Mechanical Interactions Between the Upper Airway and the Lungs that Affect the Propensity to Obstructive Sleep Apnea in Health and Chronic Lung Disease

Abstract

Obstructive sleep apnea (OSA) is a common disorder characterized by repetitive narrowing and collapse of the upper airways during sleep. It is caused by multiple anatomic and nonanatomic factors but end-expiratory lung volume (EELV) is an important factor as increased EELV can stabilize the upper airway via caudal traction forces. EELV is impacted by changes in sleep stages, body position, weight, and chronic lung diseases, and this article reviews the mechanical interactions between the lungs and upper airway that affect the propensity to OSA. In doing so, it highlights the need for additional research in this area.

Keywords: Chronic lung disease; End-expiratory lung volume; Obstructive sleep apnea; Overlap syndrome; Pharyngeal critical closing pressure.

Fig. 1.

Using the Starling resistor model, a collapsible segment is interposed within a sealed box, bound by a rigid upstream and downstream segment with corresponding upstream and downstream pressures (P_US and P_DS) and resistances. When there is no flow limitation (open airway), the critical opening pressure is the most negative with P_US > P_DS > P_CRIT, as in zone 3 of the Starling resistor model. When flow is present but slowed, as inan obstructive hypopnea, the downstream pressure is less than P_CRIT because of partial closure of the airway, and P_US > P_CRIT > P_DS as seen in zone 2. When flow is completely occluded, as in an obstructive apnea, P_CRIT > P_US > P_DS as seen in zone 1. (Susheel P. Patil et al., Adult Obstructive Sleep Apnea: Pathophysiology and Diagnosis, Chest, 132 (1), 2007, 325–337, https://doi.org/10.1378/chest.07–0040.)