Living Without a Pulse

SteamyMobile writes "Can you live without a pulse? Yes, now you can. The reason why we have a pulse is because it's hard for evolution to result in turbines or continuously spinning things. The next generation of artificial hearts may have no pulse. They also have no bearings, so they should last much longer than previous attempts. In fact, engineers don't give a predicted lifespan on these models. How would your life be different without a pulse?"

Comments

Nature's solution is best in at least a few ways.

[etymxris]

...the VentrAssist is less likely to damage red blood cells because it moves the blood more slowly with a bigger impeller.

That's why you haven't seen more propellor based solutions--they tend to chop up the cells. Propellors work great on something you don't mind mincing up, such as air for planes, water for boats, and ice for that delicious smoothie. But I'd be hesitant to send my red blood cells through a propellor. I know they're talking about impellers and not propellors, but I see little difference in damage capacity.

Pulse

[kc0re]

I heard that people without pulse get a sense of disorientation and un-equilibrium. Especially those with screw drive hearts. Since the body has operated on a pulse for so many years, I have talked to people that have these screw drive heart devices, and they initially they couldn't even sleep at night because they didn't have the pulse in their ear.

Problems

[BWJones]

There are certain advantages to having a "pulse". Examples are: The alternating low and high pressures may allow the bodies baroreceptors to better control blood pressure and there are other important feedback mechanisms associated with having alternating high and low pressures in response to the heart contracting. I would worry that some of the new pumps could undermine those mechanisms.....

Re:Problems

[BWJones]

Perhaps I should have clarified some of this for the non-biologists here. Baroreceptors are receptors found in the aortic arch and internal carotid arteries that are sensitive not only to overall pressure in the cardiovascular system, but also to rates of pressure changes which are critically important in cases where you suddenly undergo rapid loss of blood pressure. (like when you are bleeding......alot). In cases like these, your body starts a series of physiologic changes to keep you alive and interfering with those sorts of things were what I was referring to.

These issues may also be important for maintaining cardiovascular fitness as well as recovering from myocardial infarcts, and because the alternating pulse pressure is eliminated in turbine models, I would worry about possible losses of negative feedback which might result in runaway blood pressure which could lead to hemorrhagic strokes, kidney damage and other such unpleasantries.

Oh, and since the Slashdot crowd appears to be preoccupied with sex, there is some evidence that penile erections are dependant upon alternating pressures to, ahem.....get the job done.

'Detecting a pulse' for those who don't have one

[EnglishTim]

A few months back I did a first-aid course at work. One of the interesting things I found out was the technique they use for checking to see if someone's heart is beating:

Basically, you pinch their earlobe. This forces the blood out of the lobe, and then you let go. If colour returns to the lobe, then the heart is beating and blood has been pumped back in. If it does not then blood is no longer moving around the body.

This technique would probably also work for those with no pulse.

Re:Nature's solution is best in at least a few way

[sql*kitten]

I'm wondering about the little one-way valves throughout the body which aid the pulse. Does such a system damage or suffocate those valves?

Also, the heart isn't the only pump in the body - the muscles in your legs help return blood to the heart when you run. That why if you run then stop abruptly you feel faint, because suddenly the load on your heart has suddenly increased and it needs to ramp up to pump blood all the way up to your head at a usable pressure (which is one reason you should warm down properly after exercising). How would the impeller interact with "pulses" from the legs?

Re:Hmm (ex wife, but seriously...)

[D3]

Actually, I read a Reader's Digest article about a similar pump a couple years ago. Some young girl in England had a viral heart infection and would have required a transplant. Instead, they stopped her heartbeat and implanted a constant pump like this. The doctors were all concerned about the effects of not having a pulse, not having 2 bounces for blood pressure measurements.

She lived quite well with the device and the stopping of her heart actually let the heart muscle repair itself. It turned out that resting the muscle was very good for it. She was eventually taken off the device and her heart restarted.

So no, there are not the adverse effects doctors had theorized about.

Re:mdiarmspafpothama

[GPSguy]

Well, having actually spent some time doing partial and total artificial heart research, including about 6 years with the earlier LVAD (pulsatile) technology, I'm of two minds about this.

1. I don't believe we'll see increased atherosclerotic plaque deposition due to non-pulsatile flow. I'm currently subscribing to the theory that plaque is related in chronic bacterial infection of the vascular intima.
2. There was some evidence, but poorly followud up in the past, that renal function was on the short list of critical elements requiring pulsatile flow. One reason for inadequate continuing studies was that the problems with on-pump anticoagulation, infection and anesthesia tended to introduce enough variables to make isolation of the pulse issue too obscure.
3. There have been a number of reports in the past, some as long as 15 years ago, of surgeons using the Biomedicus BioPump, a similar design, for extracorporeal bridging support to transplantation, or similar to the anecdote below, to place the heart at rest to allow its recovery. I'm aware of many cases (I participated in at least 10) of multiple-day attempts, and at least 2 or 3 trials of several weeks. Realize that the patients were already moribund, so supporting them in bridging, awaiting a suitable donor, was their last and sole chance for survival. And, no, most of them didn't survive to transplant.

I'm intrigued. I'm out of the business now, but I'm convinced that we're overdue for some real breakthrough to make implantable artificial devices for continuous perfusion a viable alternative to transplantation with the limited pool of donors.

