Introduction
COPD is evaluated by lung volumes (FEV1, VR/CPT), DLCO, CT scan and arterial blood gases. Few studies investigated the single-breath double-gas lung diffusion capacity for CO (DLCO) combined with NO (DLNO) in COPD, which enables to dissociate the membrane component (Dm) and the capillary volume (Vc) participating in gas exchange. In this study, we evaluated this technique DLNO/CO in COPD, together with ventilation distribution (SBWO) and transcutaneous oxymetry (TcO2) as markers of peripheral ventilation and tissue oxygenation respectively.
Methods
Lung volumes, DLNO/CO, He slope of SBWO (SHe), TcO2 and CT-scan emphysema score (RA950%) were evaluated in 31 COPD patients (65±9 y, 61%F, FEV1: 50±17%) after pharmacological washout.
Results
Table 1. DLNO/CO according to GOLD groups (mean±SD).
| GOLD | A(N=8) | B(N=15) | E(N=8) |
| DLNO, ml/min/mmHg | 74±16 | 65±28 | 52±15§ |
| DLCO, ml/min/mmHg | 13±3 | 13±6 | 8±3§§* |
| Vc, ml | 33±10 | 34±18 | 19±8§* |
| Dm, ml/min/mmHg | 37±8 | 33±14 | 26±8§ |
§p<0.05, §§p<0.01: different from GOLD A
*p<0.05: different from GOLD B
Dm and Vc were correlated to RA950% (both r=-0.44, p<0.05) while Dm only, was correlated with SHe (r=-0.40,p<0.05) and VR/CPT (r=-0.36,p<0.05). Moreover, Vc only, was correlated with TcO2 (r=0.45, p<0.05).
Conclusion
The membrane and the vascular components of lung diffusion appear to be reduced in frequent exacerbators and emphysema patients. While the membrane component was related to the peripheral ventilation alteration and the degree of hyperinflation, the capillary volume was linked to tissue oxygenation. DLNO/CO gives additional insights on the process of gas exchange damage in COPD.