Sleep Apnoea
Sleep apnoea is a sleep disorder where the sleeper stops breathing or has episodes of shallow or infrequent breathing whilst asleep. These episodes are called apnoea’s. It is measured by the Apnoea – Hypopnea Index (AHI). The apnoea must last at least ten seconds and cause a lowering of blood oxygenation in order to be counted. The AHI is calculated by dividing the number of recorded apnoea events by the number of hours of sleep. This gives an indication of the severity of a person’s sleep apnoea.
0-4 per hour is normal
5-14 per hour is mild
15-29 per hour is moderate
30 or more per hour is severe
Each episode of shallow breathing is called a hypopnea.
Moderate to severe apnoea has been shown to reduce a person’s lifespan by up to 15 years, and untreated, it significantly increases the risk of motor vehicle or workplace accidents. Independent of other causes, sleep apnoea can cause poor sleep, night time toileting, morning headache, reduced mental capacity, anxiety and depression, fatigue, daytime sleepiness, high blood pressure, heart trouble, stroke, obesity and diabetes. Treatment and professional supervision can improve outcomes for many of these.
Diagnosis:
Sleep apnoea is generally diagnosed at a sleep clinic but some chemists in Australia are now hiring out portable sleep study units which are taken home and record apnoea events during the night. A record of the sleep study is sent by the participating pharmacy to a sleep specialist who issues a report showing the details of the sleep study and an interpretation of the patient’s AHI and apnoea score. One such organisation is Australian Pharmacy Sleep Services http://www.apsleepservices.com.au/
For some, a home sleep study unit is an easy and relatively inexpensive way to check if there is an issue before consulting a sleep specialist.
Self assessment:
You can gain a fair idea of whether you are likely to suffer from sleep apnoea if your sleep partner has noticed pauses or changes in your breathing pattern during sleep, if you awaken abruptly feeling short of breath or choking, if you snore a lot, or your snoring stops and is then followed by a sighing, shuddering snore as breathing resumes. Other signs may be awakening with a dry mouth and/or morning headache and feeling unrested upon awakening, or suffering acute morning anxiety for no obvious reason. Daytime sleepiness or falling asleep when you rest briefly or watch TV or even while talking to someone is also a good indication of a sleep debt that may be caused by sleep apnoea.
Types of sleep apnoea:
There are three types of sleep apnoea, obstructive, central and ‘mixed’ which is a combination of obstructive and central apnoea’s. Sleep apnoea can affect anyone, regardless of age or gender and most people are not aware that it is affecting them. Usually it takes an aware person who witnesses the person struggling to breathe during sleep, or an aware healthcare professional to suspect that it is happening due to clinical clues or an association with a pre-existing illness like MS.
In obstructive sleep apnoea, the airflow is blocked by a physical obstruction to the airway (the throat, pharynx or upper airway). Even though the person is breathing normally, their airway collapses in on itself, producing snoring, and a blockage of airflow to the lungs.
In central sleep apnoea, the airway is not blocked, but for some reason the person cannot produce enough respiratory effort and they ‘forget’ to breathe. This may be because of things like stroke which has affected the breathing control centre in the brain, slow circulation due to heart failure, which affects the breathing reflex, some drugs (such as antidepressants, muscle relaxants, and pain relievers), physical problems with the chest or lungs, long term obstructive apnoea that has blunted the breathing reflex, and neuromuscular diseases (like multiple sclerosis) which has either weakened the muscles required for breathing, or affected the area of the brain that manages breathing.
Treatments:
Treatments will depend on what is causing the apnoea, but it can usually be managed with a continuous positive airway pressure (CPAP) machine. These can be optimised for individual patients, and can report overnight performance daily, which can be checked online.
Oxygen levels:
When breathing is reduced or stops, oxygen levels fall, and carbon dioxide builds up in the blood stream. When the imbalance is serious enough, the brain will wake the person, and breathing will resume, oxygen levels will rise again, and the person falls asleep. The sleep/wake/sleep cycle can happen subliminally and most people will not be aware of these patterns of arousal. The cycle can be repeated hundreds of times during the night, every few minutes.
