Continuous positive airway pressure is widely used in the treatment of ARF and an evaluation of the systems is important. The authors used an artificial model to test a continuous flow system with a high compliance reservoir bag. The results confirm that the system is effective in maintaining positive pressure stability within a wide range of inspiratory peak flow rates, even when a low fresh gas flow rate is employed. Nevertheless, rebreathing of expired gases is possible and may be noticeable at high expiratory flow rates, caused by the high compliance of the reservoir bag.