The hydrostatic shock theory?

You are correct. But that is rupture of a vein caused by low-pressure, large-volume over-filling. The mechanism of a pressure wave is a momentary high pressure/low volume change; further, it is likely that the pressure wave would travel both within and along (outside) the vein, so there is no pressure differential to stretch the vein.

The importance of the vessels in the theory is that they allow the fluid pressure wave to reach the CNS, which is otherwise pretty well shielded by bone.

 

Ok, but do you realize that BLOOD does not enter, EVER the CNS, and it causes bad thing, there are membranes etc. that form a 'blood brain barrier'

boys, we are talking jedi 'force' here
really lets stick to the stuff that matter instead of trying to develop some super round or debating intangibles

there may be a mechanism, but every RELIABLE study, and hunters account don't indicate some super CONSISTENT force, rather the same ol put a hole through something vital.

 

What an odd thing to say.

Of course blood enters the CNS--otherwise the brain and spinal cord would have no oxygen or nutrients, and could not exist. The blood that enters the CNS is (of course) contained within blood vessels.

What is meant by "blood-brain barrier" is that the CNS capillaries (unlike many capillaries elsewhere) do not leak large proteins (like albumin and immunoglobulins) into the surrounding tissue; small molecules (like oxygen and glucose) do cross the barrier.

But the blood-brain barrier would provide no protection from a pressure wave traveling along the CNS vessels.

 

Another thing to keep in mind is that the pressures needed to disrupt nerve operation are VERY small.

The slight swelling around a damage site in MS creates enough pressure to disrupt nerve function over a few mm away.
this is one of the reasons that MS symptoms can appear to fade short term, but there can still be long term damage.

Nerves can also depolarize from physical blows.
just about everyone has bumped their 'funny bone.'
The slight impact causes the nerves to depolarize.
We perceive it as a 'shock' or any of the other hundreds of descriptions used.
We notice it because there are a lot of sensory nerves, but you may also notice that you cannot move certain portions of your hands after the blow.

Being knocked unconscious by a blow to the head is thought to have a similar physiology.
The nerves in the brain massively depolarize and stop working for a brief period.
Since these nerves are basic functions, you may not feel anything but will be unconscious.
As the nerves re-polarize and begin functioning you awake.

A blow that causes you to 'see stars' likely affected the visual paths in the brain, or the occipital lobes at the back of the head.

 

Which is a part of the challenge. There is no general agreement on what is exactly being discussed and so there is no general agreed on terminology. So folks on both sides can argue past each other pretty easily. It's also possible for claims to gain some traction and have a certain shelf life that don't deserve it, due to misunderstanding. I'm referring here to the claim that a fella or animal shot in the hip, or foot or shoulder, with a high powered rifle round can be killed or knocked out due to a "pressure wave" that reaches the brain and bursts capillaries there, etc. This latter bit was a theory of Roy Weatherbys ,and some others, a number of decades back.

tipoc

 

That is correct, but don't confuse force with energy. Just because they are denoted with the same measurement (force is actually lb-ft/lb, poundals or other SAE and SI units) doesn't mean that they are synonymous. Kind of like ounce-both a mass and a volume unit, but 16 fluid ounces of petroleum oil does not weigh 1 pound, and a pound of mercury will not fill a pint container.

As well, a hydraulic system on a machine is closed and has a minimum of expandable chambers (namely the hoses, which don't expand much) so the pressure is transmitted with minimal loss. In a living organism, however, all of the tissues are compressable or elastic, especially the largest organ that contains it all-the skin. So when pressure is applied to a particular point on/in the body, the tissue and/or fluids that occupied that space simply move elswhere, and the pressure is largely dissipated over a much greater area than that being compressed.

As for the hydralic shockwave itself, we'll assume for the moment that the body is filled with fluid. The pressure created is obviously greatest at point of origin (bullet's meplat). Well, a bullet is very small, and the pressure will drop exponentially as the wave moves outward, and it also does so in a semi-spherical pattern. So that shockwave's energy and velocity is reduced exponentially as it moves further from the point of origin. Further reducing the actual effect of that shockwave is the fact that no soft tissue in the human body is truly rigid.