Oxygen levels in the blood are reported as an SpO2 measurement, which refers to peripheral capillary oxygen saturation. It is usually measured by a pulse oximeter, a small, non-invasive device that is placed on a finger and shines a light through the blood vessels, measuring variations in the colour of the blood which corresponds to the oxygen levels.
Normal SpO2 levels vary between 95% and 100%. Low blood oxygen is called hypoxaemia. Levels under 90% are considered low and levels below 80% may compromise organ function. Hypoxaemia can cause cyanosis, where the skin of the sleeping person takes on a bluish colour.
If an apnoea lasts more than a minute, oxygen levels are dramatically reduced. Permanent brain damage can occur in three minutes, and a person will die a few minutes later if breathing is not resumed. The impact on the body of lots of hypoxaemic events that occur during the night is considerable and where this condition goes undiagnosed for many years, the burden on the body is huge.
The need for sleep:
We spend about a third of our lives asleep and it is crucial to our ongoing good health. This is the time we go into an anabolic state, rebuilding our nervous system, the immune system, the skeletal system and the muscular system (see page on the chronic catabolic state in MS).
When we fall asleep, we go through various cycles which each last about 90 minutes. These involve rapid eye movement (REM) and non rapid eye movement (NREM) sleep. NREM is divided into three stages, and the cycle usually goes as follows; N1, N2, N3, N2 then REM, then the cycle repeats, up to four or five times a night.
In REM sleep, most of the muscles except the eyes and the diaphragm are paralysed, probably a protective measure, because this stage is associated with dreaming.
It is thought that each stage has a distinct physiological function and therefore has a unique role in maintaining health.
As we fall asleep, our body activity slows down, temperature falls, and heart rate and respiratory rates should all decrease. Brainwaves slow. Sleep is absolutely necessary downtime for the rest, repair and restoration of the physical and emotional organism. We should slip out of the catabolic state of our waking hours (where the body burns oxygen and food to provide our energy needs to fund our physical and mental activity), and slip into the anabolic state where we conserve our energy and use it to repair and grow our body. Hormones like adrenaline and cortisol should drop and human growth hormone production should increase. It is mostly during sleep that sex and fertility hormones are released, as is a cancer killing chemical called tumour necrosis factor.
This is the time when the brain replenishes its supply of Adenosine Triphosphate (ATP) which is the chemical that supplies our cellular energy needs. The brain uses about 20% of bodily energy in the waking state, so the brain’s energy need has a considerable impact on overall energy needs.
Digestion slows, which is why it is recommended that we do not eat big meals later in the evening.
What happens when sleep apnoea disrupts sleep:
If the body needs four to five cycles of NREM and REM sleep in a night for optimal physical and emotional repair, and to slip out of catabolism into anabolism, this cannot happen properly if these cycles are disrupted. If someone is at the upper limit of moderate sleep apnoea for example, and is having 29 hypoxaemic events an hour, then a person could be experiencing at least ten seconds of hypoxaemia every two minutes or so.
If the brain is starving of oxygen and causing an arousal from sleep every two minutes, it cannot complete the full restful four or five 90-minute sleep cycles that it needs for optimal repair and restoration.
When the brain experiences a hypoxaemic event, it is like being suffocated. If you were being suffocated to the point of panic every two minutes during the day, how do you think you would feel? These hypoxaemic events trigger the flight or fight response. Life can be challenging enough during the day. No one needs their own body to conspire against them and place them in the situation where they are facing the equivalent of a life or death situation every few minutes during sleep, a time when they should be at their most peaceful, a time to recover from the day’s challenges. This continual arousal during sleep puts a tremendous strain on the body.
