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Geeking Out on Waveforms
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chill Online

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Post: #1
Question Geeking Out on Waveforms
My AHI is consistently under 1, but I still feel sleepy in the daytime. Not tragically exhausted and foggy like before, but still sleepy. I wake up often at night, rarely sleep more than 90 minutes at a time. So I decided to take a closer look at the detail of my breaths just before I awake so I can see if pressure changes or disordered breathing might be waking me up.

This has led me to some insights and questions. I will be posting some images in this thread over next couple of days for discussion and comment. I will start with this one, selected at random:

[Image: 9XPCHrP.png]

A wake proceeded by some sleep/wake junk
[Image: 9DLCGGX.png]
(This post was last modified: 06-15-2016 12:27 AM by chill.)
06-15-2016 12:21 AM
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chill Online

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Post: #2
RE: Geeking Out on Waveforms
When I started looking at SleepyHead, i thought I understood how the inhalation and exhalation worked. After some more careful thought, I think this is what the graphs mean:

[Image: SDT5EyD.png]
06-15-2016 12:37 AM
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Sleeprider Offline
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Post: #3
RE: Geeking Out on Waveforms
Hey Chill, interesting obsession. In your first diagram, those flat-topped peaks that slowly taper down on inhale are classic flow limitation and that explains the recovery breath. Sometimes higher pressure, or better, bilevel pressure solves that. DAMHIK.

In your second post image, you need to move that green line over to the right to where it crosses the zero-flow line. Exhale is all the area below zero, and inhale is all the area above zero. Each breath and exhale trails off to zero, and the inhale does not start until positive flow begins. It is fairly common to see the exhale end in an extended zero flow condition that closely traces the zero line, before the inhale flow begins. You can see that pattern at the beginning of your second image in the first post. Classic sleep architecture.

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06-15-2016 07:53 AM
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richb Offline

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Post: #4
RE: Geeking Out on Waveforms
(06-15-2016 12:21 AM)chill Wrote:  My AHI is consistently under 1, but I still feel sleepy in the daytime. Not tragically exhausted and foggy like before, but still sleepy. I wake up often at night, rarely sleep more than 90 minutes at a time. So I decided to take a closer look at the detail of my breaths just before I awake so I can see if pressure changes or disordered breathing might be waking me up.

This has led me to some insights and questions. I will be posting some images in this thread over next couple of days for discussion and comment. I will start with this one, selected at random:

[Image: 9XPCHrP.png]

A wake proceeded by some sleep/wake junk
[Image: 9DLCGGX.png]

Regarding your question "Why the flat top?': The flat top represents the closing of your airway during an Obstructive Hypopnea. You see the rise in the waveform as you start to inhale but your airway closes during this breath. It reopen as you exhale. Repeat a number of times for obstructive Hypopnea. This is going to cause a desaturation and could wake you up.

Rich

Apnea Board Member RobySue has posted a Beginners Guide to Sleepyhead Software here: http://www.apneaboard.com/wiki/index.php...SleepyHead
06-15-2016 07:53 AM
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green wings Offline

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Post: #5
RE: Geeking Out on Waveforms
I have this same obsession. Okay, pretty much any graph where something biological/dynamic is going on. Thanks

I've noticed in my breath waveforms that I almost always see the "tail-off" in the exhalation before the next inhalation starts. I rarely see exhalations that are shaped just like the inhalations like you have in your graph.

Can you tell from looking at your respiration rate when REM sleep starts? (Or also from when the waveforms in your breathing flow rate get further apart?)
06-15-2016 08:30 AM
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chill Online

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Post: #6
RE: Geeking Out on Waveforms
The green line was just an artifact of where the cursor was when I took the screen shot, it was not intended to indicate anything. When I first looked at these, I assumed that everything from the peak to the trough was exhalation and from the trough to the peak was inhalation. Then I looked again and recognized my error.

I don't really understand the flat top explanations. For a flow limitation, I would expect a rapid return to closer to zero. These seem likes a high level of inhalation maintained evenly over time. I don't know what that would be.

