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High altitude: blood clot more likely?



 
 
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  #1  
Old February 24th 06, 07:20 PM
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Default High altitude: blood clot more likely?

Another semi-OT question...

I was raised in Michigan, then at age 25 I moved to Colo and lived in
Breckenridge for a year, then LA for 6 months, then Breck for 6 months,
then Boulder for a year, then LA...so I was living and working out and
racing at both high and low altitudes for a few years.

Then I broke my leg badly at 10,000 ft and recovered back in Boulder. A
week or two into the recovery a blood clot went to my lungs and rather
shut them down, so I went to the hospital.

Now that I'm an old fart of 44 (magnum) the docs want me to start
taking a mini-aspirin every day---especially because of my history of
clotting, they say.

Well...was I messing around with blood thickness back when I got that
clot?

Hmmm, maybe I'm naturally already over the legal level for hemo and
have sludgy blood. I've never been tested for that stuff, though. I do
have a blood test for cholesterol around here somewhere. My "good"
levels are way high. Would there be a stat for hemo somewhere in a
blood report? --That's maybe of less interest for someone who's not
sporty, so maybe they don't point it out.

I'd say I've always had really good aero, vo2max, recovery, enduro, all
that kind of thing.

What I'm driving at is in general does a kind of blood that's really
good for enduro-sport also tend to have a somewhat higher risk of
clotting? And in particular if someone is living/racing at both high
and low altitudes (ranging from sea level to 11,000 feet several times
a year) is that doing anything to increase clot risk? Do hemo levels
relate to clotting?

--JP
outyourbackdoor.com

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  #2  
Old February 25th 06, 02:38 AM
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What I'm driving at is in general does a kind of blood that's really
good for enduro-sport also tend to have a somewhat higher risk of
clotting? And in particular if someone is living/racing at both high
and low altitudes (ranging from sea level to 11,000 feet several times
a year) is that doing anything to increase clot risk? Do hemo levels
relate to clotting?


Your pulmonary embolism (blood clot in the lung) after fracturing your
leg is an unfortunate but predictable complication of the surgery itself
(that's assuming you had surgery for it). All reasonably long surgery
under general anaesthesia carries a risk of DVT and PE in the
post-operative period (typically 10-20 days after the operation), but
lower limb orthopaedic surgery is _particularly_ high risk for clots. If
you didn't have surgery, simply the immobility of being in a cast and
not walking on it can be enough to predispose to a DVT +/- PE.

Living, working and training at high altitude tends to increase the
haemoglobin concentration, and hence oxygen carrying capacity, of your
blood. Your packed cell volume (PCV) or haematocrit, (which is just the
ratio of the volume of red cells to the total blood volume), will
increase, and hence your blood _will_ become more viscous.

Taken to extremes (erythropoietin overdose, rapid transfusion of packed
red cells, haematologic malignancies) the increase in viscosity can
indeed dramatically increase your risk of sludging off vessels,
especially the small ones. Simply living intermittently at the altitudes
you're talking about should not significantly increase your risk of a
venous thromboembolic event (VTE), though.

Taking half an aspirin a day if you're in your mid 40's and male is
probably good advice. It will _slightly_ lower your risk of VTE, but
dramatically lower your risk of a heart attack or stroke. There is
fairly good evidence, and some less so, of other likely health benefits
of the humble aspirin as well, if you're keen for some lengthy reading.