When the body thinks it is choking to death, stress hormones like cortisol and adrenaline are released, the very chemicals that should be downregulated during sleep. These excitatory chemicals put enormous pressure on the cardiac system; heart rate and blood pressure increases, and an inflammatory state of adrenal exhaustion may follow, with the person waking with an unexplained feeling of dread, and suffering daily from anxiety and depression, a sense of malaise, and ‘cognitive fog’. This cognitive fog may manifest as a reduced capacity to plan and initiate tasks, pay attention, work effectively, and reduced memory and capacity to learn.
Brain cells need oxygen, and they can die during hypoxaemic events. Brain damage can feed into the anxiety, depression and cognitive fog that is described above. Hypoxaemic events have also been linked to seizures, mini or ‘silent’ strokes causing lesions that are visible on MRI, and a disorder called metabolic acidosis in patients who have suffered with sleep apnoea for many years, a disorder where there is excess acid in bodily fluids. This is thought to be a result of increased carbon dioxide levels in the blood during the night. Symptoms include headaches, palpitations, chest, muscle, bone and abdominal pain, and muscle weakness.
If the body is supposed to slip out of catabolism and into anabolism during sleep, what happens when this process is interrupted every few minutes by the body going into hyperarousal to deal with hypoxaemic events? Is a chronic state of catabolism maintained?
Sleep apnoea and multiple sclerosis:
Sleep apnoea and multiple sclerosis have well known associations.
http://www.ncbi.nlm.nih.gov/pubmed/22895593
Sleep apnoea is a major risk factor for death, disease and disability in people without neuromuscular conditions, let alone in people with MS. How many PWMS have been made aware of this associaton by their doctor or neurologist, and how many PWMS have had a sleep study as a standard or routine element in their MS disease management?
With a demyelinating disease like MS, there is an expectation of a loss of neurological function related directly to lesions in the CNS. What is somewhat unexpected to patients is the progression of overwhelming fatigue, cognitive fog, pain and gradually increasing muscle weakness, without there necessarily being corresponding damage in the CNS to account for the decline. Many PWMS complain of exercise intolerance and that there is ‘nothing in the tank’. There appears to be insufficient capacity to meet the basic activities of daily living, and when extra demands are placed on muscles, the breakdown occurs without the capacity to rebuild, resulting in a series of steps downwards, with whatever level of breakdown the patient has reached, marking a new ‘low’ – a new plateau from which recovery does not seem possible, but further losses are. Could a disruption in the capacity of the body to repair nervous tissue and muscle during sleep be part of the problem?
Many PWMS complain of extremities ‘falling asleep’ during the night. This seems to particularly affect the hands. PWMS are sometimes woken several times a night, with hands that are dead numb, as though the blood supply had been shut off, but no physical compression of the veins has taken place. Is this an indication of sleep apnoea too?
A person with MS needs to maximise their health in as many dimensions as possible. They need their body to be operating at peak capacity to maximise repair and rejuvenation.
Any person with MS who suspects they have sleep apnoea, or feels they are wise to rule it out in their case, could conduct a home sleep study using a hired machine, or ask their doctor to refer them for a sleep study at a sleep clinic. The patient may need to provide their doctor with a copy of relevant research linking MS and sleep apnoea.
