Abstract
Background and aims: We have shown, in lavaged rabbits, that High-Amplitude Bubble-Continuous Positive Airway Pressure (HAB-CPAP, see figure) provides greater gas exchange and lower work of breathing than conventional bubble-CPAP (PedsResearch, June,2010). The mechanisms generating the high amplitude pressure waves are the focus of this study.
Methods: A high-speed camera (PhantomV9.1;900frames/s) was used to visualize, simultaneously, the bubbling action in the HAB-CPAP device and airway pressures (Paw) measured in the patient circuit. Signals were generated with/without an infant lung model attached to the patient circuit. Measured changes in Paw were compared with calculated values obtained using a force balance.
Results: Videos revealed sharp increases in Paw concomitantly with the release of bubbles. Water appears to rush down the inclined tube and transfers momentum to the air it contacts, producing a water hammer effect. The rapid rise in pressure was followed by rarefaction as the wave propagates through the air system. The waveform without the lung model, see figure, is similar to an under-damped mechanical oscillator. Adding the lung model resulted in an over-damped system and appeared to act as a RCI filter removing the highfrequency components. A typical sharp pressure rise was 19.8 cmH2O with a calculated value of 17.1 cmH2O.
Conclusions: The “water hammer” effect can account for the sudden oscillations in Paw. Lung mechanics dampen these pressure oscillations suggesting that the stiffer the lung, the greater the oscillations in Paw.
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Zignego, J., Tang, D., Richardson, C. et al. 337 High-Speed Video Analysis of Highamplitude Bubble-Continuous Positive Airway Pressure Demonstrates That “Water Hammer” Effects Cause Large Oscillations in Airway Pressure. Pediatr Res 68 (Suppl 1), 173 (2010). https://doi.org/10.1203/00006450-201011001-00337
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DOI: https://doi.org/10.1203/00006450-201011001-00337