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Clinical Information

Your Journey: What is OSA?


What is OSA?

OSA is the abbreviation of 'Obstructive Sleep Apnoea' (or Apnea in some literature). Apnoea is derived fom the greek word APNOIA meaning an absence of breathing. OSA does exactly what is says on the tin - it is an absence of breathing caused by an obstruction when you are asleep. Clearly the interruption to your breathing is temporary, or you would not be finding out how you can confirm you have OSA.

Not breathing is never a good thing, and we have defence mechanisms that kick in to get us started again if we stop. The primary effect of apnoea is that you don't replenish your oxygen or flush out your carbon dioxide when you are not breathing. This quickly causes an imbalance in the blood gas levels, and because this is potentially lethal, there are a lot of sensors in the body keeping an eye on our blood gases. These regulatory sensors tell the brain to do something about the situation - right now please -  and the brain quickly sends extra and stronger messages to the respiratory muscles to work harder, get the air flowing, and restore the balance.

And it does.

So the obvious question this raises is: "If the body sorts this out on its own, why should I be concerned about OSA"


Short Term Consequences of OSA

We know that OSA is caused by an obstruction of the airway, and that the usual flow of air in and out of the lungs is blocked. So, we are breathing normally but not getting any air - actually, that doesn't sound too normal. This problem - of breathing with no breath - is specifically what the brain must overcome to get breathing back where it should be.

Breathing has two phases - active and passive. We actively breathe in by triggering our inspiratoty muscles to expand our chest. This causes the pressure in our lungs to fall, and air rushes in to equalise the pressure. That's the 'active' part of breathing. Breathing out is easier. We switch off the inspiratory muscles, and they return to their resting position, as does the ribcage which has been stretched during inspiration. With the muscles no longer active, the chest returns to its resting size, causing us to breathe out as it does. That's the 'passive' part of breathing.


An obstructive apnoea interrupts this mechanism. The obstruction occurs in the upper airway, above the lungs at and around the level of the pharynx. As the obstruction starts, the normal breathing effort continues, but our blood oxygen level quickly starts to fall. The defence reflex kicks in, and the brain starts to correct the problem. We know that inspiration causes a pressure drop that sucks air into the lungs. To overcome the apnoea, the respiratory muscles must generate a pressure that is high enough to force the obstruction open and get the air flowing again.

The catch is that every time the brain tells the muscles to work harder, you wake up a little. And every time you wake up a little, your sleep is disturbed. You may still be asleep, but your healthy and restorative sleeping pattern is interrupted. In addition to the interruption to restful sleep, each of these pauses causes a drop in oxygen level that is best avoided. These drops can be quite dramatic as can be seen from the sample reports.

This whole situation is further complicated because you don't actually have to stop breathing - i.e. have an apnoea - for this to happen. Your breathing only has to be obstructed sufficiently to trigger the drop in oxygen levels to cause you problems.  This brings us the hypopnoea - most simply described as a 'mini apnoea'. One of the main results to come from your sleep study is the AHI, or Apnoea Hypopnoea Index. This value tells you how many times you stop breathing, or nearly stop breathing, on average, every hour you are asleep. The higher the AHI, the more severe the OSA.

This is not a problem if it happens a few times during the night. In fact, most of us have a few apnoeas for various reasons when we sleep, and an AHI of less than 5/hour is considered normal. If on the other hand you are being disturbed twenty, or thirty, or forty, or fifty times every hour you are asleep, then it's no surprise that OSA can cause a lot of sleepiness.

If you have OSA and suffer excessive daytime sleepiness, then you have OSAS - Obstructive Sleep Apnoea Syndrome.

This is the primary short term consequence for sufferers of OSA - constantly feeling tired, and maybe a bit cranky.

An unusual ability of OSA is to not just make you feel excessivly tired and sleepy. Your bed partner is probably suffering too.


