Characterization of bubble oscillations in the infant lung during bubble nasal continuous positive airway pressure (NCPAP) support : effects on gas transport and exchange / by Kamar Jamil Al Sahmarani.

Abstract

Bubble NCPAP is an inexpensive form of NCPAP delivery that is increasingly used to support preterm infants with respiratory distress syndrome or for apnea of prematurity. This NCPAP modality is also advocated for its characteristic wideband Bubble oscillations that are superimposed on the NCPAP signal. It is hypothesized that such oscillations, if delivered to the distal lung, could result in superior lung volume recruitment and improved gas exchange. Yet, currently available clinical or experimental data supporting this claim are indirect and inconclusive. We systematically investigated the delivery of bubble oscillations in an anatomically-detailed in vitro model of the infant nasopharynx and airway tree. We constructed a 9-generation (n=0,1,2,...,8), decreasing dimensions, symmetrically branching airway tree. Delivered NCPAP and oscillation amplitudes (ΓêåP) were calculated from simultaneous nasal cannula (Pnc), upper airway (Pua), and distal airway (Pdis) measurements performed for multiple immersion depths (di) of the Bubble-NCPAP expiratory limb at various bias flows. Power spectra for all three pressures were derived. Transfer functions were computed as power spectrum ratios. In addition, a series of experiments were performed to compare air change rates in the airway tree with and without the presence of bubbling. The NCPAP delivery pressure was expectedly higher with increasing di, and increased substantially with increasing flow. Transmitted pressure oscillations amplitudes systematically decreased when moving in the proximal-to-distal direction with relatively greater losses in the nasal cannula-nasopharynx [ΓêåPdis ΓêåPuaΓêåPnc]. For all three pressures, the power spectra were qualitatively similar irrespective of di and flow. The Pdis-Pnc transfer function showed relatively less attenuation over a wide range of frequencies including an amplification frequency band between 20 and 40 Hz. A representative power spectrum of nasal cannula Bubble NCPAP oscillations (di=6 cm, flow=8