>> At least I didn't say it was through the aorta. (That, of course, 
>> would be the way *from* the heart, not *to* it.) I bothered to get 
>> that much right. ;-)
> 
> yes and no ;) Blood exits the heart via the aorta, but it used to be the 
> standard entry point for catheters if you wanted to go to the left 
> ventricle (where many arrhythmias originate).

Heh. I don't know if it's a rule of the Internet, but it probably should 
be: For any conceivable topic, somebody else will know way, way more 
about it than you. :-}

I would have thought trying to enter against the flow of blood through 
the single largest blood vessel in the entire human body would be quite 
difficult - then again, I'm sure many people far more knowledgeable than 
me have actually tried this out. Also, I guess it would depend on where 
the hell you're trying to actually get to in the first place...

> Nowadays the route via the 
> right atrium, though the atrial septum, to the left atrium and from 
> there to the left ventricle is also often used.

Hmm, OK.

> BTW as you rightly guessed, that implies that the vast majority of 
> catheterizations go via the inferior vene cava. Entering via the 
> superior vene cava is very uncommon, except for the wires of a pacemaker 
> or ICD (I guess you ended up in webpages describing those procedures).

Actually, I just looked up the major blood vessels of the heart and 
tried to figure out which name goes with which tube on the diagram. 
(You'd think this would be easy... you'd be wrong.) I eventually 
determined that the two vena cavae are where the majority of blood 
enters from, and arbitrarily selected the superior one.

Firstly because "superior" sounds better [although in fact I gather it 
just means "higher up" in medical jargon], and partly because I imagined 
the route from the brain to the heart. Most people perceive their body 
looking down from where their head is. (Not that this has anything 
remotely to do with the surgical feasibility of inserting stuff from 
that direction...)

> In principle you can also enter via the right outflow tract and there 
> are also in general 4 lung venes (that transport oxygenated blood from 
> the lungs to the left atrium). Of the top of my head I don't know of any 
> procedure that uses any of those entry points.

Yeah, the heart is a double-pump, so there ought to be *two* entrances 
in theory. (There are apparently more because humans have two lungs, and 
because blood from above and below returns through different routes.)

On a completely unrelated note, apparently in some animals the heart is 
a single pump, and in yet others it's just a tube that sort of squirts, 
and there are no blood "vessels" at all. The internal organs just sit in 
a soup of... well, it's not even blood, it's haemolymph.

Then again, apparently some animals don't have red blood cells, the 
haemoglobin just floats in solution. Larger animals don't do that 
because to have enough haemoglobin to transport sufficient oxygen, their 
blood would be like treacle. So RBCs evolved which are packed with this 
oxygen-transport protein, but the blood remains liquid.

In other news, I spent a really absurd amount of time on Wikipedia. o_O

> To complete the picture you can also us a sternotomy or a laporoscopic 
> procedure, but don't try that at home.

Yeah, that or any other medical procedure even remotely involving your 
heart! o_O

Although I did hear about an off-duty medic who saved someone from a 
collapsed lung on an airoplane using a tube and a coathanger or 
something random like that...

Funny stuff, blood. Everybody seems to think it's red. Certainly if you 
spill it, everything within an 8-mile radius is coated scarlet and it 
looks like a chainsaw massacre has happened (when actually you merely 
got a paper cut)! But from what I've seen, blood is nearer black than 
red. I mean, if you get any real *quantity* of the stuff. It's very dark 
indeed.

Reminds me of the last time I had a nose bleed. Sure, it's only a small 
volume of blood. But it gets *everywhere*. And it feels really, really 
hot against your skin. Almost scalding hot. It really makes you feel 
like something very serious is happening - especially when it's dripping 
fast.

Somewhat unrelated, but... I remember my dad working on some plasma 
samples. He proffered a tube at me and said "well, you can definitely 
tell which volunteers had a good breakfast!" I swear, the amount of cow 
lard floating on the top of some of these samples was discusting! :-S

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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