Nasal high flow clears anatomical dead space in upper airway models

Abstract

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.

High Flow Nasal Oxygen Therapy: From Physiology to Clinic

“…When a two-hole cannula fitting in both nostrils was used, its effect on the oxygenation was more pronounced, and when a single-hole cannula fitting in a single nostril was used, its effect on oxygen elimination was more pronounced (12). In a similar animal study, Möller et al (13) randomly compared continuous airway pressures (CPAP, 2-6 cm H 2 O), HFNO in which only a small leak was allowed, and HFNO in which a larger leak was allowed in 13 newborn and spontaneously breathing piglets with lung perforations. It has been found that the tracheal pressures of CPAP and HFNO are comparable.…”

Nasal high flow therapy: a novel treatment rather than a more expensive oxygen device

“…Reduced dead space ventilation and thus reduced rebreathing of expired air in a flow-dependent manner is another benefit that is attributed to high gas flow that is delivered by this device, as demonstrated in studies using upper airway models as well as on healthy volunteers [11,12]. The mechanism differs between sleep and awake states, because of different ventilatory responses to NHF in each state.…”

“…Even without lung expansion, oxygen diffusion from the alveoli to the capillaries decreases alveolar pressure, and by increasing pharyngeal oxygen content a flow of air is generated from the pharynx to the distal airway, which is called apnoeic oxygenation [61]. High flow rates with NHF create a great oxygen reservoir in nasopharyngeal area, which together with carbon dioxide elimination by flushing of the dead space [11,12] and the generated CPAP [3][4][5][6][7][8] make NHF a promising oxygenation device in the peri-intubation period, which maintains oxygenation without a rapid and dangerous rise in carbon dioxide concentration [62].…”

COPD: High-flow-O2 reduziert auch Hyperkapnie

“…Bis heute konnten mehrfach die Vorteile der NHF-Sauersto therapie im Vergleich zur konventionellen Sauersto therapie [1] oder nicht invasiven Ventilationstherapie [2] bei Patienten mit hypoxämischer Atmungsinsu zienz gezeigt werden. Die positiven E ekte beruhen teilweise darauf, dass eine höhere Sauersto konzentration appliziert werden kann, auf einer verbesserten mukoziliären Clearance durch die Anwärmung der Atemluft [3] und auf dem Aufbau eines positiven Atemwegsdruckes bei gleichzeitiger Senkung des Totraums [4] durch den hohen Gasuss. Positive E ekte auf das hyperkapnische Atmungsversagen konnten jedoch bis jetzt noch nicht gezeigt werden, wobei aktuell die Verö entlichung mehrerer -teils abgeschlossener -Studien zur Klärung dieser Frage bevorsteht.…”