Links:
BartsMS Blog reports on sleep apnoea being more prevalent in PWMS and its relationship to fatigue
http://multiple-sclerosis-research.blogspot.com/2012/08/braley-tj-segal-bm-chervin-rd.html
PubMed article on central sleep apnoea and MS http://www.ncbi.nlm.nih.gov/pubmed/20336272
PubMed article on obstructive sleep apnoea and its association with MS http://www.ncbi.nlm.nih.gov/pubmed/22183937
WebMD article on sleep apnoea and its prevalence in MS and relationship to fatigue http://www.webmd.com/multiple-sclerosis/news/20140214/sleep-apnea-may-worsen-fatigue-in-ms-patients
This study indicates that sleep apnoea will cause the muscles of the affected person to develop an energy metabolism problem http://www.sciencedirect.com/science/article/pii/S0954611197900895
Sleep Health Foundation fact sheet on obstructive sleep apnoea http://www.sleephealthfoundation.org.au/fact-sheets-a-z/191-obstructive-sleep-aponea.html
Sleep Health Foundation fact sheet on Central sleep apnoea http://www.sleephealthfoundation.org.au/fact-sheets-a-z/204-central-sleep-apnea.html
Narcolepsy and Overwhelming Daytime Sleep Society of Australia (NODSS) sleep apnoea page http://www.nodss.org.au/sleep_apnoeas.html
Sleep specialist discusses obstructive sleep apnoea and MS http://doctorstevenpark.com/multiple-sclerosis-and-obstructive-sleep-apnea-is-there-a-link
Upper airway resistance syndrome http://doctorstevenpark.com/tired-of-being-tired-—-the-upper-airway-resistance-syndrome
Silent strokes and sleep apnoea http://www.webmd.boots.com/sleep-disorders/news/20120202/silent-strokes-and-sleep-apnoea
Sleep apnoea and white matter lesions in the brain
http://www.sleep-apnea-guide.com/sleep-apneas-effect-on-the-white-matter-of-your-brain.html
http://www.eurekalert.org/pub_releases/2007-03/ats-osa030607.php
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2546457/
Respiratory difficulty may be a global problem in MS, not just a concern during sleep. This site discusses general respiratory problems in MS
http://www.healthcarejourney.com/breathingrespiratory.html
This National Multiple Sclerosis Society (America) webpage notes that respiratory muscle weakness is common in advancing MS, that an assessment of breathing capacity is appropriate in the management of MS, and that progressive respiratory muscle training can be of benefit to people with MS in maintaining their lung function http://www.healthcarejourney.com/uploads/2/1/1/2/21124348/pulmonaryfunct.ms.clinical.bulletin.2013.pdf
Dysautonomia/POTS
Sleep apnoea is a sleep disorder where the sleeper stops breathing or has episodes of shallow or infrequent breathing whilst asleep. These episodes are called apnoea’s. It is measured by the Apnoea – Hypopnea Index (AHI). The apnoea must last at least ten seconds and cause a lowering of blood oxygenation in order to be counted. The AHI is calculated by dividing the number of recorded apnoea events by the number of hours of sleep. This gives an indication of the severity of a person’s sleep apnoea.
0-4 per hour is normal
5-14 per hour is mild
15-29 per hour is moderate
30 or more per hour is severe
Each episode of shallow breathing is called a hypopnea.
Moderate to severe apnoea has been shown to reduce a person’s lifespan by up to 15 years, and untreated, it significantly increases the risk of motor vehicle or workplace accidents. Independent of other causes, sleep apnoea can cause poor sleep, night time toileting, morning headache, reduced mental capacity, anxiety and depression, fatigue, daytime sleepiness, high blood pressure, heart trouble, stroke, obesity and diabetes. Treatment and professional supervision can improve outcomes for many of these.
Diagnosis:
Sleep apnoea is generally diagnosed at a sleep clinic but some chemists in Australia are now hiring out portable sleep study units which are taken home and record apnoea events during the night. A record of the sleep study is sent by the participating pharmacy to a sleep specialist who issues a report showing the details of the sleep study and an interpretation of the patient’s AHI and apnoea score. One such organisation is Australian Pharmacy Sleep Services http://www.apsleepservices.com.au/
For some, a home sleep study unit is an easy and relatively inexpensive way to check if there is an issue before consulting a sleep specialist.
Self assessment:
You can gain a fair idea of whether you are likely to suffer from sleep apnoea if your sleep partner has noticed pauses or changes in your breathing pattern during sleep, if you awaken abruptly feeling short of breath or choking, if you snore a lot, or your snoring stops and is then followed by a sighing, shuddering snore as breathing resumes. Other signs may be awakening with a dry mouth and/or morning headache and feeling unrested upon awakening, or suffering acute morning anxiety for no obvious reason. Daytime sleepiness or falling asleep when you rest briefly or watch TV or even while talking to someone is also a good indication of a sleep debt that may be caused by sleep apnoea.
