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.

Circadian Rhythms & Temperature

Due to a bit of an erratic week, I haven't been able to reliably measure (and experiment with) my apnoeas, so instead this was going to be a blog post about "Circadian Rhythms" (the daily sleep/wake cycle).

Given that we inhabit a planet with a 24 hour day, it is no surprise that our bodies have become roughly linked with the day/night cycle, with various hormones being released at certain stages in the rhythm enticing us to sleep or wake.  

               (Combined photos from my Sky-Watcher and solar telescopes)        

Not everyone's rhythm is the same, some people have theirs shifted (such as when you are jet lagged). Even a skew of an hour or two can make a huge difference to how easily you are able to wake up for work in the morning, or how late you can stay awake.

There are a couple of online questionnaires to help you determine your own circadian rhythm:

http://www.philips.co.uk/c/circadian/178344/cat/
http://www.bbc.co.uk/science/humanbody/sleep/crt/

Both of these decided that my rhythm was skewed, so I decided to make my own measurements and chart them here but after seeing the first 24 hours of data, something interesting emerged...

This is a normal circadian rhythm taken from the Philips website. 

In fact, this is a simplified rhythm, because it is normal to have a small dip in the energy levels around mid afternoon, hence the reason for many countries having an afternoon siesta, and the reason why we tend to slump at our desks in the mid afternoon and reach for a cup of coffee.

This dip can be seen in my graph from the BBC circadian test.

Core body temperature is a good way of charting your own rhythm because energy levels are reflected by our temperature. Our body temperature is not a static 37.5 C, in fact it fluctuates throughout the day inline with our circadian rhythm. Of course, it is also affected by ambient temperature and how active we are.

So, all it would take to chart my own rhythm would be a decent thermometer.

I decided to get a data-logging thermometer, so that I could see what was happening while I was asleep.

I ordered a thermometer capable of recording every 10 seconds (to weed out anomalous readings), and was expecting the probe to be a small thermocouple-type sensor that I could stick to the skin under my arm, but the probe was more like a bullet and wasn't adhesive plus the logger turned out to be a lot bigger than it looked in the photo!

I'd gone this far, so in the name of science, I shaved under my arm and fixed the probe there with Melonin (low adhesive dressing) and Tegaderm (a clear waterproof adhesive dressing). I then wedged the cables into my suit and went off to work.

After 24 hours (and a few weird looks) I downloaded the data to a computer. I noticed that generally the pattern was the same as that belonging to "normal" people, but that it had a few fairly severe drops in temp during the night.

I repeated this over several days.

On the graph below, the dip is around 1:30pm and again at 4:00pm. I suspect the 1:30pm dip is my normal afternoon energy dip whilst the 4:00pm dip is environmental because I was working outside at 4:00pm. 

I repeated this the following day and the dip was much more pronounced again early at around noon, but I ended the recording early as it was becoming awkward to carry the data-logger around with me, so I can't show a full 48 hour graph.

It's also interesting that the temperature drops around 8pm. That's pretty much when I start to look forward to sleep! It plateaus at 10pm for a couple of hours in a similar way to the one produced by my answers to the BBC link. This may have been because I was already asleep by then!

The first 24 hours...

Those drops in temperature during sleep are severe. When I first saw them, I suspected that they were erroneous readings, but the probe was stuck so tightly to me that there was no way that these were due to poor contact (after all, if that were the case, why didn't this happen during the day when there was more movement?). However, as the data rate on the logger was so high (240 recordings an hour), these were clearly not erroneous as they slowly crept back up to the plateau level of around 36.5°C.

I wasn't happy with this result, so I repeated it the following night. The drops in temperature were still there.

On the second night, to eliminate the possibility that these variations were due to environmental changes, my room temperature was monitored with another probe, and it was a surprisingly constant 18°C  for most of the night, so there were no corresponding dips in room temperature. I don't like my bedroom to be too warm so I switch the heating off at night.

I took a look at my sleep-stage data using the Zeo, and was surprised that the seemingly random falls in temperature coincided with awakenings from REM! (Shown as orange "wake periods" on the coloured graph, but as REM/Wake on the detailed graph. Light green = REM, Dark green = slow wave sleep, grey - stage 1 & 2 sleep. For the sake of simplicity I won't show the detailed graph, but you can see one on the blog post "My Baseline AHI").

So what's going on?

Along with the muscle paralysis that comes with REM sleep (to stop us acting out our dreams), there is also a decrease in the body's ability to regulate its temperature (thermoregulation). 

So, it seems that my temperature was dropping, causing me to wake in order to regulate my temperature, pretty much in the same way that my apnoeas cause me to wake during REM.

If this is true then it means that in order to be able to stay asleep during REM I now have two issues to deal with: apnoeas AND temperature!

During REM this decrease in ability to regulate our temperature causes us to be largely "Poikilothermic" (meaning that our temperature is governed by the temperature of our environment). So the key to eliminating this issue is to regulate the temperature of my bedroom better.

