New diagnosis: complex sleep apnea
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New diagnosis: complex sleep apnea

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Posted by dirtywater on February 27, 2009 at 02:19:15:

I was diagnosed with OSA 3 years ago. I had an MMA one year ago. According to the x-rays and CT scans, the MMA made a large improvement in my airway. But according to my sleep studies it did not improve my apnea. Subjectively speaking, I still feel sluggish and tired in the morning. I have trouble waking up at a reasonable time.

The surgeon suspected I might have a neurological issue with my sleep that previously went undiagnosed. She referred me to a sleep doctor who specializes in complex apnea, i.e. mixed obstructive/central apnea. The new doc believes that complex apnea is underdiagnosed and he is trying to get the industry to change their sleep study scoring guidelines so that complex events are accurately accounted for.

The new doc looked the raw data from my past studies. He also had me do a new sleep study at his preferred lab. The study was mostly the same drill as usual, but I think he uses an extra sensor or two to gather some additional data. And his lab does their studies in a hotel, so I got to take home the mini-size soap and shampoo from the bathroom :-) After reviewing the old and new studies, his diagnosis is that I have complex apnea. In fact my breathing pattern is, in his words, "a complete mess."

The neurological component of my apnea is apparently due to a problem with the CO2 chemosensors in my brain. Humans' involuntary breathing cycle is mostly regulated by the amount of CO2 in our blood, not the amount of oxygen. In a normal person, CO2 builds up in the blood, and when it reaches a certain threshold the brain senses this, and it decides to take another breath. Taking a breath exchanges CO2 for O2, so your blood CO2 level drops, and the cycle repeats. But when I fall asleep my brain's CO2-sensing threshold rises too high. My blood CO2 concentration rises, but my brain doesn't notice it in time. I don't breathe quickly enough. Eventually my O2 level drops and my brain realizes something is wrong, and I start breathing quickly to compensate. This cycle of too-slow and then too-fast breathing is called periodic breathing. A very similar thing happens to normal people when they travel to high altitude. Because the air is thinner, they have to breathe more quickly (hyperventilate) in order to get enough oxygen. This means their lungs are expelling CO2 at an increased rate, thus the amount of CO2 dissolved in the blood drops. When you sleep at high altitude, this reduced level of CO2 in your blood messes up your breathing cycle, because your blood CO2 levels aren't reaching the threshold needed to trigger proper breathing.

[If you've ever heard of "Ondine's curse," also known as congenital central hypoventilation syndrome (CCHS), my situation might sound similar. However my doc says the root causes are completely different. If you've never heard of Ondine's curse, look it up:
http://en.wikipedia.org/wiki/Ondine_(mythology)
Truly one of the greatest apnea-related mythologies!]

To make matters worse, there is a nasty feedback loop going on here. When my O2 level drops and my brain says "uh oh, I'd better take some quick breaths here," this jolt can interrupt my brain's sleep stage, just like a normal apnea/hypopnea would. That is bad enough, but in my case the effect comes full-circle with a vengeance. That is to say, the change in sleep stage (for example from stage 3 to stage 2) will cause a temporary interruption in my breathing. It's a classic "vicious cycle." According to my doctor, it is this second part of the cycle that is particularly severe in my case.

The doc also determined that my circadian rhythm was severely phase-delayed i.e. "delayed sleep phase syndrome." My previous sleep doc had mentioned this, but hadn't given me an aggressive plan for handling it. The new doc made it clear that this was probably contributing greatly to my sluggish mornings. Basically I was waking up at 9am but my body still thought it was the middle of the night. So he had a very specific regimen he wanted me to follow. In fact, he wanted me to fix the circadian problem first, before even beginning to address the apnea problem. So I started taking melatonin at night and dimming the household lights around 8pm. If I have to use the computer after 8pm, I use a reverse color scheme with green letters on a black background. (The traditional black letters on a white background is far too bright to be staring at in the evening and it will screw up my circadian rhythm. Hmm, I wonder if this is why so many computer geeks are late sleepers?) In the morning, he has me using a bright blue light to convince my biological clock that it is morning time. Actually my doc said that when I started this regimen back in October, my biological sunrise was at about 2pm. So he had me use the light at 2pm, then 1:40 the next day, then 1:20 the next day, etc. until my biological sunrise was back to a somewhat-normal 9am. After a couple of months I was doing much better. In the last month I've lapsed a bit, so my biological sunrise is now at about 11:00am. My internal clock is always going to want to surge forward, probably for the rest of my life, so I have to use this bright light therapy indefinitely.