Types of sleep apnoea:
There are three types of sleep apnoea, obstructive, central and ‘mixed’ which is a combination of obstructive and central apnoea’s. Sleep apnoea can affect anyone, regardless of age or gender and most people are not aware that it is affecting them. Usually it takes an aware person who witnesses the person struggling to breathe during sleep, or an aware healthcare professional to suspect that it is happening due to clinical clues or an association with a pre-existing illness like MS.
In obstructive sleep apnoea, the airflow is blocked by a physical obstruction to the airway (the throat, pharynx or upper airway). Even though the person is breathing normally, their airway collapses in on itself, producing snoring, and a blockage of airflow to the lungs.
In central sleep apnoea, the airway is not blocked, but for some reason the person cannot produce enough respiratory effort and they ‘forget’ to breathe. This may be because of things like stroke which has affected the breathing control centre in the brain, slow circulation due to heart failure, which affects the breathing reflex, some drugs (such as antidepressants, muscle relaxants, and pain relievers), physical problems with the chest or lungs, long term obstructive apnoea that has blunted the breathing reflex, and neuromuscular diseases (like multiple sclerosis) which has either weakened the muscles required for breathing, or affected the area of the brain that manages breathing.
Treatments:
Treatments will depend on what is causing the apnoea, but it can usually be managed with a continuous positive airway pressure (CPAP) machine. These can be optimised for individual patients, and can report overnight performance daily, which can be checked online.
Oxygen levels:
When breathing is reduced or stops, oxygen levels fall, and carbon dioxide builds up in the blood stream. When the imbalance is serious enough, the brain will wake the person, and breathing will resume, oxygen levels will rise again, and the person falls asleep. The sleep/wake/sleep cycle can happen subliminally and most people will not be aware of these patterns of arousal. The cycle can be repeated hundreds of times during the night, every few minutes.
Oxygen levels in the blood are reported as an SpO2 measurement, which refers to peripheral capillary oxygen saturation. It is usually measured by a pulse oximeter, a small, non-invasive device that is placed on a finger and shines a light through the blood vessels, measuring variations in the colour of the blood which corresponds to the oxygen levels.
Normal SpO2 levels vary between 95% and 100%. Low blood oxygen is called hypoxaemia. Levels under 90% are considered low and levels below 80% may compromise organ function. Hypoxaemia can cause cyanosis, where the skin of the sleeping person takes on a bluish colour.
If an apnoea lasts more than a minute, oxygen levels are dramatically reduced. Permanent brain damage can occur in three minutes, and a person will die a few minutes later if breathing is not resumed. The impact on the body of lots of hypoxaemic events that occur during the night is considerable and where this condition goes undiagnosed for many years, the burden on the body is huge.
The need for sleep:
We spend about a third of our lives asleep and it is crucial to our ongoing good health. This is the time we go into an anabolic state, rebuilding our nervous system, the immune system, the skeletal system and the muscular system (see page on the chronic catabolic state in MS).
When we fall asleep, we go through various cycles which each last about 90 minutes. These involve rapid eye movement (REM) and non rapid eye movement (NREM) sleep. NREM is divided into three stages, and the cycle usually goes as follows; N1, N2, N3, N2 then REM, then the cycle repeats, up to four or five times a night.
In REM sleep, most of the muscles except the eyes and the diaphragm are paralysed, probably a protective measure, because this stage is associated with dreaming.
It is thought that each stage has a distinct physiological function and therefore has a unique role in maintaining health.
