REM Rebound

Looking back at my post about Sleep Debt, it seems illogical to me that I can be carrying round a lifetime's worth of sleep debt...

Why on the December 1st graph, didn't my brain arrange for all the debt to be paid back in one night, why do I not have solid nights of REM or SWS to catch up on all the lost sleep of my life?

It's clear to see from the following graph that I roughly caught up on the REM sleep that I missed out on, the area below the mean REM on the debt days is roughly equal to the area above the mean on the payback days.

In fact the figues bear this out too. Assuming that my 220 day mean figure of 99 minutes is my desired amount then on the two debt days I lost 73 minutes of REM, 60 of which I caught up on over the two payback days.

Why don't we just have a night of "super concentrated sleep" without any (N1 or N2) to help us catch up on REM and slow-wave sleep? 

Maybe light sleep (N1 and N2) also serves a purpose and is desirable to the body, hence it makes sure it has some each night, maybe the body actually needs N1 and N2 as a vehicle for REM and slow-wave sleep.

Maybe REM and slow-wave sleep don't need to be paid back on on a minute-by-minute basis.

From looking at the many nights of data that I have, I think it seems clear that I generally get my "normal" amount of slow-wave sleep, and that my issue is more with REM.

Perhaps each of us has an optimal amount of REM and more than that is unnecessary, perhaps it serves a function such as recharging the immune system or cognitive functions and their respective batteries can only be fully charged and no more. There is no point in over-charging a battery, so the body doesn't waste energy trying. Maybe the brain says "Okay, your immunity was low for a day, you were sluggish in thought too, you even dipped into your reserves, so we'll top you up with 'premium' rather than 'regular' tonight"

This is bourn out by this graph of the 13 nights where I had more than 140 minutes of REM sleep...

So, by selection, there is little change in the amount of REM (140 - 153) but there is a large variation in Light (N1 + N2) and Deep (Slow-wave) sleep. This shows something else besides total sleep time governs the amount of REM that the brain desires.

Yes, the total amount of sleep and REM can't be completely independent of each other because the total REM cannot exceed the total sleep, and the brain must also arrange time for slow-wave sleep too, but this suggests that if the brain desired more REM then it could arrange for a night of the "concentrated sleep" that I spoke of in the post about "Sleep Debt"

That describes conventional REM Rebound. However, as I said above I doubt that one is able to get more than a pre-set maximum amount of REM (which will vary for each person).

I think that the weekend of the Zeo Sleep Challenge goes some way to show this. 

The idea was to have a competition where the highest sleep score (ZQ) wins. The ZQ isn't the same as "Sleep efficiency", it can be made higher by the length of time that you sleep. So my idea was to partially deprive myself of sleep for the two nights leading up to it and hope that I caught up on them for the night of the challenge.

I thought that I'd also help my chances by depriving myself of REM sleep during the time that I actually spent asleep, causing more REM to be necessary on the challenge night, hence a higher score because Zeo awards bonus points for REM and slow-wave sleep. In essence I was hoping to make use of "REM Rebound".

William Dement did this with students who volunteered in his early work in the lab. He used an EEG to determine when they were in REM sleep. As soon as he saw evidence of REM he woke them. Then let them go back to sleep until he saw another REM period. Needless to say this annoyed many of the volunteers, and some gave up.

How could I manage to do this without employing someone to watch over me?

There is an excellent piece of software called ZeoScope that has been written by a Zeo user, Dan.

It was designed to work with the Zeo Raw Data Library, so that it receives the data from the Zeo and displays it on a PC. He also added in a function where the software can sound an audio alert when you have been in a certain sleep phase for a given period of time.

The purpose of this is to use as a trigger for a lucid dream (a dream in which the dreamer knows that they are dreaming and can consciously control the dream as if they were both the author and main character of the story).

It works well for this, if you select a nice quiet tone, such as raindrops or a soft voice telling you that you are dreaming.

I found a loud alarm clock tone and set it to play after I had 2 minutes of REM. I chose the alarm clock sound because I didn’t want to have a sound that I would ignore and incorporate into the dream.

After a couple of hours things seemed okay and I’d only been woken a couple of times, but as the night wore on the sounds became more frequent and persistent until I got annoyed and chose to get up early.

