Nasal high flow clears anatomical dead space in upper airway models.
Bottom Line: There was a similar tracer-gas clearance characteristic in the tube model and the upper airway model: clearance half-times were below 1.0 s and decreased with increasing NHF rates.The level of clearance in the nasal cavities increased by 1.8 ml/s for every 1.0 l/min increase in the rate of NHF.The study has demonstrated the fast-occurring clearance of nasal cavities by NHF therapy, which is capable of reducing of dead space rebreathing.
Recent studies showed that nasal high flow (NHF) with or without supplemental oxygen can assist ventilation of patients with chronic respiratory and sleep disorders. The hypothesis of this study was to test whether NHF can clear dead space in two different models of the upper nasal airways. The first was a simple tube model consisting of a nozzle to simulate the nasal valve area, connected to a cylindrical tube to simulate the nasal cavity. The second was a more complex anatomically representative upper airway model, constructed from segmented CT-scan images of a healthy volunteer. After filling the models with tracer gases, NHF was delivered at rates of 15, 30, and 45 l/min. The tracer gas clearance was determined using dynamic infrared CO2 spectroscopy and 81mKr-gas radioactive gamma camera imaging. There was a similar tracer-gas clearance characteristic in the tube model and the upper airway model: clearance half-times were below 1.0 s and decreased with increasing NHF rates. For both models, the anterior compartments demonstrated faster clearance levels (half-times < 0.5 s) and the posterior sections showed slower clearance (half-times < 1.0 s). Both imaging methods showed similar flow-dependent tracer-gas clearance in the models. For the anatomically based model, there was complete tracer-gas removal from the nasal cavities within 1.0 s. The level of clearance in the nasal cavities increased by 1.8 ml/s for every 1.0 l/min increase in the rate of NHF. The study has demonstrated the fast-occurring clearance of nasal cavities by NHF therapy, which is capable of reducing of dead space rebreathing.
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Mentions: The clearance half-times for the two ROIs vs. the NHF rates for the CO2 clearance experiments are shown in Table 1 and plotted in Fig. 4A. The comparable clearance half-times of 81mKr-gas are shown in Table 2 and in Fig. 4B. For either ROI in the TM, all NHF rates and both imaging techniques had clearance half-times of 0.6 s or less. For all flow rates and both tracer gases, the anterior ROI (TM1) clearance half-time was always faster than the posterior ROI (TM2) (P < 0.01). For both tracer gases and ROIs, the clearance half-times decreased with increasing NHF rates (r = −0.84, P < 0.001). At 45 l/min NHF, the clearance half-time was approximately half that for an NHF of 15 l/min. The clearance half-times for the CO2 experiments demonstrated a highly positive correlation with the 81mKr-gas clearance rates (r = 0.97, P < 0.001) for both ROIs.
No MeSH data available.