As we fall asleep, our body activity slows down, temperature falls, and heart rate and respiratory rates should all decrease. Brainwaves slow. Sleep is absolutely necessary downtime for the rest, repair and restoration of the physical and emotional organism. We should slip out of the catabolic state of our waking hours (where the body burns oxygen and food to provide our energy needs to fund our physical and mental activity), and slip into the anabolic state where we conserve our energy and use it to repair and grow our body. Hormones like adrenaline and cortisol should drop and human growth hormone production should increase. It is mostly during sleep that sex and fertility hormones are released, as is a cancer killing chemical called tumour necrosis factor.
This is the time when the brain replenishes its supply of Adenosine Triphosphate (ATP) which is the chemical that supplies our cellular energy needs. The brain uses about 20% of bodily energy in the waking state, so the brain’s energy need has a considerable impact on overall energy needs.
Digestion slows, which is why it is recommended that we do not eat big meals later in the evening.
What happens when sleep apnoea disrupts sleep:
If the body needs four to five cycles of NREM and REM sleep in a night for optimal physical and emotional repair, and to slip out of catabolism into anabolism, this cannot happen properly if these cycles are disrupted. If someone is at the upper limit of moderate sleep apnoea for example, and is having 29 hypoxaemic events an hour, then a person could be experiencing at least ten seconds of hypoxaemia every two minutes or so.
If the brain is starving of oxygen and causing an arousal from sleep every two minutes, it cannot complete the full restful four or five 90-minute sleep cycles that it needs for optimal repair and restoration.
When the brain experiences a hypoxaemic event, it is like being suffocated. If you were being suffocated to the point of panic every two minutes during the day, how do you think you would feel? These hypoxaemic events trigger the flight or fight response. Life can be challenging enough during the day. No one needs their own body to conspire against them and place them in the situation where they are facing the equivalent of a life or death situation every few minutes during sleep, a time when they should be at their most peaceful, a time to recover from the day’s challenges. This continual arousal during sleep puts a tremendous strain on the body.
When the body thinks it is choking to death, stress hormones like cortisol and adrenaline are released, the very chemicals that should be downregulated during sleep. These excitatory chemicals put enormous pressure on the cardiac system; heart rate and blood pressure increases, and an inflammatory state of adrenal exhaustion may follow, with the person waking with an unexplained feeling of dread, and suffering daily from anxiety and depression, a sense of malaise, and ‘cognitive fog’. This cognitive fog may manifest as a reduced capacity to plan and initiate tasks, pay attention, work effectively, and reduced memory and capacity to learn.
Brain cells need oxygen, and they can die during hypoxaemic events. Brain damage can feed into the anxiety, depression and cognitive fog that is described above. Hypoxaemic events have also been linked to seizures, mini or ‘silent’ strokes causing lesions that are visible on MRI, and a disorder called metabolic acidosis in patients who have suffered with sleep apnoea for many years, a disorder where there is excess acid in bodily fluids. This is thought to be a result of increased carbon dioxide levels in the blood during the night. Symptoms include headaches, palpitations, chest, muscle, bone and abdominal pain, and muscle weakness.
If the body is supposed to slip out of catabolism and into anabolism during sleep, what happens when this process is interrupted every few minutes by the body going into hyperarousal to deal with hypoxaemic events? Is a chronic state of catabolism maintained?
Sleep apnoea and multiple sclerosis:
Sleep apnoea and multiple sclerosis have well known associations.
http://www.ncbi.nlm.nih.gov/pubmed/22895593
Sleep apnoea is a major risk factor for death, disease and disability in people without neuromuscular conditions, let alone in people with MS. How many PWMS have been made aware of this associaton by their doctor or neurologist, and how many PWMS have had a sleep study as a standard or routine element in their MS disease management?
