Elsevier

Sleep Medicine Reviews

Volume 17, Issue 2, April 2013, Pages 161-168
Sleep Medicine Reviews

Clinical review
Peripheral neuropathology of the upper airway in obstructive sleep apnea syndrome

https://doi.org/10.1016/j.smrv.2012.05.005Get rights and content

Summary

Obstructive sleep apnea syndrome (OSAS) is a common sleep disorder that leads to significant morbidity and mortality without adequate treatment. Though much emphasis on the pathogenesis of OSAS has been placed on a narrow upper airway space and associated muscular factors, possible neuropathy of the upper airway has not been fully elucidated. Increasing peer reviewed evidence suggests involvement of neurologic lesions of the upper airway in OSAS patients.

In this article, we review the etiology and pathophysiology of OSAS, the evidence and possible mechanisms leading to upper airway neuropathy, and the relationship between upper airway neuropathy and OSAS. Further studies should focus on the long term effects of the upper airway neuropathy as related to the duration and severity of snoring and or apnea, and also on the potential methods of prevention and management of the neuropathy in sleep disordered breathing.

Introduction

Obstructive sleep apnea syndrome (OSAS) is a common, chronic disorder that is characterized by sleep fragmentation due to apnea, hypopnea, and repeated arousals resulting from partial or complete closure of the upper airway, and occurs in patients of all ages. An essential component in the pathogenesis of OSAS is an increase in upper airway resistance and obstruction that may result from either upper airway anatomical abnormalities or problems related to neuromuscular control of the upper airway.

Though the precise contributions of neuromuscular and anatomical factors on OSA pathogenesis are still debated,1, 2, 3 it is clear that there is a significant role for neuromuscular response in keeping the upper airway patent.

Section snippets

Pathogenesis of OSAS

The human upper airway serves as a multipurpose structure for tasks of speech and deglutition, and as an air passage for breathing. Though the upper airway is composed of numerous muscles and soft tissues, it lacks a rigid support, particularly between the hard palate and the larynx. This lack of bony or cartilaginous support facilitates finely tuned phonation and articulation, but also makes the upper airway vulnerable to collapse, especially during physiological changes in sleep. In addition

Afferent sensory receptors

There are different types of sensory receptors in the upper airway. These receptors respond to pressure, respiratory muscle drive, cold, heat, irritants, and other chemicals. Among these receptors, the mechanoreceptors of the upper airway have been well studied.

The mechanoreceptors of the upper airway respond to changes in airway pressure, airflow, temperature, and to upper airway muscle tone.19 Though there is no direct evidence that these receptors are affected in OSAS, there is indirect

Possible causes of UA neuropathy in OSAS: vibration, desaturation or inflammation?

The exact cause of neuropathy in OSAS patients is not fully understood. Most OSAS patients snore due to vibration of upper airway soft tissues resulting from a narrow or partially occluded upper airway.46 Persistent vibratory trauma resulting in nerve impairment affecting the hands and arms of workers, have been well documented.47 This occurs due to prolonged exposure to vibrating tools. Therefore, it is possible that the same type of vibratory trauma may be induced in the upper airway due to

Morphological (histological) assessment: light & electron microscope

The sub-occlusive stage of habitual snoring usually precedes the development of OSAS, but the pathophysiological mechanisms underlying this progression are not known. Histological changes indicative of a denervation process of the efferent pathways to the palatopharyngeus muscle was demonstrated in OSAS patients42 and has been explained above. Furthermore, focal degeneration of myelinated nerve fibers was shown in the uvula of severe OSAS patients, and an afferent nerve lesion with impaired

Conclusion

Apart from anatomical narrowing of the upper airway as a pathogenetic mechanism in the development of OSAS, there is mounting evidence to suggest the role of neuropathy in the upper airway as well.77, *98, 99 Both the vibration caused by snoring and the hypoxia caused by intermittent upper airway collapse may affect nerves in the upper airway. These changes can impair the normal function of the upper airway mucosa (sensory) and the pharyngeal dilator muscles (motor), rendering the upper airway

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