EFFECTS OF CPAP ON LUNG-MECHANICS IN INFANTS WITH ACQUIRED TRACHEOBRONCHOMALACIA

Continuous positive airway pressure (CPAP) has been used in the treatm ent of infants with tracheobronchomalacia (TBM). However, the effects of CPAP on lung mechanics in these infants are unknown. We hypothesize d that CPAP prevents airway collapse and improves forced exhalation. W e studied respiratory mechanics of nine infants (age 15 +/- 3 mo, SEM) with acquired TBM documented by bronchoscopy, during quiet respiratio n and forced exhalation, using the esophageal balloon and rapid thorac ic compression techniques, respectively. Measurements were made when i nfants received no CPAP and repeated when 5 and 8 cm H2O CPAP were app lied to the airway opening via a modified Mapleson anesthesia circuit. Expiratory resistance (RL), midexpiratory tidal flow (VE(50)), and ma ximal flow at functional residual capacity (Vmax FRC) were compared at each level of CPAP. Vmax FRC increased threefold from baseline to 8 c m H2O CPAP (p < 0.005). In contrast, there was no difference in expira tory RL or in VE(50) at any level of CPAP. These data suggest that in infants with acquired TBM, assessments of forced expiratory flow refle ct the amount of CPAP necessary to prevent airway collapse during forc ed exhalation better than can measurements of tidal mechanics.