On a different topic, here is a look at the Respironics Hunt and Peck method of seeing if higher pressures result in better breathing:
[Image: qjwuEMb.png]

It was testing going from 10 to 11.5 and then I raised by minimum to 11 and it is now going from 11 to 12.5. Neither one seemed to result in any benefit that the machine detected. I am not sure if that means my pressure is too low, or if it means that higher pressure is not beneficial. My thought is to try some higher minimum pressures over the next couple of weeks and also to try CPAP to see if the pressure changes are disturbing my sleep. None of the pressure increases are correlated to my awakenings, but they might be keeping me out of deeper sleep.

More later, too sleepy now.
06-16-2016 12:35 AM
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green wings Offline

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Post: #7
RE: Geeking Out on Waveforms
Hi, chill. I have been running my Respironics CPAP machine in auto-trial mode, and I always see the hunt-and-peck pressure changes. I think the algorithm always does this. I don't think it means that you need to change your minimum pressure. The fact that the pressure always goes back down after an increase would seem to say that your minimum pressure is fine.

I am not really a fan of the "seeking" behavior of the algorithm, although I admit it's mostly for aesthetic reasons. I would be okay with it if the algorithm checked to see if a pressure increase was beneficial, but then stopped the hunt-and-peck until I changed sleeping position or sleep stage. I imagine the algorithm will eventually have those smarts.

During my sleep study, 95%+ of my obstructive apneas happened during REM sleep. When I run my machine in auto mode, I end up with pressure around 11 for most of the night, but increasing to 13.5-15.5 during clusters of obstructive apneas.

I seem to get about the same AHI if I just run my machine in fixed pressure mode at 11 cm, though.

Another prediction for future APAP machines: they will have more than one pressure-response algorithm. In fact, they will probably custom-tailor an algorithm for our individual apnea characteristics.

(06-16-2016 12:35 AM)chill Wrote:  On a different topic, here is a look at the Respironics Hunt and Peck method of seeing if higher pressures result in better breathing:
[Image: qjwuEMb.png]

It was testing going from 10 to 11.5 and then I raised by minimum to 11 and it is now going from 11 to 12.5. Neither one seemed to result in any benefit that the machine detected. I am not sure if that means my pressure is too low, or if it means that higher pressure is not beneficial. My thought is to try some higher minimum pressures over the next couple of weeks and also to try CPAP to see if the pressure changes are disturbing my sleep. None of the pressure increases are correlated to my awakenings, but they might be keeping me out of deeper sleep.

More later, too sleepy now.
06-16-2016 08:40 AM
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Sleeprider Offline
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Post: #8
RE: Geeking Out on Waveforms
Quote:Another prediction for future APAP machines: they will have more than one pressure-response algorithm. In fact, they will probably custom-tailor an algorithm for our individual apnea characteristics.

I wouldn't hold my breath (pun intended). The operating algorithms of auto CPAPs, especially Respironics, have not significantly changed since the early 2000s when they were discussed in patents that are still in use. The machines have changed mostly cosmetically and to incorporate improved sensors, different data recording and transmittal technology, but function is not too different. These remain positive air pressure machines, and have been refined with some features like "Flex" or "EPR". As medical devices, I don't see any demand from doctors, researchers or DMEs to make changes in actual function.

The two major competitors have very different approaches in their APAP machines, with much faster response in the Resmed, and the slow response and testing approach in Respironics. In spite of those differences, the real-world results and function is close enough that you'd be hard pressed to quantitatively defend which approach is better. The reality is, simple pressure works for OSA, and the "differences" are mainly for marketing and patent rights.

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06-16-2016 09:00 AM
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green wings Offline

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Post: #9
RE: Geeking Out on Waveforms
Oh well. *sigh*

(06-16-2016 09:00 AM)Sleeprider Wrote:  I wouldn't hold my breath (pun intended). The operating algorithms of auto CPAPs, especially Respironics, have not significantly changed since the early 2000s when they were discussed in patents that are still in use.
06-16-2016 09:23 AM
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green wings Offline

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Post: #10
RE: Geeking Out on Waveforms
You ask interesting questions. I think you may have a "collapse of noncompliant upper airway" going on. Smile

My understanding is that "flow limitation" means approximately the same thing as "flow rate limitation".

