Central sleep apnoea (CSA) is a rare disorder (only 0.14% of sleep Apnoea sufferers) in which you repetitively stop and start breathing while asleep. The pauses in breathing can last up to 20 seconds and occur mainly because your brain does not send proper signals to the muscles that control your breathing (your diaphragm and intercostal muscles). With CSA, you do not try to breathe at all, or your breathing is so shallow that the gas exchange in your lungs is insufficient.
Secondary CSA is caused by an underlying medical condition, such as stroke, brain tumour or heart failure, and can also be seen with narcotic use and sleeping at a high altitude. Primary CSA is very rare, and there is no known precipitating cause.
These phenomena can occur during wakefulness (conscious and engages in coherent cognitive and behavioural responses) or during sleep, where they are called the central sleep apnea syndrome (CSAS)
Medical Conditions and Risk Factors Associated with Central Sleep Apnoea
1. Primary Central Sleep Apnoea – This type of CSA is rare, and the causes or set of causes are unknown. Middle-aged or elderly men seem to be more affected. The idea that this condition may be inherited may be a real factor.
2. Cheyne-Stokes Breathing Pattern – Cheyne-Stokes breathing is characterized by periodic shallow breathing or under breathing that alternates with deep over-breathing with possible periods of apnoea. Cheyne–Stokes respiration involves apnea (temporary cessation of breathing) while periodic breathing involves hypopnea (abnormally small but not absent breaths).
According to www.sleepeducation.org, “[Cheyne-Stokes Breathing Pattern] occurs mainly in men aged 60 or older. It is seen in 25% to 40% of men with chronic congestive heart failure. It is also found in 10% of men who have had a stroke. It is rarely seen in women and does not appear to be inherited.”
The condition may also be caused by damage to the respiratory centres and is also seen in newborns with immature respiratory systems and in visitors to high altitudes.
3. Arnold- Chiari Malformation – Arnold–Chiari malformation, also
called the Chiari malformation, is a condition affecting the brain. It consists of a downward displacement of the cerebellar tonsils through the foramen magnum (the opening at the base of the skull).
This condition is usually due to a lack of or reduced communication between the brain and the lungs. This can result due to hydrocephalus (abnormal accumulation of cerebrospinal fluid), which results from an obstruction of cerebrospinal fluid (CSF) outflow.
The cerebrospinal fluid outflow is caused by phase difference in outflow and influx of blood in the vasculature of the brain. It can cause headaches, fatigue, muscle weakness, difficulty swallowing, dizziness, neck pain, speech problems, fatigue, nausea, tinnitus, impaired coordination, and, in severe cases, paralysis.
4. Medical Conditions – CSA may be associated with medical conditions like heart problems, kidney failure, hypothyroid disease and neurological diseases [Parkinson’s disease, Alzheimer’s disease, and amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease)], as well as damage to the brainstem caused by encephalitis, stroke, injury, or other factors.
5. Drug or Substance Use – Chronic opioid use increases the risk of CSA. Opioid substances act on opioid receptors to produce morphine-like effects. Opioids are most often used medically to relieve pain, and by people addicted to opioids.
6. High-Altitude Periodic Breathing – Altitude has a marked effect on respiration during sleep. Sleeping at altitudes higher than 15,000 feet (about 5,000 meters) triggers CSA. Anyone sleeping above 25,000 feet (about 7,600 meters) will be affected.
The physiologic effects of CSA depend on how long the person endures failure to breathe. The decreased level of oxygen in the blood may trigger seizures, even in the absence of epilepsy. In the worst cases, CSA can cause death.
Central Sleep Apnoea versus Obstructive Sleep Apnoea
Central Sleep Apnoea is rare and is less common than obstructive sleep apnoea (OSA), although their mechanisms frequently overlap. In fact, many patients with CSA also suffer from OSA and CSA is only discovered after OSA has been corrected.
OSA is caused by a blockage in the airway, therefore snoring is a major symptom, and respiratory effort is apparent during an apnoeic event. CSA, on the other hand, is not directly associated with snoring. The person has stopped breathing without identifiable ventilatory effort.
The approach to treatment of CSA is different from OSA. OSA is almost always improved with the use of a continuous positive airway pressure (CPAP) device. Treatment of CSA, however, is much more challenging secondary to the nature and causation of the condition.
Pathophysiology of Central Sleep Apnoea
In order to understand central sleep apnoea, we need to understand first how the brain controls our breathing while we sleep. Our breathing is closely monitored by the respiratory control centre in the medulla oblongata of our brainstem. The medulla oblongata is the lowest portion of the brainstem that connects the brain to the spinal cord, and it controls involuntary functions such as breathing and heart rate.
During wakefulness, the higher cortical level influences respiration through behavioural control. During sleep, however, this behavioural control is lost, and the respiratory control centre regulates ventilation through chemical control, regulating the levels of the arterial blood gases to maintain the partial pressure of arterial oxygen (PaO2) and the partial pressure of carbon dioxide (PaCO2) within normal ranges.
The central chemoreceptors (sensory extensions of the nervous system into blood vessels where they detect changes in chemical concentrations) located in the medulla oblongata and the peripheral chemoreceptors found in the aortic and carotid bodies (chemoreceptors and supporting cells located near the fork (bifurcation) of the carotid artery (which runs along both sides of the throat)) are sensitive to blood pH (hydrogen ion concentration), and they constantly send signals to the respiratory control centre. The blood pH changes with increase or decrease of carbon dioxide concentration (PaCO2), and these changes initiate compensatory response of the body during sleep.
The respiratory chemical control function is absent or reduced in a person suffering from CSA. The respiratory control centre does not respond to the changes in the arterial blood gases. Central apnoeic events occur mostly during non-rapid eye movement (NREM) sleep when the PaCO2 set point adjusts.
Treatment of Central Sleep Apnoea
Treatment of sleep apnoea is made on an individual basis. There are no clear guidelines regarding the treatment of asymptomatic CSA, especially when the CSA is determined after polysomnography is performed for a different reason. Observation may be appropriate in such cases. 20% of central sleep apnoea cases resolve spontaneously. If symptoms are present, treatments may include the following:
- Addressing associated medical problems. Addressing the medical condition that causes CSA will help alleviate central apnoeic events.
- Gradual reduction of opioid medications is advised if opioid use is causing the CSA.
- Continuous positive airway pressure (CPAP) is usually the first treatment given for CSA. It improves cardiac function in patients with congestive heart failure and Cheyne-Stokes breathing-central sleep apnoea (CSB-CSA). CPAP involves wearing a mask or nose tube while asleep. The device supplies a continuous amount of pressurized air to keep the upper airway open.
- Adaptive Servo-Ventilation (ASV) maybe given if CPAP is ineffective in treating the CSA. This is often used for treatment of CSB-CSA. The ASV device also delivers pressurized air like CPAP, but unlike CPAP, ASV changes the inspiratory pressure above the expiratory pressure similar to the normal ventilation to help eliminate central apnoeic events. The device may also automatically deliver a breath if breathing has stopped for a number of seconds. ASV is not indicated to patients with symptomatic heart failure.
- Bilevel Positive Airway Pressure (BiPAP). BiPAP is effective in treating hypercapnic central sleep apnoea associated with hypoventilation. BiPAP delivers a fixed amount of pressure when you breathe in and pressure that is lower when you breathe out. The device can also be configured to deliver a breath if you have not taken a breath within a certain number of seconds.
- Supplemental Oxygen may be effective for some people with CSA as it lessens hypoxia and promotes hyperventilation response to change PaCO2.