The Role of the Airway

The human face grows around its airway. For example, one researcher concluded, "In individuals affected by mongolism and achondroplasia, respiratory function has been protected by different kinds of facial adaptation in each group. The adaptive changes in mongoloids are 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."

There are two areas where modern human airways get restricted, the nose and the throat. Generally restrictions to the nasal airway passage cause mouth breathing, and restrictions to the pharyngeal airway passage cause snoring and sleep apnea as well as an airway protective response that produces forward head posture. Strong respiratory muscles can pull air passage through these restrictions, but muscles lose strength with age in adulthood, and resting airway flow can be compromised. The mechanics, effects, and treatment for restoring airway flow through these two areas are very different.

THE NASAL AIRWAY - is a bony tunnel that can become obstructed at any location. Usually the obstruction is due to tunnel walls that are too narrow due to insufficient expansion of the midface and upper jawbone, which form the sides of the tunnel. The roof of the tunnel, the palate, is the floor of the nose. When the palate is narrow, the nasal cavity is also narrow.

OBLIGATE MOUTH BREATHERS - When the tunnel does not allow sufficient airway passage, the body's response is to bypass it by creating an oral airway passage, which requires keeping the lips at least slightly parted. People with very narrow palates are often obligate mouth breathers. They cannot maintain a lip seal. Some people with borderline palate width 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 nasal 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, where it is needed for endothelial health. It also limits glymphatic drainage through the cribiform plate, where 15-30% of glymphatic drainage normally occurs, motivated by intranasal negative pressure during each inbreath.

In some obligate mouth breathers, especially when the nasal cavity is obstructed internally, nasal surgery may be necessary to restore adequate nasal airway flow. When the problem is narrow tunnel walls, 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.

In some people, 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. One summer I went jogging twice a week, slow enough to keep my lips sealed and breathe through my nose. By the end of that summer, 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, and their primary job is to keep the pharyngeal airway open. As a result, the muscles in their resting postures will hold the bones in any position needed to preserve resting airway flow. Pharyngeal airways usually become obstructed due to a facial growth pattern in which the mandibular corpus keeps shifting backward or rotating down and back. In response, some people develop obstructive sleep apnea, while other people employ their muscles to create a new mandibular resting posture that allows adequate resting airway passage, often by holding the tongue between the teeth. In some of those people with adaptive tongue postures, the teeth indent the sides of the tongue to produce produce visible scalloping. In other people with adaptive tongue postures, the tongue moves the teeth, producing an open bite that prevents the possibility of incising. 

The development of the pharyngeal airway depends on mandibular advancement. Mandibular advancement is needed to rapidly decrease resistance to airway flow while the growing body increases its airway demands and then later to continue slowly during adulthood 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. In people with strong jaw muscles, the jaw muscles are able to prevent the downward growth component, but the mandible is usually locked back behind the deep anterior overbite, where it cannot advance naturally.

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.