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 - travels through a bony tunnel, and it becomes obstructed when the tunnel 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 upper jawbone cannot fully expand, the base of the triangular nasal cavity can be too narrow to allow sufficient airway passage at rest. The body's response is then to create and maintain an oral airway passage, keeping the lips parted. 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 getting to the lungs. It leads to poor upper respiratory health. In obligate mouth breathers, 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 and thereby cure mouth breathing, as described in the file PALATE EXPANSION under the tab TREATMENTS.

If the nasal airway passage is obstructed internally (overgrown turbinates or a deviated septum), it may need to be reshaped. In some people, this will require surgery. In others, a routine of forced nasal breathing may be able to restore an adequate nasal airway passage by internally remodeling the nasal cavity, because 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.   

PERSONAL STORY - About 20 years ago, when I first began looking at the relationship between facial growth and airway flow, I realized that animals always nose breathe, even when running for their lives. I also realized that, when jogging, I could keep my lips sealed and breathe through my nose if I went slow enough. That summer I went jogging twice a week, always nose breathing and limiting my pace to what my nasal airway could accomodate. By the end of that summer, it could accommodate natural jogging. 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 nasal strips to spread the nostrils.

PHARYNGEAL AIRWAYS - don't travel through bones but between bones with postures controlled by muscles, and those muscles will hold the bones in any posture needed to keep the airway open. If the teeth force the front of the mandible (the corpus, containing the teeth) back into the area needed for airway passage, the muscles will use the tongue, jaw, and neck muscles in any way necessary to create a new mandibular resting posture that allows adequate resting airway passage. Since postural forces provide the light steady forces that shape bones, these airway demands shape the bones of the face and neck. 

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."

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 advancing 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, 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. In people with relatively weak jaw muscles, the blocked mandibular growth is redirected vertically; and the mandibular corpus rotates down and back, where it can impinge on the space needed for oropharyngeal airway passage. Strong jaw muscles can prevent the downward rotation of the mandible, but they usually deepen the overbite by applying all their compressive forces to the back teeth, leaving the mandibular corpus locked back behind the deep anterior overbite.

The tongue is the guardian of the pharyngeal airway, and it will attain and maintain any postural position needed to maintain airway flow. If the teeth prevent the tongue from attaining a normal resting posture up in the front of the palate, the tongue must find another position. In some people, it positions itself between the teeth, as evidenced by visible scalloping in the sides of the tongue from the indents made by the teeth. When the tongue acquires such an adaptive position by resting between the front teeth, it separates those teeth and produces an anterior open bite that makes it impossible to incise (bite things off). In these cases, any orthodontics that straightens teeth by moving them into the path of the resting tongue posture will fail, because the tongue will eventually reposition the teeth in any way needed to keep the airway passage open. In other people, the pharyngeal airway flow is restored by altering the resting posture of the cervical muscles to extend (tip back) the head 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.

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.