It was like being ripped out of another world, only to realise that you are in your bed and flapping an arm around trying to silence a non-existent alarm clock!

If I nodded off again quickly then I went straight back into REM and was greeted by an alarm again, so I quickly worked out that it was better to make sure that I was fully awake before going back to sleep.

It got to the point that as the flashing colours and shapes of dozing (hypnagogia) began to form coherent images the alarm would sound. Once I began to lucidly dream and remember thinking "Oh, I'm somewhere new... anytime now it'll go off..." and it did.

It turned out to be pretty effective...

I only clocked up 20 minutes of REM compared to my usual 1 hour and 40 minutes – mission accomplished!

I attempted to deprive myself of REM for the following night. 

I slept for longer that night and ended up with 40 minutes of REM, still an hour short of my usual amount. So if the hour-for-an-hour payback idea is correct then I would owe 2:20h of REM, which means that on the night of the challenge, all being well I'd end up with 2:20h plus my normal amount of 1:40h giving a total of 4h REM.

...but it didn't work out that way. In fact I had to force myself to stay asleep. I did manage to sleep for nearly 13 hours, but as you can see from the graph it was mainly filled with the "padding" of light sleep (N1 and N2). 

Compared to the hospital-payback night shown above I slept for 3:30h more, but only achieved 4 minutes additional deep sleep and 14 minutes additional REM. No one can say that I didn't give my body a chance to catch up on it's life long debt, and it failed to even catch up on the REM that it lost during the preceding two days.

Where is my missing REM?

Will I ever get it back?

Surely I gave my body enough chance to catch up on some much needed REM? Why did it squander the chance by filling the night with light sleep (N1 & N2)?

William Dement suggests that payback occurs over the course of many nights. That fits with my "hospital debt" being largely paid back over two nights. He recommends a period of a few weeks where you have no obligation to stay up late, or be forced awake by an alarm clock. Then after paying back the debt, your sleep will normalise into a pattern that is right for you.

I am torn between the conventional wisdom and what I experience firsthand. Perhaps the only way to reconcile them is that my awakenings during REM are the problem.

I guess that I am trying both approaches: sorting out the cause of my REM interuptions and trying to schedule my day in a way that is more friendly towards sleep.

Maybe one day I'll have a week of solid REM.

Sleep Debt

Imagine that it's midnight: you are sound asleep and the alarm is set for 5:30am as usual.

A noise wakes you up! You sit bolt-upright in bed trying to work out what it was. Eventually you get up to have a look and can't find anything so you go back to bed.

You are no longer sleepy, in fact you are now lying awake looking at the numbers on the clock as they get ever closer to the time that the alarm is set for. You stare at the clock for a whole hour...

...then eventually drop off to sleep.

The alarm goes off and you get up feeling a little more groggy than usual.

What you didn't realise is that while you were staring at the clock, you were racking up debt - sleep debt.

You don’t need to try very hard to build up a sleep debt.

Imagine losing just an hour of sleep a night for a week, the odd late night here, early morning there etc – that would take nearly a whole night of its own to pay off, not to mention the 8 hours that you’d normally spend asleep on that night.

You've been deprived of seven hours of sleep, and your brain is not going to let you forget it! The debt is going to come looking for you when you least expect it. You might be watching the TV, or sitting at your desk, or worse - driving when it creeps up on you and demands that you pay it back!

…and pay it back you will. It has a long memory as far as sleep debt is concerned... or so the current thinking says.

In his book, “The Promise of Sleep”, Dr William Dement (the sleep pioneer who named the stages of sleep and conducted many groundbreaking experiments into sleep and sleep deprivation), states that as far as his experiments were concerned, the sleep debt was still valid for at least two weeks after it was racked up. That isn’t to say that after two weeks, the debt is forgotten, but just that experiments had only explored sleep-debt for two weeks.

But what does that actually mean in practice? Does it mean that you need an additional seven hours of sleep to rebalance things? To be honest, there is division about how much of the debt needs paying back, and it may well vary from person to person.

I decided to look at my own data to see if I could find any clues.

This is a night of my sleep while I was in hospital recently with my son. I had to wake up every two hours to perform a procedure. 

There are solid chunks of wakefulness throughout the night, along with a significant drop in REM.

