These episodes of apnea can occur a few times during sleep up to even 100 times. To start with, this cessation in respiration could last only for a second or two, but with time, the duration of apnea could last longer. The more the duration of the apnea and the more the frequency, the more severe is the degree of sleep apnea.
There are three types of sleep apnea:
• Obstructive sleep apnea (OSA)
• Central sleep apnea
• Complex sleep apnea
Central sleep apnea: As the name portrays, central sleep apnea is due to lack/ uncoordinated signals from the brain to the muscles controlling breathing.
Obstructive sleep apnea: The obstructive variant is seen mostly in obese individuals, and as the name suggests is due to obstruction (narrowing or collapse) in the upper airway during sleep. This leads to a reduction or complete cessation of the flow of air for a few seconds. This complete cessation of the flow of air is called apnea.
Complex sleep apnea: This is a combination wherein there is an element of both central as well as obstructive sleep apnea.
Mechanism of Obstructive sleep apnea
There are two sets of muscles in the upper airway, the dilator and constrictor groups. There is coordination between these two groups of muscles that are responsible for keeping the upper airway patent.
The increased tone in the dilator muscles – the tensor palatini and levator palatini, the genioglossus and the hyoid muscles (geniohyoid and sternohyoid) help in keeping the upper airway patent. This is augmented by the negative intrapharyngeal pressure, that augments the tone of the dilator muscles and thus maintains patency.
In normal individuals, with the onset of sleep, the dilator activity of the dilator muscles, particularly the tensor plate decreases. This causes a reduction in the airway size, leading to decreased airflow. In people who already have a compromised upper airway, for eg: the obese, during NREM sleep, this negative pressure reflex is substantially diminished or lost completely. Virtually all neural systems driving wakefulness controlling the genioglossus and all are excitatory. Thus, when these neural systems lose activity during sleep, that muscle activity falls. Also, sleep is associated with a significant reduction in multiple neural reflex mechanisms including postural, spindle-driven reflexes.
Why does sleep apnea affect adversely?
In OSA, we see that the person has a fragmented sleep with multiple episodes of awakening or arousal. Each time of arousal, the person seems to wake up with a gasp.
Because of this stopping in respiration, there is a reduced flow of oxygen called hypoxemia and increased accumulation of carbon dioxide called hypercapnia. This hypoxemia and hypercapnia drive increasing respiratory effort, and ultimately arousal from sleep occurs, thus re-establishing airway patency and ventilation. Once the patient returns to sleep the cycle begins again. The patient thus suffers the consequences of repeated sleep disruption as well as recurrent hypoxemia and hypercapnia.
The risk factors for OSA
Most patients with obstructive sleep apnea are overweight or obese and typically have a short, thick neck. A neck circumference greater than 16 inches in a woman or greater than 17 inches in a man correlates with an increased risk for the disorder. Furthermore, increasing neck size has been shown to correlate with the severity of apnea.
When we examine these people, we find that they have a large floppy uvula or tonsillar hypertrophy or an elongated soft palate or a large tongue. This leads to a crowding of the posterior airway, leading to airway obstruction with subsequent obstructive sleep apnea. Another cause for OSA is anatomical abnormalities in the facial bones, like a small chin, maxilla, and mandible.
Loud snoring: The partner normally complains that the persons snore loud, increases in intensity followed by episodes in which the patient stops breathing (apnea) and then gives a loud gasp or snort with or without arousal.
Daytime sleepiness and morning headache: People suffering from OSA complain that they never feel fresh when they wake up in the mornings. They are sleepy and complain of a headache and feel fatigued during the day and can’t concentrate well on the activities they do. They fall off talking to people, watching television, etc.
Dozing off at a signal and motor vehicle accidents: This is what we hear from patients suffering from obstructive sleep apnea. They clearly mention that as they approach the signal they are fine. Within a few seconds of halting at the red signal, they doze off. The signal goes green and they are totally unaware. The traffic moves on, vehicles honking behind them, but they have no idea of what is going on. After much noise and honking, they wake up alarmed and embarrassed that they have slept through the signal.
Risk of cardiovascular disease
OSA leads to hypoxia, oxidative stress, systemic inflammation, sympathetic activity, and elevated blood pressure, finally leading to heart failure over the years.
Significant weight loss has seen to dramatically improve these annoying symptoms.
Octurnal polysomnography (sleep study) is the gold standard for diagnosing obstructive sleep apnea. In this technique, multiple physiologic parameters are measured like, eye movement observations (to detect rapid-eye-movement sleep), an electroencephalogram (to determine arousals from sleep), chest wall monitors (to document respiratory movements), nasal and oral airflow measurements, an electrocardiogram, an electromyogram (to look for limb movements that cause arousals) and oximetry (to measure oxygen saturation). Apneic events can then be documented based on chest wall movement with no airflow and oxyhemoglobin desaturations.
Treatment for sleep apnea
Use of CPAP works wonders in most patients who have obstructive sleep apnea. In this, through a snugly fitting face mask, air is blown into the nostrils to keep the airway open during sleep. Oxygen may be required in some cases in addition to the air under pressure. Tongue-retaining devices or bite guards can be used to bring the lower jaw forward and thereby alleviate posterior airway obstruction during sleep. Weight loss of even 10% can eliminate apneic episodes by reducing the mass of the posterior airway. If there are associated anatomic deficits in the jaw, this alone might not help.
Weight loss surgery in morbidly obese patients with obstructive sleep apnea is a very good option. Remarkable results are seen with loss of the first 10 to 15 kgs. The results may be due to a reduction in the adipose level of parapharyngeal tissues. Once all the excess weight is lost after weight loss surgery, there is complete remission for sleep apnea. The surgery of choice is the Roux en Y gastric bypass, however, the sleeve surgery could also be an option. The results are very dramatic, the person can sleep well at night without any snoring, disturbance of waking up. When the person wakes up in the morning, there is no headache, no dryness of mouth and they feel fresh (the freshness they have not experienced over years). They don’t fall asleep while talking to people or while driving at a traffic signal.
Uvulopalatopharyngoplasty involving removal of part of the soft palate, uvula and redundant peripharyngeal tissues, sometimes including the tonsils could be effective in eliminating snoring; however, it is not necessarily curative for obstructive sleep apnea, because areas of the airway other than the soft palate also collapse in most patients with this sleep disorder.
Jaw surgery for a retrognathic mandible. The surgical procedure could entail genioplasty or moving both the mandible and maxilla. In noncompliant patients with extremely severe apnea, tracheostomy may be considered.