![]() ![]() ![]() This accelerated the clearance of anatomical dead space and reduced re-breathing while increased resistance to flow resulted in higher positive end-expiratory pressure (PEEP). NEW & NOTEWORTHY The asymmetrical interface generated reverse flow in the nasal cavities and across the choana, which led to unidirectional purging of expired gas from the upper airways. Asymmetrical NHF increases dead-space clearance by reverse flow through the choanae and accelerates purging of expired gas via the less occluded nare. Pressure differences between nasal cavities led to the reverse flow observed in the optical model. The maximum pressure achieved with the AI was 6.6 cmH 2O and NHF was 60 L/min at the end of expiration. With COPD breathing, clearance by NHF was reduced but significantly improved with the AI by 45.93% relative to the SI at NHF 20 L/min ( P < 0.0001). At a higher RR (35 min −1) and NHF of 60 L/min, clearance in the upper airway was significantly higher with the AI when compared with the SI (29.64 ± 9.96%, P 0.05), (means ± SD). CO 2 kinetics visualized by infrared spectroscopy and mathematical modeling were used to study the mechanisms of clearance. Clearance was assessed at NHF of 20–60 L/min with a symmetrical interface (SI) and an asymmetrical interface (AI). Clearance was investigated with volumetric capnography in an adult upper-airway model, which was ventilated by a lung simulator with entrained carbon dioxide (CO 2) at respiratory rates (RR) of 15–45 min −1 and at 18 min −1 with chronic obstructive pulmonary disease (COPD) breathing patterns. The hypothesis is that an increase in asymmetrical occlusion of the nares leads to an improvement in dead-space clearance resulting in a reduction in re-breathing. Pressure mainly depends on flow rate and nare occlusion. Positive airway pressure that dynamically changes with breathing, and clearance of anatomical dead space are the key mechanisms of noninvasive respiratory support with nasal high flow (NHF). ![]()
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