Entries in Black Shadow (4)


Snoring Remedies? Introduction and Positional Therapy Results

Snoring occurs when the tissues of the airways relax during sleep causing the air to vibrate as it passes over them, in a similar way that deflating a balloon causes the balloon's neck to vibrate and make that familiar raspberry sound.

This can be illustrated by the following airflow waveform taken from my snoring using Stowood's Black Shadow Sleep Monitor.

What should have been nice smooth breaths like these... 


...ended up becoming jagged saw-toothed breaths like these...


...resulting in a rasping snore.

To give you an idea of what the Visi-Download software allows me to see (and how the vibrations above actually sound) I've made a short video of a few snores that I recorded on one of my baseline nights:

Snoring can simply be just that - a noise, it can be a nuisance if it's too loud as it can wake others in the house, if it's loud enough it can actually wake the sleeper! However, it can also be much more than just a noise. Besides being the cause of much nocturnal anger and maybe even the cause of a relationship breakdown, it can also be a sign of a greater health issue such as sleep apnoea.

I snore. In fact my snoring is sometimes so loud that I hear it in my dreams.

If only that were as as serious as it got, but my snoring is actually due to sleep apnoea. As documented in many posts on this blog, I have mild sleep apnoea.

I've found some ways to bring the apnoea to acceptable levels with a typical AHI of between 1 and 3, (an AHI of under 5 is considered normal if it doesn't cause symptoms such as daytime tiredness etc). The way that I did this was to keep off my back when I slept by using a Rematee belt. This also had a knock-on effect of reducing my snoring, but not eliminating it.

On the nights that I've recorded while using the Rematee to keep me off my back, my AHI has been stable and my snoring has reduced (the residual respiratory events are mainly hypopneas, although the lowest that my oxygen saturations drop to has improved, it still drops to around 79%).

Besides looking for other ways to bring my AHI down even more, I want to go further and eliminate my snoring. I guess that my long term quest is to see if it's possible to have the much hyped perfect night's sleep.

Many snoring remedies (and there are many) say that they are not suitable for snoring that is caused by sleep apnoea, so with my new found side-sleeping "normal" AHI and some residual snoring I now find myself in a good position to put them to the test.

Quantifying Snoring 

The problem is that snoring is hard to quantify. Yes, you could ask a partner, but that answer would be fairly subjective. You could judge by how you felt in the morning, but again that is subjective. You could even place a Dictaphone beside the bed to record your snoring but besides but again, how do you score the recording?

One of the channels that Stowood's Black Shadow sleep monitor measures is snoring, and it does this via a calibrated microphone, allowing you to quantify how loud each snore actually is. It also derives a second channel from the sound to identify individual snores, thereby allowing you to actually have a snore-count. From there it calculates a snore-index (a number of snores per hour, grouped according to volume).

So, my method is this:

By keeping off my back I am essentially apnoea-free, leaving only the snoring to be addressed, so to ensure this and to eliminate the effects of a variable sleep position on my snoring (and to bring my AHI to normal), I'll be wearing the Rematee belt whilst putting a different snoring remedy to the test each night hoping to eliminate my remaining snoring.

I'll record sleep data for three nights per selected remedy and calculate the mean snoring profile for each by graphing each remedy according to:

  • Hourly snores between 55db and 65db
  • Hourly snores between 65db and 75db
  • Hourly snores greater than 75db 

This "Snore Profile" will not only allow me to see if the total snores have been reduced, but it will allow me to see if the remaining snores are quieter.

This graph shows the mean snore profile for my Supine Baseline, Free-to-Move Baseline (calculated from the same nights), and my Rematee baseline. 

The majority of my snores are louder than 75db regardless of whether I sleep on my side, back or am free to move around! Not unexpectedly then, it follows that the next largest chunk of my snoring falls between 65 and 75 db with hardly any under 65db.


The "Remedies"

There are plenty of "remedies" available. Some of these are traditional remedies (using the term loosely), and some are more modern commercially available remedies.

