The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts


Rob DiBlasi1,2, Jay Zignego1, Matthew Davidson1, Thomas Hansen1, Richardson Peter1

Background: Bubble nasal CPAP (B-nCPAP) is a simple form of non-invasive support that is commonly used in infants with respiratory distress. Research has focused on the physiologic benefits of B-nCPAP, specifically, its role in lung protection, improved gas exchange and curtailing the need for intubation and mechanical ventilation. The short term non-invasive application of high frequency nasal-ventilation (HFNV) has recently been described in an animal model of prematurity which showed improvements in lung structure and function when compared to mechanical ventilation. We designed a simple B-nCPAP system that also provides HFNV; whereby the magnitude of delivered volume and frequency are managed by varying the angle of a smooth plastic elbow affixed to the distal end of the exhalation circuit submerged in a water column. This study characterizes the oscillatory pressure swings generated at the nasal interface and the subsequent volumes and frequencies delivered to an infant lung model of respiratory distress.

A passive lung model was configured with CL= 0.47 mL/cmH20 and RAW= 200 cmH20/L/sec and hermetically sealed in a calibrated plethysmograph. Hudson nasal prongs were attached to an infant head model. Nasal prong leak rates were measured at CPAP of 5 and 10 cmH20. The head model was attached to the plethysmograph and the B-nCPAP system was connected to the expiratory tubing, which was immersed 7 cm into the water column. The flow rate was set at 10 LPM and pressure was measured proximal to the nasal prongs (Paw), and within the plethysmograph (Ppleth). Pressures were recorded for 8 sec at ~1 kHz with the elbow adapter angle positioned at 0, 90, and 135°. The plethysmograph calibration was used to convert Ppleth into volumes delivered to the mechanical lung model. Fourier analyses were used to determine dominant oscillatory frequencies. Mean Paw and volume delivered to the lung model were calculated.

The figure shows the effects of the elbow adapter angle on the Paw as well as the delivered volumes and frequencies. The largest effect on the delivered minute volume was observed when the elbow adapter angle was adjusted to 135°.

Paw generated at the nasal interface by this device was sufficient to deliver volumes at a frequency that may provide partial or even full ventilatory support to an infant with lung disease. Future studies will help determine this device's impact on gas exchange, work of breathing, and lung protection