The flow or flow rate of a particular breath is limited if it doesn't have the normal rounded-peak shape.

Why is that a bad thing? I think for the same reasons that apneas and hypopneas are bad. Flow limitations mean that there is airway obstruction, which equals abnormal pressures in our chest cavity, and can cause arousals.


Some charts and graphs from a good article on flow limitations:

The role of flow limitation as an important diagnostic tool and clinical finding in mild sleep-disordered breathing from Sleep Science Volume 8, Issue 3, November 2015, Pages 134–142


Quote:Assessing for inspiratory flow limitation requires recognition of both flow and intrathoracic pressure changes [21]. A decrease in flow normally is accompanied by a compensatory increase in intrathoracic pressure. This is illustrated in Fig. 1 in the setting of differentiating a central and obstructive event via airflow and esophageal pressure monitoring [18]. Inspiratory flow limitation, which does not meet criteria for an obstructive hypopnea is illustrated in Fig. 2.

[Image: 1-s2.0-S1984006315000516-gr1.jpg]
Fig. 1.
Airflow and esophageal pressure monitoring on PSG. (A) A central event with reduction in airflow without any change in esophageal pressure signal during the event. (B) A reduction in airflow with an increase in esophageal pressure for the duration of the event, indicative of an obstructive hypopnea. Flattening of the airflow signal can also be seen during the obstructive event suggestive of flow limitation.

[Image: 1-s2.0-S1984006315000516-gr2.jpg]
Fig. 2.
Polysomnographic recording of a subject with snoring and inspiratory flow limitation during slow-wave sleep. There is no fluctuation in oxygen saturation on pulse oximetry however flattening of the nasal waveform, coinciding with snoring, is present.



Result in one patient of lowering CPAP pressure by 1 cm H20.
[Image: 1-s2.0-S1984006315000516-gr4.jpg]
Fig. 4.
(with permission) from: Condos et al. (1994) [20]: Continuous tracing of flow in one patient during transition to lower CPAP. At the arrow, CPAP was lowered by 1 cm H20. Note the increase in the esophageal pressure swings that occurs over five breaths and results in more than a twofold increase in estimated resistance. Simultaneously, the inspiratory flow contour loses its rounded shape and develops the characteristic plateau of flow limitation. )


Quote from the linked article:

Quote:The upper airway is submitted to at least three forces during inspiration: phasic activity of the dilator muscles (activated at or prior to the onset of inspiration), negative airway pressure (maximal at mid-inspiration), and tracheal traction support (maximal at end-inspiration). The investigators reasoned that the inspiratory flow shape could provide information on upper airway behavior throughout inspiration


Explanation for how data was collected for Table 1 & Figure 5:
Quote:Postmenopausal women and male patients with established OSAS treated with uvulopalatopharyngoplasty were selected as patient groups. A control group was also selected. Inspiratory flow signals were evaluated on a breath-by-breath basis, and each inspiratory flow shape was extracted from an automated classifier. Recorded breaths were sorted into 7 classes of inspiratory flow shapes with their significance as it relates to anatomic flow abnormality (Table 1, Fig. 5). Based on the results seen, significant differences were seen in control subjects and patient group, but also between males and females [31].


[Image: h5Q7Ubf.jpg]


[Image: 1-s2.0-S1984006315000516-gr5.jpg]
Fig. 5.
(with permission) from: Aittokallio et al. (2001) [30]: The distribution of flow shape classes in experimental and control subjects.


I stopped here. It's a very long article.




(06-16-2016 12:35 AM)chill Wrote:  I don't really understand the flat top explanations. For a flow limitation, I would expect a rapid return to closer to zero. These seem likes a high level of inhalation maintained evenly over time. I don't know what that would be.
(This post was last modified: 06-16-2016 03:33 PM by green wings.)
06-16-2016 03:32 PM
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