Modelling the Relationship between Bubble CPAP Pressure, Flow, and Canister Bubbling Sounds

Bubble continuous positive airway pressure (bCPAP) supports neonatal respiration by directing air flow through an expiratory limb submerged in a water canister at a fixed pressure, thereby generating pressure oscillations that aid lung expansion, airway stability, and gas exchange. Proper system function is typically assessed by listening to bubbling sounds from the water canister and the patient's lungs. This paper describes the bCPAP canister bubbling sounds and develops a linear regression model relating the sounds at specific frequencies to system pressure and flow rate. Bubbling was found to consistently occur between 100-10,000 Hz, with different settings altering magnitude but maintaining similar minima and maxima within frequency bands. The model accounted for more than 81% of variance across experiments, though refinement is needed to address inter-day variability.Clinical Relevance-This work provides insights into the properties of bCPAP bubbling sounds as used in clinical settings and models their behavior as a function of system pressure and flow rate. By establishing a data-driven approach, it enables the potential development of real-time feedback tools that can quantitatively assess the quality of bubbling as a surrogate metric of the effectiveness of the bCPAP system, thereby improving the consistency and precision of respiratory support in neonatal care.