Influence of Changing the Diameter of the Bubble Generator Bottle and Expiratory Limb on Bubble CPAP: An in vitro Study

BackgroundThe noisy component of bubble continuous positive airway pressure (CPAP) is thought to contribute to breathing efficiency and lung volume recruitment, mainly because of stochastic resonance. The magnitude and frequency of the superimposed noise are vital to this process. We wanted to evaluate the in vitro effect of changing various parameters of the bubble CPAP circuit regarding the magnitude and frequency of pressure oscillations transmitted to the lung model.MethodsIn a bubble CPAP lung model, we immersed different sizes (3.0∼12.5 mm) of the expiratory limb of the CPAP circuit into different depths under water (2.0∼10.0 cm) and used various diameters (2.9∼9.0 cm) of bubble generator bottles. We also varied the compliance of the model lung. We measured the changes in mean, magnitude, and frequency of pressure oscillations transmitted to the lung model at three different flow rates (namely 4, 8, and 12 L/minute).ResultsIncreasing the size and submergence depth of the expiratory limb of a CPAP circuit and decreasing the diameter of the bubble generator bottle intensified the magnitude but diminished the frequency of noise transmitted to the lung model. Decreasing compliance of the lung model intensified both the magnitude and frequency content of pressure oscillations in the model lung.ConclusionThe size and submergence depth of an expiratory limb of a CPAP circuit, the diameter of the bubble generator bottle, and the compliance of the model lung all influence the magnitude and frequency of the transmitted pressure waveform. Therefore, these factors may affect lung volume recruitment and breathing efficiency in bubble CPAP.