What is Sleep Apnea?

Apnea is defined as the stopping or pausing of breathing. Sleep apnea is a common condition in which a person stops breathing intermittently during sleep. This occur a few times during one session of sleep or hundreds of times per hour.

There are three kinds of sleep apnea:

•       Obstructive Sleep Apnea (OSA)
•       Central Sleep Apnea
•       Mixed Sleep Apnea

Obstructive sleep apnea occurs when the upper airway is blocked multiple times throughout sleep, resulting in less or no airflow. Sleep apnea can also occur when the brain does not send signals to the muscles responsible for controlling breathing (central sleep apnea). Mixed sleep apnea is when both conditions occur. In some cases, when OSA is being treated, symptoms of central sleep apnea will occur.

Obstructive sleep apnea

OSA occurs when the airway either completely or partially collapses resulting in reduced oxygen saturation or the person waking up. The upshot is interrupted, non-restorative sleep.

The upper airway muscles

The pharynx is the cavity behind the nose and mouth that connects the nose and mouth to the esophagus. This region consists of over 20 muscles that contribute to both breathing and non-breathing related functions. A group of muscles called the upper airway dilator muscles stabilize the airway during breathing. While awake, these muscles fight against collapsing pressures generated during inspiration. However, the activity of these muscles are reduced during sleep. When combined with other factors, this can lead to airway collapse.

The strongest dilator muscle, the genioglossus, receives input from both the brainstem and pharyngeal receptors resulting in more activity during inspiration and less during expiration. The activity of this muscle is also reduced during sleep. Another muscle, the tensor palatine muscle, is less sensitive to changes in pressure than the genioglossus, but still acts in a similar way to larger changes to pressure, including during the sleep state. Impairment of these muscles are thought to contribute to OSA.

Many individuals with OSA have weak genioglossus response to airway narrowing during sleep, requiring a change in pressure that can only be achieved by waking up to activate the muscles. Thus, enhancing the response of these muscles may improve or prevent OSA development even in the case of anatomical contributions. Another potential cause of OSA may be unsynchronized stimulation of the genioglossus muscle by the central nervous system (CNS) and the muscle receptors.

Classification: the different types of OSA

There are three levels of OSA:

•       Mild OSA
•       Moderate OSA
•       Severe OSA

Symptoms of mild OSA include feeling sleepy doing activities that require little attention (such as reading). Moderate OSA is defined by experiencing sleepiness while doing an activity that requires attention such as (participating in a meeting). Severe OSA is defined by feelings of sleepiness when doing an activity that requires a higher level of attention such as talking or driving.