The size and behavior of the human upper airway during inhalation of aerosols

ABSTRACT

Introduction: The mouth, the pharynx and the larynx are potential sites of aerosol deposition in the upper airway during inhalation of aerosolized drugs. The right angle bend of the lumen at the back of the mouth, the position of the tongue, the variable size and shape of the lumen in the pharynx and the larynx, and the breathing pattern could increase aerosol deposition in the upper airway and decrease lung deposition.

Areas covered: In this review, the anatomy of the upper airway from the oral cavity to the glottis and the impact of mandibular protrusion and incisal opening on the size of the upper airway are highlighted. In addition, the impact of inhalation maneuvers, inhaler mouthpiece geometries and a stepped mouthpiece on the size of the upper airway are discussed.

Expert opinion: The structure of the upper airway lumen does not have a fixed cross sectional area and is susceptible to both constriction and distension during inhalation. The size of the upper airway can be enlarged through mandibular protrusion and/or incisal opening which might decrease aerosol deposition in the upper airway and increase lung deposition.

KEYWORDS:

• Upper airway
• mandibular protrusion
• incisal opening
• inhalation
• inhaler mouthpiece
• stepped mouthpiece

Article highlights

• There are several advantages of the delivery of locally acting drugs through the upper airways to the lungs for the treatment of diseases of the lungs including direct targeting to the airway surfaces and relatively rapid onset of action in comparison with swallowed drug.

• The upper airway is, however, a potential site of aerosol deposition during oral inhalation as the variable position of the tongue during inhalation, the variable size and shape of the lumen in the pharynx and larynx, and the breathing pattern could – in addition to aerosol characteristics - promote upper airway deposition and restrict lung deposition.

• The upper airway cross-sectional area and volume can, however, be expanded through mandibular protrusion and incisal opening.

• The impact of mandibular protrusion and incisal opening on the size of the upper airway during inhalation of aerosol might decrease upper airway deposition and increase lung deposition.

• The new stepped mouthpiece designed for inclusion in or addition to inhalers provides both mandibular protrusion and incisal opening during inhalation of aerosols.

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Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Additional information

Funding

This paper was not funded.