by Dr Antonis Pantazis, consultant cardiologist at the Heart Hospital, London
Sleep apnoea is a sleep disorder characterised by pauses in breathing during sleep.
These episodes are called apnoeas from a Greek word meaning “no breath". The periods of missed breaths must have a minimum duration before they are formally characterised as “apnoea” and they may occur several times during sleep.
Further hints that need to be taken into consideration for the definition of the disorder are signs of an impact on the brain during the “apnoea” or drop of the oxygen level in the blood.
There are two main types of sleep apnoea. The central form is characterised by interrupted breathing associated with a lack of respiratory effort and the obstructive form where breathing is interrupted by a physical block to airflow despite effort. There is also a mixed type which combines the two.
Prevalence and predisposing factors
Sleep apnoea is likely to remain an unrecognised condition for many years. The individual with sleep apnoea is rarely aware of having difficulty breathing, even upon awakening. Sleep apnoea is recognised as a problem by others witnessing the individual during the episodes or is suspected because of its effects on the body.
Awareness of the disorder has increased recently but it is still likely that many cases remain undiagnosed. Because of the above, the prevalence of sleep apnoea has better been studied in the context of certain clinical scenarios where medical surveillance is done. Generally speaking, obstructive sleep apnoea is much more frequent than central sleep apnoea.
Obstructive sleep apnoea is typically more frequent in obese people with particular heaviness at the face and neck, especially middle aged and older people. In a heart failure population the incidence of sleep apnoea, usually central, can be up to half. In children and young adolescents it is almost always caused by obstructive tonsils and adenoids. Adult women suffer typically less frequently and to a lesser degree than men.
Symptoms
The hallmark symptom of obstructive sleep apnoea in adults is excessive daytime sleepiness.
But symptoms may be present for many years without identification as the sufferer may become adjusted to the daytime sleepiness and fatigue associated with significant sleep disturbance.
Typically, an adult or adolescent with severe long-standing obstructive sleep apnoea will fall asleep for very brief periods during usual daytime activities if given any opportunity to sit or rest.
Additional signs of obstructive sleep apnoea include restless sleep and loud snoring with periods of silence followed by gasps.
Other symptoms are non-specific: morning headaches, trouble concentrating, irritability, forgetfulness, mood or behaviour changes, decreased sex drive, increased heart rate, anxiety, depression, increased frequency of urination, esophageal reflux and heavy sweating at night.
Toddlers and young children with severe obstructive sleep apnea usually also feel tired during the day and may fail to thrive.
Diagnosis
After clinical suspicion is raised, a sleep study, which is called polysomnogram, is required for the diagnosis. Because there is night-to-night variability in the frequency of respiratory events in patients with milder forms of sleep-related breathing disorders, a “negative” study does not rule out sleep-related breathing disorders in a symptomatic patient.
Mechanism of sleep apnoea
Normally sleep is accompanied by reductions in spontaneous nerve activation, heart rate, blood pressure and cardiac output. Muscle tone of the whole body ordinarily relaxes during sleep. So, at the level of the throat, the human airway, which is composed of walls of soft tissue, can collapse during sleep, particularly in the obese.
Recurrent obstructive apnoea disrupts sleep because the efforts of drawing in air during each of the episodes generate negative pressure in the chest, which subsequently changes the pressures in the heart and the blood vessels. In this situation the cardiac pump has to operate under stress conditions and its performance is temporarily diminished.
Sleep apnoea may also affect the amount of oxygen in the blood causing problems to the heart muscle and the brain. In the case of central sleep apnoea, the nerve system which continuously monitors and regulates breathing either does not receive accurate feedback from the circulation or suffers an intrinsic fault.
Together with several health conditions, sedative drugs and alcohol can be responsible for this disorder. Nevertheless, nocturnal periodic breathing with central apnoeas has also been recognised in healthy people.
Clinical implications
Hypertension (high blood pressure)
More than half of patients with obstructive sleep apnoea have high blood pressure and this percentage is significantly higher than that expected for their age and general health. It is often observed that their blood pressure does not drop during the night as it typically does in normal individuals. Studies with patients suggest that treating obstructive sleep apnoea can effectively lower daytime blood pressure. Sleep apnoea may therefore be one of the hidden contributing factors in idiopathic (of an unknown cause) or primary hypertension.
Coronary artery disease
Studies have suggested that sleep apnoea probably increases the risk of coronary artery disease, but one has to be cautious when assessing a multi-factorial condition like this.
Heart failure
The relation between sleep apnoea and heart failure, for example in dilated cardiomyopathy patients, is two-way in many cases. Central sleep apnoea is highly prevalent in patients with asymptomatic (symptom-free) cardiac dysfunction and moreover, severe symptomatic heart failure is often associated with episodes of sleep apnoea. This can be the result of abnormal circulatory conditions caused by the heart dysfunction and may unfortunately increase the risk of some complications from the heart failure, such as arrhythmia, and contribute to some degree to disease progression.
Co-existence of obstructive sleep apnoea exposes the patients to further blood flow irregularities secondary to the instability of the pressures in the heart and circulating system and the lungs, and makes their treatment more difficult.
Some data suggests that in patients being treated for heart failure, treatment of co-existing obstructive sleep apnoea reduces systolic blood pressure and improves heart function. The relationship between sleep apnoea and hypertrophic cardiomyopathy is unclear although some limited data has been published.
Management
Treatments involve lifestyle changes, such as avoiding alcohol and medications that relax the central nervous system (for example sedatives and muscle relaxants), losing weight and quitting smoking.
Some people are helped by special pillows or devices that keep them from sleeping on their backs or oral appliances to keep the airways open. Especially in young people, having their tonsils and adenoids out may be considered if the obstruction is caused by lymphoid tissue.
Sleep apnoea can be relieved by therapy with continuous positive airway pressure (CPAP) which delivers air through a mask worn over the nose, mouth or both. CPAP reduces the frequency of obstructive events and improves oxygen levels in the blood during sleep. Clinically significant effects of this kind of treatment have been suggested by studies involving mainly patients with hypertension and heart dysfunction.
Clinical awareness has a key role in the recognition and diagnosis of this manageable disorder which may have various cardiovascular implications.
Dedicated to Damian McLoughlin, who died age 20 of cardiomyopathy. This site is supported by Damian's family and friends.
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