I normally get around 1:40h of REM and 40m of deep sleep. It's interesting that although my REM suffered, my deep sleep didn't. This suggests that the brain values deep (slow wave) sleep more than REM, so it makes it a priority before it catches up on REM.

Then the following night we were able to have a lie in on the ward, during which we caught up and paid back some of the debt (resulting in more REM and a higher score). 

The bulk of the debt was paid back on the first night, although the debt continued to be paid back the following night too. 

This is easier to see with the following graph covering the two consecutive nights of sleep debt (the first of minor debt and the next of more significant debt shown above) along with the two nights of payback. 

Besides charting your sleep every night, there are other ways of measuring sleep debt. 

People get used to being tired in the day and consider it to be normal, so simply asking someone how tired they are is a little too subjective. The Epworth Sleepiness Scale was designed to be more objective.

You can take the short test here http://www.predictonline.com/epworth.htm

Most of us are familiar with the fact that if you are tired then you can pretty much drop off to sleep as soon as your head hits the pillow. The technical measure of the time it takes to get to sleep is called "Sleep Latency".

Sleep latency is actually a good marker of sleep debt - the quicker it takes for you to get to sleep, the greater your debt. Eventually the time to sleep onset reaches zero, then you have what is called a "sleep attack" - when the brain's desire for sleep is so great that it just blacks you out, even if just for a few moments. This can have disasterous effects, especially if you are driving at the time!

The brain is choosy about the currency that you use to pay back the debt. If you missed out on REM then it wants REM paid back (this is called REM-rebound). If you missed out on slow-wave sleep (deep) then it wants paying back in slow-wave sleep. 

This screenshot of the week leading up to (and including) the sleep debt shows how an unusually low amount of REM is caught up on:

I imagine that the brain would arrange the payback at the expense of the light sleep (N1 and N2) which largely appears to me to be "padding" to keep us asleep and out of trouble (evolutionary hang-up) or a vehicle necessary for the two types of restorative sleep: REM and SWS. I tend to think of this as a "more concentrated" form of sleep.

This is nicely shown by this graph of my REM for the above period, shown as a percentage of total sleep:

When the need arises, REM can form a larger part of total sleep, proving that it isn't accrued in relation to time spent asleep, that is to say that there isn't a formula that says "For every hour of sleep, 15 minutes of it will be REM".

So it seems unlikely that a total-sleep payback of an hour-for-an-hour of whole sleep is likely, although this may be true for REM and slow-wave sleep.

This all seems very well for small debts but it didn't seem to work for a larger debt...

Non-Invasive Ventilation

I could rehash the many excellent write-ups of non-invasive ventilation (NIV) that already exist on the internet, but I thought it would be more personal for me to tell how my son came to use it, explaining NIV along the way...

Bear in mind that these events took place over a period of 10 years and involved many medical professionals from various hospitals and clinics, although it may read as if it took just a few nights. 

A person's breathing might not be enough to sustain them for various reasons including:

• Illness (short term or long term)
• Injury (critical phases)
• Neuro-muscular issues

Sometimes a person will need respiratory support during these times. Sometimes it can be for a short while whilst in intensive-care or a high-dependency unit, other times it can be a life-long need, in which case they will likely have to have a tracheostomy tube fitted in order to leave their face free and unobstructed.

There are also people who only need respiratory support whilst they are asleep.

Due to changes in our respiratory drive and how our muscles respond during sleep our breathing undergoes many changes, this can even vary depending on the stage of sleep we are in. 

The following graphs contain information about how much air I was breathing per minute during the various stages of sleep (as scored by Zeo)...

I won't go into great detail about the why here, instead I want to concentrate on what can be done about the problems that these changes can cause.

At the time of writing, there is a good Wikipedia article about these changes entitled "Sleep & Breathing" 

When he was first paralysed, my son was on full time ventilation. This was considered to be a long-term and possibly a life-long situation and he was give a tracheostomy tube (a tube inserted through an opening in the neck and directly into the windpipe) to allow the ventilator to be connected to him.

10 years on, he is still paralysed but fortunately after several months of being in hospital the tracheostomy tube was able to be removed because the higher part of his spine had partially recovered. He had been slowly weaned off ventilation.

