Back pressure

I know a lot about hydraulics. The circulatory system is basically a closed hydraulic system with arteries being the pressure side and veins being the return side. Backpressure on the return side is a serious concern with hydraulic systems. It reduces efficiency of the whole system and causes various other problems that they write whole books on.

I'm bringing this up because PM leads are run down a vein (return side of our system). What happens to the back pressure created? Does the vein grow larger in time? Can't the back pressure cause localized heart damage if it decreases/stops the flow of blood? My cardiologist never addressed this issue and I've never seen anything about it on this site.

It just seems to me that this issue may be what is causing some people heart pain after PM installation. It would be worse in people who have smaller viens (children, women, inactive, out of shape, etc). At the least, it would cause less efficiency under stress for everyone. If it expands, teh body would overcome it. But it would be a definite issue when first exerting oneself after PM installation.

Any experts out there who can satisfy my curiosity????

9 Comments

More on backpressure...

by donr - 2012-09-01 04:09:04

...Dave, my Cardio & I have discussed this issue. There are several things that happen - at the constriction & throughout the vein w/ the wires in it, the velocity of flow increases to account for the requirement that a certain volume of blood pass through the vein w/ each compression of the heart. The heart is essentially a fixed displacement pump, moving the same amount of blood w/every contraction. Things are fine till you clog the vein w/ too many wires, then you start having some back pressure problems. That was my EP's concern when he had to replace a broken lead I had at 4 yrs.

As you say, the veins are elastic & can expand to handle the increased demand on them, within certain limits. Whether they actually grow in diameter under stress, he never said. But some growth would make sense - except that coronary arteries don't seem to spontaneously grow larger when they start filling w/ plaque.

Could it cause pain? Dunno, but under increased floi rates at the constriction, there would eventually become turbulent flow & potential cavitation - forming bubbles in the blood that just might cause severe discomfort.

Don

Joke

by growler9 - 2012-09-01 07:09:25

Did you hear the one about the two engineers who got pacemakers........

Alan

no, but...

by donr - 2012-09-01 07:09:46

...there are at least Three of us who'd like to hear it.

I assume it is insulting.

Good!

Don

Keep up teh questions?

by ILoominatedEKG - 2012-09-02 02:09:16

I can't help but keep up the question. I frequently tick the "experts" off with all of the questions. LOL

Thanks for the input. I don't know why I didn't think of thepositive pressure throughout. That's why BP consists of the PRESSURE measurementsw of the systolic and diastolic phases.

Educated idiots really bother me; all the more when I am it. LOL

I think I'm going to present the question to my cardio guy and see what kind of answer he gives me. This should be interesting. I'm guessing he won't give me anymore than we're already discussing here.

Thanks again for the input guys.

Dave

Back pressure

by ElectricFrank - 2012-09-02 02:09:40

One thing to keep in mind is that the blood vessels both pressure and return side are soft flexible hoses. There has to be a positive pressure even in the return line as opposed to solid tubing. The atrium isn't capable of creating a negative pressure so again it requires a positive pressure to fill it. There is also a lot of compliance in the vessels. The cuff method of blood pressure depends on it. Of course the cuff method of BP measurement doesn't pass the laugh test as far as I'm concerned.

I'm an electronic engineer and have worked a lot with hydraulics in missile control systems so I know how you are thinking. I've pretty much taken charge of specifying the settings for my pacer.

The difficulty I have is that medicine relates everything to studies and statistical data. As an engineer I just want to know the parameters of the system and I can work out the answers.

Keep up the questions. There are several of us on the site that are interested in such things.

frank

Me too

by ILoominatedEKG - 2012-09-02 04:09:09

That thought crossed my mind as well. I can't help but think a little bit of the oxegen carrying blood that ought to feed the area directly around that lead isn't going to get there. It just might pump with a little less efficiency. It's still infinitely better than dying!!!! But I just like to know the real parameters I'm working with. I trim trees for a living, so I am already anticipating a few more breaks while I'm in the tree. I'll deal with whatever I have to deal with. I just hate surprises.

Dave

I'm Thinking........

by Tattoo Man - 2012-09-02 04:09:29

....does this go any way to explaining why so many Runners on this Forum have noted a performance drop-off after recieving a PM..ie..increased heart reliability but with a reduced rate of blood flow as a trade -off ??

Just a thought...

TM

Would you rather

by ILoominatedEKG - 2012-09-02 12:09:43

they based their opinion on 200 studies or pure speculation? I prefer the studies even if it's just a couple of them. On the other hand, if there is one thing I know which the docs seem not to know, it's that they sometimes don't know and don't know how to say they don't know. Did I say that right?

Reduced efficiency

by ElectricFrank - 2012-09-03 12:09:54

Actually, this problem has more to do with the electric system. The contraction of a a heart chamber starts with an electrical trigger from a nerve bundle, which isn't a point source like a pacemaker electrode. So the contraction spreads differently than with the natural situation giving a different pressure wave coming out the aorta. For most of us this isn't a problem, but with high aerobic athletes who need every last ounce of blood flow into those poor abused muscles it could be.

By the way the pacing current into the electrode can also influence a paced chambers contraction. In a volume conductor like the heart wall a point source current spreads out in a pattern of decreasing level. Since there is a threshold level required to trigger the tissue, the higher the current the larger the area of initial contraction.

I had a go around with my cardio on this one. I maintained that higher than necessary pacing current can initiate the heavy heart beats that are sometimes felt. I also think it can increase the incidence of PVC's. Since one cause of PVC's is irritable heart tissue, and higher pacing current tends to irritate the heart wall..well you get the picture.

By the way I keep referring to pacing current.The pacer only provides a way to set pacing voltage, but since voltage/electrode impedance= current and the impedance is fairly constant it all works out.

Now I have to say I haven't read any this anywhere so I'm just giving it an engineering guess.

Yikes, I got carried away.

frank

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You invested in the Energizer battery company.

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