Snoring
Snoring is an abnormal breath sound caused by partially obstructed, turbulent airflow and vibration of tissues in the upper respiratory tract which occurs during sleep. It usually happens during inhalations.
Primary snoring is snoring without any associated sleep disorders and usually without any serious health effects. It is usually defined as apnea–hypopnea index score or respiratory disturbance index score less than 5 events per hour and lack of daytime sleepiness.
Snoring may also be a symptom of upper airway resistance syndrome or obstructive sleep apnea. In obstructive sleep apnea, snoring occurs in combination with breath holding, gasping, or choking.
Classification
In the International Classification of Sleep Disorders third edition, snoring is listed under "Isolated symptoms and normal variants" in the section "Sleep-related breathing disorders". The manual defines snoring as "a respiratory sound generated in the upper airway during sleep that typically occurs during inspiration but may also occur in expiration."Primary snoring is snoring without any other associated medical condition. Primary snoring is not associated with episodes of sleep apnea, hypopnea, respiratory-effort related arousals, or hypoventilation. Traditionally, primary snoring is considered as benign and having no significant health effects for the individual. However, the idea that primary snoring without sleep apnea has no negative health effects is being increasingly challenged, especially primary snoring in children. For example, there is evidence that primary snoring causes excessive daytime sleepiness, and it may be linked with several other medical problems, some of which are serious. Even so, it is generally accepted that primary snoring cannot be diagnosed in the presence of sleep apnea.
Snoring is one of the main symptoms of obstructive sleep apnea, in which case it is apneic snoring. In obstructive sleep apnea, snoring occurs in combination with other features such as breath holding, gasping, or choking. There are also other features like daytime sleepiness, non-restorative sleep, fatigue, or insomnia.
Snoring has also been classified according to frequency as occasional snoring and habitual snoring.
Snoring has been classified according to apnea–hypopnea index score and severity of associated sleep disorders. Therefore, snoring as a symptom exists as a spectrum of severity, with primary snoring being the least severe, snoring with upper airway resistance syndrome being of intermediate severity, and snoring associated with obstructive sleep apnea being the most medically significant. This spectrum of conditions represents increasing degrees of airway obstruction and severity and frequency of disruption of breathing during sleep.
Obstructive sleep apnea may be subdivided into mild, moderate, and severe types.
- Asymptomatic, non-apneic snoring. No daytime sleepiness and apnea–hypopnea index less than 5 per hour.
- Non-apneic snoring with upper airway resistance syndrome. Daytime sleepiness present. Apnea–hypopnea index less than 5 per hour. Between 5 and 10 respiratory-effort-related arousals per hour. Oxygen saturation more than 90%.
- Apneic snoring. Apnea–hypopnea index more than 5 per hour. Oxygen saturation less than 90%. Deviating pattern on electroencephalogram.
Snoring severity has also been classified according to average maximum volume:
- Mild. Roughly equivalent to quiet conversation.
- Moderate. Roughly equivalent to a car driving past at low speed.
- Severe. Roughly equivalent to busy traffic or a vacuum cleaner.
Distinguishing stertor and stridor
Stertor is distinguished from stridor by its pitch. Stertor is low-pitched, and can occur when breathing in, out or both. Stertor and stridor can occur together, such as when adenotonsillar hypertrophy and laryngomalacia occur together.Mechanism
Snoring has been mathematically modelled wherein the upper airway is a tube which has an elastic or collapsible section. As the section of the upper airway narrows, resistance to the flow of air increases. There is a cyclical obstruction and reopening of the airway at the partially or fully collapsed section as air flows past. This obstruction and reopening occurs at approximately 50 times per second, which causes vibration and noise. The airflow becomes unstable and turbulent.The structures that obstruct the airway and vibrate are various soft tissue structures at different levels along the upper respiratory tract or aerodigestive tract. These are the uvula, soft palate, faucial pillars, palatine tonsils, adenoid tonsil, walls of the pharynx, epiglottis, or lower structures. These structures may relax during sleep and move position, especially under the influence of gravity. This results in partial obstruction or complete obstruction of the airway. Partial obstruction of the airway is more associated with primary snoring, whereas complete obstruction is more a feature of obstructive sleep apnea. The following structures were found to vibrate during snoring: soft palate in 100% of cases, pharynx, lateral pharyngeal wall, epiglottis, and tongue base. In primary snoring there may be vibration of the soft palate alone, termed "palatal fluttering". In mild to moderate obstructive sleep apnea, there may be vibration of the palate and lateral pharyngeal wall. In severe obstructive sleep apnea, there may be vibration of the tongue base and epiglottis in addition to the above structures.
The snoring sound mainly occurs during inhalation, but it may occur during exhalation. Snorers have more negative pressure in their airway, increased inspiratory time, and limitation of respiratory flow. On polysomnography, snoring is usually louder during slow-wave sleep or rapid eye movement sleep. Snoring in obstructive sleep apnea usually occurs when airflow turbulence is maximum, which is during hyperpnea episodes at the end of apnea events.
Causes
Snoring is often considered according to the location of structure that is causing the obstruction and vibration. However, the sites causing the snoring vary from one person to the next, and the same individual may have multiple different sites which are contributing to the problem. Snoring is usually caused by partial obstruction of the upper airways, at the level of the nasopharynx or oropharynx.Nasal cavity
While it is generally not possible for the rigidly supported structures inside the nose to vibrate, the patency of the nasal airway is important in the development of snoring. The nasal cavity causes over 50% of the total airway resistance, particularly at the internal and external nasal valves. The internal nasal valve is located approximately 1.5 cm from the nostril and constitutes the narrowest part of the upper airway. The external nasal valve is the tissue immediately around the nostril. Nasal valve collapse refers to weakening or narrowing of the supporting cartilage at the nasal valves. As per the Hagen–Poiseuille equation, a minimal reduction in the diameter of a tube results in an exponential change in airflow. Nasal valve collapse is a cause of snoring.Nasal congestion reduces sleep quality. Common reasons for nasal obstruction are allergic rhinitis and nonallergic rhinitis. Nasal septum deviation and inferior turbinate hypertrophy are present in almost all cases of snoring and obstructive sleep apnea. Masses in the nasal cavity such as nasal polyps or tumors may also cause snoring.