Why a blue light instead of the large, super-bright, full-spectrum lights you may have seen before? Within the last few years, researchers discovered that the "magic" ingredient in the full-spectrum lights isn't the fact that they are full spectrum; it's the fact that they include certain blue wavelengths that normal household lights don't include. So all you need to do is produce a light that emits those blue wavelengths.

Now for the central apnea / periodic breathing. There are a few ways to address this problem:

1) Surgically alter the chemosensors in the brain to make them more responsive to CO2 levels. I'm sure somebody somewhere is researching how to do this. Heck, maybe they've already figured out how to do it in rats or worms. However, I have no short-term plans to pursue this type of surgery :-)

2) Take medication that raise the brain's respiratory drive. There has been research in this area with mixed success. I've started taking Diamox, a medication that causes the kidneys to excrete more bicarbonate. This acidifies the blood and causes the brain to breathe faster. (Not surprisingly, Diamox is also the drug of choice for preventing altitude sickness.) So far the only side effect is that I get a mild tingling feeling in my hands a few times a day. This is a very common side effect of Diamox.

3) Take medication that keeps you in the deeper stages of sleep. This way the periodic breathing won't bounce you in and out of different sleep stages. I'm taking a low dose of clonazepam, a benzodiazepine. I take it about an hour before bedtime.

4) Breathe a higher concentration of CO2 during sleep. This tricks the brain into breathing more frequently. This is an area that my doc is actively researching. One way to accomplish this is to use a machine that injects CO2 into the CPAP mask. Another way is to use a CPAP mask with increased "dead space" which allows for more rebreathing of exhaled CO2. I have been prescribed a nonvented mask:
http://www.resmed.com/ja-jp/products/masks/ultra_mirage_non-vented_full_face_mask/ultra-mirage-non-vented-full-face-mask.html?menu=products

There is a piece of tubing totaling 50cc attached to the mask's input. At the other end of the tubing there is a vent valve. At the other end of the vent valve there is the normal CPAP hose leading to my CPAP machine. The idea is to introduce some "dead space" so that I can re-breathe some of my exhaled CO2.

5) Lower the CPAP pressure. High pressures can can cause central apneas in some patients. The doc has lowered my CPAP pressure from 13cm to 10cm. He says I can't handle more than about 10cm without inducing central apneas.

6) Use an ASV-PAP, or "adaptive servo ventilation." It is a PAP machine designed for people with complex apnea. According to my doc, 1/2 the people that try it in the lab do great, and the other half do miserably. There is not much middle ground. I tried this machine in the sleep lab and the doc said it worked fine, but he said the CPAP worked just as well. So I'm sticking with the plain old CPAP for now.


So what is the end result of all these mad-scientist therapies? I wish I could say that one of these, or even all of these in combination, is the "magic bullet" that has cured me. Alas it is not that simple. Some days I wake up feeling great, but other days I feel crummy for hours after getting out of bed. It is hard to see a pattern. I have the most confidence in the bright light therapy, which I've been using the longest. When I'm using it regularly in the early morning, I feel much better. I've only been on the other therapies for about a month now, and I'm still trying to gauge my body's response. I may have to work with my doctor to tweak the dosages of the medications.

As an aside: with so many variables in play, and such inconsistent results, I've decided to try another mad scientist technique. My problem can be stated in general terms like this: "Sometimes I get result A, sometimes B, sometimes C. I have identified over a dozen variables that could be causal, but I don't know what the relationship is between these variables and my result." The way you solve problems like this is by gather a bunch of data, then using statistical modeling software to look for patterns in the data. I don't know much about modeling so I'm going to start with a simple linear regression analysis. The input variables are things like "Time I went to bed," "# of mg of Diamox taken," "Time Diamox was taken," "# of hours slept," "minimum blood O2 saturation," "time I ate dinner," "CPAP pressure," "hours spent on CPAP," etc. The output variable is simply, "How crummy did I feel on a scale of 1 to 10". I will gather this data every day (I already have 3 months worth of some of these variables), then run the software on it. Hopefully the software will give me back a set of numbers that tells me, "on the days when variable B was high or variable F was low, you tended to have a very crummy morning." If this technique produces any useful results, I will certainly post about it.

Jeremy

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