3 ms·

They address this but I still don't really understand why I should care about pulsatility. Humans can live for a very long time without pulsatile flow (LVAD). (

They address this but I still don't really understand why I should care about pulsatility. Humans can live for a very long time without pulsatile flow (LVAD). (And sure, to pre-empt critics: the needle has turned back towards at least intermittent pulsatility, but this is largely for device thrombosis prevention.) They seem to bring up theoretical concerns without addressing the practical (again, in human) successes of non-pulsatile flow.

iancmceachern 3y ago
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!
- yencabulator 3y ago
  > Look up "pump head". That doesn't seem to be exactly the same. https://en.wikipedia.org/wiki/Postperfusion_syndrome 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.
- bobmaxup 3y ago
  > Look up "pump head". https://en.wikipedia.org/wiki/Postperfusion_syndrome https://en.wikipedia.org/wiki/Postperfusion_syndrome
  - matheusmoreira 3y ago
    Not to be confused with: https://en.wikipedia.org/wiki/Reperfusion_injury https://en.wikipedia.org/wiki/Reperfusion_injury
- carbocation 3y ago
  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.
  - iancmceachern 3y ago
    Clearing up some things. There is lots of literature here: https://en.m.wikipedia.org/wiki/Postperfusion_syndrome 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.
    - carbocation 3y ago
      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.
      - iancmceachern 3y ago
        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.
tomr75 3y ago
Results in lower GI bleeding too (pulsation). Don’t know the physics but ?less shear stress
carbocation 3y ago
I tried to pre-empt this but apparently I didn't do a good enough job: my questions are with respect to the pig model system developed in the actual paper being discussed, not humans.

iancmceachern 3y ago

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!

yencabulator 3y ago
> Look up "pump head". That doesn't seem to be exactly the same. https://en.wikipedia.org/wiki/Postperfusion_syndrome 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.
bobmaxup 3y ago
> Look up "pump head". https://en.wikipedia.org/wiki/Postperfusion_syndrome https://en.wikipedia.org/wiki/Postperfusion_syndrome
- matheusmoreira 3y ago
  Not to be confused with: https://en.wikipedia.org/wiki/Reperfusion_injury https://en.wikipedia.org/wiki/Reperfusion_injury
carbocation 3y ago
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.
- iancmceachern 3y ago
  Clearing up some things. There is lots of literature here: https://en.m.wikipedia.org/wiki/Postperfusion_syndrome 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.
  - carbocation 3y ago
    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.
    - iancmceachern 3y ago
      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.

tomr75 3y ago

Results in lower GI bleeding too (pulsation). Don’t know the physics but ?less shear stress

carbocation 3y ago

I tried to pre-empt this but apparently I didn't do a good enough job: my questions are with respect to the pig model system developed in the actual paper being discussed, not humans.