I repeated this for two more days, and then concentrated on the nights and gathered more data (total of 5 nights). It seems that these overnight drops in temperature aren't always correlated with REM sleep (sometimes they are just before and sometimes just after), so until my more accurate thermometer arrives, I decided to calculate the mean temperature from the week's recordings to get a better idea of my rhythm and to try to eliminate the overnight drops.

This gives a much nicer picture and goes some way to reducing the environmental effects. The data fits well with how I feel throughout the day. I tend to get a bit tired at 1pm, then start considering bed around 8-9pm.

Compared to the BBC graph, it lines up fairly well, although my "energy drop" happens earlier in the day at a more accurate time.

I'm not comfortable with this experiment as there is much that could be improved on:  

• Better temperature sensor (on it's way)
• Eliminate environmental temperature effects (maybe on a day where I stay at home)
• I still am not convinced whether these changes in temperature are an effect of activity. After all, it stands to reason that when we are more active our bodies produce more heat, so it would be interesting to do this on a day where I forced myself to do nothing, stayed at home and forced myself to stay awake past my usual bedtime, that way I could see whether these changes are still evident on the graph. That said, some of the nights were recorded with an 11pm bedtime although my temperature still dropped as usual around 8pm, so it could be accurate.

One thing that it has shown me is that it is essential to have your sleeping environment just right for you...

A good sleep routine involves making sure that your bedroom is the right temperature. It should be cool but not cold. In days gone by, the outside temperature dropping in the evening acted as a cue for our ancestors' bodies to sleep. Of course, in days where our homes are heated, this confuses the body and can lead to poor sleep.

The same is true with light. Nowadays we have artificial light filling our homes and offices, and that also interferes with our sleep/wake cycle as we don't receive the nighttime cues.

So sunlight during the day and a cool, dark bedroom goes some way to remedying this.

Update on Friday, December 9, 2011 at 8:46AM by Hypnagogia Blog

My new monitor arrived. It's able to record temperature, blood pressure, ecg trace, heart rate and oxygen saturations together.

I still saw temperature drops, and they still correlate with REM sleep.

The following screenshot (combined with the Zeo hypnogrm) shows the temperature drop along with changes in heart-rate during a REM period.

Key

Zeo hypnogram
Oxygen saturations
Pulse rate
 Temperature

What is an "Apnoea"?

If you search for "Apnoea" on Google, you will probably be given results for "Apnea" - it's the same thing but with an American spelling.

Quite simply, an apnoea is a pause in breathing.

There are different types and causes of apnoea, and in the last 10 years one type: "Obstructive Sleep Apnoea " has taken centre-stage. According to a recent tweet by @RespironicsUK it has gone from being not really recognised to a "huge epidemic".

Obstructive Sleep Apnoea occurs when the muscles of the throat relax in sleep, effectively closing the airway off and preventing breathing. This is despite the breathing muscles of the chest and diaphragm still moving. It's akin to trying to breathe with your mouth closed whilst someone is pinching your nose.

This is a graph of an apnoea. The blue line is the airflow (breaths). The highlighted portion shows anpnoea.

The purple line is the heartrate. The red is the oxygen levels.

The oxygen doesn't drop instantly (after all, we can hold our breaths for a fair while before we gasp for air), but when it does drop it drops rapidly past a certain point due to the oxygen desaturation curve (the graph looks a little like a slide in that you can shuffle along the top descending slowly but when you reach the tipping point you shoot down fast).

So, the blood oxygen levels fall (while the CO2 levels rise - not graphed). This causes the brain to briefly wake the sleeper so that they breathe normally. Sometimes they wake up with a snort, or a choking feeling.

So, they wake up and problem solved?

Not really.

Waking up deals with the immediate issue of low oxygen and high CO2, but this can happen hundreds of times a night, often without the sleeper realising it. In the morning they wake feeling groggy and tired because they have been deprived of sleep.

During sleep monitoring the number of apnoeas and hypopneas is recorded and converted into an hourly rate known as the AHI - Apnoea Hypopnea Index. 

A low AHI (under 5) is considered acceptable unless the sleeper is experiencing problems. but with a high AHI the sufferer isn't just "a bit tired" they are sleep-deprived and have to deal with the effects of that:

• making mistakes 
• napping
• falling asleep at inappropriate times
• depression
• heart problems
• stroke
• headaches
• weight gain

Obstructive sleep apnoea can be made worse by alcohol (it relaxes the throat muscles more) and by being overweight (because the increased mass around the neck adds to the burden). By losing weight and reducing alcohol consumption it is (in some cases) possible to eliminate the problem.

There are treatments available ranging from lifestyle changes to surgery. A common solution is a CPAP machine that keeps your airways open during sleep by maintaining a constant pressure of air in your airways via a face mask. 

Treatments  will be the subject of a later post. For now I just wanted to make a start.