mechanical heart valve

[Lloyd]

Dr. Deco,
This was posted on the medical forum and I would like to run it past you.
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My brother and I are avid divers. He was born with a congenital heart valve defect and recently had a mechanical valve put in. He is on coumadin. Can anyone advise as to whether it is a problem for him to continue diving?
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Could the increased turbulance from the mechanical valve induce bubble formation in a super-saturated state during decompression? I was wondering if it could have the same effect as shaking a Coke.
Thanks,
Lloyd

 

[Dr Deco]

Hello readers:

Mechanical Valves

As a biophysicist, I am interested in mechanical prosthetic heart valves because they have been suspected of creating cavitation bubbles within the blood. When monitored with transcranial Doppler ultrasound, emboli are detected. Since it is currently not possible to resolve gaseous from solid emboli, they are referred to as “high intensity transient events” or “HITS.”

The process by which this might occur has been studied by the manufacturers of these devices. They are considered to be a potential source of neurological problems because the valve-formed bubbles could flow to the brain and embolize it. Of the many devices in use, it is not clear that there are serious problems from gaseous emboli; anticoagulants are used to mitigate the formation of small clots. Cognitive problems have been reported from prosthetic valves [(1) REFERENCES below].

Experiments have purported to demonstrate that these are gas bubbles and are indeed detectable in the circulation of the brain (2,3). Clots produced from, e.g., rheumatic heart disease, are well know to cause health problems. A literature search on PubMed indicates that severe neurological problems have not been demonstrated by gaseous emboli (4).

Diving

Since there are not any reported problems, this must indicate that whatever is produced while diving does not appear to be in sufficient numbers to result in a problem. That is not an entirely satisfying answer, however.

One can always ask, “What if there is a first time, and I am it?”

Dr Deco :doctor:

References :book3:

• (1) Deklunder G, Prat A, et al. Can cerebrovascular microemboli induce cognitive impairment in patients with prosthetic heart valves? Eur J Ultrasound. 1998 ;7(1): 47-51.
• (2) Bumgartner RW, Frick A, et al. Microembolic signal counts increase during hyperbaric exposure in patients with prosthetic heart valves. J Thorac Cardiovasc Surg. 2001 Dec;122(6):1142-6.
• (3) Georgiadis D, Wenzel A, et al. Influence of oxygen ventilation on Doppler microemboli signals in patients with artificial heart valves. Stroke. 1997 ;28(11): 2189-94.
• (4) Georgiadis D, Lindner A, Zierz S.Intracranial microembolic signals in patients with artificial heart valves: drowning in numbers. Eur J Med Res. 1998 Feb 21;3(1-2):99-102

 

[Saturation]

Thanks Dr. D & Lloyd, and as always kudos to Dr. D's unique insight. This is clearly a potential problem for divers, and your references make a very convincing point about cavitation bubble formation in the arterial circulation.

I've never seen a case of a stroke, either trasient or permanent, in patients with prosthetic valves that were not due to low levels of anticoagulant or from bacterial endocarditis.

However, you bring up a vital point concerning to divers and flyers.

Consider gas loads in patients at 1 ATA: such patients tolerate TEE with bubble contrast without AGE symptoms, and that no supersaturated state exists to stimulate the bubbles to grow beyond a critical size ... suggest that cavitation is less an issue for patients breathing ambient air and acclimatized to pressure. However, in rapid decompression it could be an issue in flight or diving.

For patients in flight, the reduced pressure in planes may induce bubble growth to the critical diameter, but again, I've not heard of an sudden in-flight transient or permanent stroke ... and moreso if it symptoms were improved by 02 [which is common protocol by attendants treating emergency inflight issues.] Further, bubbles would be difficult to find, as landing increases ambient pressure and compress the bubble to terrestrial dimensions.

Diving poses interesting issues, while it maybe possible to dive with a prolonged decompression stop or surface 02 .. a constant source of cavitation seeds the diver until inert gas levels drop below a critical pressure, what such a pressure is from ambient is unknown, and worse, there is an undefined hazard for in-water AGE as the diver begins to surface.

Again, a most unique and helpful insight. I have not heard this issue addressed in diving medicine anywhere but here. The common knowledge is this:

http://www.diversalertnetwork.org/medical/faq/faq.asp?faqid=65

... and I do not recall a mention of bubbles induced by mechanical prosthetic valves in either Bove or Bennett's textbook.