Kind regards,
Chris Cole




  #3  
Old February 25th 06, 07:52 AM
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Chris,
I'm a clotter so is my whole family, Uncle almost died last year,
cousin who almost died. So my uncle is a doctor who is obsessive in
the research area. I'll send him your message and get his 2-cents to
you.
I can tell you that i have had classic clotting symptoms after intense
training, and i can tell you i feel i saved myself by taking a ****load
of aspirin AND fish-oil.
As a matter of fact, almost my whole family is on Coumadin, and i feel
the reason i've never had a blood-clot episode is because of the
fish-oil. The research on it is outstanding. M.D's and Phd's have
told me it is safe to take up 30 capsules of fish oil a day, which i
do. Yes, it can THEORETICALLY cause a MARGINAL increase in hemmorhage,
but i'm much more scared of clotting. High quality fish oil cap's with
a high-potency of a balance of EPA and DHA, from the better companies
that screen,filter,and distill it for contaminates, is something you
might want to try. I recommend NOW, Source Naturals, and probably
TwinLab for the best. And, at risk of sounding like a nut, I do
recommend mega-dosing, it has saved me. My doc is very doubtful there
is great danger from the mega-dosing.
There are other supplements that help to some degree, i think
b-vitamins, acetyl-carnitine, and inositol, and ginko biloba, and
others. I much prefer to be on these supplements than have to take
coumadin for the rest of my life. (knock on wood.)
At least take 15 caps a day, and reduce if if messes with your
digestive tract. You get used to most of the side effects, and it's
worth noting that omega-3 fatty-acids are being researched for all
kinds of disorders from cardiovascular to neurological and psychiatric
conditions. Some doctors even go so far as to belieive a generalized
deficiency of omega- and fish in our populations diet is a global
health problem,
Good luck.
Chris Cole wrote:
What I'm driving at is in general does a kind of blood that's really
good for enduro-sport also tend to have a somewhat higher risk of
clotting? And in particular if someone is living/racing at both high
and low altitudes (ranging from sea level to 11,000 feet several times
a year) is that doing anything to increase clot risk? Do hemo levels
relate to clotting?


Your pulmonary embolism (blood clot in the lung) after fracturing your
leg is an unfortunate but predictable complication of the surgery itself
(that's assuming you had surgery for it). All reasonably long surgery
under general anaesthesia carries a risk of DVT and PE in the
post-operative period (typically 10-20 days after the operation), but
lower limb orthopaedic surgery is _particularly_ high risk for clots. If
you didn't have surgery, simply the immobility of being in a cast and
not walking on it can be enough to predispose to a DVT +/- PE.

Living, working and training at high altitude tends to increase the
haemoglobin concentration, and hence oxygen carrying capacity, of your
blood. Your packed cell volume (PCV) or haematocrit, (which is just the
ratio of the volume of red cells to the total blood volume), will
increase, and hence your blood _will_ become more viscous.

Taken to extremes (erythropoietin overdose, rapid transfusion of packed
red cells, haematologic malignancies) the increase in viscosity can
indeed dramatically increase your risk of sludging off vessels,
especially the small ones. Simply living intermittently at the altitudes
you're talking about should not significantly increase your risk of a
venous thromboembolic event (VTE), though.

Taking half an aspirin a day if you're in your mid 40's and male is
probably good advice. It will _slightly_ lower your risk of VTE, but
dramatically lower your risk of a heart attack or stroke. There is
fairly good evidence, and some less so, of other likely health benefits
of the humble aspirin as well, if you're keen for some lengthy reading.

Kind regards,
Chris Cole


  #4  
Old February 25th 06, 04:08 PM
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wrote:
First, thanks, Chris for the info.

Now the next post makes me wonder a bit.


Yeah, he seems very keen on his fish oil. =)


The biggest line in it that caught my eye is that he felt the effects
of clotting after a workout. Well? What are those effects? I'd think
that a workout would have blood flowing at its optimum and that maybe
the clotting risk might come on after sitting at a desk job all day. ??


Exercise does not cause venous thromboembolic events. He is likely
referring to symptoms which are unrelated to thrombosis. You are at
higher risk of VTE from immobility... hence the much reported "economy
class syndrome", i.e. a high risk of DVT in long distance travellers who
don't get to move around much.

...Coumadin the rest of your life? If you get a cut on that stuff don't
you bleed dangerously? Sounds terrible.


Coumadin is a particular brand of the drug warfarin, which is the active
ingredient in Ratsak. =) It's an anticoagulant that works by inhibiting
the production of vitamin K dependent coagulation factors in the liver.
How long you might bleed for if you cut yourself is determined by how
much warfarin you're taking, and therefore how relatively deficient you
are in clotting factors 2, 7, 9 and 10 (the ones warfarin affects).

People are placed on short-term warfarin therapy (3 to 6 months) for DVT
and PE. Some people are on it permanently, usually for chronic atrial
fibrillation, and for other reasons (people known to be particularly
pro-thrombotic for whatever reason... of which there are many).


