SVD and Sleep Apnea Study
Research type
Research Study
Full title
The Brain Changes in Sleep Apnea Study
IRAS ID
233766
Contact name
Jo-Anne Robertson
Contact email
Sponsor organisation
University of Edinburgh
Duration of Study in the UK
3 years, 11 months, 29 days
Research summary
Summary of Research
Sleep disorders like snoring, are common and cause daytime sleepiness. Severe sleep disorders can lead to lack of oxygen (sleep apnea) and raised blood pressure, can increase the risk of heart disease, stroke, and of developing brain damage which can be seen on scanning, called ‘small vessel disease’. “Small vessel disease’ also increases the risk of stroke and dementia. Some recent laboratory and patient studies suggest that sleep disorders and ‘small vessel disease’ are linked since both may affect the drainage of waste products from the brain that keeps the brain healthy.
Sleep disorders such as apnea are usually treated by wearing a special mask at night that helps to hold the air passages open to prevent snoring and apnea. This is called Continuous Positive Airway Pressure therapy (CPAP). This study aims to assess whether treatment for sleep apnea using a special breathing mask may reduce the visible damage in the brain due to small vessel disease and improve the function of the blood vessels in the brain.
We will recruit 40 patients with sleep apnea in Edinburgh (to combine with 40 patients being recruited in Toronto). The patients will be asked questions about sleep patterns, medical history, smoking, exercise, thinking skills and memory. Then the patients will wear small portable watch-like machines at home for a week to measure blood pressure, activity and sleep quality, then have a magnetic resonance brain scan to show how well the blood vessels work, and a blood sample taken. Then the patients will start treatment for the sleep apnea using CPAP according to current guidelines. After four months, we will repeat the tests to see if the brain scan, cognitive tests or general health have changed. This study will tell us more about sleep, brain health and prevention of stroke and dementia.
Summary of Results
The Brain Changes in Sleep Apnoea Study Participant End of Study SummarySleep is important for our health although we do not yet fully understand why. Disturbed sleep can lead to heart and brain diseases. Obstructive sleep apnoea is a condition that affects a person’s breathing while asleep. Someone with sleep apnoea can stop breathing multiple times during the night, and this may have medical consequences beyond tiredness during the day. The main treatment for sleep apnoea is Continuous Positive Airways Pressure (CPAP), a device worn at night to ensure that breathing does not stop.
We recruited 88 people with a diagnosis of sleep apnoea, 44 from the Royal Infirmary of Edinburgh Sleep Clinic and another 44 under the same protocol but with local ethics approval at the Sunnybrook Health Sciences Centre in Toronto. Participants provided a huge amount of data from medical questionnaires, cognitive tests, MRI scans, and sleep assessments, both before and after CPAP treatment.
We were particularly interested in whether CPAP affected the brain. However, we also knew that CPAP can be difficult to use. It involves wearing an airtight mask and it can cause problems with falling asleep, stuffy noses, and dry mouths. These constraints mean that not everyone finds CPAP helpful and consequently some may not use it very much. Therefore, we wanted to account for how much CPAP was was used in our analyses. We divided participants into two groups – those who could use CPAP for at least 4 hours for at least 70% of the nights, and those who used it less.
Previous research has suggested that one reason why sleep is important is that the brain clears out waste and toxins during sleep via small tubes around the brain blood vessels known as perivascular spaces. When this waste clearance process is not working well, these perivascular spaces can become bigger. To look at this, we used the MRI scans to take measurements of the total volume of perivascular spaces at the start of the study and after an average of 4 months of using CPAP. We found that for people who used CPAP less, the total volume of perivascular spaces increased by a small amount. For people who used CPAP more than 4 hours per night for at least 70% of the nights, the total volume of perivascular spaces did not change over the course of the study. This suggested that the CPAP treatment was stopping the worsening of the perivascular spaces and the blood vessel health, while the blood vessels and perivascular spaces in those who did not use the CPAP much just continued to get more unhealthy.
For the 44 people recruited in Edinburgh, we also looked at scans of the retina at the back of the eye. Since eyes share a blood supply and other features with the brain, we wanted to see if we could link information about tiny blood vessels from the retinal scans to the function of those blood vessels in the brain scans. Specifically, we looked at tiny veins and arteries in the retina and their width and how this related to both CPAP use and perivascular spaces. We found that people with worse sleep apnoea at the start had narrower veins and arteries, but people who used CPAP more increased the width of their veins and arteries. We also found that people with worse perivascular spaces had narrower retinal veins and arteries. Since narrow veins and arteries are bad and wider ones are good, this also suggested that the CPAP treatment was helping to maintain more healthy veins, arteries and perivascular spaces.
Another analysis looked at how stiff the brain’s veins and arteries were. Ideally veins and arteries should be flexible, and able to expand or contract according to how much blood is needed by the brain. One way to test this is to ask the patient to breath carbon dioxide, a naturally occurring gas in the air we breathe, which encourages the blood vessels to widen. This can be detected using MRI brain scanning. We asked participants to breathe air with extra CO2 while in the MRI scanner and measured how the veins and arteries responded. Similar to the analyses with perivascular spaces, we found that people who used CPAP at least 4 hours per night had less stiff veins and arteries at the end of the study than people who did not use CPAP very much.
We already knew that CPAP can help people breathe properly at night and it ensures that the level of oxygen in their blood does not drop to suboptimal levels. We wanted to see what the other effects of CPAP could be, over and above baseline blood oxygen levels and other factors known to affect brain health such as age. This study has shown that CPAP can also affect the blood vessels and perivascular spaces in the brain and the eyes in positive ways, and will allow other researchers to plan their own studies, for example, into the effect of alternatives to CPAP. We hope that it might provide encouragement to doctors to refer patients with sleep apnoea for CPAP treatment and patients with sleep apnoea to try to use the CPAP treatment as much as possible.
Finally, we would like to give our grateful thanks to all the participants, who so generously gave their time and energy to this study. None of this would have been possible without them.
Refs
Continuous Positive Airway Pressure and Progression of Enlarged Perivascular Spaces in Adults With Obstructive Sleep Apnea | Neurology 2025 Retinal microvascular phenotypes can track small vessel disease burden and CPAP treatment effectiveness in obstructive sleep apnea - JCBFM 2024 available at PMC In preparation: Continuous positive airway pressure treatment for sleep apnea and effect on cerebrovascular reactivity, perivascular space morphology and cognitive function.REC name
West of Scotland REC 5
REC reference
17/WS/0198
Date of REC Opinion
26 Sep 2017
REC opinion
Favourable Opinion