Long Term Risks of Untreated OSA

OSA does not develop overnight. Progressively louder snoring is often the first sign that things are not quite right, and that OSA should be considered. OSA can creep up over quite a long period, and slowly enough that it may be hard to notice that something serious is happening. Because OSA usually develops over a fairly long period of time, many people suffering with OSA believe that feeling 'not-quite-as-good-as-I-did-a-couple-of-years-ago' is simply associated with getting older. Falling asleep in front of the telly becomes the new norm, and we can always find the end of the programme on catch-up TV anyway. Falling asleep while driving will not have such a simple remedy. Untreated OSA carries quite a few risks, and researchers in a variety of fields are finding associations with OSA. These include:



Heart disease

Atrial fibrillation





The links and associations of OSA with these very serious conditions are not vague and hypothetical. OSA is being recognised through ongoing research to be a very real risk factor in developing these conditions. This is not an exhaustive list, but it clearly demonstrates the wide ranging and potentially severe outcomes of living with untreated OSA. Luckily it is a fairly straightforward condition to manage.


A lot of research is available on the topic of car crashes attributed to OSA, and estimates of the increased risk vary. It seems  likely that the minimum increase in risk is by a factor of 2.5, but increased risk factors up to 8 have been reported. The tragedy of this particular risk factor is that is does not apply just to the person driving with untreated OSA. It can have devastating outcomes for drivers, cyclists, pedestrians unlucky enough to be in their vicinity when they nod off at the wheel. And of course, their families.


There may be implications for your driving status if you have untreated OSA, and not all of the information you find online is accurate. SATA - The Sleep Apnoea Trust Association - is a charity supporting sufferers of OSA, and they can provide guidance regarding driving and the DVLA. SATA is manned by volunteers who have OSA themselves and will give impartial advice, with helpful information on how to stay legal if you have OSA. You can follow this link to the relevant page, and it is worth looking around their website for a lot more information on diagnosis and treatment, written from the patients' side.


Other types of sleep apnoea

OSA is the commonest form of sleep apnoea, but there are others. A central sleep apnoea occurs if the brain forgets to tell the chest to expand and initiate a breath. Our breathing is regulated automatically while we sleep, but if there is a pause in the regulated pattern, the result is an apnoea, and a consequent fall in oxygen level.  A mixed apnoea is a combination of central and obstructive. The apnoea starts out as a central with neither effort nor airflow, followed by an obstructive period of effort but no airflow, and finally the apnoea is overcome and normal breathing is restored. If the ratio of non-obstructive events to the total number of events is high, this is described as Complex Sleep Apnoea. It can be associated with certain chronic diseases, and also with opioid use.

Positional sleep apnoea - POSA - is a subset of OSA that is highly dependent on body position. Obstructive events, and indeed snoring, tend to occur more frequently when you are sleeping on your back. If a very significant majority of obstructions occur while on your back, this may be classified as POSA. This is usually seen only in mild OSA.

OSA Illustration.webp
OSA Driving.webp

Falling asleep while driving

Our Mission: Test and Treat

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Healthy Sleep: Foundation for Health

Testing for OSA

Do I Need A Sleep Study?


OSA is a very common sleep disorder. For many years sleep professionals used incidence rates of 2% to 4% in men and women over the age of forty. More recent estimates put this estimate much higher, and OSA incidence is likely to be in the 20% -50% range in individuals who are overweight. All of the research into OSA agrees that it is a big number.

Clearly you have concerns regarding your sleep quality and the potential increased risk of ill health associated with ignoring it. There is a lot of information available about assessing your risk and deciding if you should have a sleep study. There are evaluations of sleepiness, general health, and risk factors for OSA. The most common signs/symptoms/risk factors are listed below. If you recognise more than a couple of these indicators, then you should really get tested for OSA.


Unexplained daytime sleepiness

Witnessed apnoea - bed partner sees you not breathing

Waking up with a headache

Short term memory impairment/Mild Cognitive Impairment (MCI)


Loss of libido

Being overweight

More than one bathroom visit during the night

Collar size > 17"

Dozing off when you don't want to

Having high blood pressure

Needing daytime naps

Struggling to concentrate at work

Loud snoring

Losing your energy and enthusiasm for life



A quick point about 'sleepiness' - we are talking about inappropriate daytime sleepiness, and the likelihood of nodding off unexpectedly at inappropriate times. This is not the same as feeling tired because of workload, or because of the normal stresses of life in general. Conversely, having an hour or two asleep in front of the telly every night is not appropriate, just because you do it every night. 'Inappropriate' means just that - falling asleep in situations that are not normally (or shouldn't be) accepted to be part of a healthy sleeping pattern.

