Why don't elephants get embolisms?

[fisherdvm]

My observation is, with my patients with both venous and arterial diseases of the leg, I usually can not use more than a class I or II compression stockings due to increased claudication.

Some of the wetsuit I've worn, I swear, must be at least equivalent to a class I or II stocking... So that's my question.

I am glad you can continue to dive... I think it is a very relaxing sport...

 

[Kim]

My observation is, with my patients with both venous and arterial diseases of the leg, I usually can not use more than a class I or II compression stockings due to increased claudication.

Some of the wetsuit I've worn, I swear, must be at least equivalent to a class I or II stocking... So that's my question.

I am glad you can continue to dive... I think it is a very relaxing sport...

Thank you for your concern...really! Don't worry.....the constrictions and problems were all in the Aorto/Illiac area which has now been bypassed. Scans of the Femoral and lower arteries show no signs of any constriction or problem.

It's a simple lesson. Smoking is bad for your health! I gave up two months before the operation.......about 35 years too late!

 

[miketsp]

If they dove to 33 ft, that would be 2 atm, if it is to 16 ft, that would be 1.5 atm. If the elephant dove to 3.3 ft, that would be 1.1 atm.

I venture to say, without doing mathematics, that 1.1 atm is much less than the 4 to 5 mm hg that the pulmonary artery/venous system is able to generate.

I read the thread through but I needed to pick you up on this point.
If 760mm hg = 33 ft water then
5mm hg = only 2.6 inches of water.

 

[fisherdvm]

Wow, cool, KIM, look...

Someone already looked into this problem:

http://physiologyonline.physiology.org/cgi/content/full/17/2/47

 

[fisherdvm]

Unfortunately, the figures and drawings can not be clipped...


Physiological consequences of snorkeling
Top
Introduction
Physiological consequences of...
Evolution's solution
References


Snorkeling at depth creates very large pressure differences in the immediate vicinity of the lung. The reason for this is shown in Fig. 2B, which is drawn assuming that the bottom of the elephant lung is 2 m below the surface of the water. This is a reasonable assumption because the shoulder height of an African elephant can exceed 4 m. At this depth, the water pressure is ~150 mmHg, and this means that all of the vascular pressures are increased by the same amount. If this were not the case, no perfusion of the tissues with blood would be possible. However, the pressure in the alveoli is close to atmospheric because they are connected to the surface by a tube. Therefore, near the outer surface of the lung the pressure abruptly changes from 0 to ~150 mmHg. This is the basic dilemma faced by the pleural membranes.





View larger version (21K):
[in this window]
[in a new window]
FIGURE 2. A: approximate distribution of pressures (in mmHg with respect to atmospheric pressure) in and around the lung for most terrestrial mammals. B: distribution of pressures in the snorkeling elephant. The bottom of the thorax is assumed to be 200 cm below the surface, and therefore the water pressure is ~150 mmHg. Systemic arterial and venous pressures will rise by the same amount, but the pressure in the alveoli is atmospheric (0). A microvessel in the parietal pleura has a pressure within it of >150 mmHg because it is supplied by systemic blood. If the anatomy were the same as shown in A, the transmural pressure of the microvessel would be >150 mmHg (compare Fig. 3). Evolution's answer is to replace the delicate pleura with dense connective tissue. The visceral pleura is also at risk and thickened. A layer of loose connective tissue, indicated by stippling, allows some sliding of the two pleural surfaces.




The problem is highlighted by considering the small blood vessels in the parietal pleura. Figure 3 shows the histology of the parietal pleura from a typical mammal, in this case a sheep. Note that the pleural membrane is only ~30 µm thick and that it lies on the endothoracic fascia. There is a single layer of mesothelial cells, and the microvessels are very close to the pleural surface. The transudate from these microvessels enters lacunae and is then discharged into the pleural space, thus providing the fluid that lubricates the two pleural surfaces so that they can slide over each other.




View larger version (80K):
[in this window]
[in a new window]
FIGURE 3. Photomicrograph of the parietal pleura and endothoracic fascia from a sheep. The parietal pleura is only ~30 µm thick. There is a single layer of mesothelial cells, and the microvessel is close to the pleural space and provides the transudate that traverses lacunae and lubricates the pleural surfaces. Courtesy of K. H. Albertine.




