Inspiration expiration ratio

I've been stuck with an AHI in the 4-7 range for at least 2 months. I plan to post data in a new thread, but now I'm focused on the narrow observation that my (90%) inspiration : expiration ratio is averaging 1.3-1.4, which is not normal. I do have sinus bradycardia. I'm wondering if the bradycardia can cause abnormal ventilation and if either somehow causes resistance of my OSA to therapy. Some quick searches don't pull up anything definitive.

Thanks, -Ron

Please ask your doctor.
Or his staff.

rkl122 wrote:I've been stuck with an AHI in the 4-7 range for at least 2 months. I plan to post data in a new thread, but now I'm focused on the narrow observation that my (90%) inspiration : expiration ratio is averaging 1.3-1.4, which is not normal. I do have sinus bradycardia. I'm wondering if the bradycardia can cause abnormal ventilation and if either somehow causes resistance of my OSA to therapy. Some quick searches don't pull up anything definitive.

Thanks, -Ron

Ron, I don't think you'll find much on this because I:E is a term used primarily in mechanical ventilation. I:E ratios greater than 1 (termed "Inverse") is a strategy of mechanically holding the Inspiration period longer than the expiration period for patients on ventilators in order to provide greater opportunity for oxygenation. I have found no references where this statistic was used for diagnostics purposes in sleep disordered breathing.

Typically, the inspiration period is shorter than the expiration period so the I:E would be less than 1.0. Greater than 1.0 would mean some exhalation periods are shorter than inhalation periods.

I suggest you look to the shape of your Flow Rate Waveforms when the I:E ratio is greater than 1 for some clues as to why it might be so. I suspect that it could reflect mouth breathing, or some attempt at restricting mouth breathing, or leaks. You may find it is also occurring in the presence of apneas which are causing abnormal flows. The I:E ratio is a statistic, but it is not the cause of anything. It is the result of something, maybe akin to panting or hyperventilating.

Edit: I am not an expert, the above is only my lay understanding of the subject and I'm not trying to dismiss or downplay your bradycardia. Certainly, it would be appropriate to consult with your Doctor about your concerns.

Thank you Jay for the informative and compassionate response.

Jay Aitchsee wrote:
Ron, I don't think you'll find much on this because I:E is a term used primarily in mechanical ventilation. I:E ratios greater than 1 (termed "Inverse") is a strategy of mechanically holding the Inspiration period longer than the expiration period for patients on ventilators in order to provide greater opportunity for oxygenation. I have found no references where this statistic was used for diagnostics purposes in sleep disordered breathing.

Yup, I finally concluded the same from my searching.

................ I suggest you look to the shape of your Flow Rate Waveforms when the I:E ratio is greater than 1 for some clues as to why it might be so. I suspect that it could reflect mouth breathing, or some attempt at restricting mouth breathing, or leaks. You may find it is also occurring in the presence of apneas which are causing abnormal flows. The I:E ratio is a statistic, but it is not the cause of anything. It is the result of something, maybe akin to panting or hyperventilating.

Yup, understood the ratio is best utilized when averaged over time, and an abnormal value could stem from something unrelated or peripheral to the OSA. I'm not sure about significance of SH instantaneous values, since most would occur in the middle of a breath. I do some mouth breathing (dry mouth), but little or no snoring and almost no major leaks. From some oximetry, I do seem to have borderline hypoxia as well.

I was going to start a new thread showing zooms of apneas which I *think* are due to micro-awakenings. I get them every night, and if they are "junk," then it's that junk that keeps me from the under-5 club. But last night, I bumped the pressure for the first time in a long time, and lo, the AHI got ~halved (3.3)! Unfortunately, I'd forgotten to put the card back in the machine, (Doh!) so I don't have the flow data. Will gather more data & keep fingers crossed. But FWIW, I'll include here a couple of typical apneas from prior but recent nights. Would appreciate opinions on whether these look like "junk." They do remind me of traces you've posted yourself to illustrate junk.

http://imgur.com/8BFZR5Y
http://imgur.com/piYyDl7

Sorry, when I try to embed the imgur link for inline display, the image gets truncated at the right. Gotta figure out how to scale it down.

Edit: I am not an expert, the above is only my lay understanding of the subject and I'm not trying to dismiss or downplay your bradycardia. Certainly, it would be appropriate to consult with your Doctor about your concerns.

Understood and much appreciated. I am scheduled to see both the cardiologist and the sleep doc next month. I'll certainly have this issue on my list.

-Ron

rkl122 wrote: Would appreciate opinions on whether these look like "junk."
http://imgur.com/8BFZR5Y http://imgur.com/piYyDl7

Yes, both of these images depict events preceded by periods of disturbed breathing which indicates probable arousals or awakenings led to the events and might be considered "junk".