It's important to consider a basic negative impact on health caused by OSA. The interruptions to restful and restorative sleep tend in a general sense to increase sleepiness or tiredness, decrease energy and interest in doing things. It becomes more attractive to put things off until tomorrow. In general OSA leads to a more sedentary lifestyle. The obvious consequence is that if we don't cut back on our food when we become more sedentary, we are going to put on weight.

This is now the start of a vicious cycle. More weight usually means more severe OSA and more disruption to sleep. More disruption to sleep means more tiredness. More tiredness means less activity. Less activity means more weight gain ... etc. ... etc. ... etc. ...

Confirming OSA and doing something about it is the way to go to break this vicious cycle. A  number of treatments are available to manage OSA, and they generally work immediately, allowing you to reset your life and start feeling a lot better straight away. Not to mention improving your health outlook too.


What exactly is a sleep study?

'Sleep study' is a pretty wide ranging term. There are different types of study available to investigate any problems you have when you are asleep. The depth of investigation, and the accuracy and usefulness of the results, ranges from simple screening for instance using an app on your phone, through to spending a night in a bed in a sleep clinic, where everything it is possible to record while you sleep is recorded.

Awareness of sleep disorders has grown over the last few years, driven to a large degree by increased media attention improving awareness of the problem. This is hugely beneficial to individuals and to wider society as we live in a time where we have the ability to take more interest and become more proactive with regard to our health and wellbeing.

Routine sleep studies have largely moved from specialist sleep laboratories and into the home, driven to a large extent by demand far exceeding sleep laboratory capacity. In reality most people don't need the very specialist additional measurements that are made in a sleep laboratory, and these resources are used where they are most needed clinically. Screening using a simple device - or a smartphone - does not really answer the question. This type of screening often produces more questions than answers, and usually leads to doing a sleep study anyway.


The answer is polygraphy - a multi-channel recording of the essential parameters, and this is precisely what we provide. Using the same equipment at home ensures quality and integrity of the data, and a report that a sleep specialist can work with. Polygraphy is now the standard used for most sleep studies.​



Diagnostic or Screening?

As awareness of OSA and other sleep condition has grown, there has been a parallel growth in diagnostic options. Many of these options are smartphone based, and impressively claim to be as accurate as an old fashioned sleep study. While it can be interesting to explore these apps, results obtained should be viewed with caution. Smartphones are indeed pretty smart, and software is getting better all the time, but if you don't measure something, can you really report on it? Only by making a lot of assumptions, and when the 'data' generated by these assumptions is then used to feed into further assumptions that generate the next level of 'data' things can quickly lose all meaning.

To properly investigate OSA you must as a minimum measure these parameters:

  • Airflow in and out of the mouth and nose

  • Snoring

  • Oximetry - continuous monitoring of oxygen levels in the blood

  • Breathing effort - preferably both the thoracic (chest) and abdominal (tummy)

  • Body position

Additional parameters such as actigraphy can be helpful in addition to the core measurements.

Continuous recording of these signals detects apnoeas and hypopnoeas (no or reduced airflow) and differentiates into obstructive (effort but no flow), central (no effort or flow), and mixed events (initially no effort or flow, then effort but no flow). Drops in oxygen levels associated with the pauses in breathing are clearly seen, and will also indicate the likelihood of other conditions associated with prolonged low levels of oxygen such as OHS - Obesity Hypoventilation Syndrome. Recording snoring will indicate if the problem is just snoring, or if it is OSA. Recording body position can identify a particular type of OSA - POSA or positional OSA.

Devices used for sleep screening - smartphone based or otherwise - that do not accurately measure and record these physiological parameters are providing data derived from some other measurement. This is generally achieved by extrapolating or inferring from the limited measurements made. If you decide you should have a sleep study, the least you should expect from the study is that it does not give you inaccurate test results because these most basic parameters are not even recorded during the study. A video is available demonstrating the setting up of the SOMNOTouch Resp in preparation for a sleep study.