I certainly don't have hard figures on how much pressure a what velocity various organs and tissues can withstand before tearing/rupturing, but my own eyes and the experience of many others (experts included) seems to indicate that the hydraulic shock generated at normal handgun velocities is insufficient to cause the kind of peripheral wounding associated with high velocity rifle bullets where man-sized targets are concerned. Obviously, the aforementioned bunny simply lacks the overall mass to absorb the temporary cavitation caused by a handgun bullet-but as I mentioned in another thread, the affects of a rodent shot with a large caliber handgun are comparable to a human taking a howitzer round by scale. The temporary cavity at a given velocity is proportionate to the projectile size, so a 2" thick bunny getting hit with a .45 caliber bullet is like a normal sized person taking a 120mm shell.

I suppose we need to define fluid-like, because unless something is seriously wrong with you, your abdominal cavity is not filled with liquid. Are you considering internal organs to be fluid-like? Because I don't; They're a solid mass composed of cells. The cells may be primarily fluid in composition, but the membrane contains that fluid (a "sack", if you will). The only place where there is fluid within the torso (aside from blood in the vascular system) is between the membranes of the diaphragm (and boy does it hurt when an area geos dry [pleurisy]) But it's only a thin, lubricating amount.

 

Can you not think of it like this?
Take fire cracker and ignite it on the ground or empty can. Small damage.
Put that same fire cracker in a can full of water and you have a lot more damage and force given off.

 

They're a fluid-like medium, in that if you strike them you get a shock wave to propogate. The standard ballistic "tissue stimulant" is a 10% gel, and we (along with everyone else) can argue whether a gel is "most like" a solid or a liquid. But there is little doublt that when you stirke a gel, you get a noticeable wave.

Some false statements here.

Theres lots of fluid in the torso: fluid in the stomach, in the intestines--the intestines actually "float" in peritoneal fluid. As for the tissues themselves, they not only have fluid within the cells, but also "interstitial fluid" between the cells. And the cell membrane is also not solid.

Pleurisy is inflammation of the pleural space, and is typically accompanied by excess fluid there; it is not the pleura "going dry."

I'm not convinced the "pressure wave" theory is correct; but those who wish to convince people it's false seem to be in possession of a lot of anatomic misinformation.

 

I won't argue that you do cause a pressure wave when you strike soft tissue, but to that end, things that we consider true solids will also twist/contort with pressure wave, albeit not like soft tissue. However, I do not consider something that cannot flow to be a fluid/liquid; A kidney or lung does not sublime into a puddle when removed from the body and placed on a table. Internal organs and other soft tissues, similar to ballistic gelatin, exhibit properties between a liquid and a solid. They are soft and easily distorted, but more rigid than a substance like pudding or any true fluid.

True. I suppose I should have been more specific in saying that the only part that is full of fluid is the Pleura. The stomach has only a small amount of digestive fluids that do not occupy it's entre space, nor is the peritonial "sack" full.

No argument. Just that those fluids are all separated by membranes or in between the cells; they do not constitute a significant reservior.

Poor wording, it's just what I've always referred to the phenomenon as when it is that momentary occurance of the membranes sticking together that causes a sharp pain when breathing, but goes away relatively quickly. I'm not a doctor. lol. Just spent a fair amount of time in A&P books.

 

But they do flatten out and distort their shape vs. being supported in the body.

A water balloon would be a good example.
What percentage of the contents is water?
How does it behave when struck or force is applied?

Our tissue is overwhelmingly water, with cell membranes giving it some shape and form.

When it is struck, especially by fast moving objects like bullets, it behaves as a gel.

A material that is somewhere between a pure liquid and a solid.

Bones behave closer to a solid, but still contain marrow and pother cells that are NOT a solid (calcified).

Is cartilage a solid?

 

Suggested reading - http://www.m4carbine.net/showthread.php?t=34407

 

I'll point out again, that blood vessels are not empty hoses. Every few inches is a valve and if those valves are overcome it can be seen even from the outside of the body. If you know a current or former IV drug user, take a close look at their arms. Most of them will have concavities where their veins are, instead of the normal convex appearance of a healthy vein.

Of course, you wouldn't see this on an artery since they lie deeper in the body, but coroners would certainly note it on an autopsy.

 

Vessels are not rigid pipes. They are elastic, which stretch and dampen the amplitude of the "blood pressure spike". They are also connected to other vessels, which disperse and dissipate the "blood pressure spike". In addition the lungs dampen the "blood pressure spike".

