OSA as soft-wired dysfunction

The intent of this editorial is to present a body of sound, established, and accepted science that suggests a revised multidisciplinary framework on which to base future study of the clinical treatment of obstructive sleep apnea (OSA). Incorporating recognized information in a new way challenges the validity and rationales of established treatment methods and may shed light on more effective treatment modalities.

There is a complex interrelationship between head posture, breathing, speech, swallowing, and the position of the teeth in human mouths. Teeth and the dental alveoli lie in a position of balance between the cheeks, lips, and tongue. Ideally, the tongue is in contact with the roof of the mouth at rest, during swallowing, and nasal breathing. Interventions that disrupt nasal breathing cause opening of lips, low tongue position, head forward posture, and malocclusions. Protruding the tongue affects oropharyngeal dilation and decreases airway resistance. Retruding the tongue increases oropharyngeal resistance to air flow. It is within these anatomic limits that OSA and speech originate.

Treatment of OSA requires a thorough understanding of the biomechanics, biochemistry, pathophysiology, and morbid consequences of this complex phenomenon; but more than that, the human airway is part of our complex evolution. Evolution can be illogical, and evolution is often quite strange. It is not always predictable [1]. The thought is that understanding the history of what was may lead to clues to cope better with what is.

It is important to note that the evolutionary adaptations that had to occur to get bigheaded human babies to successfully emerge from the birth canal are the very same ones that resulted in the production of speech [2], namely:

• Change in position of foramen magnum from behind to under the skull

• Fontanelles in newborn skull

• Disappearance of snout

• Flat face

• Smaller chin

• Shorter oral cavity

• Changes in jaw function

• Repositioning of ears behind the jaws

• Ascent of the uvula and descent of the epiglottis

• Right angle bend in tongue

• Creating combined, compliant, and flexible airway-foodway

• Speech

• Bigger brains

To orchestrate their survival as a species, humans have to survive with repositioned, reconditioned, rebuilt, redesigned, miniaturized; and in many cases, head parts of inferior design for olfaction, mastication, swallowing, hearing, breathing, and conditioning of inspired air [3]. To avoid choking, human swallowing requires more neurologic precision and coordination than in lower animals. A very positive evolutionary development resulting from the flexible, compliant adult human airway is the capability to create formant sounds, instrumental in the articulation of speech [4].

In nonhuman mammals, the uvula and epiglottis overlap. This arrangement separates the foodway from the airway and allows simultaneous nose breathing and swallowing. It is referred to as an intranarial airway.

In humans, the ascent of the uvula, descent and right-angle bend of the tongue in the oropharynx create a more flexible, compliant airway, the survival value of which is to facilitate speech. It is referred to as non-intranarial.

In adult humans, the pharynx remains open for passage of air at all times, except during swallowing and regurgitation. Breathing cannot occur simultaneously with swallowing [5]. The negative consequences are choking, snoring, and OSA. OSA occurs when the luminal cross-sectional area of the upper airway collapses during inspiration, at or below the level of the soft palate and above the epiglottis.

The apneic collapse can be caused by muscle flaccidity, negative airway pressure brought about by increased nasal airway resistance, a combination of both, predisposed by muscle fatigue, CNS misfiring or incoordination, pulmonary diseases, or neuromuscular diseases. Combinations of the following can also contribute to the airway blockage: swollen, hyperplastic or redundant tissue, large tonsils, obesity, nasal obstructions, deviated septum, dysphagia, broken nose, long–soft palate, large uvula, macroglossia, and edentulous collapse [6].

Evolution is not the same as biologic engineering, where a designer has a goal in mind and tools or components are created to fulfill the new function. Evolution is random and opportunistic. Evolutionary changes in the head encompass modularity, integration, and multifunctionality of existing parts. Bones in the skull share walls, so that bone growth in one region accommodates growth in an adjacent area. The roof of the mouth is the floor of the nose. The lateral wall of the nose is the medial wall of the eye. The top of the nose and eye is the floor of the brain. The chewing muscles and Temporomandibular Joint (TMJ) attach to the skull. Tongue movement, nose breathing, mouth breathing, swallowing, speaking, and OSA are complexly integrated in terms of development, structure, and function so that new and different function in one part may stimulate or retard others from developing as growth continues.

Human speech is an activity of five functional systems:

• 1. supraglottal lungs (including diaphragm)

• 2. larynx (tension of pharyngeal muscles)

• 3. supralaryngeal airway (including glossopharyngeal tongue function)

• 4. mouth (and tongue hypoglossal function)

• 5. the voluntary respiratory control center of the brain.

