End-expiratory lung volume and ventilation distribution with different continuous positive airway pressure systems in volunteers

Background Continuous positive airway pressure (CPAP) has been shown to improve oxygenation and a number of different CPAP systems are available. The aim of this study was to assess lung volume and ventilation distribution using three different CPAP techniques. Methods A high-flow CPAP system (HF-CPAP), an ejector-driven system (E-CPAP) and CPAP using a Servo 300 ventilator (V-CPAP) were randomly applied at 0, 5 and 10 cmH(2)O in 14 volunteers. End-expiratory lung volume (EELV) was measured by N(2) dilution at baseline; changes in EELV and tidal volume distribution were assessed by electric impedance tomography. Results Higher end-expiratory and mean airway pressures were found using the E-CPAP vs. the HF-CPAP and the V-CPAP system (P < 0.01). EELV increased markedly from baseline, 0 cmH(2)O, with increased CPAP levels: 1110 +/- 380, 1620 +/- 520 and 1130 +/- 350 ml for HF-, E- and V-CPAP, respectively, at 10 cmH(2)O. A larger fraction of the increase in EELV occurred for all systems in ventral compared with dorsal regions (P < 0.01). In contrast, tidal ventilation was increasingly directed toward dorsal regions with increasing CPAP levels (P < 0.01). The increase in EELV as well as the tidal volume redistribution were more pronounced with the E-CPAP system as compared with both the HF-CPAP and the V-CPAP systems (P < 0.05) at 10 cmH(2)O. Conclusion EELV increased more in ventral regions with increasing CPAP levels, independent of systems, leading to a redistribution of tidal ventilation toward dorsal regions. Different CPAP systems resulted in different airway pressure profiles, which may result in different lung volume expansion and tidal volume distribution.