With a demyelinating disease like MS, there is an expectation of a loss of neurological function related directly to lesions in the CNS. What is somewhat unexpected to patients is the progression of overwhelming fatigue, cognitive fog, pain and gradually increasing muscle weakness, without there necessarily being corresponding damage in the CNS to account for the decline. Many PWMS complain of exercise intolerance and that there is ‘nothing in the tank’. There appears to be insufficient capacity to meet the basic activities of daily living, and when extra demands are placed on muscles, the breakdown occurs without the capacity to rebuild, resulting in a series of steps downwards, with whatever level of breakdown the patient has reached, marking a new ‘low’ – a new plateau from which recovery does not seem possible, but further losses are. Could a disruption in the capacity of the body to repair nervous tissue and muscle during sleep be part of the problem?
Many PWMS complain of extremities ‘falling asleep’ during the night. This seems to particularly affect the hands. PWMS are sometimes woken several times a night, with hands that are dead numb, as though the blood supply had been shut off, but no physical compression of the veins has taken place. Is this an indication of sleep apnoea too?
A person with MS needs to maximise their health in as many dimensions as possible. They need their body to be operating at peak capacity to maximise repair and rejuvenation.
Any person with MS who suspects they have sleep apnoea, or feels they are wise to rule it out in their case, could conduct a home sleep study using a hired machine, or ask their doctor to refer them for a sleep study at a sleep clinic. The patient may need to provide their doctor with a copy of relevant research linking MS and sleep apnoea.
Links:
BartsMS Blog reports on sleep apnoea being more prevalent in PWMS and its relationship to fatigue
http://multiple-sclerosis-research.blogspot.com/2012/08/braley-tj-segal-bm-chervin-rd.html
PubMed article on central sleep apnoea and MS http://www.ncbi.nlm.nih.gov/pubmed/20336272
PubMed article on obstructive sleep apnoea and its association with MS http://www.ncbi.nlm.nih.gov/pubmed/22183937
WebMD article on sleep apnoea and its prevalence in MS and relationship to fatigue http://www.webmd.com/multiple-sclerosis/news/20140214/sleep-apnea-may-worsen-fatigue-in-ms-patients
This study indicates that sleep apnoea will cause the muscles of the affected person to develop an energy metabolism problem http://www.sciencedirect.com/science/article/pii/S0954611197900895
Sleep Health Foundation fact sheet on obstructive sleep apnoea http://www.sleephealthfoundation.org.au/fact-sheets-a-z/191-obstructive-sleep-aponea.html
Sleep Health Foundation fact sheet on Central sleep apnoea http://www.sleephealthfoundation.org.au/fact-sheets-a-z/204-central-sleep-apnea.html
Narcolepsy and Overwhelming Daytime Sleep Society of Australia (NODSS) sleep apnoea page http://www.nodss.org.au/sleep_apnoeas.html
Sleep specialist discusses obstructive sleep apnoea and MS http://doctorstevenpark.com/multiple-sclerosis-and-obstructive-sleep-apnea-is-there-a-link
Upper airway resistance syndrome http://doctorstevenpark.com/tired-of-being-tired-—-the-upper-airway-resistance-syndrome
Silent strokes and sleep apnoea http://www.webmd.boots.com/sleep-disorders/news/20120202/silent-strokes-and-sleep-apnoea
Sleep apnoea and white matter lesions in the brain
http://www.sleep-apnea-guide.com/sleep-apneas-effect-on-the-white-matter-of-your-brain.html
http://www.eurekalert.org/pub_releases/2007-03/ats-osa030607.php
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2546457/
Respiratory difficulty may be a global problem in MS, not just a concern during sleep. This site discusses general respiratory problems in MS
http://www.healthcarejourney.com/breathingrespiratory.html
This National Multiple Sclerosis Society (America) webpage notes that respiratory muscle weakness is common in advancing MS, that an assessment of breathing capacity is appropriate in the management of MS, and that progressive respiratory muscle training can be of benefit to people with MS in maintaining their lung function http://www.healthcarejourney.com/uploads/2/1/1/2/21124348/pulmonaryfunct.ms.clinical.bulletin.2013.pdf
Dysautonomia/POTS