Going back to the I:E ratio, it has been my anecdotal observation that people with higher AHI and more difficulty adapting to CPAP seem to have this inverse ratio, and it shows up in the average or median inspiration time,and expiration time as well, not just the ratio. In addition most of these people seem to have slightly lower tidal volume and minute vent. I have tried over the years to also research what significance I:E ratio has, and the best I could come up with was RobySue's conclusions in the Beginners Guide to Sleepyhead, that we just don't know and it may not have any significance at all. Still, if you go back to many posts where data is posted, there is this "coincidence".

The CPAP machines are not infallible in measuring the time of inspiration and expiration. I have seen breathing patterns with abrupt exhalation, followed by a rebound the machine may interpret at the start of inspiration. Let me give some examples. This graph has a high rate of OSA with the inverse I:E ratio we are discussing:



Here is an example of the exhale rebound, also from someone with inverse I:E ratio. Again, we don't know what significance this has.



The O.P. for this thread posted a wave form that shows a less pronounced quick exhale rebound. The expiratory wave form shows a fast exhale followed by a return to zero flow, and a small continuation exhalation, until the next inhale. It could be the machine is simply misinterpreting the length of expiration (not counting the zero tidal time). This actually looks like more normal I:E ratio, but the return to zero following expiration is not very smooth. Probably meaningless, but curious.

Re: IE

My opinion is that we see it only because certain machines report it (which makes sense, doesn't it ). Those machine are in the more advanced model lines which are capable of some forms of noninvasive ventilation. For example, the S9 VPAP line which includes BiPAP to ASV models. In the application of ventilation, I:E may become a consideration, therefore the statistic is available and can be affected by certain machine settings. Here, even though the BIPAP model (VPAP Auto) has only comparatively minimal ventilation capability and has no trigger setting to affect the I:E, it still reports I:E.

Interestingly, even though the S9 VPAP Auto reports I:E, ResScan does not display it as a graphic, but only as statistical data. Probably because the designers didn't see a need. The graphic is only available in SleepyHead.

Similarly, For my S9 Autoset, Sleepyhead produces a graphic for I and E times (but not I:E) as well as Respiration Rate, Tidal and Minute Volumes while Rescan only produces a graphic for Minute Volume. Again, I'm guessing it is because the S9 has no ventilation capability and the Statistics of RR, VT, and I:E would be seen as measures which would be most useful in the application of non invasive ventilation.

So, I don't think we've seen much in terms of diagnostics using I:E primarily because the statistic hasn't been thought of in that way and it has not been available using less than the more advanced machines with non invasive ventilation capability. But that is not to say it can't be useful. In my own limited experience, when Inverse I:E occurs for prolonged periods (more than a few breaths), it does signal a definite and significant abnormality. I personally have not experienced this, but I have assisted (indirectly) another who has and at the same time was experiencing a rather high rate of OSA. In this particular case, Increasing IPAP and PS beyond that seemingly necessary to suppress the apnea seemed help sustain a "normal" I:E without recurrence of the apneas.

I too, think we might see this Inverse ratio occur in people who are having difficulty adapting to the therapy. In particular, I think it could be more evident in those prone to expiratory mouth breathing or mouth leaks. In this case, the shape of the expiratory portion of the Flow Rate Wave is sometimes significantly changed. Often deeper with a more sudden rise to zero which increases the I:E. Similar to that posted above as an example of exhale rebound.

Going a bit further: In the attempt to correct mouth leaks, some people use tape to completely prevent oral exhalation. While this works, I think it could create another problem, and now we're getting in to theory. Occasionally, we exhale through the mouth to increase oxygenation (or more properly, to increase CO2 wash out) by reducing the respiratory dead space of the nasal passage. Think of mild exercise. Now, what if during the night the normal response to excess CO2 build up would be to exhale through the mouth, but the mouth was taped. Wouldn't that lead to quicker breaths and a possible arousal? A theory for you to ponder.

Most auto CPAPs, and I think many fixed CPAPs will also report inspiration time and expiration time (minimum, average or median, x-percentile and max). Fewer machines calculate the I:E ratio, but all you need is to look at the average I or E time, and it's readily obvious when E is 2-3 times I.

As I said, an inverse I:E ratio is supposedly not the norm, but it is disproportionately present when people complain of persistent apnea clusters and difficulty with therapy. It is also more likely to be present when someone presents with low tidal volume. I think it would be great if there was some research on this, but if it exists, I sure haven't found it, other than how it applies to invasive ventilation.

Sleeprider wrote:Most auto CPAPs, and I think many fixed CPAPs will also report inspiration time and expiration time (minimum, average or median, x-percentile and max). Fewer machines calculate the I:E ratio, but all you need is to look at the average I or E time, and it's readily obvious when E is 2-3 times I.

Right, I think my S9 Autoset generates I and E times it since it is available in SleepyHead (unless SH calculates it from the Flow, which is possible), but ResScan doesn't present it for my machine type in any form - statistic, summary, or graphic. Therefore, healthcare professionals would not normally not see it.

