Low blood pressure and Chicago Marathon?

What would be your advice for heat adaptation? I live in Chicago and am racing just outside of Las Vegas in four weeks. Believe it or not, it's already gotten cold here, but I will be racing in the afternoon, probably at close to 70 degrees.

To the original poster, I'm glad to hear that you are ok. Thanks for starting this interesting thread.

I also had blood pressure issues in the Chicago Marathon this year. I came in in good shape and was right on my pace through the first half, drinking water and gatorade at each stop. The wheels really fell off during the second half (I also felt a significant "shock" moving from shade to heat) and I ultimately ended up walking half of the last mile. When I crossed the finish line I was taken straight to the medical tent for both over heating and very low blood pressure (70 over 40) . The medics told me I actually wasn't really dehydrated either. I puked out a large volume of liquid after being placed in an ice bath. After lying down for 45 min my blood pressure rose to 100 over 60 and I was able walk out on my own, feeling slightly week.

I'm really glad I saw this post and could read some of the insights. I have had similar bad finishes to races where my blood pressure was super low but I always just assumed it was due to was dehydration or not eating enough. In this case it definitely wasn't either. I didn't realize there was this much more to the equation.

Water is also a diuretic. In fact studies have shown caffeine to have only a slightly more diuretic effect than water. So, if you are drinking coffee you have two diuretic sources...the caffeine and the liquid you ingest.

Also, the simple act of aerobic exercise will actually cause your blood pressure to drop after you stop exercising because your blood vessels are still dilated.

Alan

Hi Epberlin

Heat adaptation happens (relatively) quickly - the studies in this field have all shown that 'full' adaptation occurs withing about 4 to 6 days of arriving in a hot environment, provided you expose yourself to that heat.

For example, studies in Denmark (where a lot of our knowledge on heat originates) have found that if you take men who are completely unused to the heat and then make them exercisethem in a hot (35 Celsius, about 95F) environment to exercise, they suffer the first day, but every day thereafter they get better and better. By about the 6th day, they are back to normal (which is what they did in the cool before) and then they DON'T continue to improve after day 6. So in otherwords, you get better for 6 days and then stop. The implication is that if you are running this race you'll need to be accustomed to 70F temperatures, and in your case, you have time on your side.

70F is not THAT hot, if you look at the original post on this topic (http://scienceofsport.blogspot.com/2007/10/investigating-heatstroke-how-fast-do.html), you'll see that it's probably cool enough that heat adaptation is not that critical. It depends on your weight and your target time though. If you'd like to reply, I'll work it out for you and we can see what the "thermal limit" to running at 70F is for you.

However, little things between now and then will help, such as running in a slightly warmer jacket (but not to get hot! - I have to stress that you don't need to worry about the heat if it's 70F, only once it starts hitting 80 plus). But I would just go into the race with an open mind, don't psyche yourself into feeling hot before your start, and between now and then, take opportunities to lift the temperature very slightly when you can.

Good luck!

Ross

Hi there

Thanks for your story as well, it contributes to what is a growing argument for blood pressure, and not dehydration or heat stroke as the possible cause of what we saw in Chicago (at least, most of the cases).

In your case, if I might make an example of the medical tent in two respects.

Firstly, did they measure your body temperature in order to diagnose that you had over heated? If so, what was the value? Because it's really important to realise that someone is not necessarily overheated just because they feel hot. they've just run a marathon, their body temperature will be about 102F, no matter what (it's a normal temperatuer at the end of exercise) and their skin feels hot. So I suspect what often happens is that people feel the runner's skin, it's hot, the runner feels hot, and so they diagnose over-heating. That is likely to be incorrect. As I said, a runner who has true heat stroke (104F and above) is like a wilted flower - they have nothing left, and seem almost paralysed.

But the second thing is the treatment - when you STOP exercise, that muscle pump stops working and so the fact that all your blood has been sent to the skin to cool you is suddenly a problem, because it means that your central blood volume is very low. And with no muscles to help get the blood back from the legs, your BP suddenly drops. Which is why people faint when they STOP exercise, and not during (usually). I am repeating what I said in an earlier post, sorry.

But the treatment is simply to lie down. And the body knows this, which is the reason you faint. Because by fainting, your blood no longer has to work against gravity, you are horizontal and all that blood from the legs suddenly returns to the centre of the body much more rapidly and your BP rises again. The best treatment for a collapsed runner (once you've eliminated other more serious possibilities like heart attacks etc.) is to have them lie down with their legs up at about 30 degrees (it's called the Trendellenburg position). This helps the blood back even faster and they recover.

