A reduction in specific airway conductance has been reported in infants with a history of an apparent life-threatening event (ALTE). It is unclear, however, whether this reflects upper or lower airway narrowing. We performed a controlled study to determine small airway patency in infants with ALTE. Lung function tests were performed in 26 infants with a history of ALTE and 27 healthy controls. Partial expiratory flow-volume curves were obtained during quiet sleep using the rapid chest compression technique; thoracic gas volume (TGV) and expiratory airway resistance (RAW) were measured by whole body plethysmography. Compliance of the respiratory system (Crs) was measured using the single breath occlusion technique. The median maximal flow at functional residual capacity (VmaxFRC) was 85 ml/s (range 10-198 ml/s) in patients and 123 (range 47-316 ml/s) in controls (P = 0.003). VmaxFRC corrected for TGV was 0.5 s(-1) (range 0.06-1.3 s[-1]) and 0.9 s(-1) (range 0.4-1.8 s[-1]), respectively (P = 0.001). TGV, RAW and Crs were not significantly different between patients and controls.
Conclusion: Reduced small airway patency may play a role in the pathogenesis of ALTE.