Overall and peripheral inhomogeneity of ventilation in patients with stable cystic fibrosis

We studied distribution of ventilation in patients with cystic fibrosis (CF ) who had not had an exacerbation washout test (VC test) or a modified sing le-breath washout consisting of 1 L inspired from functional residual capac ity (FRC test) of 90% oxygen (O-2), 5% helium (He), and 5% sulfur hexafluor ide (SF6). We computed the slopes of phase III of N-2, concentration from t he VC test (S-N2 (VC)) and the phase III slopes of the He (S-He): The SF6 ( S-SF6), and curves from the FRC test. S-N2 (VG) may be regarded as an index of overall ventilation and the difference (S-He - S-He) as an index of per ipheral ventilation. Three groups were studied: CF, 28 CF patients (8-36 ye ars of age); normal controls (NC), 33 normal nonsmokers (9-55 years of age) ; and a smoking group (SG), 42 non-GF smoking patients (39-79 years of age) . Compared to the NC group, S-N2 (VC) is increased in the CF group, reflect ing an overall Ventilation impairment. There is no difference in S-N2 (VC) between the CF group and the SG group, suggesting that S-N2, though sensiti ve, is nonspecific. Compared to both NC and SC groups, (S-SF6 - S-He) is decreased in the CF gr oup, being on the average negative. This may imply that there is a peripher al impairment in the distribution of ventilation that originates in termina l and respiratory bronchioles. Negative (S-SF6 - S-He) is statistically ass ociated with the youngest CF patients, suggesting that terminal and respira tory bronchiolar involvement is linked to early stages of the disease. In o lder CF patients, (S-SF6 - S-He) is more often positive, suggesting that ev en more distal airways, such as alveolar ducts, become involved in peripher al inhomogeneity of ventilation.