It's clear to see the positive effect that side-sleeping has on reducing my snoring. It reduces my snoring by over 50%, so it is likely that this in itself will be a clear leader in the remedy league table. I suspect that for many snorers (where their snoring is not caused by apnoea) that the Rematee and side-sleeping could eliminate snoring completely.

  • Mandibular Advancement Devices
  • Nasal dilation
  • Snore Spray
  • Humidifier by the bedside
  • Anti-Snore Ring (Acupressure)
  • Anti Snore strip (on roof of mouth)
  • Drinking a glass of water before bed
  • A night time garlic gargle
  • Toothpaste under the nose
  • Electric snore-shocker devices
  • Nasal irrigation

 I also want to explore the following to see if they have an effect on my snoring.

  • 5-HTP
  • Melatonin
  • L-Tryptophan
  • Blood sugar levels
  • Large dose of vitamin B6

I'll pick from this list (avoiding some completely) and put them to the test for three nights to get a mean snoring value. To avoid creating a very long post I intend to create a separate post introducing each remedy (and how well it performed). When I've finished I'll then chart the results together. 

Besides bringing my AHI to an acceptable level to address the residual snoring, part of the reason for staying on my side for the entire night is that it will allow a fair comparison of snoring in all sleep stages (I typically spend around 2h10 minutes in REM and 45 minutes in Slow Wave Sleep). I'll also be keeping an eye on my Zeo stats to see if any of the methods have an effect on my sleep composition. I expect that the methods that rely on disturbing you during snoring episodes may have a negative effect on REM or Slow Wave Sleep.


Sleep Paralysis as a Result of Nocturnal Disturbances and Respiratory Events?

A few years ago I had three instances of sleep paralysis in the same night, leading to finally meeting "The Stranger In The Room". Since then I haven't been afraid of sleep paralysis, in fact I've welcomed it as it's a fairly easy way to initiate a lucid dream.

The other night I experienced sleep paralysis which progressed to an Out of Body Experience (OOBE) then to a Lucid Dream, and it's given me more of an insight into a possible mechanism, which seems to fit with the episode that occurred a few years ago, only this time I was wearing 2 sleep monitors so I've been able to "capture" some elements of it and piece together my theory of the events.

This has led me to realise that there are common factors in the events leading up to sleep paralysis and the subsequent spontaneous lucidity.


I'll begin by describing what happened several years ago. I'm well aware that it didn't happen literally, but bear with me as I think it's best to describe it as it appeared before taking it apart scientifically. I've put the account in a quote-box, so if you really can't bear hearing other people's dreams you can easily skip over it...


I briefly mentioned in this post that as far as getting over the fear of sleep paralysis goes, the turning point for me was a night several years ago when my son had a chest infection causing his nocturnal oxygen levels to drop lower and more frequently than usual meaning that I had to carry out assisted coughing and nasal suction several times. Needless to say our night was very disturbed and we were both very tired. This was the second such night in a row.

On three occasions when I returned to my bed I suffered from sleep paralysis. It was something that I'd grown used to because it had been occurring roughly once every couple of months from the age of around 13.

I'd be laying in bed listening out for his oximeter alarm, then I'd get the familiar whistle in my ears, a crackling noise, then my body would feel crushed and each muscle would feel as if someone had deflated it squashing me further into the bed. Then the familiar (but still frightening) feeling of someone watching me as I lay there struggling trying to talk but only managing a throaty "uugh" noise.

By the third time I almost found it funny (maybe because it had never happened to me so frequently, so this time it felt familiar, almost to the point that I knew I was safe). I kept telling myself that my body was effectively asleep. "Okay, so my body is asleep but somehow I (whatever makes me me) is awake, so that 'me' is going to get up".

"I" then rose above my sleeping self about a foot or two, rolled left (now facing the wall), then floated to the foot of the bed and ended up standing on the floor looking back at my sleeping-self.

This all seemed normal at the time. 