Re:Hmm (ex wife, but seriously...)

[GPSguy]

When you place the heart at rest, you remove the load it sees, and use an artificial pump to do the work.

You don't stop the heart. Even today, with cardioplegic solutions significantly advanced, supplemented with NAD-compounds and amino acids, stopping the heart bears the significant risk that you can't get it restarted again.

Cardioplegia for cardiac surgery involves infusing a potassium-rich solution into the coronary arteries, which stops the heart in diastole. Further, the solution is cold, and the heart is bathed in an iced saline slush to cool it further and diminish its metabolic requirements. At this point, the heart is *NOT* getting a blood rich perfusion (barring the use of blood-based cadioplegia, which I'm still not sure is as good an idea as some others think) medium.

If you were to start reperfusing the arrested heart with blood, with a normal electrolyte composition, the extra potassium would be washed out, the heart would rewarm, and if it has sufficient energy stores, and a sufficiently normal physiology, it would begin to contract again.

So: To put the heart at rest, you unload it, keep the blood chemistry as normal as possible, maintain good nutrition status (parenteral alementation), and see if the heart muscle recovers.

Re:He's Dead, Jim.

[ReTay]

"The problem is no-one's going to check your wallet for a consent card for CPR, so she's had her chest tatooed with a warning saying something like "Get thos f*cking this away from my f*cking chest. If you revive me I'll sue your arse off!". "

Kind of remindes me of my EMT instructor, She has three tattoos
There is an "X" two fingers above her zyphoid process (where you put your hand for chest compressions)
and underneath is says push here.
She has the outline of two fingers on her right wrist.
And a circle around her vein in her arm.

Lets just say that if she didn't train them she doesn't trust them.
Then again she is of the opinion that no matter how far along a woman is in labor when you pick them up in an ambulance if the baby is not born in a hospital your driver is to slow.

Re:Hmm (ex wife, but seriously...)

[lucifuge31337]

While I mostly agree with you, I have one nit-pick/addition. As a former meat wagon operator (oh, sorry...I mean paramedic), checking for blood flow in extremities can be done by checking capillary refill as well.

Huh? Yeah...push on your fingernail. The nailbed turns white. The time it takes to go back to pink/red is your capillary refill time. Should be 1-2 seconds max, or you've got problems....not necessarily low bp....dehydration and low o2 saturation will do it too.

That being said, no pulse....how the hell do I get a BP? I'm guessing my pulseox won't work either. Do they have an LCD control panel mounted on their chest so I can check and adjust their BP with a little screwdriver? I can see this type of thing really compilcating/confusing emergency medicine.

Plausible explanation

[Peter Millerchip]

You said: Can anyone offer a plausible explanation for how any one of the pieces of a bacterial flagellum would offer that bacterium some sort of advantage?

Why yes, I think we can!

A nice quote from the conclusion: ...the very fact that a step-by-step Darwinian model can be constructed that is plausible and testable significantly weakens the suggestion that extraordinary explanations might be required.

Nice try though...

Re:lack of pulsatile flow and coronary vessles

[henryhbk]

I am an internist, but we deal a lot with cardiac surgery patients.

A major problem with continous flow would seem to be the diastolic part of the cardiac cycle (when the heart is refilling) is critical for back-flow from the body (arteries do not have valves) into the coronary artieres (the arteries that feed the heart). The aorta (main artery from the heart to the body) is elastic, so a large bolus (fluid surge) of blood is ejected into the aorta, stretching the aorta during systole (contraction of the heart). When the heart then relaxes (diastole) the stretched aorta recoils, and squeezes blood both forward and backwards. The heart has an output check valve at the aorta (aortic valve) which prevents it from completely flowing back; however a small takeoff (the sinus of valsalva) allows the blood to surge into the coronary arteries, and since the heart is relaxed, flow all the way to the muscle of the heart. I don't know if someone has looked into coronary blood flow during these continous pumps, but it might be useful to see, since these hearts are in bad enough shape without becoming ischemic (oxygen starved)

Re:lack of pulsatile flow and coronary vessles

[cellocgw]

Blood will always flow if there's pressure behind it (doh). I'd expect, based more on physics than any experience in cardiology, that a continuous flow at maybe 100mm (well below common systole) would work just fine without overstressing any part of the system.
But if future studies were to show that a pulsing system really does something useful, it shouldn't be too hard to put a controller chip that has the impeller spin up and spin down at some reasonable rate.
BTW, just because it's different from nature doesn't mean it's harmful. For example, it may have taken 50 years (largely due to politics) but it's now considered medically safe for women to take continuous contraceptives and go without menstrual cycles for all or most of the year.

Marine snipers could take longer shots

[osjedi]

My pulse is my biggest hurdle when taking high-power rifle shots at long rages (>600 meters). Without a pulse I could hold steady on a much smaller target. If you've never shot a scoped rifle, your pulse makes the crosshairs bounce with each heartbeat. You can slow your heart-rate down and time the beats, but it would still be nice to be able to hold steady on a 1,000 meter target and not have any movement. If you get excited it all goes out the window - if your pulse quickens you might as well be riding on the back of a horse.

I imagine there are other tasks besides shooting that are impacted by pulse. I'm sure there are types of micro-surgery for example that could be negatively impacted by the surgeon's pulse.