Are you saying the aspirin trick isn't enough to reduce the clotting?

Is clotting a measurement? So can you tell if aspirin or fish oil or
coumadin are doing enough, to the right level, to get the right dose of
these drugs?


It's important to understand that aspirin has no effect whatsoever on
the coagulation (clotting) cascade in your blood. Aspirin, and other
drugs such as clopidogrel, tirofiban, etc., work by inhibiting the
activity of platelets (also known as thrombocytes). These are small
cellular fragments that circulate in the blood and provide the very
first line of defence against bleeding. When they come across a damaged
vessel wall, after you cut yourself on something for instance, they are
activated and become "sticky". They cling to the defect, and release
mediators that attract and activate other platelets. A platelet plug is
formed and this serves to halt the bleeding temporarily. They also
release factors that help trigger the clotting cascade itself, though
this system is also activated by the damaged tissue itself without
mediation by the platelets. Unfortunately, platelets also stick very
enthusiastically to atheroslclerotic plaques which have cracked or
ruptured, inside your coronary or carotid arteries - these blockages
cause heart attacks and strokes, respectively.

The clotting cascade, on the other hand, is a series of enzymatic
reactions that eventually causes the preciptation of normally dissolved
proteins out of solution, to form a fibrous meshwork that covers and
stabilises the platelet plug. Think of the difference between raw egg
white and what you get when you cook it. The clotting cascade involves
upwards of 12 different clotting "factors" which are proteins made in
the liver. Warfarin buggers up the production of 4 of them, and so you
have a harder time forming a decent clot.

Sooooo.... to answer your question...

Aspirin and warfarin work on _very_ different aspects of your clotting
ability. It _is_ possible to measure the effect of aspirin by doing
platelet function studies, but these are rare. In clinical practice, a
normal dose of aspirin is enough to irreversibly disable every platelet
in your body at the time. You only regain platelet function as you
produce new platelets in your bone marrow. This process takes days. This
is why you'll often be asked to stop taking aspirin a week before any
significant surgery.

The effects of warfarin on the clotting system, however, are wildly
variable depending on dosage and the individual (what you're eating,
what other drugs you're taking, etc. all play an important role), and
everyone who takes warfarin has their clotting ability monitored from
time to time. A measurement of the time it takes your blood to clot is
compared to the "standard" time it "should" take, and the ratio of these
is expressed as the International Normalised Ratio (INR). An INR of 1.0
is therefore, by definition, normal. If you've had a DVT or PE we
usually aim for an INR of between 2.0 and 3.0 (we want your blood to
take twice to three times as long as usual to clot) to be confident you
won't extend your thrombus.

So, because these two drugs work in very different ways on different
aspects of the clotting machinery, it doesn't make much sense to compare
them in terms of levels of anti-clotting-ness, etc.

Many studies have been done, of course, to determine whether aspirin
alone, warfarin alone, or both, is better or worse at preventing VTE.
Aspirin has a very minimal effect on the rate of VTE, I'm afraid.
Warfarin very definitely is quite protective. Heparin (which you can
think of as doing the same sort of thing as warfarin) is also protective
against VTE.

Platelet inhibiters like aspirin, however, _do_ prevent arterial
ischaemic events like heart attacks and strokes, very effectively. We
often get very bemused looks from patients who arrive in the emergency
department with a good-going heart attack, to whom we immediately say
"Damn, you're having a heart attack. Quick! Take this aspirin!". ;-)


Well, thanks for the thoughts on these things. (And I think I'll stick
to this common scrip of mini-aspirin and not sweat it.) --JP


Half an aspirin a day will certainly help with your risk of ischaemic
cardiac and cerebrovascular disease. It will make you bleed a little
more freely when you are injured, but not dramatically so. It will not
do very much to reduce your risk of venous thromboembolic events,
though. But keeping active (and x-country skiing definitely counts!)
certainly will.

That having been said, if you're worried you might have a predisposition
to VTE, you should ask your GP about having a thrombophilic screen
(bunch of tests that look at genetic oddities that make you more likely
to form clots than the average camper).

Cheers,
Chris

 




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