Save the life of an obese person, and my research project. You may win a prize :)

[basmoq]

OK, I'm working with someone who designed (and patented, so don't get any ideas...) a backboard that has a ridge down the middle to support the spine of a grossly obese person (300+lbs) while doing chest compressions (CPR). The idea is that the compressions done on these people are inneficient or innefective due to the large fat pads on either side of the spine. Because the fat doesn't accumulate as thick directly over the spine, supporting directly under it should bypass the springy effect of the fat pads and allow for full compression.

Now the problem, proving it. I have a $3K Laerdal CPR dummy at my disposal, I can do anything to it that I want, and I want to make it respond like a obese person. On a flat backboard, it should not compress easily or even fully, and when used on the special backboard, it should. Now think of the dummy as nothing but a rectangular box in the shape of a torso, with a pressure sensor in the middle. I say box because the back is a solid, stiff, rectangle...

My idea is that, like the compression sensor in the dummy, I can use springs to simulate the fat on either side of the dummy along the axillary lines (from the armpits straight down). My logic behind using springs rather than ballistics gelatin is that they can be calibrated to replicate a specific force (spring force = F = -kx) for a low price. To use ballistics gelatin would require a walk in cooler, an obese man (I have one of these), lots of plaster to mold his back, lots of free time, time to play with the formula because ballistics gelatin is formulated to replicate muscle not fat, and last but not least, lots of money... (it's $350 for a 50Lb tub of the gelatin)

So with a row of springs down either side of the dummy, with it lying on a flat backboard, performing chest compressions would first compress the springs(fat pads), and then compress the chest sensor when the springs I added are fully compressed.

On the backboard with the ridge, the dummy would be supported along the midline and therefore all compression force would be directed directly to the chest compression sensor.

Now the problem. How do I determine the correct spring strength to use with the dummy??? I have absolutely no clue how to measure the force required to squish an obese person's fat...

BTW, I'm a medical student, I'm not tied to this project financially in any way and will not benefit from the approval of it for medical trials, so don't ask me for money if we figure this out, I'm not going to get any

[Willravel]

You live in Ohio and you can't find a fat person? Really, the best way to test this is to get feedback from the "dummy".

[basmoq]

Aww, come on Willravel, it's the corn industry that's to blame, if they didn't fill all our food with corn syrup, there wouldn't be fat people, JK

[Plan9]

Find a fatbody and pay them with fast food. BAAM!

[Fotzlid]

The idea is that the compressions done on these people are inneficient or innefective due to the large fat pads on either side of the spine.

i think you'd need to take into account the fat on the chest wall as well. it can be like doing compressions on jello.

[pig]

Two comments:

1. Don't forget to consider how accurate the spring = fat model is. You may need to independently confirm this, as you don't want to rig your experiment to get the results you need.

2. Animal fat. You get animal fat and measure the compression under a given force, if you're going to calibrate a set of springs to simulate fat compression. As you mention, Hooke's Law => your spring constant.

3. Bad Idea


Regardless, best of luck.

edit: Rethought #3...probably more trouble than you want to get into.

[basmoq]

Originally Posted by Fotzlid

i think you'd need to take into account the fat on the chest wall as well. it can be like doing compressions on jello.

Like on the back, the sternum, manubrium, and xiphoid process are all rather thin on fat, so it's not so much of an issue from our perspective, and it wouldn't be altered by the backboard, so it doesn't affect our project...

[The_Jazz]

Why not use animal fat? Does, say, pig fat compress differently than human fat? I would think that would be something that you could obtain easily at any butcher shop, especially if you explain to the butcher why you want it. You'd most likely have to pay something, but it seems like an easier fix to me than springs, especially since you'd have to calculate how much fat compresses and find springs that compress accordingly.

The simplest answer, it seems to me, is to contact your local medical school and see if they have an obese cadaver they'd be willing to loan you. My understanding is that medical schools are generally pretty good about research, but your results may vary.

[basmoq]

I'm a medical student, as stated above, and no, a medical school will not accept an overweight candidate for a cadaver due to the complexity of dissecting an obese person (believe me, fat is your worst enemy in Gross lab). The other complication is that a dead person's fat behaves differently than a living person's fat and we can't get a cadaver that hasn't been preserved. As for why I wasn't thinking about using an animals fat for the actual experiment is because it would be hard to find one solid mass of fat large enough to suite my needs, most stock animals are bread to be lean, not fat, so although pigs pack on the pounds, most of it is muscle.