The same five functional systems are involved in both speech and OSA

OSA occurs at the first instant of inhalation. Speech only occurs on exhalation. Complex brain planning is required to coordinate breathing with speaking when a person is awake. Depending on the length of the sentence and how loudly it is being spoken, there is a programmed “hold back” function to distribute even air flow during the entire intended sentence. Before a word is uttered, the brain programs the lung and diaphragm to maximally hold back the initial spring force of expelled air so it does not instantly collapse like a released balloon. As the lung volume falls, the air pressure out is regulated by the brain to achieve level speech volume to finish the intended sentence. Speech is so essential to our concept of intelligence that its possession is virtually equated with being human, and it is unique to human beings [7].

“The human language capacity is overlaid in sensorimotor systems that originally evolved to do things other than support language”[8]. The human brain and the evolution of speech, cognition, and language are evidence from contemporary neuroscience that our brains do not operate in a manner analogous to digital computers [8].

Neural networks are three-dimensional, operating at all levels of the brain. Functional language systems are distributed over many parts of the brain. The location and distribution can be different in different individuals. Distributed neural networks are massively redundant. Similar operations are performed in parallel redundancy in different anatomical sites. The system is dynamic, enlisting additional neuronal resources as task complexity increases. Many new circuits are formed as humans learn to execute more skilled motor programs [9].

People’s brains differ as much as faces, feet, teeth, hearts, and immunological responses. There is no “phrenology map” in the human brain. Different functional systems exist at different places to achieve particular goals. Individual muscles are influenced by neurons in multiple, separate locations in the motor cortex. Human neural architecture that regulates a particular aspect of behavior is neither logical, parsimonious, or predictable.

Humans have two distinct brain areas for neurological control: the subcortical basal ganglia and the cerebral cortex. In humans, the subcortical basal ganglia (our more primitive reptilian carryover) is referred to as hard-wiring. Pathological damage to the hard wiring system is almost universally irreversible. An operating system does exist in newborn humans for basic functioning, such as sucking, swallowing, crying, breathing, defecation, and urination. Because these functions precede birth and are universal to all human newborns, they are generally referred to as hard-wiring of the brain. Limping on a sprained ankle or women experiencing menses are basically gene-regulated functions and considered examples of hard-wired neurological effects [10].

In newborn humans, the cerebral cortex (outer layer) is about six cell layers thick, having about 20 billion of the brain’s 80 billion cells. At birth, the cerebral cortex is like a blank slate, having no specific programming, but being programmed to learn. Most of the brain’s neurons were born in fetal life or early infancy and last for a lifetime. Neural networks interconnected within the cerebral cortex and programmed by experience are said to be soft-wired.

As the brain strengthens its connections between neural networks by way of life’s activities, some can be strengthened, modified, or lost. As a skill is developed, the neural route for successfully performing that new skill becomes stronger. Skills developed and not used are eventually erased or lost. The cerebral cortex is the brain structure responsible for most of our memories, reasoning, planning, thinking, language skills, and daily functioning, such as working, eating, and playing. Throughout life experiences, our skills, behavior, world view, and neural networks are being challenged and modified. Training to swallow correctly and relearning to use the nose to breathe after tonsillectomy and adenoidectomy are soft-wired functions.

OSA is a disease or dysfunction that usually occurs later in life. Trained opera singers rarely have apnea. Vocal training in young people as an alternative treatment for OSA has been shown to be effective. A total of 30,000 h of practice may change one’s structural plasticity [11]. Angela Cain [12], in the UK, reported reducing the AHI of OSA patients by teaching singing methods. Puhan [13] reported in the British Medical Journal, December 2005, that didgeridoo training significantly reduced the AHI in a group of Swiss students with OSA. It is more than just ironic that Guimares [14], in 2009, also demonstrated that oropharyngeal exercises from traditional speech therapy techniques reduced the severity of OSA. These decreases in AHI with exercise practices indicate with a high degree of certainty that OSA is soft-wired and does not involve subcortical basal ganglia. Natural, noninvasive techniques of activating the human brain’s own transformative capacities for healing are being currently developed by such leaders in human brain plasticity as Norman Doidge [15] and Michael Merzenich [10]. This soft-wired concept would seem to be a natural fit for physical therapists, speech therapists, and myofunctional therapists.

OSA and speech share the same neuroplastic, non-modular control system. Apnea and speech are soft-wired phenomena. The conclusion suggested by this discussion is a paradox. That the same non-intranarial airway, the collapse of which results in OSA, also resulted in the gift of speech and may hold the key to more successful treatment methods for OSA, better designs for oral appliances, or perhaps even a cure for OSA.