After the tube was removed his oxygen levels were continuously monitored and it was discovered that his oxygen saturations plummetted when he was asleep, but they always picked up again. We left hospital with a pulse-oximeter (a device that monitors pulse rate and blood oxygen saturations via a finger probe).

On some occasions his levels dropped as low as 65% (Generally speaking most people maintain a level of >92%). It was this that prompted me to buy the equipment to record his oxygen saturations so that I could show the relevant doctors involved in his care. Although, not a chart of the lowest that he dropped, this is a chart from early on (right) that is a good guide to what used to happen.

Each row is 4 hours of data (grey parts are when the machine was not monitoring due to him being awake).

Red = heart rate (bpm). Green = oxygen saturations (%) 

 

Left: How the chart should appear (taken from a fairly recent night when he was breathing oxygen via a mask)

 Right: His chart from a typical night

So why not just use oxygen, if it makes the graph all straight and pretty?

Well, oxygen is only one of the gasses involved in breathing, granted it's an important one, but Carbon Dioxide is also involved.

At school we were all taught that we breathe in air, use the oxygen then exhale carbon dioxide, but the carbon dioxide actually serves a purpose. It is used as a trigger to breathe. When the levels rise to a certain level, we breathe to remove the CO2.

If the "sense and control" mechanism in the brain is damaged, or if the muscles are not able to respond to its signal to breathe, then CO2 can build up in a condition known as hypercapnia.

That is what was going on while my son was using oxygen. We were able to see this by the use of a split cannula. It looks like a standard nasal cannula for oxygen delivery, but the tube to one nostril is used to deliver oxygen whilst the other is used to monitor the CO2 using an end-tidal CO2 monitor / Capnograph.

High CO2 can lead to other health issues, and it actually affects the Ph of your blood.

So my son was trialed on a type of ventilation known as Continuous Positive Airway Pressure (CPAP). This involves a constant pressure of air being delivered into your nose (or nose and mouth) via a mask. 

If you ask a child to blow a balloon up, then they will probably struggle, but if you "do the tricky bit" and start it off for them then they will probably be able to top up what you've started and finish inflating the balloon.

That's essentially the idea of CPAP. The airways are kept open by the pressure, leaving the user the task of inflating their lungs.

CPAP can be a great help when people suffer from Obstructive Sleep Apnoea. It can prevent the airway closing off, thus allowing the sleeper to breathe normally.

However, CPAP wasn't preventing my son's apnoeas.

This could have been because he needed much higher pressures, or because the apnoeas were "central" and not "obstructive" in nature.

A central apnoea is where the brain doesn't tell the sleeper to breathe.

Fortunately, the CPAP machine records the overnight data to an SD Card and can decide whether the apnoeas are obstructive (airway closed) or central (airway open but no flow).

It showed that he had mainly obstructive apnoeas with hypopneas, but also the odd central apneoa, along with many apnoeas tagged as "unknown".

The night above shows them towards the end of the night. This didn't fit with the pattern of oxygen desaturation that we saw begin around an hour after sleep onset, even whilst on CPAP, hence we weren't sure how much to trust the detected central apnoeas as they seemed few and far between. However, if someone has both obstructive and central apnoeas, CPAP can reveal those central ones after it has removed the clutter of obstructive apnoeas. 

The CPAP that he was prescribed was "Auto-titrating CPAP" this means that the machine decides which pressures are needed. You can see this in the graph above (the pressure line varies throughout the night). Intriguingly, the when the pressure is the highest there are no apnoeas, but he still desaturated.

The auto-pressure function can be set to choose between limits, or forced to give a constant set pressure. After many nights of alarms. We obtained a chart from a night at 6cmH20 (left) and a night at 15cmH20 (right) to see what was going on.

 6cmH20 had little effect. 15cmH20 was better, but still unacceptable and uncomfortable for him.

He would wake in the middle of the night and not be able to call out due to the mask over his nose and mouth. His heart rate would then increase and his alarm sound to alert me. I'd have to turn the CPAP off and it would have to be re-ramped again (start at a low pressure and build up over time, hoping that he was asleep before it delivered high pressure again). 

Because his blood-oxygen only dropped at certain times of the night rather than be low ALL night it was suspected that it had something to do with a particular stage of sleep. Below is a picture of a normal hypnogram (a graph detailing the stages of sleep, as shown on the Zeo entry of this blog) overlaid with a graph of his oxygen levels from one night.

