Comment by iancmceachern | Hacker News Reader

Comment by iancmceachern | Hacker News Reader

Parent Full thread

Excellent question.

I've worked in the LVAD and artificial heart industry, designed several.

You are right, that most modern LVADs are rotary pumps which are technically non pulsatile. I say technically because yes, if you test the pump on a bench of course it's not pulsatile. But once they're implanted, and working in concert with the native heart the net result is somewhere in between. You have more flow that you did before, less puksatile, but still pulsatile.

The implant guidance for most lvads calls for the clinicians to lower the speed setting of the lvad until they can see the aortic valve intermittently opening and closing on echo. If they set the setting too high and the valve stays open, or too low and it doesn't often open, it will calcify in one of those two positions.

If they follow this guidance, the net flow is pulsatile.

Onto your question.

Look up "pump head". This is what happens to the brain on truly non puksatile flow, like you get when your on extended periods of support on a heart lung bypass machine.

Check out a company "ventriflo" who is working on a pulsatile pump in this space to overcome these traditional challenges. I helped design this too.

Cheers!

> Look up "pump head".

That doesn't seem to be exactly the same.

https://en.wikipedia.org/wiki/Postperfusion_syndrome says

> Physicians have theorized that the syndrome is caused by tiny debris and air bubbles (microemboli) that enter the brain via cardiopulmonary bypass

which doesn't seem to be related to the pulse, as such.

The linked article says

> current methods for artificial control of cerebral circulation can abolish pulsatility-dependent vascular signaling or neural network phenomena such as the electrocorticogram even while preserving individual neuronal activity.

So to this layman, they're saying the nervous system behaves differently without the pulse, and the study the animal is being used for might suffer from those differences.

A couple of comments:

The literature I'm familiar with doesn't suggest specific cognitive decline attributable to continuous flow vs pulsatile flow LVAD. Most likely, the consequences have to do with waves hands everything else going on and wash out if you have proper controls. For the briefer bypass for CABG, the literature does not clearly demonstrate a difference between on-pump and off-pump, but it seems to be an area of ongoing interest for the surgeons.

The failure of the aortic valve to open leads to thrombosis rather than calcification.

If the authors of the original post that we're discussing had run a comparison to a continuous-flow device and shown some sort of difference, then I'd be sold that their method is important. But since they are just comparing to the literature, the significance of the achievement remains unclear to me.

Clearing up some things.

There is lots of literature here: https://en.m.wikipedia.org/wiki/Postperfusion_syndrome

>The failure of the aortic valve open leads to thrombosis not calcification. - Wrong. It can lead to both. Calcification is when calcium deposits build up and make it so the valve doesn't work, a lot like mineral deposits building up on your faucet valve and making it noe work anymore. Thrombosis is blood clotting. This can happen any time. Both of these things can happen, both aren't really related to eachother. They're both mutually exclusive, and often happen together.

There are known differences, see literature linked above.

These comments appear to conflate the surgical bypass and VAD literature.

Also, the timeframe for valvular calcification and thrombosis are not similar. Thrombosis is the killer when it comes to devices.

There is no way to conflate them. They are the same, they both have to do with the human body and its needs. It doesn't matter if you have one article about weed wacking that says some things about grass, and another article about mowing that also says things about grass. If one wanted to know about grass, it's reasonable to assume you would aggregate the knowledge from both weed wacking and mowing sources so as to have the most complete picture of grass.

Same here, we don't have a lot of studies on this whole cutting a head off and keeping it alive. The closest two things we have are artificial hearts/lvads, and CPB pumps. It's reasonable for us to take those knowledge bases and like with the grass, learn the most from what we have.

You are right, those processes are different and as such have different time frames and clinical implications.

Another interesting point of note. Every artificial heart that is still implanted (Syncardia, Carmet), is about to start to ve implanted (Swedish realheart, bivacor) or has been implanted (abiocor, jarvik 7 which is now the syncardia, etc) were/are all fully pulsatile.

There is one case where Cohn and Frazier implanted a truly hand made bubble gum and duct tape pump made from 2 heartmate ii lvads fiberglassed together, that wasn't pulsatile but the patient was never expected to live long and it was really something they shouldn't have done.

I cannot stress how different routine cardiopulmonary bypass is versus VAD implantation. From patient selection to procedural considerations, no clinician would treat them as if they were the same thing. I'm saying this for the benefit of other HN readers.

100%.

I'm speaking from a design perspective.

When we design a pump, any pump, we need to design it to certain design inputs.

Say we're designing a well pump. We need the pump to pump a certain amount of water, a certain height, with a certain input power.

It's the same when we design LVADs or CBP pumps, peristaltic blood pumps for dialysis machines, etc.

One example. I lead the team that designed the peristaltic blood pump (and most of the whole system really) for the Outset medical Tablo kidney dialysis machine. I also have designed several other peristaltic pumps that pump other fluids. Pragmatically, the designs are almost identical. It's because pumps are pumps. The renal technician is going to say that the pump on their Gambro Dialysis machine is completely different than the pump in the Wendy's frosty machine down thr street, but the design engineer that designed them both knows better.

Back to this topic.

When we design a blood pump, it needs to meet certain design requirements. To test our design we need to model the body, it's response to inputs, etc. When we do this, we use the exact same models, exact same tools, exact same design principles, exact same process, amd exact same requirement s in many cases.

Indeed, no clinician would ever treat these things the same just like no mechanic would treat a Ford the same as a Toyota. But at the design level, they're the sake. They're both designed using the same CAD software, share many of the same suppliers and middle ware suppliers, etc.

I cannot stress how similar so many things are in medicine, in medical device design. So many people try to put up walls like this. It's not helpful to highlight differences, it's helpful to identify similarities, because that's where the economy of scale lieslies, that's where we can come together and solve problems.

Actually, it's important to distinguish things that are not clinically similar. The physical principle being the same, in this case, has little to no bearing on the clinical context or consequence.

Not at all.

Physics is physics, it doesn't magically stop just because it's in the body. Just because we put two identical things into use doing 2 different things, doesn't mean they're not the same.

A person with a back ache could be prescribed aspirin. Another person with blood clots could also be prescribed aspirin. Clinically these are very different things. The aspirin, and the factory that makes it, and the biochemistry by which it works, is the same.

Blood pumps are blood pumps, aspirin is aspirin. What you do with them clinically, and how, can vary widely. Agreed. But that doesn't mean the chemistry, physics, engineering behind them does too.

> Look up "pump head".

https://en.wikipedia.org/wiki/Postperfusion_syndrome

Not to be confused with:

https://en.wikipedia.org/wiki/Reperfusion_injury

Reply on news.ycombinator.com