It is easy to see that this anatomic arrangement would be impossible in the snorkeling elephant. The microvessels of the parietal pleura are supplied from the systemic circulation, in which the venous pressure exceeds 150 mmHg (Fig. 2B). Therefore, the pressure inside the pleural microvessels shown in Fig. 3 must exceed that. However, the pressure in the pleural space (if one exists) will be very close to alveolar pressure (that is, atmospheric), only differing from this by the elastic recoil of the lung. In other words, the microvessels of the parietal pleura will have a transmural pressure approaching 150 mmHg. Clearly, they would either rupture or the great imbalance of the Starling forces would rapidly cause massive transudation.
The microvessels of the visceral pleura may face a similar problem, although here the situation is more complicated. In large mammals such as the sheep, pig, horse, and human, the capillaries of the visceral pleura are supplied by the systemic bronchial circulation (1,7). However, in smaller mammals such as dog, cat, and rabbit, the blood supply comes from the low-pressure pulmonary circulation. No direct anatomic information exists in the elephant, although because of its very large size the blood supply is presumably from the systemic circulation. In addition, the distance between the surface mesothelial cell layer and the underlying microvascular network is greater in the visceral than the parietal pleura (1), so this would make them less vulnerable.


Evolution's solution
Top
Introduction
Physiological consequences of...
Evolution's solution
References


As indicated above, the most vulnerable tissues during snorkel breathing at depth are those at the junction between the outside of the lung and the rest of the body, that is, the pleural membranes. Evolution has provided a remarkable solution to the problem by replacing the normally delicate parietal and visceral pleurae with sheets of dense connective tissue that prevent damage to the pleural blood vessels or excessive transudation. Figure 4 shows a photomicrograph of a portion of parietal pleura from an 18-yr-old male African elephant (3). Some intercostal muscle can be seen at the bottom of the micrograph, and above this is the parietal pleura, composed of dense connective tissue up to 500 µm thick in this example. Contrast this with Fig. 3, which shows the very delicate parietal pleura, only ~30 µm thick, from a sheep. There are no obvious vessels in the dense connective tissue layer shown in Fig. 4, but if there were any, they would be protected from rupture and edema formation, unlike the microvessels in Fig. 3, which are very near the pleural surface. Also note the layer of loose connective tissue in Fig. 4, which takes the place of the potential pleural space in other mammals and allows sliding to occur between the two pleural membranes.

 

[Thalassamania]

That is an interesting and insightful question. Surface supplied diving systems (like the tourist hats) supply gas at ambient pressure, so it’s just like scuba in that sense. Diving hats are all equipped with a non-return valve at the block which prevents that diver being sucked up into the hat if there were a compressor failure, there’s a lot of black humor from the early days about divers being “buried in their hat” as a result of that sort of incident.

You are right about the elephant; it is the only mammal that can remain submerged far below the surface of the water while snorkeling. As you suggest, the differences of pressures in the lungs puts the animal in potential danger of rupturing. Selective pressures have replaced the normally delicate pleurae with dense connective tissue, and separated visceral and parietal pleurae with loose connective tissue that permits sliding movement.

I happen to know a little bit about elephants, I helped dissect one that died at the zoo when I was at university. An elephant's lungs are high in the thoracic cavity, reaching almost to the animal's dorsal surface. The head of water pressure that they must draw against is equal to the distance between the most ventral point of the lung (basically about 2 meters below the elephant’s back) and the surface of the water. Despite what the elephant web site says, elephants do draw air into their lungs by negative pressure, which is created by the diaphragm. The difference is that the lungs are attached directly to the diaphragm and the chest wall. This permits a much greater vacuum to be developed, both for “snorkeling” as well as to suck water up from ground level. There is no positive pressure pump forcing air in.