Hello readers:

Mechanical Valves

As a biophysicist, I am interested in mechanical prosthetic heart valves because they have been suspected of creating cavitation bubbles within the blood. When monitored with transcranial Doppler ultrasound, emboli are detected. Since it is currently not possible to resolve gaseous from solid emboli, they are referred to as “high intensity transient events” or “HITS.”

The process by which this might occur has been studied by the manufacturers of these devices. They are considered to be a potential source of neurological problems because the valve-formed bubbles could flow to the brain and embolize it. Of the many devices in use, it is not clear that there are serious problems from gaseous emboli; anticoagulants are used to mitigate the formation of small clots. Cognitive problems have been reported from prosthetic valves [(1) REFERENCES below].

Experiments have purported to demonstrate that these are gas bubbles and are indeed detectable in the circulation of the brain (2,3). Clots produced from, e.g., rheumatic heart disease, are well know to cause health problems. A literature search on PubMed indicates that severe neurological problems have not been demonstrated by gaseous emboli (4).

Diving

Since there are not any reported problems, this must indicate that whatever is produced while diving does not appear to be in sufficient numbers to result in a problem. That is not an entirely satisfying answer, however.

One can always ask, “What if there is a first time, and I am it?”

Dr Deco :doctor:

References

• (1) Deklunder G, Prat A, et al. Can cerebrovascular microemboli induce cognitive impairment in patients with prosthetic heart valves? Eur J Ultrasound. 1998 ;7(1): 47-51.
• (2) Bumgartner RW, Frick A, et al. Microembolic signal counts increase during hyperbaric exposure in patients with prosthetic heart valves. J Thorac Cardiovasc Surg. 2001 Dec;122(6):1142-6.
• (3) Georgiadis D, Wenzel A, et al. Influence of oxygen ventilation on Doppler microemboli signals in patients with artificial heart valves. Stroke. 1997 ;28(11): 2189-94.
• (4) Georgiadis D, Lindner A, Zierz S.Intracranial microembolic signals in patients with artificial heart valves: drowning in numbers. Eur J Med Res. 1998 Feb 21;3(1-2):99-102

 

[Dr Deco]

Hello readers:

Arterial Bubbles In Diving

The question of mechanical valves would seem to argue that bubbles, if they really are present, are not all that problematic if only few (a relative term) in number.

In laboratory experiments where I implanted sheep with Doppler transducers on their carotid artery and one transducer measuring exit flow on the sagittal sinus, I found bubbles to enter and leave the brain within seconds. Whether this is a quantitative, one-for-one, measure I do not know, as the technique did not allow such measure. [For some description, see the Powell et al. references, below.]

The sheep in question did not ever appear to demonstrate neurological problems (at least of a recognizable type). They were plain old, good-natured sheep before and after the bubbles. [None were able to write their name legibly following the study, but then none could write before, either.]

Clinical Reports

Surgical situations with transcranial Doppler monitoring often demonstrate that many bubbles are present during surgical procedures, e.g., with lung bypass devices and carotid endarterectomy. Patients do not generally show much in the way of gross neurological deficit, although cognition changes are reported.

Sticking Bubbles

The references below indicate some evidence that bubble will be held up in capillaries only if they are present in a large volume (relative to capillaries and arterioles) and appear within a short time frame. This is evidence of retention only when the bubble length is long in the capillary (somewhat similar to strike-slip dynamics).

This relationship of brain problems to gas volume might explain why there is not a strong correlation between a PFO (even a hemodynamically large one), a high Spencer Grade of bubbles, and the presentation of neurological DCS. Very likely, a requisite bubble volume, mercifully, is seldom reached in recreational, i.e., NDL diving. Missed decompression from deeper depths presents a more tragic picture.