The Sleep Study Report


Your sleep study produces a comprehensive report on your sleep status. There are quite a few results listed on the report, many of them acronyms that don't have an obvious meaning, and other parameters that are self-explanatory. An annotated sample report is available for illustration purposes.

A glossary of the terms used follows. Please remember that the report is one part  - albeit a vital part - of your journey to resolving your sleep problems. The report should be fully interpreted by a sleep specialist, who will have a more complete picture of your situation. The clinician will have your medical history, your medications list, and will be aware of any other relevant information. You will not have a diagnosis of OSA - or no OSA - in your hand when you look at the report. Having said that, a number of the measurements obtained are used routinely to investigate, diagnose, and treat your sleep problem. Severity of, or absence of OSA will be based upon some of these numbers. The report will help you to decide where you want to go next.


Some parameters are reported both as absolute values - number - and as an average value per hour of sleep - [index].

TIB: Time in bed

Obstructive/mixed/central [index] : apnoeas scored by type

A+H [index] : Total Apnoea + Hypopnoeas scored

RERA [index] : Respiratory Effort Related Arousal

RDI [index] : Respiratory Disturbances[index]

Position results [index] : indicate which respiratory events are associated with each body position, be used to assess POSA

O2 Saturation : measure of oxygen in the blood

Desaturations [index] : number of times Oxygen levels fell by at least 4%

Baseline saturation : Your normal resting oxygen level

Minimum SpO2 : The lowest recorded oxygen level while asleep

Biggest/Longest desaturation : biggest fall %/ longest duration drop recorded

Snore [index] : Number [index] of snores recorded

Cheyne Stokes [index] : Number [index] of occurences of a particular breathing pattern

Heart rate max/min : Fastest and slowest heart rate recorded

Acceleration/deceleration [index] : number of times [index] your speeded up/slowed down

The 2 parameters most frequently used are the AHI and the desaturation index as they give an overall measure of the number of times your breathing is interrupted, and how often these interruptions cause your oxygen level to fall by more than 3%.

Severity of OSA is classified according to the AHI value as follows: 0-5 normal; 5-15 mild; 15-30 moderate; >30 severe.

If you have any of the signs and/or symptoms of OSA described earlier, and your AHI is elevated, you really should see a sleep specialist for advice. Even if your AHI is normal, but you are sleepy or have other concerns, we strongly advise that you see a sleep specialist.

Treatment for OSA

Couples Therapy
Accessing Treatment


We work with  Sleep Physicians to provide appropriate treatment for snoring and OSA. Our CPAP management service includes the CPAP device and mask, and other accessories. Crucially, we provide ongoing support to all CPAP users, with regular reviews to ensure treatment is optimised. Additionally, a helpline is availble outside of the scheduled reviews. To make an enquiry, please contact us here.

Management of OSA


The optimal method of managing your OSA will be determined in consultation with your doctor. A number of differing therapy types are available, and the choice is largely dependent on the severity of your OSA.

If you are overweight, you will almost certainly be advised to try to make some lifestyle changes to initiate weight loss. Apart from the general health benefits, slimming down can improve OSA status. The blockages that cause OSA are related to the weight of fat in the neck (hence the collar size indicator) and simply put, the less fat you have around the neck, the less likely it is to contribute to OSA.

You need to be realistic when talking about weight loss as a 'cure' for OSA. If you weigh 25 stones and lose 5 stones, you still weigh 20 stones. That weight loss is a huge step in the right direction, but it's obvious that by itself, this is unlikely to cure your OSA. Some people - admittedly a small percentage - suffering from OSA are not overweight to start with, so weight loss is not going to help this group very much. Many of us know from experience that losing weight does not transform our bodies back in time. Yes, we will look and feel better after losing weight, but not all the changes associated with the weight gain are necessarily reversed.

If that all sounds a bit gloomy, let's consider what you can do to manage the condition.

Obstructive Sleep Apnoea is a medical condition, but it can be helpful to think of it as a mechanical problem that has medical consequences. Your airway is becoming physically occluded when you sleep - and that is definitely a mechanical problem. Clever people have been solving mechanical problems for millenia, and quite a few clever people have come with mechanical solutions for this particular problem, including the notable work by Dr Colin Sullivan in Australia in the 1980s.