ResScan and Resmed S9 Clinicians Manuals wrote: Therapy devices gather data relevant to the type of treatment being provided. The parameters displayed in the Summary Graphs and Detailed Graphs tabs will depend upon the therapy device from which data has been downloaded.

S9 Detailed Data
Apnea or hypopnea events
Flow limitation
Leak
Minute ventilation
Pressure
Pulse Rate (via adapter)
Snore
Oxygen saturation (via adapter)
High resolution respiratory flow data (autoset and elite)

Sleeprider wrote:As I said, an inverse I:E ratio is supposedly not the norm, but it is disproportionately present when people complain of persistent apnea clusters and difficulty with therapy. It is also more likely to be present when someone presents with low tidal volume. I think it would be great if there was some research on this, but if it exists, I sure haven't found it, other than how it applies to invasive ventilation.

I agree it could be useful and I haven't found any guidance for using it, either. Probably because it is not routinely available to health care professionals - at least not from a large number of their patients using ResMed machines.

Sleeprider wrote:Going back to the I:E ratio, it has been my anecdotal observation that people with higher AHI and more difficulty adapting to CPAP seem to have this inverse ratio, and it shows up in the average or median inspiration time,and expiration time as well, not just the ratio. ...........

...........

The O.P. for this thread posted a wave form that shows a less pronounced quick exhale rebound. The expiratory wave form shows a fast exhale followed by a return to zero flow, and a small continuation exhalation, until the next inhale. It could be the machine is simply misinterpreting the length of expiration (not counting the zero tidal time). This actually looks like more normal I:E ratio, but the return to zero following expiration is not very smooth. Probably meaningless, but curious.

I'm the OP. Just to be clear, by "inverse ratio" you refer to an inspiration time:expiration time of less than unity, right? Most of the refs I've found define that ratio for a normal, resting, awake adult to be 1:1.5. I've seen quotes from 1:1 all the way to 1:4 - ie. less than unity. So a bit confused at referring to mine, which is greater than unity, as normal. As for the rough return to zero, I get events even more weird than that, just about every night. Here's an example.

http://imgur.com/gyKKQwn Note the flow all through the "CA."

....an inverse I:E ratio is supposedly not the norm, but it is disproportionately present when people complain of persistent apnea clusters and difficulty with therapy....

Yup. Looks like I'm one of those lucky ones. Will post back if the docs offer enlightenment. Ain't holding my breath...

-Ron

Try not to hold your breath, especially between inhale and exhale.
That is when people hiccup.

chunkyfrog wrote:Try not to hold your breath, especially between inhale and exhale.
That is when people hiccup.

holding my breath between inhale and exhale is how I usually get rid of hiccups!

Ron, an Inverse I:E is greater than 1.0. Typically, if not on a ventilator, the I:E ratio is less than one. Meaning the time of expiration is greater than the time of Inspiration, say something like 1.5 seconds inhale and 2 seconds exhale. The ratio would be 1.5 : 2.0, or 1.5/2.0, or 0.75 As you mention, "normal" seems to include anything less than one down to about 0.2

As I explained above a couple of posts, an Inverse I:E is a strategy sometimes used to ventilate patients to provide a greater opportunity for oxygenation. If we turned the above around it would be Inverse, meaning the inspiration period is greater than the expiration, and would be 2 seconds inhale and 1.5 seconds exhale. A ratio of 2.0 : 1.5 or 1.33.

Inverse I:E, or I:E, are really only terms that are used in conjunction with patients being ventilated. However, Sleeprider and I agree, if an Inverse I:E is present, it might suggest an abnormality. However, neither of us has been able to find a reference where it was used as such.

It is probably not terribly unusual for one to experience some brief periods of Inverse I:E. However, long periods might be indicative of a problem which should be addressed.
To do so, one would need to investigate the underlying cause which could be varied.

I don't doubt that your nightly statistical I:E Max is greater than one. I would be surprised, however, if your statistical average for an entire night was greater than 1.0 as you imply when you say your I:E, "...is greater than unity, as normal".

I think that a lot of your I:E ratio and sawtooth tidal volume is due to your inhalation curve. In this set of charts you start to inhale and then you drop back into a slight exhale before your actual inhale gets started. I am not sure why or how but it looks like your body recognizes that it is running out of time if it wants to get enough breaths to oxygenate properly and it forces the exhale. I think that the machine is recording 2 tidal volumes for each actual breath you are taking.

It might help if you adjust the trigger and/or cycle sensitivities. If it were me, I would start by lowering the sensitivity on the trigger a notch and see what happens to my flow rate curve and tidal volumes.

These are my thoughts based on what I see

WickedLoki wrote:It might help if you adjust the trigger and/or cycle sensitivities. If it were me, I would start by lowering the sensitivity on the trigger a notch and see what happens to my flow rate curve and tidal volumes.

Excellent suggestion, Wicked, but is his PR System One REMStar 60 Auto CPAP, capable of trigger and cycle sensitivity adjustment?