On another note, the idea of using animal fat to measure it's elasticity sound like a great idea. The only question would be, how to do the actual measurement??? I certainly need to compress the fat, but how d I measure the force being applied and the force being absorbed by the squishing of the fat? If I can figure this out, I think I will be halfway there.

[pig]

basmoq:

as to the last point, the first thing I think of is a weighted compression between two metal plates, with the weights being attached to the top plate. You know the mass of the weights, use F=mg to get the force. Measure the compression distance, and you get F=-k*x to give a spring constant. It depends on how exact you need to be, and what your budget is. I'm sure someone like ASTM has a standard test for this type of thing, but their standard equipment tends to be fairly expensive. If y'all are looking to do this on the cheap, rig something yourself. If you really want to do it correctly, you'll probably need to spring for standard compression measurement equipment. People do this sort of thing all the time in mechanical / civil engineering. I would think a carefully placed call or email to the right professor or testing laboratory would tell you the standard method in the field.

[basmoq]

Thanks pig, that's something I can look into, we will see if it helps.

[Bear Cub]

How about using a ballistics gel and making a mold, Mythbusters style?

[basmoq]

Originally Posted by ChassisWelder

How about using a ballistics gel and making a mold, Mythbusters style?

Please read the whole post before chiming in, this was covered in my origional post...

[Bear Cub]

Originally Posted by basmoq

Please read the whole post before chiming in, this was covered in my origional post...

My mistake, skimmed over the springs portion and missed that.


The main reason that popped into mind originally, is that the shape/contour of an obese person will not match that of a rigid dummy, despite how it may be replicated with springs.

I'd think that the hips and buttox would factor in quite a bit as far as how the person is oriented on the ground, general posture affecting the curvature of the spine, and if there are the fatty pads on the back, the tendency for the shoulders to rotate upwards, none of which will be realized with the traditional dummy.

I don't think the issue will be getting an accurate compression reading upon the back brace being used, but rather, finding a valid way of incorporating all these variables when obtaining the original compression reading.

I do see that you're located in Ohio as well. It may be worthwhile to contact Dr. Freuler from Ohio State's engineering department. We did a multitude of work with various force and strain gauges back when I was there, and as Pig mentioned, that may be a viable source of obtaining free labor/use of test equipment with a few phone calls.

[basmoq]

That's the kind of help I'm looking for, being that I went to Purdue and don't have the ability to drive out there with two kids at home... I realize that this project is well beyond my personal abilities, however I got roped into saving the project for my wife, so now I just have to find a way to let her save face...

The actual objective is to show the need for an obese dummy and convince Laerdal to produce a realistic one, along with promoting the backboard. There are a few other side objectives as well, but none of them pertain to the problem at hand.

[pig]

basmoq:

What's your deadline for this problem? I somehow keep thinking about this thread when it pops up, and my currently line of thought wonders how you plan to modify the dummy you have, without permanently damaging it.

I might approach this by first building a simplified dummy out of plywood, a box, whatever, that showed the same compression measurements as the 'normal' dummy you have. I would argue that the use of springs is an a-priori assumption, and then use springs to calibrate your "normal" mockup so that it reads the same compression as the dummy you purchased. I would use this as my baseline. I would then add springs to the 'fatboy' dummy to simulate the affect of, well, being fat.

I say this because if you fuck up your $3k dummy trying to 'fatten' him up...then you're sort of screwed. If you only use it as a baseline for performance, then you can mess up a bunch and not lose your control.

[basmoq]

there is really no need to modify the Laerdal dummy to fatten him up, all things of interest are occuring below the dummy's back, so I simply plan to lay it on top of whatever fat simulation setup I come up with, at best using velcro or screws to hold it from sliding around. The dummy itself is nothing but a rectangular box with arms, legs and a head... All the sensors are contained within the box of a torso, so there is no need to do anything but attach it to my rig and try it out

As for deadline, my wife has about two months to feasibly do this project under her funding and with the Laerdal manequin, I on the other hand will have all summer to do research assuming I can find my own funding (which shouldn't be that hard if I can show that her research led me in the right direction to getting a useful result). There is tons of funding available for medical students to do their own research. I'll likely go the gelatin route personally, but I simply don't have time for that now. I'm simply blessed to have the opportunity to work with the inventor of this backboard and hope to possibly turn up data that will save some lives.