Seeing this was a goosebump moment...

The pattern of his oxygen desaturations matched up really well with a standard hypnogram, so it was pretty certain that his condition was REM related. However, this wasn't a graph of his REM.  A way of working out and recording when he was in REM was needed.

New equipment was also needed...

Due to the possible presence of central apnoeas, it seemed unlikely that CPAP was going to be an effective solution, afterall there is little point in keeping the airway open if the brain isn't initiating a breath (or the muscles aren't able to respond to the signal to breathe). It was suspected that he would need Bi-level ventilation. Well known brand names for this are BiPAP and VPAP.

These are both Bi-level Positive Airway Pressure devices. Bi-level delivers two alternating pressures. The higher one is the IPAP (Inspiratory Positive Airway Pressure) and the lower one is the EPAP (Expiratory Positive Airway Pressure). The IPAP is essentially the breath, while the EPAP is the amount of pressure required in order to keep the airway open. Usually the breaths are triggered by the sleeper's breathing efforts, but to cover the possibility that he did indeed also have central apnoeas we used a BiPAP machine that could also be set to deliver "backup breaths" if my son didn't breathe a certain number of times a minute.

The CPAP / BiPAP was delivered via nasal pillows. These are fantastic as they allow the user to speak whilst using them. However, this left us with no way of being able to reliably monitor his CO2 using a capnograph.

CO2 monitoring is essential, without this it would be too easy to adjust the ventilator so that there were no oxygen desaturations, but actually be hyperventilating him, or worse causing trauma to his lungs and airways; so unless we could find a way to reliably monitor his CO2 we couldn't go any further. A different type of CO2 monitor was bought in...  A transcutaneous CO2 monitor.

The transcutaneous CO2 monitor gathers its data by way of a probe that is attached to the skin of the chest or arm. It then heats up the skin and evaluates the gasses given off. The probe needs to be removed after several hours and placed on a new site in order to reduce the risk of probe burns to the skin.

The titration process wasn't a one night affair, so we had the luxury of being able to record readings at home between appointments. However, at home we didn't have an EEG machine to record brainwave data, so we couldn't tell what stage of sleep he was in.

We needed to see when (and if) he achieved REM sleep while his settings were adjusted over the course of several nights. We also needed to make sure that the pressures weren't waking him up. Afterall, if he didn't have much REM (or his REM was disturbed) then his oxygen levels would look good and give the false impression that the settings were working. The Zeo was perfect for this.

This graph is from one of the first nights of BiPAP (when the settings were good but not optimal) and it shows a great correlation between his oxygen desaturations and Zeo's calculations of REM sleep. (The dips in the green oxygen line are a near perfect match for the green chunks of REM from Zeo), as are the rises in pulse rate and CO2.

This gave me a lot of confidence in the Zeo's decisions as REM is probably the hardest state to detect due to its similarity to being awake. In fact I'd even feel confident enough to say that the piece of missing data from the Zeo (headband was too loose) would have shown REM.

The result of a few nights adjustments during REM was that BiPAP at the correct pressures eliminated his oxygen desaturations completely and allowed him (and me) to sleep all through the night for the first time in a very long time.

It turned out that obtaining a machine that could provide additional "backup" breaths was a good investment... Pressures alone weren't enough to prevent his oxygen levels dropping, so a backup-rate was set of 13 breaths per minute.

This meant that if he didn't breathe 13 times a minute of his own accord, that the machine would make up the number of breaths. 

 

The graph on the left is with BiPAP pressures set to 18/10. This was fine for his oxygen requirements, but it still was uncomfortable for him (but tolerable). The high EPAP of 10cmH20 made it hard for him to exhale (remember that he has neuro-muscular issues).

The pressures were re-titrated but this time with a lower EPAP. This seems essential for him to be able to exhale effectively, and provides a more comfortable night.

These settings will be reviewed periodically by the medical professionals that have been involved in his care to see if they are still optimal.

He now loves the BiPAP machine and doesn't like sleeping without it, he doesn't sleep in until noon at the weekends, he doesn't fall asleep at school and can stay awake until long into the evening. He also has a ZQ of 137 which he likes to use to mock my awful average ZQ of 68.