Dr Deco :doctor:

References :book3:

• Gorman DF, Browning DM. Cerebral vasoreactivity and arterial gas embolism. Undersea Biomed. Res. 1986; 13 (3): 317.
• Gorman D, Browning FDM, Parsons DW. Redistribution of cerebral gas emboli: a comparison of treatment regimens. In: Proceedings of the Ninth Symposium on Underwater Physiology. Bethesda, MD,. 1987:1031.
• Powell MR, Spencer MP. The pathophysiology of decompression sickness and the effects of Doppler-detectable bubbles. Seattle: IAPM, 1980: O.N.R. Contract N00014-73-C-0094.
• Powell MR, Spencer MP, von Ramm O. Ultrasonic surveillance of decompression. In: Bennett PB, Elliott DH, eds. Physiology and Medicine of Diving, 3rd Edition. London: Baillière - Tindall, 1982: pp 404- 434.

 

[Saturation]

The sheep in question did not ever appear to demonstrate neurological problems (at least of a recognizable type). They were plain old, good-natured sheep before and after the bubbles. [None were able to write their name legibly following the study, but then none could write before, either.]

That's very Henry Youngman.
Patient: " Doc, can I play the piano after the surgery?"
Doc: "Sure, why not?"
Patient: "Funny, I couldn't do it before."

This relationship of brain problems to gas volume might explain why there is not a strong correlation between a PFO (even a hemodynamically large one), a high Spencer Grade of bubbles, and the presentation of neurological DCS. Very likely, a requisite bubble volume, mercifully, is seldom reached in recreational, i.e., NDL diving. Missed decompression from deeper depths presents a more tragic picture.

What I see in this thread is a prosthetic valve creates bubbles by cavitation like a diver doing strenuous exercise after diving creates bubbles via nulceation. There should be no problem in either state should the bubble volume be low. However, with the diver loaded up with dissovled inert gas from the prior dive, preformed bubble made by nulceation and cavitation now how the fuel to grow. Would this be right to say?

 

[Aeolus]

I responded positively to this question on the other forum. Now I wonder about the validity of proceeding. I am set to go to Akumal next week. I had an aortic valve installed 3 1/2 years ago along with the ascending aorta. I try to dive as often as I can (several times a year). Is there a difference in bubble production depending upon which valve it is? Is there anything that I should do to mitigate the occurances? Should I assume (dangerous) that everything is OK, since there have been no symtoms until now? Is this more of a research type circumstance? You know how that goes; you can never duplicate the lab results in the real world. Apparently, there have been no known events that can be lniked to the valve. Where do we go from here? Thanks for your advice.

DSDO

 

[Dr Deco]

Hello Saturation:

There is one difference between tissue (or capillary) bubbles and the ones from a mechanical valve during the off gassing surface interval. The microbubbles in tissue are exposed to the dissolved nitrogen and can grow, while there is not an increase of dissolved nitrogen for the blood around aortic valves because the blood has passed through the lung circulation. It is no longer oversaturated but contains dissolved gases as would be present in the ambient air. At the surface, I would not expect increased growth in valve cavitation bubbles.

Dr Deco :doctor:

 

[Lloyd]

Thanks for the input. That is what I suspected. I have been of on a medical mission to Honduras with Baylor and got back yesterday so I didn'tget to participate much.
Thanks,
Lloyd

 

[IlikeItwetPls]

To all the doc's:
After reading the replys, just curious if the bubble turblance effects hemoglobin, and the binding of O2 that might cause minor/moderate neuologic insufficiency not detectable in a sheep?

 

[Saturation]

Hi Dr. D,

Sorry for late reply, somehow this msg not flag on my reply notifications.

I concur and thanks for the insight.

As I have not heard of many bent-over-the-norm divers akin to PFO divers, its likely whatever occurs to divers with prosthetic valve is not clinical significant.

What do you think of microbubbles as seeds for inspired gas at depth? As diver ascends and the ambient pressure drops, these microbubbles have higher gas pressure relative to ambient pressure, as ambient drops on ascent? Since tissue tensions are supersaturated and need to offgas, there is less of a diffusive gradient for such bubbles to collapse as it circulates in tissues until tissues give up some of their gas.

Hello Saturation:

There is one difference between tissue (or capillary) bubbles and the ones from a mechanical valve during the off gassing surface interval. The microbubbles in tissue are exposed to the dissolved nitrogen and can grow, while there is not an increase of dissolved nitrogen for the blood around aortic valves because the blood has passed through the lung circulation. It is no longer oversaturated but contains dissolved gases as would be present in the ambient air. At the surface, I would not expect increased growth in valve cavitation bubbles.

Dr Deco :doctor: