Low blood pressure and Chicago Marathon?

Not at Chicago, but something very similar happened to me in the last mile of a 10k two years ago. Someone caught me right before I hit the pavement.

I remember hearing the EMTs in the ambulance discussing my low blood pressure - I can't remember how low it was, exactly, just that they were alarmed by it.

Hopefully someone with more knowledge of physiology will weigh in, but I think that low blood pressure goes hand-in-hand with the whole dehydration/overheating phenomenon. So it's not surprising that yours was low.

Glad you're OK. Friends of mine ran Chicago, and several of them ran into trouble, too.

link from the letsrun front page. scroll down a bit for the blood pressure part.

http://scienceofsport.blogspot.com/2007/10/death-at-chicago-marathon-report-and.html

I saw that article, but it doesn't address 'why'. Personally, it felt like a complete shock to the body when we went from the shade to being exposed. All I can figure is at that point, the rate of fluid loss started to exceed the rate of fluid intake.

why? postural hypotension is a good place to start

I'm not a doctor, but it would make sense to me that dehydration would cause low blood pressure.

Also, just to make a distinction, there is a difference between intake and absorption. My guess would be that your body couldn't absorb the water you were drinking as fast as you were losing it through sweating, so you were left with water sitting in your stomach. Pfitz has a piece about this:

http://www.pfitzinger.com/labreports/dehydration.shtml

Ok, thank you very much (the hydration article and the postural hypotension). So is the answer for preventing this to drink more water right before the race (1-2 hours before)? Maybe I should have drank more. I had my usual cup of coffee for breakfast and sipped water and gatorade in the hour before, but maybe it wasn't enough (?).

Top 100 at Chicago wrote:

So is the answer for preventing this to drink more water right before the race (1-2 hours before)?

You know, I considered this all summer as my long runs seemed to always be in extreme heat. It's hard to say what the answer is, it seems like you just have to experiment. I think there's just a limit to how much you can store, or replace by drinking. After that point, I think it's a matter of trying to reduce sweating --- a favorite trick of the ultra guys is using a sponge or wet towel on your neck and head.

Isn't coffee a diuretic?

Hello everyone

Came across this thread as a result of the link to the site where I wrote the article where I suggested that the cause of MANY of the collapses might have been low Blood pressure. I see that Rojo and Wejo posted a link to it as well, and so I'm obviously grateful...!

But I do recognize that I did not in fact explain the WHY? which was perhaps a little short-sighted of me. So I apologize, but I will say that I didn't want to go into detail for fear of writing what would have been a MONSTER article! But perhaps I can try to explain it now...

The reason the blood pressure drops at all during exercise (not withstanding the heat, which I'll get to in a moment) is because during exercise the body faces TWO challenges.

1. It has to get blood to the muscle where it is needed.

2. It has to get blood to the skin where it is needed for cooling.

Now the problem is that when the blood is redistributed to the skin, it lowers what has been called a number of things, but let's go with Central Blood Volume, because that is what is easiest to conceptualize. Effectively, what is happening is that the body is sending its blood away from the centre of the body, which is where all the sensors for blood pressure are. The result of this, is that the blood pressure DROPS.

HOWEVER, when you are exercising, the legs are pumping blood back to the heart, in effect, helping the circulation and defending that central blood volume. This prevents the drop in blood pressure.

Now, ON A VERY HOT day, the problem is that you need to send even more blood to the skin (because you have to cool off more), and so this means that the "muscle pump" of blood back to the centre of the body must be even more effective, which it sometimes is not.

Perhaps if I can give an example, it makes sense - think of soldiers standing on parade. Or perhaps of a group of children lined up at attention for some kind of assembly. Almost invariably, one of them faints and falls over. Why? Because what is happening is that gravity combined with the heat is forcing the body to send blood away from the centre of the body and to the skin (to cool off) and to the legs (because of gravity). The problem is that this person is standing dead still, so there's no muscle in the legs to "help" that blood back to the centre, and the blood pressure falls. That's why they faint over in a parade!

Now, applying this to exercise, what happens is that you are running along and your muscles are 'pumping' blood back to the heart - this keeps your blood pressure normal. But AS SOON AS YOU STOP, the 'muscle pump' stops working and so all of a sudden, there is a drop in the blood pressure. Hey presto, you faint! That is the reason why MOST PEOPLE COLLAPSE WHEN THEY STOP. If you think about it, how many of you have actually seen someone collapse while they are running? It's incredibly rare! It usually happens when you stop. Therefore, it is the act of STOPPING that causes the collapse, because suddenly that pump that was helping before is gone! I hope this makes sense...?

