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.
No MeSH data available.
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Mentions: An anatomically accurate 3D upper airway model (UAM) was developed to better represent the expected gas clearance when using NHF therapy in practice (Fig. 3A). The UAM was based on segmented images from a computer tomography (CT) scan of a healthy volunteer, which was then constructed using a High Definition (HD) 3D printer (Projet HD3000, 3D Systems). Nasal valve area in both noses was 56 mm2. There was no anatomical structure beyond the nasal cavity, and the unit led into an 18-mm ID tubing, which exited at the bottom of the model. The material in the 3D printer is highly absorbent in the MWIR spectrum. Therefore, only the 81mKr-gas gamma camera imaging was used. The UAM was then integrated into a plastic head model to enable the attachment of the cannula interface. The position of the UAM in front of the gamma camera and the attachment of the NHF cannula interface are shown in Fig. 3A (left panel). The anterior and posterior ROIs (UAM1 and UAM2, respectively), illustrated in Fig. 3A (right), were overlaid with a CT image of the UAM (Fig. 3B) showing the detailed anatomical accurate nasal cavity structures contained within the model. For this protocol, the UAM was filled with 81mKr-gas, via the tubing from bottom, while the nasal cannula was located in the nares, in line with normal use. As for the TM experiments, both the filling and 15 s of 81mKr-gas clearance were captured by dynamic gamma camera imaging.
No MeSH data available.