Background: Bubble CPAP is created by submersing the expiratory limb of the pressure tubing in a water column placed to the desired water pressure. Studies evaluating the effectiveness of varied ventilation paradigms have demonstrated the superiority of bubble CPAP over ventilator CPAP. Recently, a number of canister CPAP devices have become available that provide for simpler set up and use. The Babi plus is one such device that comes with a pressure pop off that is designed to limit bubble CPAP to its applicable range. Purpose: we asked if the pressure pop off on the Babi Plus might limit the amplitude of bubble CPAP and not allow for the maximal effectiveness of the bubbling. Methods: According to established use, wall flow was connected in line to the Babi plus. To simulate actual use and to eliminate the effect of water vapor inline, the heater was kept inline but not turned on. A pneumotachograph (Validyne) was connected inline to the Babi plus device. Measures of flow and pressure were obtained at settings of 4,5, and 6 cm H2O. Flow was varied from 1 to 8 lpm in increments of 1 lpm. ANOVA was used to analyze the pressure data. The lower and upper quartile of pressure measurements or the "bubble" zone were compared in both contexts. Results: Inter and intra rata differences were significant (p<0.05). Removing the pressure pop off from the circuit resulted in higher pressures in the "bubble zone. Please see figures below. Discussion: the effect of not having a patient in line cannot be discounted. Patient effort may provide additional pressure and flow at various times during the ventilatory process. Flow and pressure increments appeared to be predictable from the increases in flow and pressure. The effect of not having a pressure pop off inline produced a discernable but consistent shift of the bubble amplitude. Conclusion: The Babi Plus pop off valve provides a different CPAP experience when engaged. Clinical trials must be performed to establish the utility of the pop off valve in providing a clinically significant different ventilator paradigm.