Optimal directional volatile transport in retronasal olfaction

Area of Science:

• * Aerodynamics and Biomechanics
• * Sensory Science
• * Human Physiology

Background:

• * Distinguishing food flavors relies on retronasal olfaction, where airborne food compounds stimulate nasal olfactory receptors.
• * The preferential airflow dynamics for retronasal versus orthonasal pathways remain poorly understood.
• * Understanding these airflow differences is crucial for explaining flavor perception mechanisms.

Purpose of the Study:

• * To investigate the airflow dynamics in the human oropharynx during inhalation and exhalation.
• * To determine how airway geometry influences the transport of food volatiles via retronasal and orthonasal pathways.
• * To provide experimental evidence for anatomical adaptations facilitating efficient retronasal smell.

Main Methods:

• * Acquisition of computed tomography (CT) images of a human subject's orthonasal airway.
• * Fabrication of a 3D printed experimental model based on CT scans.
• * Analysis of airflow fields within the 3D printed airway model.

Main Results:

• * During inhalation, the oropharyngeal structure forms an 'air curtain' that impedes volatile transport towards the lungs.
• * During exhalation, airflow preferentially directs volatiles through a specific cavity, enhancing retronasal transport.
• * This asymmetrical transport efficiency exhibits a peak at an intermediate Reynolds number (around 800).

Conclusions:

• * The human oropharyngeal geometry is adapted to preferentially direct food volatiles towards olfactory receptors during exhalation.
• * This mechanism enhances retronasal smell, contributing significantly to flavor perception.
• * The findings offer the first experimental evidence for airflow-driven adaptations in the oropharynx for olfaction.