It was then that I could finally see the person that had been watching me. He was standing next to me at the foot of the bed. He stepped aside, smiled and gestured towards the mirror at the end of my bed. Then I passed through the mirror, through the wardrobe and then through the wall into my son's room next door. A few moments later I was back in my bed, awake and able to move.

The feeling was incredible, even if it did leave me a bit confused as to whether I was really awake this time. From that moment on I have not been afraid of sleep paralysis.

Now here's a brief account of the episode I had the other night, then I'll draw some parallels between the two nights...

I'd had little sleep the previous night as I had to be awake around 3am for a journey to Manchester. When I got home I was tired, so after dinner I made a point of not staying up late (bed by 9pm). Keen to carry on my experiments with 5-HTP I took 200mg of 5-HTP, connected some channels of the Black Shadow sleep monitor (SPO2, Pulse, Airflow, Body Movement and Sound), put the Zeo headband on, started to record the raw Zeo data with ZeoScope and went to sleep. I was also wearing the Rematee belt (as is normal for me now).

I was asleep within 6 minutes (a fair indicator of sleep-debt). Another indicator of sleep-debt is the fact that I was briefly in REM sleep within 9 minutes of getting into bed!

At 4:02am (I know this from the raw data) I was woken from REM by a noise near my bedroom window. I woke suddenly thinking that I had an intruder. I shuffled round the bed a bit listening for more noises and then lay there replaying the noise in my head trying to make it fit with a known noise. At the time I also considered that it was a hypnagogic noise. It was a multiple banging noise, and I imagined it was probably a picture falling off the wall and bouncing on the wooden floor.

I'd spent around 10 minutes trying to work out a cause of the noise as I dozed in and out of sleep, then the familiar whistling noise of Sleep Paralysis stirred me. I got excited and tried to turn it into an OOBE by pushing "myself" from my head, but that just stopped the noise so I stopped too. Then the whistling returned and I tried rolling "myself" out of my body. It worked, I sat on the edge of the bed and felt sad that I'd actually woken myself up. It turned out to be a false-awakening because I then floated to the end of the bed, realised that I was still dreaming, and from that moment on was in a lucid dream (albeit of the out-of-body variety).

I went to my bedroom door, floated out into the hallway (something I've never been able to do before as doors usually take me to the wrong place).

It was dark, so I put my hand into the adjacent room and tried to put the light on except there wasn't a switch, just a lump of plastic. Again, this prompted me to stay lucid. So I went to the front door (in search of the cause of the noise). As I got to the front door I hesitated because I really wanted the door to take me outside and I was afraid that it would take me to the wrong place (despite the earlier door working correctly), so I "poured" myself through the letterbox and ended up outside on the driveway.

It was still dark outside, and I had trouble seeing, I imagined that this was because I knew that my eyes were shut because I was asleep, so I took my dream-hands and prised open my dream-eyelids in a way that only someone who has ever had conjunctivitis will know. Then it became daylight.

On my driveway was a postman in a bright red fleece. Instantly I was standing next to him and he acknowledged me. I was confused because I knew that this was a dream so expected that I was ghost-like and he wouldn't be able to see me. (I didn't realise it at the time but I was losing lucidity and becoming the observer of the dream again rather than the creator).

The postman apologised for the noise and said that he'd been trying to get a large parcel through the tiny letterbox.

I thanked him, took the parcel and opened my front-door, only to find myself back in bed and waking up.

I then pressed then event-marker on the Black Shadow Monitor and recorded what I remembered of the dream before getting out of bed.  

There are a few key similarities that I think are worthwhile extracting from these accounts, and some I've only become aware of in light of the lucid-dream I had the other night.

  • Sleep debt from previous night
  • Disturbed Sleep that night
  • Waking and being fully alert during the night before returning to bed
  • Remaining alert for an anticipated noise
  • Sleep Paralysis leading to a dream which became lucid ending with me going off in search of the source of the noise.

In the morning I was keen to playback the audio recording of the night's sleep to see if the sound was real, or hypnagogic in nature. I also wanted to see what the various monitors managed to show of this experience.

