Abstract
Nasal high flow (NHF) cannulae are used to deliver heated and humidified air to patients at steady flows ranging from 5 to 50 l/min. In this study, the flow velocities in the nasal cavity across the complete respiratory cycle during natural breathing and with NHF has been mapped in vitro using time-resolved stereoscopic particle image velocimetry (SPIV). An anatomically accurate silicone resin model of a complete human nasal cavity was constructed using CT scan data and rapid prototyping. Physiological breathing waveforms were reproduced in vitro using Reynolds and Womersley number matching and a piston pump driven by a ball screw and stepper motor. The flow pattern in the nasal cavity with NHF was found to differ significantly from natural breathing. Velocities of 2.4 and 3.3 ms−1 occurred in the nasal valve during natural breathing at peak expiration and inspiration, respectively; however, on expiration, the maximum velocity of 3.8 ms−1 occurred in the nasopharynx. At a cannula flow rate of 30 l/min, maximal velocities of 13.6 and 16.5 ms−1 at peak expiration and inspiration, respectively, were both located in the cannula jet within the nasal valve. Results are presented that suggest the quasi-steady flow assumption is invalid in the nasal cavity during natural breathing; however, it was valid with NHF. Cannula flow has been found to continuously flush the nasopharyngeal dead space, which may enhance carbon dioxide removal and increase oxygen fraction.
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Acknowledgments
We would like to thank Fisher & Paykel Healthcare and St George’s Radiology, in particular C. White and Yasamin Al-Tiay, and S. Wells and C. Stevens, respectively, for supporting this work.
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Spence, C.J.T., Buchmann, N.A. & Jermy, M.C. Unsteady flow in the nasal cavity with high flow therapy measured by stereoscopic PIV. Exp Fluids 52, 569–579 (2012). https://doi.org/10.1007/s00348-011-1044-z
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DOI: https://doi.org/10.1007/s00348-011-1044-z