FisherDVM suggested a a great review article, you really need to look a the diagrams.http://physiologyonline.physiology.org/cgi/content/full/17/2/47

There are competing arguments about why elephants have this unique feature:

1.[FONT=&quot] [/FONT]It is a long standing snorkeling adaptation. Elephants (and the Sirenia) may be descendent from an aquatic or semi-aquatic ancestor. A.P. Gaeth of the Department of Zoology at the University of Melborne performed Embryological studies of the African elephant and demonstrated Nephrostomes, a feature of aquatic vertebrates. Garaeth also indicated that the elephant, like the dugong, is one of the few primary testicond mammals. His goes on to state the the paleontological evidence suggests that the elephant's ancestors were aquatic, and that recent immunological and molecular evidence shows an extremely close affinity between present-day elephants and the aquatic Sirenia (dugong and manatees). John B. West of the Department of Medicine, University of California San Diego reported that the thickness of the endothoracic fascia of fetal African elephants when compared with those of human, rabbit, rat and mouse fetuses of about the same stage of lung organogenesis is an order of magnitude thicker. This very early development of a thick parietal pleura suggests an extensive history of snorkeling in the elephant's possibly aquatic ancestors.
2.[FONT=&quot] [/FONT]It is a newly developed snorkeling adaptation that stems from preadaptive structures which developed as a result of selective pressures for obtaining water.
3.[FONT=&quot] [/FONT]It is an adaptation resulting from the mass of the lungs (the only other animals with lungs of such a size are whales that are supported by water).

As far as giraffes are concerned, I’ve never seen one swim, but I know that they have a bunch of special adaptations to keep from blowing their brains out when they put their head down to drink.

 

[Rick Murchison]

My observation is, with my patients with both venous and arterial diseases of the leg, I usually can not use more than a class I or II compression stockings due to increased claudication.

Some of the wetsuit I've worn, I swear, must be at least equivalent to a class I or II stocking... So that's my question.

I am glad you can continue to dive... I think it is a very relaxing sport...

I'm just curious what you think...
In my prior life I was a Navy Attack Aviator (A7's), where, due to repeated excessive "G" forces I blew the valves out of the veins in my left leg. When lesions first started showing on my ankle, they looked like the Southeast Asian creeping crud, and the vein problem went undiagnosed for another decade or so. Twelve years ago it became apparent that the problem was the valves. I had the veins stripped in that leg, and afterwards things looked pretty good for a decade. This year the ankle is again showing some signs of poor bloodflow at the skin.
I went in to the vascular surgeon expecting another round of vein stripping but after an ultrasound was told that as the valves were blown in the deep veins there really wasn't anything to be done other than to wear a stocking every day.
That's given me some marginal improvement (no ulcers at the ankle at least)
Strength is good.
No neuropathy.
I do get some really awful itching from time to time...
Is there a surgical or medical or mechanical solution for me on the horizon, or am I in a race to the grave with my leg? (winner gets there first)
Rick

 

[victor]

So you think that someones blood pressure in their ankles is more than at their heart?

Definetly, back to my giraffes
Why do they have the highest blood preasure in the animal kingdom.
Not because their heart is so much higher than their feet.

Its because there head is so mgh higher than their heart. The need the blood presure to pump the blood up to the brain. On the reverse side the column of blood from the brain down to the heart of about 10ft.

To do this a giraffe's heart is two feet long, weighs 25 pounds and has walls three inches thick.

 

[fisherdvm]

I'm just curious what you think...
In my prior life I was a Navy Attack Aviator (A7's), where, due to repeated excessive "G" forces I blew the valves out of the veins in my left leg. When lesions first started showing on my ankle, they looked like the Southeast Asian creeping crud, and the vein problem went undiagnosed for another decade or so. Twelve years ago it became apparent that the problem was the valves. I had the veins stripped in that leg, and afterwards things looked pretty good for a decade. This year the ankle is again showing some signs of poor bloodflow at the skin.
I went in to the vascular surgeon expecting another round of vein stripping but after an ultrasound was told that as the valves were blown in the deep veins there really wasn't anything to be done other than to wear a stocking every day.
That's given me some marginal improvement (no ulcers at the ankle at least)
Strength is good.
No neuropathy.
I do get some really awful itching from time to time...
Is there a surgical or medical or mechanical solution for me on the horizon, or am I in a race to the grave with my leg? (winner gets there first)
Rick

When the venous disease affect too many veins in the leg, isolated removal of one "bad" vein is no longer an option. Then you simply have to rely on external support hose to improve the valve function - of what is left.

I wish there were a way to surgically repair these valves ... but not in the immediate future, as far as I know. But I am not a vascular surgeon.

 

[Penguinboy]

Interesting Question.

Changing the subject slightly - why don't other marine mammals like whales and dolphins get DCI? They surface from extreme depth, yet seem fine all the time!