If I may end off with some speculation about your specific incident, Top 100. I think that what probably happened is that in moving from shade to direct sun, your skin suddenly heated up. We know that the skin responds to heating by 'asking' for more blood - it's called vasodilation. This vasodilation, as I explained above is what causes blood to move away from the centre of the body. The muscle pump, which as this stage is going as hard as it can, cannot keep pace and the new 'distribution' of blood to the skin causes a drop in BP. Your body senses this, and you start displaying the symptoms of a drop in BP - you feel a little ill, can't drink anymore, you can't run etc. That seems to me to be exactly what happened to you...

Now, as for what to do, it may surprise you to hear that DEHYDRATION AND DRINKING ARE NOT THE ANSWER - the drop in BP is in no way causes by dehydration. If you think for a second about the reality of running - the fastest guys drink the least. Maybe 400 to 600ml IN THE WHOLE RACE. They finish the race and have lost perhaps 2 or 3 kg, which is maybe 5 to 7% of their body weight (these are real numbers, incidentally, based on research I've been involved in at marathons and IronMan triathlons). yet they are fine! No low blood pressure, no dehydration, no heat stroke, no death...

that should immediately be a sign that it's not so straightforward. And this is already a MONSTER reply, so I won't go into too much detail on this (perhaps in the future, I will do a post on this on the website - in fact, I definitely will). But let's just say that drinking all you can would only have made you feel even more sick and possibly be fatal.

Instead, the answer is heat adaptation. The FIRST adaptation to heat exposure, which happens in a day or two, is that your blood pressure regulation improves. Suddenly, where it was a problem before, it isn't anymore. In that article quoted earlier and on the Letsrun site, I mentioned the story of the soldiers sent to SE Asia - three days is all it took and they were fine. I won't go into reasons for this, but some heat adaptation would prevent this. This is the reason I wrote that the biggest issue in the race on Sunday was simply that the runners were 'ambushed' by the temperatures. It was very unfortunate to have that kind of day for the race.

But I'm pleased you're recovered, and hopefully no worse for wear! Again, sorry for the mega-long post, but I really should have put it up the first time.

Regards

Ross

(science of sport web blog co-author)

great post. thanks.

Just read your post again Top 100, and saw that in fact family had to pull you off the course. I will still stick with the low BP option there, but I would want to ask whether when they did those tests on you, they measured your blood sodium concentration? Your symptom is remarkably similar to one that many athletes experience when they have a condition called hyponatremia.

This condition is the result of excessive dilution of the blood sodium through the over-consumption of water. Think of a jug of lemonade to which you just add more and more water - ends up tasting tepid and weak... The condition was first identified in 1981 at the Comrades marathon, where a woman had to be removed from the race after about 60km because she didn't recognize her husband. Reading your post again just reminded me of that story, and so I was curious - did you have it measured? I'd be curious to know, particularly since you also mentioned that you could no longer drink anymore. That would be a sign of being bloated from the possible over-drinking of water.

The water drinking issue is a whole new story - basically, thirst is a good guide, tells you exactly what you need to know. And the example of the elite athlete illustrates just how 'dehydrated' the body can get before anything bad happens. But overdoing it, drinking too much, well, that can be fatal. I know that at least one of the major critical collapsed runners from Chicago had a low sodium content, which is definitely a sign that he drank too much water...

My experience was very similar. I had a very low blood pressure (said the nurse) at medical tent by mile 23. The wheels came off for me at about mile 16, ran even splits to about the 25k mark. I drank at every station too.

Wow, thank you for responding! No worries on making a long post. I'm sure everyone here appreciates your feedback.

In terms of adaptation-- I live only 2 hours from Chicago and had been training in the late morning in the few weeks leading up to the marathon (in case it was hot, ha!). It was that period in the race of going from shade to no shade that suddenly (and significantly) affected how I felt(which you describe perfectly!). I guess I should have trained more in direct sun, as I mostly train on tree-covered paths.

Regarding the coffee question. I only drink 1 cup a day, and I really didn't want to change anything about my routine the morning of. I could understand several cups causing dehydration, but surely not 1 cup!

Reading these, I really do feel even more convinced that the low blood pressure hypothesis is the answer to MANY problems (not all, mind you, I think that over-drinking is a big one too).

The only way to really know is to have both measured, be it sodium in the blood or blood pressure. Same goes for heat stroke - you can't diagnose it until it is measured. But given the symptoms I was reading (and here you can help with some facts, perhaps) a lot of people were saying nausea, vomiting, convulsions etc. Those are not the symptom of heatstroke. I remember when I was working the medical tent at a local ultra-marathon (56km Two Oceans), a guy came in with heat stroke. He was out. It's a terrible analogy, but it's like a flower that has been left on the window sill too long - it simply wilts. The brain stops activating the muscle, and so the athlete is completely 'paralysed', often not consious. A very different thing to hyponatremia or even low blood pressure and feeling lousy from over-exerting on a hot day.

