Dynamics of airflow in a short inhalation

TL;DR

This study uses high-resolution simulations to analyze airflow dynamics and gas transport during rapid inhalation, revealing distinct phases of flow development and non-uniform gas distribution in the airways.

Contribution

It provides detailed insights into flow transition, fluctuations, and gas concentration profiles during a short inhalation, advancing understanding of airflow behavior in the respiratory system.

Findings

Flow transitions rapidly in the supraglottic region within 20 ms.

Flow fluctuations are large-amplitude during inhalation, diminishing during decay.

Gas concentration shows non-uniform build-up and wash-out in the nose.

Abstract

During a rapid inhalation, such as a sniff, the flow in the airways accelerates and decays quickly. The consequences for flow development and convective trans- port of an inhaled gas were investigated in a subject geometry extending from the nose to the bronchi. The progress of flow transition and the advance of an inhaled non-absorbed gas were determined using highly resolved simulations of a sniff 0.5 s long, 1 litre per second peak flow, 364 ml inhaled volume. In the nose, the distribution of airflow evolved through three phases: (i) an initial transient of about 50 ms, roughly the filling time for a nasal volume, (ii) quasi-equilibrium over the majority of the inhalation, and (iii) a terminating phase. Flow transition commenced in the supraglottic region within 20ms, resulting in large- amplitude fluctuations persisting throughout the inhalation; in the nose, fluctuations that arose nearer peak flow were of much reduced intensity and diminished in the flow decay phase. Measures of gas concentration showed non-uniform build-up and wash-out of the inhaled gas in the nose. At the carina, the form of the temporal concentration profile reflected both shear dispersion and airway filling defects owing to recirculation regions.