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

Abstract

We studied distribution of ventilation in patients with cystic fibrosis (CF) who had not had an exacerbation for some time. Patients performed either the vital capacity nitrogen (N(2)) single-breath washout test (VC test) or a modified single-breath washout consisting of 1 L inspired from functional residual capacity (FRC test) of 90% oxygen (O(2)), 5% helium (He), and 5% sulfur hexafluoride (SF(6)). We computed the slopes of phase III of N(2) concentration from the VC test (S(N2) (VC)) and the phase III slopes of the He (S(He)): The SF(6) (S(SF6)), and curves from the FRC test. S(N2) (VC) may be regarded as an index of overall ventilation and the difference (S(SF6) - S(He)) as an index of peripheral ventilation. Three groups were studied: CF, 28 CF patients (8-36 years of age); normal controls (NC), 33 normal nonsmokers (9-55 years of age); and a smoking group (SG), 42 non-CF smoking patients (39-79 years of age). Compared to the NC group, S(N2) (VC) is increased in the CF group, reflecting 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 sensitive, is nonspecific. Compared to both NC and SG groups, (S(SF6) - S(He)) is decreased in the CF group, being on the average negative. This may imply that there is a peripheral impairment in the distribution of ventilation that originates in terminal and respiratory bronchioles. Negative (S(SF6) - S(He)) is statistically associated with the youngest CF patients, suggesting that terminal and respiratory bronchiolar involvement is linked to early stages of the disease. In older CF patients, (S(SF6) - S(He)) is more often positive, suggesting that even more distal airways, such as alveolar ducts, become involved in peripheral inhomogeneity of ventilation.