Effects of Positive End-Expiratory Pressure on Oscillated Volume during High-Frequency Chest Compression in Children with Cystic Fibrosis

Abstract

OBJECTIVE: To investigate the effects of positive end-expiratory pressure (PEEP) on end-expiratory lung volume (EELV) and mean oscillated volume (V_osc) during high frequency chest compression (HFCC).DESIGN: A clinic-based prospective intervention study.SETTING: Pulmonary function laboratory, University of Alberta, Edmonton, Alberta.POPULATION: Nine children with cystic fibrosis with little or no obstructive airway disease who were selected from the outpatient Cystic Fibrosis and Pediatric Pulmonary Clinics at the University of Alberta Hospital, Edmonton, Alberta.METHODS: Each child received HFCC alone (at 10 Hz with chest wall pressure of 8 cm H₂O) and HFCC plus PEEP. A closed circuit spirometry system was used to measure HFCC- and PEEP-induced changes in EELV, expressed as per cent baseline functional residual capacity (FRC) measured using helium dilution. An isothermic chamber permitted measurement of V_osc.RESULTS: HFCC caused a significant 9% decrease in EELV. Adding 2.0±0.3 cm H₂O of PEEP increased EELV back to at least the FRC level. With HFCC alone, V_osc was significantly lower during spontaneous expiration than during spontaneous inspiration, but adding PEEP to HFCC increased V_osc, especially during spontaneous expiration.CONCLUSIONS: Adding PEEP during HFCC prevents the decrease in EELV and increases V_osc. Therefore, PEEP may improve HFCC-induced mucus clearance in children with cystic fibrosis.