It turned out the sound was real and the Black Shadow's microphone was sensitive enough to capture it. It was possible to hear a car driving past the house (causing me to stir) followed 6 seconds later by the sound that I heard: it sounded like a rat-a-tat-tat on the letterbox but I still couldn't identify the noise.

The first sound is much clearer through headphones or good speakers.


The next morning when I went to my car I found the cause of the noise. The passing car had lost a plastic hubcap which had hit the front of my house (my bedroom wall) and spun on the concrete before settling down, in a similar way to a spinning coin running out of energy on a tabletop.

Looking at the graphs from the Black Shadow and the Zeo, it became fairly clear that this wasn't the trigger for the dream, but it was a very important factor because it caused me to wake up fully. I was very alert as I listened out for the cause of the noise, I was anxious and to be honest a little afraid. This likely put me in a state of heightened awareness and self-consciousness, which on some level carried over for the next few minutes into the dream.

I've annotated the 30 minutes covering the noise and finally waking from the lucid dream (click for a larger version).

The raw single-channel EEG data is displayed at the top. I've selected the point that I first woke after hearing the noise. This section aligns with the marker in the brainwave frequency lines (coloured as indicated by the key). 

The hypopneas were the likely cause of the sleep paralysis. I suspect the third one was the trigger as body movement is shown after the first and second along with the noise of bedclothes moving, so sleep paralysis had not set in by then.

I suspect the evening went something like this:

  1. Initial car and hubcap noise occurred
  2. I woke suddenly causing a rise in delta wave "noise" as I moved.
  3. My heartrate more than doubled to 101 bpm (startled and fear) (in line with the delta increase)
  4. I lay in bed listening for further sounds until...
  5. I drifted to sleep and quickly went into REM
  6. My respiratory issues are exacerbated by REM so hypopneas followed (yellow blocks)
  7. I had micro-awakenings due to the hypopneas (shown by the blue blocks and reduced pleth)
  8. Due to my heightened state I failed to go back into normal REM and became aware that I was asleep.
  9. Possibly the final hypopnea ended the dream.
  10. I laid still for a few moments before dictating the contents of the dream into the microphone

So I suspect that to reliably induce sleep paralysis and/or lucid dreaming two factors are required;

  1. True wakefulness in the night, not just snoozing a 4am alarm
  2. A cause of micro-arousals / micro-awakenings.


Wild speculation...

I was hoping for a clear indication of something on the EEG and frequency tracings.

The brainwave frequency analysis in more detail with the purple section believed to be the dream.

If I had to be pushed to look for a trend then I'd say that there was a slight increase in Alpha waves (blue) during the time identified as the dream-period also becoming nearly equal to the Theta wave activity (green) at one point, which declines as I wake, but that is possibly stretching things too far at the moment. However, this overlapping (or meeting) of Theta and Alpha occurs in other places in my sleep (and wake) without any memory of lucidity, so I imagine that finding a simple pattern from a single EEG site is unlikely as things are likely a lot more complicated than that.

For the future

I hope to record the events surrounding more sleep paralysis / lucid dreaming episodes and document any trends that arise rather than just basing my hypothesis on one night.

I'd like to learn to signal to the Zeo that I'm dreaming using eye movements, so that I can further pinpoint when lucidity occurs. Maybe this signal could be on a regular basis (or as regular as the dream permits) to help pinpoint when lucidity begins and ends and normal dreams take over.


The Stranger in the Room / The Presence / The Dweller on the Threshold / Guardian of the Threshold in literature, religion and folklore

Sleep paralysis and psychopathology - Mume & Ikem "Sleep paralysis occurs frequently after arousal from REM sleep""


Sleeping Position - Supine AHI: A Baseline Measurement

Looking at my previous data for my 5-day mean AHI, you can see some variation on the day-by-day AHI measurements. 

It makes sense that each night will be slightly different but I still wanted to identify and eliminate some of these variables. Now that I know that my sleep-apnoea is positional (mainly when supine) I can attribute some of the night-by-night changes to my sleeping position.

