Rationale: Ventilation inhomogeneity (VI) may be an early sign of obstructive airway disease. The lung clearance index (LCI) has been suggested as a sensitive marker of VI, although it has not been well characterized in young children in health and in those with CF and asthma. Objective: To determine if LCI can detect VI in asymptomatic infants and preschool-age subjects with CF or wheeze/asthma compared to healthy controls. Methods: Sulphur hexafluoride (SF6) multiple breath washout (MBW) testing was completed in all subjects. Results: LCI was found to be dependent on age in a large healthy cohort. Accounting for age, LCI was significantly elevated in disease groups compared to healthy controls in early childhood, illustrating early presence of VI in wheezy infants and the progression of disease in CF. Furthermore, the effects of breathing pattern and the variability of MBW parameters showed positive associations with age and VI.

Rationale: Ventilation inhomogeneity (VI) may be an early sign of obstructive airway disease. The lung clearance index (LCI) has been suggested as a sensitive marker of VI, although it has not been well characterized in young children in health and in those with CF and asthma. Objective: To determine if LCI can detect VI in asymptomatic infants and preschool-age subjects with CF or wheeze/asthma compared to healthy controls. Methods: Sulphur hexafluoride (SF6) multiple breath washout (MBW) testing was completed in all subjects. Results: LCI was found to be dependent on age in a large healthy cohort. Accounting for age, LCI was significantly elevated in disease groups compared to healthy controls in early childhood, illustrating early presence of VI in wheezy infants and the progression of disease in CF. Furthermore, the effects of breathing pattern and the variability of MBW parameters showed positive associations with age and VI.