The function of the nose
The nose is an integral part of our respiratory system. We breathe all the time, usually through the nose. The nose functions to condition each breath so that the inhaled air is ‘ready’ for the lungs. It warms and humidify the air, and filter dust and any other environmental pathogens or irritants.
How does a blocked nose cause sleep apnoea?
Humans are born obligatory nose breathers. If the nose is obstructed, breathing will be difficult. Recall those nights when you sleep with a stuffy nose e.g. when having the flu. Sleep becomes disrupted. You probably have woken up with headaches, facial congestion, dry throat, and an unrested sleep. This is because when our nose passage is obstructed, inspiration will be limited. There will be an increased respiratory effort. This not only leads to turbulent airflow but also further narrowing of the upper airway downstream due to Starling’s Law (see diagram below). The collapsed is maximum at the level of the pharynx. Our soft palate falls back against the back of the throat, shutting the throat from the nose. Alternatively, the palate flutters like a sheet of paper in the air. These lead to loud snoring and gasping. The tongue and pharyngeal wall collapsed inwards to further obstruct the airway. This phenomenon is what happens during obstructed sleep apnoea.
What is the natural way to overcome a blocked nose? Yes, we opened our mouth! This bypasses the nose and we can breathe again. However, mouth opening during sleep especially when sleeping on our back (supine), worsens the obstruction? Mouth opening causes the tongue to fall further backward and narrows the airway. This is worse when the person is overweight with a thick neck.
How do we know we are mouth breathing?
Mouth breathing during sleep can be subtle. Mouth opening dries the oral cavity and throat. It is more apparent if the aircon or the fan is blowing at the face. Hence, if you frequently wake up with the dry mouth or sore throat, you are probably mouth breathing.
Sleep apnoea and its assessment
Sleep apnoea is a phenomenon when there is the cessation of airflow during sleep. It can be obstructive, central, or mixed (both obstructive & central). Obstructive sleep apnoea accounts for the majority of cases especially among those who are obese. Obstructive sleep apnoea is due to obstruction of the upper airway during sleep due to loss of muscle tone during sleep. This leads to the collapse of the throat muscles and tongue and blocks the airway. Other causes of obstruction include swollen tissue within the nose, deviated nasal septum, large adenoids or tonsils. Thick subcutaneous fat around the neck also contributes to the amount of collapse and hence obstruction.
The sleep study is performed to determine the apnoea-hypopnoea index (AHI) which indicates the frequency of cessation of breathing or ineffective breathing leading to a dip in body oxygen. A nasendoscopy is performed to assess the anatomy of the upper airway, particularly to look for the causes of obstruction mentioned above.
Treatment of obstructive sleep apnoea