 

ONLY in VEINS.

Arteries do not have them (or need them).

The valves in veins allow for random muscle movements that can compress the veins to aid the return flow of the blood to the heart.

The valves allow one way flow, back towards the heart.

Just as a point, folks who have heart bypass surgery are kept on stool softeners for a few days.
The force of trying to defaecate could cause the new joints in the cardiac arteries to blow out until they have started to knit and heal.

that's right, pushing to poop could cause enough additional pressure at the heart to blow the connections.

 

An excellent perspective on the topic, the best that I've read in a long time.

In his book, "Bullet Penetration", MacPherson treats calibrated 10% ordnance gelatin as a "soft solid" with a high viscosity (~150 Poise) since it's able to sustain shear forces whereas fluids cannot. For the purposes of such discussion, it is a description that seems to "hold water" (I couldn't resist the pun, sorry ) very well for how the material behaves under projectile impact forces.

 

What acts on your palm is momentum (Momentum = mass * Velocity.) Kinitic energy is calculated as Energy = mass * Velocity^2.

 

Very good point. I think the response would be along the lines of a "high-pass" filter: that a system that is flexible enough to totally absorb a low energy (slow) deformation may transmit a higher energy wave pretty well. So that a blood vessel that flexes in response to a heartbeat may act fairly rigid during the brief transmission of a ballistic pressure wave.

The high-pass aspect doesn't change the fact that the energy would attenuate with distance; but it would not dampen as quickly.

I think both kinetic energy and momentum would be imparted from the gun to my palm, and from there distributed elsewhere.

 

If that were true, your palm would suffer as much damage as the target.

 

Well according to an article posted in a medical journal on neurosurgery the phenom of hydrostatic shock is well established.

 

Are there no trauma surgeon/gun enthusiasts on here that can put this to rest once and for all?

I've read stuff from a morgue worker and he said that rifle fire was almost always lethal and almost always killed in one round. Now correct me if I'm wrong, but a 7.62 is smaller diameter than a 9mm, but both flavors in FMJ will over penetrate.

Then the 9mm should be better than the 7.62. But it isn't.

He said that rifle victims were rare, but were almost always instantly lethal. He said that a 7mmMag victim had liquified organs. Massive trauma. Most rifle and shotgun wounds he saw were head shots, suicides. But the few that came through with COM shots were nasty.

He also noted that 9mm victims came in with several shots. Usually .40 and .45 were one or two shots. Obviously whoever was firing didn't feel the 9mm was putting them down fast enough.

So it would seem for pistols, that bigger is better. For rifles, faster is better. I think this arguement has become a cycle, I've been interested in this kind of thing since I first started shooting when I was 8yo. I've read about it until the internet came along, then discussed it. We're still where we were 20 or 30 or more years ago.

That really is the bottom line. Until we get a trauma surgeon on here to set us straight, it'll just have to be a little mysterious yet.

 

Appreciate the perspective, Odd Job. Good stuff to chew on. Most of the response would I think again center on concussion: that loss of consciousness can at times be observed (with direct blunt trauma to the skull) even without cerebral contusion or other clear signs of injury (other than changes in the concentrations of some neurotransmitters and some inflammation mediators).

It remains the case that, even if pressure-wave-induced unconsciousness occurs, it seems to be an undependable phenomenon.

(Oh--and I always thought Odd Job was the best Bond henchman. Way better than Jaws. )

 

moot point. This is not a description of hydrostatic shock. The gases caused by the rapid conflagration of the firecracker simply displace the water. Since water cannot be compressed, it has to move out of the way. This is why it ruptures the can. As for more force given off, that's simply impossible. The same type of firecracker will give off approximately the same force. It draws no other strength from the water it's in.

 

The bullet and the gun have about the same momentum. The momentum of the gun will be a little higher because of the momentum of the powder gasses that act primarily on the gun.

K.E. is a totally different situation. Since it's based on velocity squared, the bullet has much more energy than the gun. In the earlier post with the .357 mag example the velocity and K.E. numbers are:

2 lb .357 mag at 17.25 fps = 9 ft-lbs
158 gr bullet at 1250 fps = 548 ft-lbs



The K.E. of the gun is also distributed over the surface of your hand in contact with the gun. The K.E. of the bullet is distributed over a much smaller area.