Mechanical Valves - Perhaps A Silly Question

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R

Rush20

Well-known member
Joined
Jan 14, 2004
Messages
265
Location
Bradenton/Lakewood Ranch, FL. (Heart Still In Chi
As a St. Jude Mechanical Valve user, I often wondered why the artificial valve is designed basically as a bicuspid valve? I had a natural bicuspid and had to have it replaced due to a bacterial infection caused by oral surgery. Or so they say. :confused: Anyway, I was wondering why the actual artificial design is a bicuspid valve? Since the more common tricuspid aortic valve is more efficient, I wonder why they haven't tried to design an artificial tricuspid aortic valve. I imagine it would be more difficult of a design. ???
 
Ross is right.....again

Ross is right.....again

They have designed one and are doing clinical work on it. It is a more difficult design to engineer because the tri-leaf design has to close on themselves rather than the valve base. It main advantage is that it offers a central flow like a natural or tissue valve. Lots of good things coming, let hope they work and come to market soon :)
 
hosacktom said:
So, with a tri-leaf design that has the leaflets closing on themselves, will the recipient need anticoagulants?
Click to expand...

Still to be determined :rolleyes:
 
I'm just getting old, but...........

I'm just getting old, but...........

Rush20 said:
Since the more common tricuspid aortic valve is more efficient, I wonder why they haven't tried to design an artificial tricuspid aortic valve. I imagine it would be more difficult of a design. ???
Click to expand...

I forgot that my first valve was a tri-leaf valve.
 
More moving parts, more complexity, more things that can go wrong.......


I wouldn't be suprised if, at least in computer modeling, the "physics" of a tri-leaflet valve are better than a bi-leaflet valve. The big concern is how much of the physical valve is impeding the flow of blood through the valve and how much of that diverted flow is going to cause problems which would damage the valve in some manner?

There's a thing in fluid dynamics (as I recall) called "cavitation" where a fluid (water for example) tends to break apart into more basic components or elements when passing by a hard surface. This is important for naval vessels (especially submarines) because the little gas bubbles that cavitation create make lots of noise which other ships (or submarines or whatever) can hear. In fact, they can even identify certain classes of submarines, even identify specific subs, based on these noises.

In the human heart, that cavitation can seperate oxygen and nitrogen from the bloodstream which can then move around in it's gaseous state and wreak havoc in various places, most notably the brain. This cavitation is also part of what leads to calcification on the valves (though there's some other stuff involved too such as how platelets and white blood cells have a tendency to stick to foreign matter such as artificial valves...)

Anything yo ucan do to minimize all this stuff is beneficial of course. Id a tri-leaflet valve does that better than a bi-leaflet like what most people get these days, then that's a good thing. Just that the trick is designing one that doesn't have all the other complications a more complex artificial valve might produce.

Remember, the old ball and cage valves pretty much SUCK compared to what's used most of the time now, however there are still a lot of ball and cage patients running around banging away loud enough to interupt a night at the opera.... :D
 
Harpoon -- thanks for your post, reading what you wrote I came up with a silly question of my own, and did some interesting reading:

-- Why do valve manufacturers go for smoother surfaces, I think the fluid flow is actually more laminar around rough surfaces than smooth ( for e.g. golf balls with serrations travel further )

So I started reading about the design of heart valves, went to the website of the On-X valve and did some searches on cavitation and Computational Fluid Dynamics applied to artificial valve design. The use of 3-D computational fluid dynamics in evaluating artificial heart valves seems a recent development and numerically solving the navier stokes equation for small valves with parts ( e.g. hinges ) which are comparable in size to large blood cells seems to be a very computer intensive task. Here is a recent paper from Georgia Tech:

http://www.bbriefings.com/pdf/1102/yoganathan.pdf

As they start using better computing techniques in mechanical valve design they are probably going to find more optimal solutions to the current problems with HITS, cavitation and turbulence around the hinge area. All this reading still didnt quite satisfy my initial question -- maybe the answer is some sort of bio-compatibility issue:

http://www.mcritx.com/carbon_valves.htm

I am a bit surprised though at the seeming lack of funding for this sort of thing -- there is government funding ( about $1.4 mil to Georgia Tech ) but I didnt see any indication of indstrial funding. Nowadays to do massive parallel computation of this sort is well within the reach of companies like St. Judes.
 
