  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.