OSA is categorised by severity, primarily by using the measured AHI value. Although not strictly applicable to every case, OSA is in general a progressive condition, and the progression is often linked to a corresponding progressive weight gain - the vicious circle referred to earlier. Increasing weight - or body mass index BMI - will almost certainly mean the amount of fat around the neck is getting heavier. The fat present in the neck is a prime cause of apnoea.

When we sleep the muscle in our neck and around our upper airways relax. The tongue slips backwards, and the weight of the neck compresses the entrance to the lungs. Once this compression reaches a critical point, air is prevented from entering and leaving the lungs as it should and we soon start having apnoeas. Overcoming this blockage to 'clear' the airway is achieved by making more and more effort to breathe, until the effort generates enough pressure to overcome the blockage.

The amount of pressure needed to overcome the blockage is directly related to the amount of compression, and the the amount of compression is - usually - directly related to the severity of OSA. Preventing this blockage of the airway fully resolves OSA. If the airway is not blocked, you can breathe normally, and immediately be free of OSA. It is important to identify the best method of treatment, and medical supervision is a necessity for successful long term teatment. Again, although not applicable in every case, there are a range of treatments available that can be used to treat OSA.


Mild sleep apnoea can sometimes be successfully treated by using a mandibular advancement device, or MAD. This is in the form of a brace that fits in the mouth, pulling the lower jaw forward slightly. In mild cases, this small change can sufficiently improve access to the upper airway to the point that apnoeas no longer occur.

A specific type of mild OSA is a positional OSA, or POSA, where a very significant percentage of apnoeas happen in one postion, almost always while supine. Many people are familiar with the punch in the ribs to make you move off your back, and grant some peace to your partner! A POSA device can help you stay off your back while asleep, thereby reducing the frequency of apnoea and improving your quality of sleep. POSA can only be reliably disgnosed with a full sleep study, and if used inappropriately, a POSA device is unlikely to be of any benefit.

In reality, the majority of OSA sufferers need the gold standard treatment of CPAP therapy. Continuous Positive Airway Pressure - CPAP - can effectively treat almost every case of OSA. Since the first device produced by Dr Sullivan in the eighties, CPAP devices have come a long way, with very clever algorithms predicting and preventing apnoeas automatically.

The principle of CPAP is deceptively simple. By applying a small pressure within the airway, the closure of the airway that happens during an apnoea is prevented, and OSA is eliminated. The amount of pressure needed for this to happen is completely dependent on the individual's situation, including but not limited to weight/BMI, collar size, anatomical variation of the jaw and neck, the size of the tongue etc. There is however a direct correlation between the degree of effort a person must make to overcome an apnoea, and the amount of CPAP pressure needed to prevent one. Again it's a bit of a generalisation, but the more severe the OSA, the higher the pressure needed to fix it.

Using CPAP successfully is not a given. There is no doubt that it feels a bit weird at first, and most people have to work at it for a while before it becomes part of the routine.  A useful analogy is the feeling you had as a child if you put your head through the window of a moving car. The immediate response is "I can't catch my breath" but that doesn't make sense when you think about it. If anything, air will be forced into your airway because of the forward motion of the car. It does feel different at first for sure, but within a handful of breaths you probably don't even notice it any more. The reason for the weird feeling is not the breathing in, but the breathing out. You are having to breathe against a small increased pressure, and while it does feel strange initially, it very quickly becomes unnoticeable, because our physiology adapts very quickly to the increased pressure, and so fully that we don't even notice it.

We can apply the same beautifully non-scientific term - weird - to starting CPAP. Some people have absolutely no problems from day one - which is fantastic for them - but most people have to learn to love, or at least tolerate CPAP. The biggest motivator is that results are usually immediate. After years of waking up groggy, tired, maybe with a headache, the first morning you wake up on CPAP therapy really is the first day of the rest of your life. You have actually had a good night's sleep.