But heat stroke is an amazing condition - not so straightforward. The guy I mentioned earlier came into the tent with a temperature of 110F (normal is 98F). They diagnosed heat stroke by measuring body temperature (the only way to do it, as said), and put him in a cold water bath. 30 minutes later, his body temperature was 115F!! He actually GOT HOTTER WHILE SITTING IN AN ICE-BATH!! Another 24 hours passed, the guy just stayed at the same temperature! They put him on ice for a day, and he didn't cool off. Eventually it dropped and he was discharged from hospital and recovered.

That's not normal physiology, and it suggests that people who get heatstroke must have some serious malfunction of their metabolism, because they literally burn up from inside. That remains a mystery though...

ANyway, that's too much writing...

No, they didn't test my blood sodium.

I was consciously making an effort to drink both gatorade and water at every station (not that I craved either and I didn't feel overheated at all). I also took a glucose tablet every 30min.. When we got into the sun, I craved water, and I felt like I couldn't drink enough of it at the stations to quench my thirst. So there may have been some sort of imbalance. I had practiced all of the above in training (and in a half a month before), but not of the same magnitude/frequency.

Thanks for the good information, Ross. Again, I'm not a doctor or exercise physiologist so I'll accept that I have limited knowledge here, but dehydration certainly can cause low blood pressure (http://www.merck.com/mmhe/sec12/ch158/ch158b.html) . Also, the confusion being reported by these athletes is a common symptom of dehydration. It might be that it's not the leading contributor to their problems, but I sure wouldn't throw it out just because a few elite athletes can operate effectively at 5% body loss.

Oh, I do want to add that I will try to educate myself from your post and related articles. I've just skimmed over it at this point.

Hi sweathog

Thanks, and really, no need for apologies - you're right actually, dehydration CAN cause low blood pressure, but NOT during exercise, and not in the levels that you see during exercise.

If you are for whatever reason not exercising and dehydrated beyond about 6 to 7% of your body weight, like when vomiting, having diarrhoea etc., then it is possible for the blood pressure to fall to the point of hypotension.

But during exercise, the presence of the muscle pump, mentioned earlier, prevents this and also, you never get this level of dehydration, at least not volitionally - thirst protects it from happening, so if you drink to thirst, then you find that athletes typically replace about 60 to 70% of fluid losses. This means they end up losing maybe 2 kg in the course of a 2 hour run. That's probably 3%, which is quite safe and very normal.

So perhaps the first thing is to define what we mean by dehydration - the CLINICAL definition, which is any lose of body water, is not appropriate for exercise, because during exercise, it's quite acceptable to lose up to 4 or 5% of body weight during exercise with no negative effects whatsoever.

So dehydration takes on a completely new meaning. And the site you referred to, the Merck one, is quite right, but that's not the exercise situation. A lot is different during exercise. For example (and this may seem random), your body temperature when you exercise probably rises from 98F to about 102F quite easily, but you don't even feel a thing! I guarantee you that if you were reading this post and your temperature was 102F, you'd be at home, in bed, sipping on hot tea and hoping your fever went away soon! Point is, what we consider "normal" is different for exercise and rest.

In terms of dehydration, our bodies are quite content with up to 4 or 5% body weight loss, provided we are not thirsty. It knows that we can easily replace this fluid later on, after we finish. I don't want to get into the details too much, but I accept that my earlier argument that elite runners don't have a problem is not sufficient. That's ONE of the many arguments to be made.

But the key is to recognize that trying to maintain your body weight during exercise can be very dangerous, and it's not necessary. We looked at thousands of marathon runners, triathletes etc. and perhaps 95% of them finish having lost betwee 1 and 3% of their body weight - that's what happens drinking to thirst. And they were fine, all of them. The ONLY ones who were in trouble were those who drank too much and did not lose weight as a result of exercise - if you finish the race as heavy as you started it, you might well be in trouble...

Ross

Actually, I had the same thing happen in a 1/2 marathon in Austin a couple years ago. I know I was not drinking too much water, because I did not really take much water at all (maybe two cups the whole time). It was much hotter than I had anticipated (and really humid). Anyway, after mile 8 I just started slowing down (even though I felt like I was running pretty fast) and when I hit the finish line (5 mins off my goal pace) I was on the ground.

I did not go to the first aid station right away, and instead walked all over the finishing area like a drunken person (it was really weird). After about 30 mins I was feeling really really bad and walked to the aid station. They could not find my diastolic pressure after 3 trys.

It took me about 4 weeks to feel "normal" again. I was never sure if it was dehydration or something else that caused this ...