"...did some searches on cavitation and Computational Fluid Dynamics applied to artificial valve design. The use of 3-D computational fluid dynamics in evaluating artificial heart valves seems a recent development and numerically solving the navier stokes equation for small valves with parts ( e.g. hinges ) which are comparable in size to large blood cells seems to be a very computer intensive task."

Ow... Now my head hurts... Shame on you for making me think when I haven't had enough sleep...

:D

Actually, I was kinda curious about that too. Surfaces have an effect on how fluids flow over them. Look at the "minor" stir over swimsuit designs before and during the last Summer Olympics. I think the dimple thing in the golf ball is for life and stability, not so much reduced air friction, but I'm not sure.

You're right though, having a "perfectly" smooth surface may not be the best approach to prevent some of the complications mechanical valves can present with.


Good stuff iffin' you're an engineer or at least a sciences buff...


Hope we're not making anyone's head spin though. :eek:
 
Difficult subect

Difficult subect

Actually if I remember correctly the dimples are there to give lift created by
turbulent(drag) like in an aircraft wing. I think laminar flow is when you want to decrease drag.

My understanding of HITS is they are not considered a problem in adults, because there is a longer distance for the blood to flow till it reaches the brain and the air has a chance to be reasorbed.

As far as valve design goes, this problem has been explored by Hufnagel, Harkin, Braunwald, et al over fifty years ago long before they knew what the problems were. Should we design a more machine like solution that would be very durable( ie., the early ball and cage valves) or should we go with something that tries to duplicate a human valve( ie., Braunwald's leaf type).
I should stop now before I completely bore everyone to death. :D
 
RCB said:
Actually if I remember correctly the dimples are there to give lift created by
turbulent(drag) like in an aircraft wing. I think laminar flow is when you want to decrease drag.

My understanding of HITS is they are not considered a problem in adults, because there is a longer distance for the blood to flow till it reaches the brain and the air has a chance to be reasorbed.

As far as valve design goes, this problem has been explored by Hufnagel, Harkin, Braunwald, et al over fifty years ago long before they knew what the problems were. Should we design a more machine like solution that would be very durable( ie., the early ball and cage valves) or should we go with something that tries to duplicate a human valve( ie., Braunwald's leaf type).
I should stop now before I completely bore everyone to death. :D
Click to expand...

You are not boring me!

But I dont want to give anyone a headache -- I dont think this is as hard to read as it is to write anyway :eek: probably because I dont have a good understanding, never really studied fluid dynamics in depth....

Greater laminar flow ( fluid flow in distinct layers that dont mix ) does not necessarily happen around smooth surfaces.

I think I understand ( plus I cheated and read about this but perhaps I am not entirely clear yet ) what happens when you create flow around a convex rough surface e.g golf ball.

The velocity close to a rougher surface increases more gradually than it would around a smoother surface and the fluid ( air ) detaches later for certain ( lower ) velocities and creates less turbulent wake i.e. less drag.

For valves someone should have studied this somewhere and come to the conclusion that either
a) There is less drag for a smoother valve surface because of the chemical and physical properties of the fluid ( blood )
b) There is less cavitation, or
c) There is more biocompatibility ( somehow ) the smoother the surface.
or maybe some other reason exists for smooth mechanical valve surfaces -- I doubt if natural valves are as smooth as the pyrolitic carbon ones

Anyway I will try to search for references for whether anyone has done study a) for a bit maybe by the people you mentioned ( as an excuse to get away from my own stuff for a while more )
 
Interesting, very interesting. I really like this tread and just hope that the designer of the St. jude Valve did as much thinking as you guys.
Eowyn Rose
 
Friends:

WOW! A few years ago, I brought up this same subject, but it didn;t seem to have the interest. When my husbands echo report indicated significant cavitation, I "googled" cavitation, and found the topic very interesting. I am not sure I agree that HITS are not as important , or don't happen as often in adults. I was convinced at the time, and remain so, that many of the "ocular" experiences of mechanical valve patients are the result of cavitation.

That being said, gentlemen, I look forward to your continuing this discussion on this thread. The physics may be beyond my humble brain, but your conclusions are not.

Good going.


Marybeth

PS - I would also like you to discuss the effects of smooth vs "dimpled" as it might relate to red blood cells. My husband, and I know Joe, Nancy's husband have anemia caused by damage to the red blood cells as they pass by their dual valves.
 
For a long time I have wondered why mechanical valves are bicuspid.

It is good to hear that experimentation is going on for tricuspid mechanical valves.

That brings up another question:

Are all tissue valves tricuspid?

If so does that make them better as far as patient abilities, fatigue, etc ?
 
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