Snoring (or stertor, ) is an abnormal breath sound caused by partially obstructed, turbulent airflow and vibration of tissues in the upper respiratory tract (e.g., uvula, soft palate, base of tongue) which occurs during sleep. It usually happens during inhalations (breathing in).
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 (as diagnosed with polysomnography or home sleep apnea test) and lack of daytime sleepiness.
Snoring may also be a symptom of upper airway resistance syndrome or obstructive sleep apnea (apneic snoring). In obstructive sleep apnea, snoring occurs in combination with breath holding, gasping, or choking.
Classification
In the International Classification of Sleep Disorders third edition (ICSD-3), 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 not associated with episodes of sleep apnea (cessation of breathing), hypopnea, respiratory-effort related arousals, or hypoventilation. especially primary snoring in children. For example, there is evidence that primary snoring causes excessive daytime sleepiness,
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. 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. This obstruction and reopening occurs at approximately 50 times per second, which causes vibration and noise.
Nasal cavity
thumb|right|alt=Sagittal section of nasal cavity (nose). |Sagittal section of nasal cavity (nose).
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 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 (in this case the nasal airway) results in an exponential change in airflow. Nasal valve collapse is a cause of snoring. In one study, 18% of people with mouth breathing reported awareness of snoring. The oropharynx is a common site which causes snoring noises. An enlarged tongue, termed macroglossia, is a potential cause for snoring.
Alcohol
Alcohol causes muscle relaxation via its depressant effect on the central nervous system. This muscle relaxation seems to be more pronounced for the tongue,
Pregnancy
Sometimes snoring starts during pregnancy.
Hereditary factors
Some people have a genetic predisposition to snoring, a proportion of which may be mediated through other heritable lifestyle factors such as body mass index, smoking and alcohol consumption. The DLEU1 gene (part of BCMS) has been linked to snoring.
Possible consequences
Most people with primary snoring do not have any significant health problems as a result of the snoring.
In one study, treatment of snoring in males (with continuous positive airway pressure) resulted in 13% better sleep efficiency and an average of 1 hour of extra sleep for their female sleeping partners. and 28% increased risk of coronary artery disease / ischemic heart disease (probably in part explained by snoring with obstructive sleep apnea). Impaired balance between the sympathetic and parasympathetic nervous system may also be involved. This may be related to cerebral hypoxia, hypercapnia, and temporary increased intra-cranial pressure.
Other investigations may sometimes be done, such as nasal function testing (e.g., rhinomanometry), pharyngeal manometry, allergy testing, acoustic analysis, or medical imaging. Recommended lifestyle changes include stopping smoking, and sleeping on the side (lateral position). Myofunctional therapy is theorized to improve the tone and positioning of the muscles. When myofunctional therapy combined with CPAP is compared to myofunctional therapy alone, there may be little to no difference. Occasional snoring is almost universally present in humans. Habitual (primary snoring) is less common but still a common problem.
Society and culture
There are descriptions of snoring in the fifteenth century. CPAP was first used for snoring and obstructive sleep apnea in 1981.