Am designing an fMRI experiment on apnea - need some advice on breath-up technique

[[xeno]Julios]

Hi all,

For one of my courses, we get to design and run an experiment using our fMRI lab. I thought of measuring brain activity as it relates to increasing "air hunger" (dyspnea). I will have subjects perform a few static breath holds for as long as possible, and before the last breath hold, they will be performing a breath-up exercise to increase their maximum breath hold (I know that they'll progressively get longer and longer times just by virtue of doing a few successively, but I'm hoping to elicit a significantly longer breath hold time in the last trial by having them warm up properly).

When I dabbled in freediving almost a decade ago, I read some tutorials that recommended a breathe in:hold:breath out ratio of 1:1:2 (so, for example, you'd breathe in for 5 seconds, hold for 5 seconds, and exhale for 10 seconds). You repeat this a number of times, then do a few deep and fast breaths (mild hyperventilation), and then start the actual breath hold.

I also came across this:

How to Hold Your Breath Like David Blaine, World Record Holder (and Now, Me)

there, the "deep breathing" portion seems to recommend a much different ratio (more like 1:1:10)

I would greatly appreciate some guidance here, keeping in mind that whatever technique that I use, it will only be used once before the last breath hold attempt.

Since this is a class project, and we are not going through ethics, we will be unable to publish this data, but if the results look interesting, we might actually carry out the study with the proper formalities.

thanks!

 

[trux]

Re: Am designing an fMRI experiment on apnea - need some advice on breath-up techniqu

Any prolonged hyperventilation will lead to hypocapnia and consequently to the constriction of carotid arteries, and hence cerebral hypoxemia already prior the breath hold. And any unnatural deep breathing presents very likely hyperventilation, regardless the exact pattern. The long exhales stimulate bradycardia, on the other hand hyperventilation triggers tachycardia, so in some way such breathing pattern allows hyperventilation without too high HR. It is a questionable technique, and it is a question whether you need any hyperventilation for the MRI study. Personally I would rahter advice instructing the subject to breath absolutely normally and flatly to avoid any hyperventilation. But on the other hand, if you need to avoid contractions for a long time (to avoid that the subject moves during the scanning), the hyperventilation may show useful.

In fact, with the MRI you could also study exactly this - the influence of the breath-up on the oxygenation of the brain before and during apnea. Since I learned that oxygenated and deoxygenated hemoglobin have completely different magnetic properties, MRI is very well suited for such purpose.

 

[[xeno]Julios]

Re: Am designing an fMRI experiment on apnea - need some advice on breath-up techniqu

Thanks for the reply.

Am I correct in assuming that part of the purpose of the breathe up is to slowly oxygenate the blood so that the person can endure longer apnea durations? If so, I'm assuming this can be done without hyperventilation.

If so, what kind of breathe up schedule would you recommend?

Yes contractions were something I was worrying about for the reason you mentioned, however I'm hoping that because none of these subjects have a lot of experience with apnea, they'll likely not be able to hold their breath long enough to experience contractions.

As for the effects of breath holding on the BOLD signal, there have been a few interesting studies that examine this, so we'll be able to account for these "global" changes. What I'm interested in is looking for particular brain areas that show a gradual increase in intensity as the subject experiences more and more air hunger, and also for any unique patterns that occur just prior to exhalation. (because we're in a scanner, I think it best that subjects not be allowed to gradually exhale to relieve diaphragm pressure as a means to prolong their breath hold, so the trial ends when they exhale violently).

 

[trux]

Re: Am designing an fMRI experiment on apnea - need some advice on breath-up techniqu

Further replies in the related thread in the Science subforum: http://forums.deeperblue.com/freediving-science/93099-am-running-fmri-study-breath-holding.html