One last obvservation is that a lot of people have been throwing up and puking water. That suggests to me that people may definitely have been over drinking a little. Not a lot, because I only know of one case so far of hyponatremia. But enough to get themselves. I think this is definitely an issue to consider. Here's a radical idea though: Is it possible that the shortage of water in Chicago might have saved lives, as a result of denying people a chance to overdrink? I realise that sounds mad, but it does seem a real possibility?

Anyway, more investigation required.

I had a very similar experience. I was also well trained and well hydrated prior to the race. I was shooting for 2:30 range and was on pace for the first half. I realized quickly though that the heat was really effecting me and I was experiencing stomach cramping and muscle tightness. The last half was purely survival and people were dropping like flies. After crossing the finish line I passed out and spent some time in the medical tent. My blood pressure was 90/50 with a resting heart rate of 106 (usually 50). The way they described it to me was that I lost so much water (10 lbs) that my body was working over time to pump blood to the muscles. The fluid levels in the blood were so low that it raised my heart rate and dropped my blood pressure. Kind of like filling up a hot air baloon with a match.

Ross Tucker: Thank you for your response. The average high temperature for Vegas at that time of year is about 70 (and I'll be running in the afternoon when the high occurs). It could be hotter or cooler. (The record high for that day is 85, which is lower than the high here on Sunday!) But I will be used to running in 40 degrees. I realize that 70 is not dangerously hot, but I do find that I feel a 25-30 degree jump in temperature no matter what, even if I'm going from 20s to 50s when I travel. So I'm concerned with performance, not necessarily heat stroke. I take from your post: (a) I don't need to worry about this much until about a week out; and (b) about a week out I should try to keep myself as reasonably warm as possible when running and generally. I arrive in Vegas a day before the race, so I won't get a chance to acclimate there. Thanks again.

I went down at 22 - for the four nights since, I have slept like I've never slept before. More hours and more deeply than I remember over such a stretch. I would expect it for a night or two, but this is more than I'd expect. Are others who crashed at Chicago experiencing similar sleep?

Ross Tucker wrote:

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...

Thanks for sharing your knowledge, Ross. I appreciate how you've picked apart a complex set of conditions associated with exercise in the heat and delivered a very readable explanation. Why are you calling the example above a mystery? As I read it, the case you described above is a classic example of fever response resulting from the cytokine cascade -- a hyperthermia-induced leaky gut. Your thoughts? I'd be interested to know if the latest literature has shown that cytokine is not part of the cascade? I suppose that you could be calling it a mystery in the sense that the fever response per se has a neurological component to the mechanism that is still a fairly "grey" box for us?

I have been sleeping a lot as well. I am out at about 9pm and wake about 6am. On Monday I slept for about 3 hrs in the afternoon and went to bed at 8pm that night. My body is just fatigued. I caught a cold on Wednesday...I truly never get sick either, so this is another side effect. My immune system is lacking. I jogged this morning though and didn't feel too bad. I refuse to lose the shape I'm in, and I can't wait to rip up the Chicago Marathon course next year.

Ross,

Do you mind listing your credentials? I have not found them on you website. I am a second year medical student who is just learning about the intricacies of human physiology, so I won't pretend to be an expert. But from what I have read thus far, your posts seem largely remedial and inaccurate. I would ask any physiologists or MDs to chime in and answer these important questions appropriately.

Wile E.

Ross,

Do you mind listing your credentials? I have not found them on you website. I am a second year medical student who is just learning about the intricacies of human physiology, so I won't pretend to be an expert. But from what I have read thus far, your posts seem largely remedial and inaccurate. I would ask any physiologists or MDs to chime in and answer these important questions appropriately.

Wile E.

Ross and Jonathan, are you guys students of Dr. Noakes?

As terrible as the Chicago Marathon was, it seemed to provide the perfect microcosm for learning how people coming from different backgrounds/environments responded to it. Hope a lot can be learned from it!

Dr Ross Tucker- PhD Exercise Physiology

http://web.uct.ac.za/depts/essm/students.htm

Wile E. Coyote wrote:

Ross,

Do you mind listing your credentials? I have not found them on you website. I am a second year medical student who is just learning about the intricacies of human physiology, so I won't pretend to be an expert. But from what I have read thus far, your posts seem largely remedial and inaccurate. I would ask any physiologists or MDs to chime in and answer these important questions appropriately.

Wile E.

