 0.68, p = 0.003). In CB, the diffusion parameters and the spirometric values were unaffected and there was no correlation between these two sets of variables. Diffusing capacity of the lung is a sensitive and early parameter of lung function loss in DPLD, showing a decline even when commonly used spirometric values are near-normal or only slightly abnormal. Thus, measurement of DL,CO and KCO should be highly recommended in monitoring patients with the diseases of this heterogeneous group.