The second generation of nasal continuous positive airway pressure devices. Are they created equal?

Nasal continuous positive airway pressure (NCPAP) is considered the preferred medical treatment of obstructive sleep apnea. Because NCPAP exerts its beneficial effects by maintaining positive airway pressure, we proposed to test the ability of the newer "second generation" NCPAP machines to maintain a constant airway pressure during simulated breathing on a lung model. Each of the seven new NCPAP devices tested were examined under conditions of changing inspiratory flow, end expiratory pressure (EEP) and resistance added to the patient end of the NCPAP hose. During inspiration airway pressure fell and in expiration it increased relative to the EEP in all machines. Using the standard NCPAP hose and a breathing pattern consistent with normal breathing during sleep, the maximum decline in pressure during simulated inspiration and excess pressure during simulated expiration was -0.5 cm H2O and 0.6 cm H2O, respectively. Adding resistance, increasing inspiratory flow but not EEP exaggerated this effect. All of the machines behaved similarly in this regard. Further, the performance of the NCPAP devices did not deteriorate after 6 hours of uninterrupted operation. We conclude that the second generation NCPAP machines may be interchanged without another laboratory trial to readjust the EEP.