Hello Wile E

Not at all - someone found them, but I can perhaps add, I obtained a PhD in Exercise Physiology from the University of Cape Town, under the supervision of Prof Tim Noakes. My PhD investigated the regulation of exercise by the brain, with a focus on the understanding of fatigue during exercise in the heat.

I have also been involved within our unit on studies examining fluid intake, thermoregulation and dehydration and the impact of these on exercise performance.

So those are my areas of interest. I did my undergraduate in Physiology and Biochemistry and I am currently employed within the University of Cape Town to conduct further research on performance,fatigue and the brain, and on exercise and thermoregulation. My specific areas include performance, training adaptations and coaching.

Just to respond to what you are learning - what has to understand that exercise and what you are learning in your physiology are quite different in certain respects. At the risk of dredging up a 'remedial' post, I made the point previously that when one exercises, the body temperature can very easily rise to 103 to 104F and this is absolutely normal.

When you are in lectures next time, you ask your lecturer what he would make of a body temperature of 103F - he'll tell you the person has a fever and should be treated accordingly. Now, the way you interpret cardiovascular physiology during exercise as opposed to in a diseased state or at rest are vastly, vastly different. We have many examples of how MDs have written in to complain about the principles we explain, but they are actually wrong (I have no doubt someone will lay into me for that, but I have right on my side in this one!!!) Just as I have a basic understanding, for example, of kidney function, I would never ever go into a debate with a neprhologist and anticipate to know his area of speciality, and that's the analogy. Not that I claim to have all the answers, because I don't.

All I can say then, is that you have to read the literature and NOT allow yourself to be pointed in the "right direction" by anyone (including me). I believe I am giving out accurate, hopefully non-remedial info, but as a student of the sciences, you have an opportunity to read up yourself. And I'm not entirely sure which post you feel is inaccurate, but if it's on the whole dehydration and heat stroke thing, well, that's a huge debate, one we can certainly go into - our email address is at the top of the page. But if it's the circulation and blood pressure one, the very first paper that showed this was by a guy called Ethan Nadel in 1979, because until that point, it had been thought that the cardiovascular system was the limiting factor in the heat. He showed that it wasn't, and the Danes subsequently picked up on it and developed the field first. The names to look for there are Nybo, Nielsen and Savard - very good research.

As for the hypotension, Noakes is the big name there, a controversial one but the one to look at nevertheless.

But it's good to debate, thanks!

Ross

coll div wrote:

Thanks for sharing your knowledge, Ross. I appreciate how you've picked apart a complex set of conditions associated with exercise in the heat and delivered a very readable explanation. Why are you calling the example above a mystery? As I read it, the case you described above is a classic example of fever response resulting from the cytokine cascade -- a hyperthermia-induced leaky gut. Your thoughts? I'd be interested to know if the latest literature has shown that cytokine is not part of the cascade? I suppose that you could be calling it a mystery in the sense that the fever response per se has a neurological component to the mechanism that is still a fairly "grey" box for us?

hey Coll div

Thanks for the post! The cytokine cascade theory is interesting, one that has been put forward, but remains a mystery because it's never been described during exercise. The only literature I'm aware of is in epithelial cells and in humans at rest...But from a conceptual point of view, one could see the cytokines driving the core temperature up, but not that much. We did a study about 4 years ago where we infused IL-6 into runners during a 10km time-trial. Their body temperatures were definitely higher than in controls, but still not anything like heat-stroke cases, and they responded rapidly to cooling once they finished the run. So something else malfunctions too, or the cascade goes into overdrive...

The other one is the ryanodine receptor, of malignant hyperthermia fame. But it remains unclear what triggers this - there is one theory that there is bacterial infection that precipitates the fever response, another that it's viral, and still others that are neither viral nor bacterial, but malfunctions in cascades, like the cytokine one you brought up. The cytokines are themselves a mystery as pertains to exercise, actually. But more and more, people are figuring out the pathways and functions and it's becoming increasingly clear that they are major 'players' in many physiological "failures" - overtraining is one of them where cytokines are heavily involved.

But to my knowledge, it's not yet been identified in a runner or as a result of exercise. Now, the thing is, true heat stroke is rare enough that an abnormality, be it biochemical, physiological, metabolic, could very well explain why people do overheat during exercise. But it remains a mystery, a "grey" box because I don't know that it's ever been described in exercise - all hypotheses and postulations.

One thing that has been described is that exercise in the heat compromises immune function - so they are looking at it the OTHER WAY AROUND - it's known that the cytokine levels are raised by exercise in the heat and this might compromise immune function. But no studies yet on the cytokine stimulating hyperthermia in exercise. But I'm open to the option...