Using the Black Shadow sleep monitor, I am able to automatically record my body position during the night. This is a recording of my sleep position for a single night.


 AHI = 9.30

As you can see from the above chart I spent a fair chunk of the night on either my right or left side. Those short spells on my back are when my sleep apnoea kicks in (or the snoring is so loud that it wakes me up). The reason that they are only short spells is that the apnoeas briefly wake me causing me to move onto my side for an hour or so before ending up on my back again (and beginning the cycle again). Towards the end of the sleep I remained on my back despite the apnoeas causing repeated micro awakenings (micro-arousals).

Prior to having access to accurate sleep position data I was aware that sleeping position (and other variables) could affect my AHI, so in my previous experiments I tried to eliminate its effects by recording 5 consecutive nights and calculating a mean AHI. Solely recording one night could have given a falsely low AHI because if by sheer chance I managed to spend the majority of the night on my side then my AHI would have been lower. This lower AHI would actually be masking my problem.

A recent paper by Sunnergren, Broström & Svanborg shows that "Position–dependent obstructive sleep apnea (POSA) was common both in subjects that by American Academy of Sleep Medicine classification had obstructive sleep apnea as well as those without. The severity of obstructive sleep apnea, as defined by American Academy of Sleep Medicine, could be dependent on supine time in a substantial amount of subjects".

This hints that people are slipping through the net and missing out on a diagnosis and treatment. 

It is for this reason that a sleep-study conducted in a sleep-lab or a hospital tries to have at least part of the night recorded with the patient sleeping on their back (and with some REM sleep too).

The Visi-Download software allows me to include/exclude portions of the night based upon custom criteria, so I manually selected only the times that I slept on my back and re-ran the analysis.

Using this method, my Supine AHI for the 9.30 night shown above was actually 12.73, for which I snored at a level of above 55db for 95.5% of the time! For the record, my lowest oxygen desaturation took me to 79%.

Using this method, my supine AHI is more stable, (although not completely the same every night) this demonstrates that this is actually a more consistent method of calculating my night-time AHI, although for others with non positional apnoea it may well be a different story.

I plan to carry out some further monitoring without the Rematee, so this is the method I will use to ensure a fairer compaison between nights.


Black Shadow: A Multi-Channel Sleep Study Device


In my experiments so far I've only looked at a few "channels" of data such as airflow, blood oxygen levels and sleep stage, but when you have a full sleep study in a hospital or sleep-lab many more channels are monitored, all of which provide insights into the cause of your sleep problem.


I've recently been using a hospital-grade multi-channel sleep study device that is new to the market. It's designed to be used at home or in a sleep lab / hospital. I've been using it at home. It's called the Black Shadow and it's made here in the UK by Stowood Scientific Instruments.



The Black Shadow is capable of monitoring:

  • Nasal Airflow (via a nasal cannula)
  • Oral & Nasal Airflow (via a thermal sensor)
  • Respiratory effort (ie breathing movements) (via 2 inductance belts)
  • Pulse oximetry
  • Pulse rate (via pulse oximetry)
  • Plethysmograph (pulse profile)
  • Sound recording and snore detection (from a small microphone on the cannula)
  • Actigraphy body movement
  • Body position: Left, right, prone, supine & upright
  • ECG (one channel)
  • Separate leg movements (via EMG or movement sensors)
  • Event marker (via a patient activated button)

The system also has provision for auxiliary inputs (4). It also has provision for ECG/ EEG/ EOG/ EMG data (via an additional unit).

The prospect of having all the data available in an automated unit really intrigued me. In subsequent blog-posts I'll show how I've used the Black Shadow to verify some of my previous experiments and create some new ones, but this post is really going to be an introduction to some of the things that the Black Shadow has revealed about my sleep.

In many sleep labs and hospitals, you are connected to several bedside monitors by long wires allowing you to move in bed, but making it hard if you need to get up in the night to use the bathroom. The Black Shadow overcomes this by being wearable, so once you're connected, you are free to move around should you need to.



