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The biggest advantage to the rotor-style or axial pumps is that they are small and relatively simple. The AbioCor heart, for example, is so large that it can only be implanted in people with large chest cavities, making it inappropriate for most women. "Axial pumps are about the size of an adult thumb and can pump more blood than a normal heart," says Frazier.
Continuous flow pumps are also more durable, due to the simplicity of their design--the only moving part is the rotor. "Other pumps work well, but there are lots of moving parts so they are subject to mechanical wear," says Cohn. The longest the AbioCor heart functioned in clinical trials was 18 months, while continuous flow devices are being designed to operate for 10 or more years.
Frazier also says continuous flow pumps are better able to respond to the body's changing needs for blood. "If you're walking, more blood is pumped back to the heart and the heart will automatically pump more," he says. If pressure on one side of the pump increases, flow through the device automatically increases, allowing the pump to respond like a native heart, Frazier says.
But what about the long-term impact of living pulse-free? That question is a matter of lively debate in the cardiac device community. Akif Undar, a clinician and cardiac researcher at Penn State University, says pulse is important to get blood to all the small capillaries feeding the organs. "I think you would see organ damage in animals given a [non-pulsing] heart," he says. Others, like Yukihiko Nose of the Baylor College of Medicine, say that animal studies conducted by his group show that continuous flow devices can be as safe as devices that use a pump with a pulse.
Frazier and team aim to answer this question more definitively with long-term animal experiments, pending funding for the project. (The longest experiments the researchers have carried out so far lasted 20 days.) The team is also designing specialized pumps tailored for use as artificial hearts, with rotors that respond more efficiently to changes in flow. "A lot of work needs to be done before this can even be considered for clinical application," cautions the NHLBI's Baldwin.
It's not yet clear who would be the prime candidates for the pulseless heart, should it prove safe and effective in animal studies. Because artificial heart technology is still so risky, the current FDA approval for the AbioCor heart limits the device to patients with heart failure who are not eligible for transplant and would likely die within a month. Cohn hopes that in the future, artificial heart technology will become much safer and easier to use, broadening the potential pool of patients. "It wouldn't surprise me if at the 2050 Olympics, there were standard and modified [competitor] divisions," he says.
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I am very impressed with the research on this, and will look forward to reading more on the extended trials...but before this is ever implanted in someone who is going to walk out of the hospital there has to be some way to permanently "mark" the patient as having no pulse. Can you image what would happen if an EMT (or insert-medical-personel-here) came across an unconscious patient with no pulse...
I recall the early days of such turbo pumps--then imagined largely as booster for weak hearts. My one worry,,, well, one of them,,, is that not much study is reported on what the turbo blades do to blood cells. Current heart bypass pumps are not used for long periods in part because of damage they do to fragile blood cells--in other words, our hearts are made this way for a reason.
Also, the heart is more than a dumb pump. It produces regulatory chemicals, it is an organ just like any other, with multiple functions. I would advise some research into the hearts--aortic arches--of insects. They are like stacked simple pumps, and seem mechanically simple. If an artificial version could be fitted into a failing human heart, leaving most of the human heart, it could possibly perform all needed functions.
The Medic Alert bracelet is a standard way of telling EMTs something that you want us to know in an emergency. "Artificial Heart - no pulse" on the tag would do fine.
I've done thought experiments of pulseless blood-flow using nanobots, and utilizing their swarm nature -- swimming like a school of fish carrying blood with them; of course these devices don't exist yet, but give it about 15 years. From this it was my feeling that a pulseless flow of blood would not keep blood vessels elastic, making them more susceptible to damage. And getting fluid between the cells would prove more difficult without an extra bit of force to "get in there". Would that contribute to clogging of an already inefficient lymphatic system?
Why not build into the device a "fluid capacitor" that builds a little pressure in a balloon-like structure then discharges for the pulse effect? Blood would continuously flow but an extra "push" every 5 to 10 seconds or so would emulate the heart beat giving the body the desired effects of a pulse.
John
I`m not a doctor, or someone with vast knowledge in the theme, but I think it`s clearly important to consider the role of chemistry in this problem. while every labotarory is concerned about the physcis part, refering to replace a "pump" no one is considering that this "pump" doesn`t only obey to mechanical/physical stimulation, such as running, they are ignoring situations of danger, imagine someone who is in mortal danger, and his body starts producing adrenaline, the natural heats respond to this stimule, pumping faster the blood, but how can an artificial heart, axial, nanobots, or any artificial heart designed until today would respond to this if this artifial doesnt respond to this stimulation? And the thing is, how this is going to affect the patient in his response to the situation?
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wdilwort
1 Comment
Best of Both Worlds
I would agree that the axial pump is the most reliable but could they not put a feed-back circuit from the output of the pump back to the imput of he pump. In this "pipe" insert a valve that would close say 60 time a minute. When the valve is closed blood would be forced through the body and when it is open blood would take the bypass back to the inpt of the pump. The pump would stay very reliable and the body would see a pulsed blood flow.
The value would be controled by a circuit with a default setting of say 60 pulses a minute. This could be over road by a senser monitoring the lungs rate or even a oxygen sensor in the bood stream.
Well, I guess I just made it more complicated and thus more problem prone to problems but it seems like a simple way of getting the best of both worlds.
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