Ross,

Thank you for your reply. In fact, the first thing that struck me in your posts was that there was zero mention of the kidney's role in the regulation of blood pressure. How can we have a discussion of volume status and salt balance without discussing the renin-angiotensin-aldosterone system? Also, there is no discussion of blood pressure in the context of changing metabolic needs over the course of endurance exercise (a hypovolemic state in the context of depleted glycogen stores). You have simplified your argument to the body's need to resist overheating and supply the muscles with oxygen. I will argue that the body is much more concerned with supplying the brain with oxygen. In addition, has anyone asked the original poster what medical treatment he received? I am willing to bet that he was given an IV of isotonic saline. If this is indeed what happened, how can you argue that it is detrimental for endurance athletes to maintain their euvolemic state during competition?

Wile E.

Thanks for the reply, Ross. Yeah, I'd read your lab's great study with the IL-6. Very nice. If I remember right, though, your subjects were not much dehydrated.

With the "heatstroke cascade" scenario, we add the dimension that the muscles are taking priority over other organs (skin, gut) for blood flow. Now we are losing our ability for heat dissipation with the concurrent threat of the cytokine fever response.

You said that folks are looking at it the OTHER WAY AROUND. I've been imagining it as a positive feedback loop. ALL THE WAY AROUND, with dehydration being the precipitating factor. Loss of capacity for heat dissipation, increased body temp, gut cells get leaky (they are very heat sensitive, plus now they are also getting less blood flow), cytokine enters bloodstream, fever response, more heat production, more cytokine enters,... all the time our capacity for heat dissipation is compomised by dehydration -- decreased evaporative cooling AND even radiant cooling.

It's the feedback loop that is the phenomenon, the overdrive, not just the fever response. My view on it, of course, and I will continue to defer to your knowledge on the subject if you can take the time to reply.

Sure, point taken. But the role of the kidneys and the RAA system is another issue altogether. There is no evidence that the RAA system plays a role in the collapse of atheltes during or immediately after an athletic event. If you have this information DURING EXERCISE (this is critical - what you have learned and are now applying to exercise is not always directly relevant) then I'd happily consider it. There is a good deal of work going on in this area - the measurement of aldosterone, ADH, renin and such during exercise, but it's RELATIVELY insignificant during exercise. Why? Because the sympathetic nervous system is active, and its activity is responsible for most of the blood pressure regulation during exercise. The entire situation changes.

As for the oxygen supply to the brain, yes, you're quite correct, but nowhere did I suggest that this was not important. The whole point behind the system I explained yesterday is TO PREVENT A FALL IN BLOOD PRESSURE. So you're not actually disagreeing with me at all. The point is that during exercise, there is a challenge to supply oxygen to muscles and to cool the body - the supply of oxygen to the brain is a given. Blood pressure is THE defended variable, because the supply of oxygen to the brain is critical. So the reason the athlete eventually collapses is precisely because they have to defend BP. Your argument is thus taken, but it's been in play all along, that's the exact reason that one collapses, not because muscle needs more oxygen. Apologies if I portrayed it that way.

And then finally, we did ask the original poster, and while I don't wish to speak for her, she responded very rapidly to being made to lie down. She felt much better almost immediately afterwards, and that strongly suggests that it was BP. And then finally, the practice of just whacking an IV in there is likely to kill as many people as it saves. ONe day, when you're a doctor, you may treat people in medical tents and if you do this, and just throw an IV in because "it's the done thing", you may very well be doing a huge disservice to the athlete. There are cases where it's prescribed, but a lot where it is not. We've done five studies in the last 3 years on this very topic - restoring euvolemia is NOT the key determinant to discharge from the medical tent, and our understanding of that line of treatment is changing. THe isotonic IV is still done, yes, but not all the time and it doesn't mean that was the problem to begin with. That's a key difference.

Again, I cannot emphasize enough that exercise physiology is not the same as textbook physiology - a sodium content of 145mM after a marathon is normal, just as an elevated body temperature is normal. Do you know, for example, that the sodium concentration of people who end up in the medical tent IS NOT DIFFERENT to that of people who finish marathons and don't end up being treated? People don't collapse because of dehydration, pure and simple. The only research that will tell you otherwise is funded by Gatorade - that's a conflict of interest you cannot ignore...

But I don't think this is the forum for a scientific debate, and so I apologize that you don't feel the initial response was 'appropriate'. But don't hestitate to email directly and we can resume the debate, but this is not pubmed, so perhaps better not to get in depth on the science.

Ciao

Ross