Wednesday, November 23, 2011

Cardiac Variability at Night During Apneas/Hypopneas (Sleep Apnea)

 If I have directed you to this topic of my website, it's because you have sleep apnea, and I wanted to point out just one of the things that is happening to your heart during your breathing events.... I realize it's long, but it's to inform you about something your body is going through.If you stumbled across this and you may (or do) have apnea... I believe it is just as relevant to you and hope you will consider its implications as well.

This is from a patient's sleep study I am just now reading, not the textbook example, but it illustrates the point, and this particular patient (a male) is coming in to see me after this long weekend, so I thought I would take his name off and put this in my blog for him to see, and because I think it is important as a teaching point for many of my other patients in which this is seen quite frequently.

So first, be patient as I try to show these pictures to you. I promise they aren't as confusing as they might look to someone at first glance. I have cut out of the frame much of what you don't need to see, and I explain the pictures step-by-step if you will just read a touch and then glance at the picture again.

Okay, so in this first picture, you see a bunch of squiggly lines which are labeled on the left, not that you can read them easily. This is part of a screen I will see during my review of this patient's sleep study. He slept about 5 hours the night of his study, and this screen represents about 30 seconds in the top half and 2 minutes in the bottom half, so I look at hundreds of these screens to get a feel for what this person's sleep is like during the night.

I'll separate them out in a second, but I want you to notice just a few things here.
-On the very top are some EEG leads that go on the head to know whether you wake up or not and what stage of sleep you are in.
-Then we have a few chin leads that tell me if there is some muscle activity in your chin, usually present when you are awake and it should be completely flat when you dream
-Then (the blue wave lines) are eye movements.
-THE RED LINE is very important and is the easily recognizable EKG lead for you heart seen on 1 million episodes of Grey's Anatomy/ER/House/Scrubs/etc...
-Then we have two leads for your legs to watch them move or not
-Then there is the purple line for what body position you are in (sleeping on your back, right side, left...) At this particular time, he is on his BACK ("supine" is the name for it here)
-Below that is the snore mic
-Then we have a series of lines devoted to helping us measure your breathing in different ways. In this particular study, they are the series of squiggles interrupted by flattened valleys... it isn't supposed to look like that (see below)
-And below that we have the oxygen saturation. The red BOLD below is telling us that it is dropping uncomfortably fast at this point.

This is the fuller picture below, with the above picture over to the left and smaller so you can see the rest of this important screenshot

Now the bold PINK up-and-down lines I've drawn below are to tell you where the top half of the screen lines up with what is going on in the bottom half of the screen. The top and bottom are running at different speeds because they need to for me to see the different waveforms better.

But even from this zoomed out view, you can see a pattern:

At the BOTTOM pink line, which comes just BEFORE the TOP PINK line, there is a flattening of the breathing waveforms. It lasts about 15 seconds.... That is because this person is NOT breathing well during that time. Then, you can see BELOW that his black snore mic line squiggles a bit more as he tries to take a better breath, and he does eventually (the breathing waves get suddenly bigger). By the way, this is a hypopnea, NOT an apnea. There a couple differences potentially, but an apnea is worse and I am showing you an example of a hypopnea in the particular instance.
This takes us to the TOP pink line, where he wakes up briefly. If you look very closely at the top EEG lines, you can see his brain waves get a little more squiggly than just before the pink line. His chin lead also helps because it gets more active. AND you can see the BLUE eye movement leads becoming a little more wavy.

BUT I want to highlight the red EKG line in a second here.

Here it is in closeup:
1. Flattened breathing lines because he's not taking a good breath due to some obstruction in his airway
2. It lasts for awhile (about 15 seconds or more).
3. His brainstem gets worried and thinks a leaf fell in his mouth or something and makes him try to take a better breath
4. He does (at the arrow)
5. At the same time you can see a soft snore on the mic (circled)

Now at the same time, you can see the resultant changes in the top half of the recording screenshot, blown up here:
1. His chin starts moving (square)
2. His EEG/brainwaves show that his brain is waking up a bit to make sure everything is okay even though it's not waking up enough for him to remember waking up (pink circle)
3. His eyes are moving under his eyelids a bit (blue lines with some light blue highlights)
4. His EKG speeds up (aqua circle)

Here I just circled some of the things I was showing you, all together on the same screen.

Okay. It took me too long to actually get to the point. I cut out the heart rhythm during the event and after and put it here below, but I want you to understand what is happening in context. There are many problems with sleep disordered breathing at night, and one of them is the stress on your heart. Your heart is supposed to relax at night. To keep taking it to task each night adds up over the days-weeks-months-years... to cause damage.

The scale for these two rhythms below is the same. They are cut from the above pictures you were just looking at. And even though I can't line it up exactly here, you can see that two of the first lines can fit into one of the bottom. The top line is a doubling of his heartrate during the choking episode.
It's speeding up suddenly too much during his choking and then slowing suddenly afterward, back and forth all night. This pathologic cardiac variability damages the heart in the long run, along with the other problems associated with sleep apnea.