Illustration of obstruction of ventilation
Apnea vs Hypopnea
Apnea means temporary complete stoppage of breathing for 10 seconds or more caused due to complete obstruction of airway. During apnea there is no movement in respiratory muscles. Hypopnea is a condition wherein the breathing is slow and shallow reducing the oxygen supply to lungs. It is caused due to partial obstruction to the airway path. Hypopnea is less severe as compared to apnea.
Normally, the muscles in your nose, mouth and throat keep your airways open which help normal breathing. When you are asleep, these muscles relax and the tongue falls back on the airway tract stopping the air entry and breathing; this is called as apnea. It is temporary, for about 10 seconds or more, till the brain senses that oxygen levels have dropped, alerting you to wake up. This generally occurs in sleep apnea, the patients wake up, breathe normally and the cycle reverses and they fall asleep again. This occurs several times at night. Causes of apnea can be voluntary; voluntary apnea can be achieved by closing the vocal cords at the same time closing the mouth and nose. Drug induced apnea may occur due to opium toxicity while apnea may be mechanically induced by strangulation or choking, neurological diseases or trauma.
Causes for hypopnea are those which lead to partial airway obstruction such as acute tonsillitis or adenoiditis that cause a partial pressure on the airway thus, obstructing the normal airflow entry. Other causes of hypopnea are congenital defects present since birth such as nasal septum deformation, use of sedatives like sleeping pills which relax muscles, obesity, neuromuscular diseases such as Gullian Barré syndrome and muscular dystrophy which lead to partial paralysis of respiratory muscles.
As a result of hypopnea and apnea, carbon dioxide level in the blood increases and oxygen level decreases. Decrease in oxygen level depends directly on the severity of obstruction. This in turn causes decreased oxygen supply to the vital organs of the body. Symptoms of apnea and hypopnea are somewhat similar as both are caused due to a similar mechanism i.e. airflow obstruction. Most common symptom of hypopnea is excessive sleepiness during the day; this occurs because of repetitive awakening at night. Patients generally have loud snoring caused due to partial obstruction. Other symptoms such as anxiety, depression, inability to concentrate, irritability, forgetfulness, mood or behaviour changes, and headaches might persist. These symptoms are seen in both sleep apnea and hypopnea.
Patients having prolonged apnea without recovery suffer from brain death resulting in coma or death due to decreased oxygen supply to the organs. Sleep apnea is diagnosed by proper history taking correlating symptoms, proper examination and sleep study called polysomnography which is the diagnostic test for sleep apnea. This study records brain activity, heart rate, blood pressure, amount of oxygen in your blood, snoring and chest movements. It is performed at sleep centers or labs; patients have to just sleep as usual and sensors attached to limbs, chest, face, and scalp do the elaborate recording. Nowadays, home based portable monitors are also available.
Treatment of apnea and hypopnea depend on the cause. In cases of mild hypopnea, in obese patients weight reduction is advised. Smokers are advised to quit smoking. Other treatment is use of CPAP machine i.e. continuous positive airway pressure. Surgery is the last option if adenoids or tonsils are cause of obstruction.
SUMMARY: Apnea is complete stoppage of breathing caused due to complete obstruction of airflow from nose to lungs whereas hypopnea is shallow or slow breathing caused due to a partial obstruction. Hypopnea is less severe compared to apnea. Both conditions have similar causes, symptoms and plan of treatment.