Flow limitation in infants assessed by negative expiratory pressure

Forced expiratory flows by the rapid compression technique are often used t o assess airway function in infants; however, it remains unclear as to whet her flow limitation (FL) is achieved. Studies in adults have used negative expiratory pressure (NEP) at the airway opening as a noninvasive technique to assess whether FL is achieved. An increase in flow with NEP indicates th at FL has not been achieved, whereas no increase in flow with NEP indicates FL has been achieved. In the adult studies, the change in flow was assesse d by visual inspection of the flow-volume curve. We evaluated whether NEP c ould be used to assess FL during forced expiration in infants. In addition, we quantified the change in flow secondary to NEP. We applied -5 cm H2O NE P to four infants during forced expiratory maneuvers. The step increase in flow with NEP was always less than 5% at high jacket compression pressures and consistent with FL. For one subject, FL was also confirmed from isovolu me pressure flow-curves measured with an esophageal catheter. We conclude t hat NEP can be used in infants to assess FL during forced expiratory maneuv ers by the rapid compression technique.