Date of this Version

7-18-2017

Keywords

airway resistance, biomechanics, hypopnea, obstructive sleep apnea, pharynx, sleep disordered breathing, upper airway physiology

Abstract

To understand the mechanisms of snoring and sleep apnea a first-principles biomechanical analysis was done for airflow through branched parallel channels, separated by a freely movable soft palate, and converging to a common channel at the base of the tongue in a “Y-shaped” configuration. Branches of the Y describe slit-like passages on the nasal and oral sides of the soft palate, when the palate is pushed by backward movement of the tongue to form a wedge between the tongue surface and the posterior pharyngeal wall. The common channel of the Y describes the oropharyngeal passage between the base of the tongue and posterior pharyngeal wall. Channel resistances are characterized by a generalized Poiseuille Law for laminar flow. Pressure changes from flow through channel resistances and also from the Venturi effect are specified quantitatively. The resulting equations are solved both algebraically and numerically to describe motion of the soft palate and tongue during snoring and sleep apnea. Soft tissue motions are produced by counterbalanced Venturi pressures on opposite sides of the soft palate and by counterbalanced Venturi pressure and elastic recoil at the base of the tongue. Multiple physical mechanisms were discovered that can produce tissue motion at typical snoring frequencies in this system, some with the mouth open and some with the mouth closed. These palatal and tongue movements resemble motions of pendulums that oscillate in potential energy wells. Specific physical conditions leading to sleep apnea are identified, in which narrow gaps and unbalanced Venturi pressures lead to stable and effort-independent airway occlusion. The present analysis shows how the phenomena of both snoring and sleep apnea are fundamentally related and are governed by the same equations.

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