Optimising your treatment is very important, and ongoing continuous support during therapy is critical. If ten people bought CPAP devices today, there might be three or four of them still using the devices in one month's time. If these same ten people are supported throughout, we can expect eight or nine to succeed. There will always be a small minority who simply cannot tolerate CPAP therapy and that has to be accepted when it happens. The secret to success is keep these numbers to  an absolute minimum by providing the appropriate support.

Every individual responds a little differently to, and feels differently about CPAP. Because of the multitude of differences between people, there simply isn't a one size fits all support solution. If you are supported through therapy by S-Med, you can be absolutely assured you will have the same quality of support that you would get from the best sleep departments in the country.​

Weight loss is self-evidently a good thing. It can help with OSA, but weight loss will not guarantee your OSA will disappear. Unfortunately, curing OSA  is often used as a carrot to motivate people to lose weight. While it is certainly admirable to encourage people to lose weight, this is not a  fair promise to make, as many if not most people will not cure OSA through weight loss alone. In these cases, it is very easy for people to become frustrated and even depressed. Few things are more frustrating than to lose the two stones off your tummy, and find it has made no difference to the OSA. So much for that carrot.


OSA generally occurs in an older population, and most people know that losing weight is not the same as reverting to a twenty something year old body. Anyone who has ever tried to lose weight understands that not all of the age related looseness can be transformed into the tightness of youth. Please do try to lose some weight, you will look and feel healthier. But please don't expect weight loss alone to fix your OSA. If it does, that is fantastic and congratulations are very much in order.

If the OSA persists, please don't panic, there are very effective therapies available to manage it. Just remember, there are very few reliable cures for OSA, but lots of very effective treaments to make you feel a whole lot better.

Healthy Sleep


It is hard not to find references to sleep and sleep quality across the media these days. References cover everything from consumer accessories to medical interventions, and it can be  difficult to understand which items are relevant, or even true. The sheer volume of articles and information leads clearly to the conclusion that sleep is important.

Quality of sleep has been impacted by the new normals of life - stressful jobs and the difficulty switching work off, 24/7 availability of information and advice, push messaging and targeted marketing, and enabling most of this is the smartphone. Fantastic devices that have opened up the world but they do come with a price.

From the effect of the screen itself on sleep quality, to the interruption of sleep by constant notifications, it has to be recognised that smartphone use has impacted sleep quality for many people. Many of the basics of sleep hygiene have got lost in the data driven age.

Try to remember some of the basics of sleep hygiene

Stick to a routine

Avoid the blue light of smart devices before bedtime

Avoid unnecessary stimulation before bedtime

Avoid caffeine after lunch

Maintain daytime exposure to natural light

Don't watch television in the bedroom

Remember the limitations of technology when monitoring your sleep

There is a huge market for apps and devices that allow you to track your sleep quality and quantity. The smart wristwatch is a prime example of a consumer product that has been 'upgraded' to a type of medical device. It is worth remembering how little data these devices record in relation to how much information they provide in their sleep reports. The simple truth is that if these devices could do what they claim, as accurately and simply as the marketing suggests, they would just be handed out by the NHS and there would not be any waiting lists for sleep testing. Using these devices can even cause harm to some people who become fixated by the numbers produced, with an overall worsening of sleep the outcome, rather than any of the claimed benefits.

Sleep is itself of great importance to health

Traditionally sleep has been seen as something that may be affected by some other cause. This may still be true, but fixing the sleep problem can be as important as fixing the cause too. A common sleep problem is OSA, often caused by being overweight. Being overweight has many health risks, and  weight loss will always be suggested as a good thing to do, which it is. The OSA associated with weight gain is itself of importance, and this should be treated directly, and not just as an adjunct to weight management. There are many examples of this type of approach to sleep.

Medical care in sleep disorders

It has never been easier to get direct access to diagnostic testing and therapy in sleep. This reflects a growth in the wish to self-manage health. Self-management should always be encouraged, but it cannot replace medical care, and care should be taken not to take self-management so far that it becomes dangerous. Public health services are stretched to breaking point and waiting lists are a way of life now. The self-pay route is very accessible and can cut down wait times for diagnostics, but please do not forget that this does not replace medical care.

Sleep study report
Testing for OSA
What is OSA
Healthy sleep
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