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79Eric
04-27-2007, 02:05 PM
I listend to a lecture by a doctor who was a researcher in the 60s in South America studying hemorrhagic fevers.

When the question came up whether some doctors have accidently stuck themselves and got ill or died the answer was (of course) yes. He told us a couple of personal stories.

This led to the follow up question, if someone is stuck in the thumb by a needle infected with a hemorrhagic fever why don't they cut of their thumb to prevent further infection.

He said that it wouldn't be possible because if you are stuck in the thumb in about 10 seconds the virus has already traveled as far as your heart.

That seems awful quick. If this is true then just HOW FAST does blood travel in your body.

04-27-2007, 05:38 PM
It'll depend on a few factors, but it looks like a typical speed for a red blood cell to move along is in the area of 12-15 millimeters per second. (http://www.geocities.com/gastroyu/dec2001/portalVelocity.htm) So, in ten seconds, it's moved 150 mm or six inches.

Out of the thumb, for sure, but not quite up to the elbow, and unless you had an ax on hand to perform an emergency amputation at the shoulder, blood cell velocity is going to be faster than you can act.

gazpacho
04-27-2007, 05:51 PM
I think you misread that page. All the velocities seemed to be in cm/s not mm/s so your speed calculations are off by a factor of 10. So 10 seconds to the heart seems pretty reasonable.

pinkfreud
04-27-2007, 06:03 PM
"The maximum velocity for digital and forearm arteries was about 20 centimeters per second and 50 centimeters per second, respectively."

(Found here (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1995677&dopt=Abstract).)

picunurse
04-27-2007, 06:09 PM
Also, gotpasswords, your reference refers to blood flow in the face of portal hypertension in the hepatic vasculature. It isn't indicitave of normal blood flow.

pinkfreud got it right.

Sapo
04-27-2007, 06:45 PM
So what's the point of sucking the poison from a snake bite?. It sounds like you would only have a split second for that to be effective.

Chief Pedant
04-27-2007, 06:45 PM
I listend to a lecture by a doctor who was a researcher in the 60s in South America studying hemorrhagic fevers.

When the question came up whether some doctors have accidently stuck themselves and got ill or died the answer was (of course) yes. He told us a couple of personal stories.

This led to the follow up question, if someone is stuck in the thumb by a needle infected with a hemorrhagic fever why don't they cut of their thumb to prevent further infection.

He said that it wouldn't be possible because if you are stuck in the thumb in about 10 seconds the virus has already traveled as far as your heart.

That seems awful quick. If this is true then just HOW FAST does blood travel in your body.

Blood gets back to the heart via veins. The cite upthread gives an average velocity of 17 cm/second, or about 6 or 7 inches/second, for a large central vein.

That seems about right to me. As an example, in clinical practice we sometimes give a medicine call adenosine for a fast heart rate. We inject it in the crook of the elbow into a vein that's usually about 1/8" across or so. Within 10-15 seconds we'll see the heart respond. That includes transit time to the heart, the arteries to the heart muscles and time for the medicine to work.

How fast a peripheral stick gets to the central circulation depends on a lot of factors, including the size of the vessels that get penetrated, but 10-30 seconds seems reasonable. It may seem counterintuitive because something like a poisonous snake bite takes longer to have systemic effect. That is because much of the poison remains in the soft tissue space and is only slowly absorbed. Nevertheless a tiny amount gets distributed immediately, and for something like a virus particle, at least some are going to get into the central circulation within seconds.

KarlGauss
04-27-2007, 07:14 PM
Another way of looking at this is by considering what's called the "circulation time", i.e. the time it takes from blood to go from the artery side to the vein side or vice versa (they should be equal otherwise you'd get pooling on one side of the circulation). Used in this context, the time for blood to make one complete circuit is twice the circulation time.

The typical time it takes for blood to go from right side of the heart, through the lungs, and into, say, the big toe, is around about 18 seconds. Reference #1 (http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=439671&blobtype=pdf). Reference #2 (http://zuniv.net/pub/bholding.pdf).

And, the average time it takes blood to go the other way, from the veins to the heart and then to the arteries/capillaries is measured to be around 15 to 18 seconds. Reference #3 (http://jap.physiology.org/cgi/content/abstract/10/3/451).

So, if I've considered this correctly (and if my med school memory is not totally screwed up), the time it takes for blood to make one complete circuit is about 30 to 40 seconds.

Believe it or not, this was a simulpost with Chief Pedant. It just took me a long time to get the references and do the formatting

athelas
04-27-2007, 07:37 PM
So what's the point of sucking the poison from a snake bite?. It sounds like you would only have a split second for that to be effective.

It would still reduce the amount of poison getting into you, which is always good. Doesn't blood flow more slowly in capillaries than in large vessels? That might throw off linear estimates of blood flow.

04-27-2007, 07:54 PM
So what's the point of sucking the poison from a snake bite?. It sounds like you would only have a split second for that to be effective.
There is no point to it. It's an old wives tale and doing so causes more harm than good.

This Emedicine link has a nice section on field treatment, which emphasizes the ABC's (airway, breathing, circulation) and warns against doing funky stuff like tourniquets, incisions, and sucking on the damn wound.
http://www.emedicine.com/med/topic2143.htm

gazpacho
04-27-2007, 07:57 PM
So what's the point of sucking the poison from a snake bite?. It sounds like you would only have a split second for that to be effective.I don't think that they advocate sucking the poison from the wound anymore. Mainly because it does not work.

Sapo
04-27-2007, 08:07 PM
There is no point to it. It's an old wives tale and doing so causes more harm than good.

This Emedicine link has a nice section on field treatment, which emphasizes the ABC's (airway, breathing, circulation) and warns against doing funky stuff like tourniquets, incisions, and sucking on the damn wound.
http://www.emedicine.com/med/topic2143.htm
great link (even if a bit over my head, at some points). Thanks. Luckily, I have never been in a situation where this has been an issue, but sucking poison never struck me as a smart thing to do.

brownsfan
04-27-2007, 08:18 PM
I'm not advocating the indescretions of my youth, but when shooting drugs, the effects are quite rapid. Five seconds, tops. Not sure if it's germane to the conversation, but you also tasted the drug after shooting up. Anyone know why?

Chief Pedant
04-27-2007, 09:38 PM
I'm not advocating the indescretions of my youth, but when shooting drugs, the effects are quite rapid. Five seconds, tops. Not sure if it's germane to the conversation, but you also tasted the drug after shooting up. Anyone know why?

B/c it goes to the circulation for the taste buds as well...goes everywhere.
Had a kid once we used to try to sneak chemo to while he was sleeping but the taste always woke him up...

Chief Pedant
04-27-2007, 09:43 PM
great link (even if a bit over my head, at some points). Thanks. Luckily, I have never been in a situation where this has been an issue, but sucking poison never struck me as a smart thing to do.

Couple guys out hiking. Snake bites one guy--right on the end of Mr Happy.
Snakebit guy: "Call for help!! Find out what to do!!"

The friend calls. Advice: "You must suck out the poison immediately."

Snakebit guy: "What did he say? What did he say?!!"

Friend: "He said you're gonna die."

I only know feeble and old jokes.

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