Epidemiology: What is the incidence of OSA?

OSA is a common sleep disorder. It occurs along with daytime sleepiness in approximately 3% to 7% of adult men and 2% to 5% of adult women. There are some people that are more likely to experience OSA including individuals that are:

•       Overweight
•       Obese
•       Minorities
•       Older

Prevalence is similar among most continents, suggesting that it is similar in both developed and developing countries. Patients with OSA have a higher risk of mortality than those without OSA. Mortality rate also increases with the severity of the OSA. However, this risk can be reduced with treatment.

Pathophysiology: How are physiological processes altered in OSA?

OSA pathophysiology can be divided into two categories:

•       Non-anatomical contributors
•       Anatomical contributors

Anatomical contributors include:

•       A pharyngeal airway susceptible to closure during sleep

o   Narrow pharyngeal airway

o   Increased airway length

o   Unusual pharyngeal lumen shapes

o   Large neck circumference (>17 inches in males and >16 inches in females)

o   Specific craniofacial morphology

o   Specific positions of the hyoid bone

o   Tongue scalloping (tongues with rippled edges)

o   Tongue fat

Non-anatomical contributors include:

•       Impaired pharyngeal dilator muscle function
•       Premature awakening
•       Mild airway narrowing
•       Unstable control of breathing

While a combination of non-anatomical and anatomical contributors may lead to OSA, the leading causes are anatomical resulting in one or multiple areas of upper airway collapse.  

There are three processes that are affected in OSA:

•       Decrease in the forces of the pharyngeal dilators
•       Negative inspiratory pressure (pressure generated against a blocked airway—a marker of respiratory muscle function and strength) generated by the diaphragm
•       Improper upper airway anatomy

The upper airway is vulnerable to collapse primarily because of the hyoid bone. This bone is the attachment site for the pharyngeal dilator muscles. It is not fixed in place to skeletal structures. The airway is vulnerable to collapse in specific areas in the upper airway. The retropalatal region of the oropharynx is the most common site of collapse.