The Role of the Airway

There are two areas where modern human airways get restricted, the nose and the throat. The mechanics, effects, and treatment for restoring airway flow through these two areas are very different.

THE NASAL AIRWAY - is a bony tunnel that becomes obstructed when any part of it is too narrow, usually due to insufficient expansion of the midface and upper jawbone. The palate, in the center of the midface, forms the roof of the mouth and the floor of the nose. When the palate is narrow, the nasal cavity is narrow.

OBLIGATE MOUTH BREATHERS - have a narrow nasal cavity that does not allow sufficient airway passage through the tunnel. The body's response is then to bypass the tunnel by creating and maintaining an oral airway passage, keeping the lips parted. People with narrow palates are often obligate mouth breathers. They cannot maintain a lip seal. Some people have nasal passages that are barely wide enough to allow sufficient airway flow, and they become obligate mouth breathers whenever a cold or allergy causes swelling of the mucous lining. 

Mouth breathing causes serious health problems. It prevents the nose from warming, filtering, and moistening the air that strikes the back of the throat. It prevents nitric oxide from the sinuses from getting to the lungs, where it is needed to dilate the vessels. It prevents glymphatic drainage through the cribiform plate, where 15-30% of glymphatic drainage occurs. Obligate mouth breathers need an adequate nasal airway pasage so they can use it. In some obligate mouth breathers, nasal surgery may be necessary to restore the nasal airway passage. In others, palate expansion with a removeable appliance worn most of the time for a few months can make the nasal cavity wide enough to allow normal nasal airway flow, as described in PALATE EXPANSION under the tab TREATMENTS.

A routine of forced light nasal breathing can assist the process of restoring the nasal airway passage by internally remodeling the nasal cavity. Localized areas of high speed turbulent airflow trigger regressive osseous remodeling that removes obstacles to airflow, which is one of the mechanisms by which the face grows around the airway passage. Long ago, after learning that animals always nose breathe, even when running for their lives; I tried jogging with my lips sealed, very slow at first, but soon increasing until I could run a good natural pace with my lips sealed, and I still do. 

SMALL NOSTRILS - In some people, the limit to nasal airway flow is at its entry through the nostrils, and normal nasal airway flow during sleep can be restored with by using simple technologies like nasal cones or magnetic nasal strips to spread the nostrils.

THE PHARYNGEAL AIRWAY - travels between bones rather than through them. The postures of these bones are controlled by muscles, which will hold them in any position needed to keep the airway open. If the teeth force the mandible back into the area needed for airway passage, the pharyngeal airway can become trapped between the mandible and the cervical spine. For that reason, the only phenotype that is consistently associated with sleep apnea is mandibular retrusion. 

Pharyngeal airways usually become obstructed due to a facial growth pattern in which the mandibular corpus keeps shifting backward or rotating down and back. The mandible is programmed to elongate slowly during adulthood so its corpus can continuously shift forward (advance) in order to gradually decrease resistance to airway flow as the strength of the respiratory muscles also decreases slowly during adulthood. However, mandibular advancement is largely powered by bite forces, which have weakened considerably in the last couple of decades.  Also, natural mandibular advancement can be inhibited by a deep or steep overbite that locks the corpus to an upper jawbone that grows by expanding rather than advancing. When mandibular advancement is blocked, mandibular growth is often redirected vertically; and the mandibular corpus rotates down and back, where it can impinge on the space needed for oropharyngeal airway passage.

Strong jaw closing muscles are able to prevent the mandibular corpus from growing vertically downward, but they usually deepen the overbite by applying all their compressive forces to the back teeth, leaving the mandibular corpus locked back behind a deep anterior overbite. The mandibular corpus cannot advance, because it is closely surrounded by the upper front teeth.

There are two common responses to the resulting restrictions of the pharyngeal airway.

1) The head extends in order to pull the mandible up and forward away from the cervical spine to increase the amount of airway space behind the mandible. However, head extension also produces a forward shift of head posture, as described in THE ROLE OF BODY POSTURE under the TMJ DISORDERS tab and in more detail in BITES AND POSTURE under the FOR DOCTORS tab.

2) The tongue finds an adaptive resting posture that allows adequate resting airway passage, usually by holding the tongue between the teeth, producing scalloping on the sides of the tongue or an open bite produced by the front of the tongue. When the tongue acquires such an adaptive position by resting between the front teeth, it can also separate those teeth  produces an anterior open bite that makes it impossible to incise (bite things off). Orthodontics that straightens teeth by moving them into the path of the resting tongue posture will fail, because the tongue will reposition the teeth in any way needed to keep the airway passage open.

 One researcher concluded, "When we examine cephalometric landmarks in individuals affected by mongolism and achondroplasia, we see that respiratory function has been protected by different kinds of facial adaptation in each group. The adaptive changes in mongoloids have been described earlier as very localized effects on parts of the skull that spare the respiratory passages but reduce the size of the olfactory and masticatory components. In achondroplastics nasal airway volume is protected in spite of the mid-face deficiency and the increased cranial base flexure by an adaptive counter-clockwise rotation of the palatal plane. The biologic problem of respiratory survival is solved by a shortened palate in one group and by downward or counter-clockwise palatal tipping in the other."

The problem of the backwardly rotated or backwardly positioned mandible can be treated preventively by advancing the mandible using a functional orthodontic appliance or by adjusting the bite to enable it to shift anteriorly. Treatment by functional orthodontics is described in the file entitled THE ROLE OF ORTHODONTICS under the tab TMJ DISORDERS. Adusting bites is described in THE ROLE OF THE BITE under the tab TMJ DISORDERS. Active treatments for snoring and sleep apnea are summarized under the tab SLEEP APNEA and described in detail in MULTILEVEL TREATMENT OF SLEEP APNEA under the tab FOR DOCTORS.

Some technologies are now being marketed to dentists who treat sleep apnea to measure the size of the pharyngeal airway. The hope is that they can determine who needs treatment and show that treatment can increase the size of the airway; however, the pharyngeal airway is far too dynamic to be easily measured.