I've no intention of posting a photo of me in pyjamas wearing the device on the internet, so I fitted it to a mannequin to illustrate how it's worn.

The next few photos illustrate some of the sensors in a bit more detail (click for larger images).




Under the shirt the mannequin is wearing three adhesive electrodes which are used to record ECG data.





The microphone and thermal sensor fix to the nasal cannula, which is then worn around the ears:





Heel / Ankle straps are also worn to detect leg movements in the night:



Also an oximeter sensor is worn on the finger which connects via a long lead to the top of the central unit. It's a flexible probe and actually a lot more comfortable than the plastic "crocodile-type" probes that I'm used to. My mannequin's hands are a bit like mittens, so I haven't fitted the oximeter probe to him.

I decided to start from scratch and take a baseline recording of my sleep (no vitamins, no supplements, no Rematee and no alcohol). After connecting myself to the various sensors I pressed the button on the front of the unit, waited for the recording light to flash and then went off to sleep.


The Black Shadow is Bluetooth capable, which allows you to configure the device wirelessly, and to see live data via bluetooth at the beginning of the night in order to check that all the channels are configured correctly. So after pairing with my laptop, and checking that everything was fine, I was ready to sleep.

Analysing the Data

The data is recorded to a high speed SD Card.
In the morning I removed the SD Card from the Black Shadow and downloaded the data to the Visi-Download software.


Not only was there a lot more data than I'd had access to before, but I was able to manipulate it and interrogate it in ways that I've never been able to do previously.



Once downloaded, I was able to see a graph of all the channels on one page along with some additional channels derived from the data: "Pulse Transit Time" (an indicator of intrathoracic pressure and an indicator of autonomic arousals in sleep), "R-R interval" and "Flatness".


The channels are able to be moved up and down the screen so that you can, for example, put the SPO2 (oxygenation) on top of the airflow channel, making it easy to spot correlations.

The software will perform an analysis on the data (using customisable criteria) and display it in a multi-page report. Once the data has been analysed, markers appear on the graphs showing events such as apnoeas, hypopneas, pulse rate changes, oxygen desaturations, snores etc.

Zooming in on an event allows you to verify it, and if necessary disregard it.

Positional Data

As expected, it was easy to spot that I did indeed have respiratory events through the night. Once analysed, my AHI was calculated to be 7.24 which agrees nicely with my previous 5-day mean score of 7

Comparing selected channels with the body-position channel, it was also easy to see that the vast majority of my respiratory events occurred while I was sleeping on my back. (Click for larger image).

The body position channel (3rd down) shows the first half of the screen with me on my back turning onto my right side for the second half.

Comparing the supine to side-sleeping data it is clear that (From the top down):

  • My SPO2 (oxygen saturations) are higher and stable with side sleeping
  • My pulse is lower and stable
  • Change in body position from Supine to Right
  • My snoring stops (filtered sound channel)
  • My oral/nasal airflow is stable
  • My leg isn't twitching
  • My body movement is greatly reduced

The improvement is revealed in a table in the report:

It's possible to exclude periods of data from the analysis by highlighting them; so for example, by only looking at the periods when I slept in a supine position (on my back) I could see how my AHI was if I only slept on my back.

All of this is a great indicator that positional therapy such as the Rematee would help my sleep problem.

Obstructive vs Central Apnoeas

The two respiratory effort channels allowed me to see whether my apnoeas were obstructive or central in nature. Obstructive apnoeas are where the body still tries to breathe (ie the intercostal and diaphragm muscles still move as normal) but the airway is obstructed, rendering the effort useless. Central apnoeas are where the brain doesn't signal the muscles to breathe, or the signal is blocked for some reason.

Each respiratory effort graph relates to one of the inductance belts that are worn around the chest and stomach. The graph therefore shows the chest and stomach movements, and hence if an effort to breath was made how strong it was in relation to other breaths.

My graph showed that I still attempted to breathe and yet no airflow was recorded, this makes my apnoeas obstructive in nature. (Click for larger version)

Audio Recording & Snore Detection

The Black Shadow records sounds continuously through the night, so unlike my attempts with a voice-activated dictaphone, you are able to hear sounds leading up to an event rather than just a second or so after the event itself.

Because the microphone is calibrated, the sound channel is graphed according to sound amplitude in dB. The software also creates a second sound-channel of sound that is filtered to highlight snoring. The detected snores are then marked automatically, making it easy to click on the graph and actually hear the snore. Listening to sound can be done at any point of the night, not just snores, so it's possible to hear sleep-talking and other noises.

I'd like to say that I sleep silently, and that the Black Shadow didn't detect any snoring from me, but that would of course be a lie because I snored a lot. The report (above) showed that I snored at a level of above 55dB for 90% of the night! 158 snores were louder than 75dB, which is roughly the noise level generated by a lawnmower!

This is a screenshot of 23 seconds of my sleep. Four snores are shown which were detected and marked automatically, these correspond to the snores that have been isolated on the filtered channel. What I find interesting about this screenshot is that the vibrations caused by my snoring are visible on the airflow channel (top - orange line).

(Click for a larger image)

Again, I was able to see that most of my snoring took place while I slept on my back.

Leg Movements

When I took a look at the leg movement data I saw something that surprised me.

Like most people, as I drift off to sleep, I twitch a bit. If I'm laying on my back I know that my left leg is prone to having the odd twitch (since I injured a disc at L5 in my spine), and this also happens when I'm sitting using my computer late at night, but I didn't suspect it happened when I was asleep. Looking back, I probably should have done.

Sometimes arousals from respiratory events will cause a body or leg movement, but I was seeing these twitches in periods of sleep that were free of respiratory events.

This is what I saw when I looked at a 12 minute section of my data (click for larger image):

At 1:15 am my left leg (leg 1) started to twitch slightly, and as you can see the amplitude increased almost with each subsequent movement over the next 4 minutes. This then caused me to turn from my back onto my left side (shown by the Body Position channel in blue). This happened several times a night, in all sleeping positions and on more than one night. Although I haven't been able to eliminate them, maybe this is an indication of why the Vitamins and Minerals improved my sleep as Iron is thought to be beneficial to Periodic Limb Movements.

Those legs movements and the subsequent turning over could be a problem if it happened often enough because it is yet another thing that can cause a sleeper to awaken briefly. These small awakenings are called micro-awakenings (or micro-arousals). The higher the number of these there are in a given night, the more your sleep is disrupted and the greater the likelihood of waking in the morning still feeling tired. If I want to improve my sleep further then these are the sort of things that I need to be aware of.

Pulse Rate Increases

The Visi-Download software also shows other arousals which are calculated from my heart-rate data.

This section of my sleep shows how a cluster of respiratory events (marked by the blocks under the airflow line) affected my oxygen saturations (top red line). If you look at the other data shown in line with those events you'll see that not only was my heart rate affected, but also my Pulse Transit Time - a very good indicator that I was continuously being woken (brief)y by my respiratory disturbances, causing fragmented sleep.

The Pulse Plethysmograph also shows changes, even on this timescale because the arousals went on for a prolonged period of time. Shorter micro-arousals are able to be seen using the PTT and Pleth channels when looking at a smaller timeframe.

Event Marker

Pressing this button during recording causes a marker to be inserted into the data. This could be for any event, such as being woken, waking from a nightmare, feeling unable to breathe, or even (as I plan to use it) for marking lucid dreams and sleep paralysis. 


The Black Shadow opens up many additional ways for me to explore and hopefully improve my sleep and I'm looking forward to experimenting further with it.


Additional Links

Non-invasive Monitoring of Vital Signs Utilising Pulse Wave Transit Time

Use of Pulse Transit Time as a Measure of Autonomic Arousals in Patients with Obstructive Sleep Apnea

Pulse Transit Time Improves Detection of Sleep Respiratory Events and Microarousals in Children - Pepin et al

Obstructive Apneic Events Induce Alpha-receptor Mediated Digital Vasoconstriction - Zou et al