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Friday, October 12, 2007

Post-Chicago analysis continued: One patient's details

The news media are slowing down a bit here in Chicago, but the questions still remain---and we are not talking about why the race ran out of water, if they even ran out of water, or why they shortened the course. Rather, we are most interested in the runners who remained in the hospital on Monday evening. News outlets stated on Monday that 10 remained in the hospital, although no details were ever divulged about the diagnoses of these runners, which raises questions about the reasons they were admitted overnight.

Heat stroke - diagnosis?

First, if indeed the diagnosis is heat stroke then the first thing that must be done to confirm this diagnosis is a rectal temperature. As we have stated here previously, this is a crucial measurement that must be made for this differential diagnosis. Without it, you simply cannot confirm if the person has heat stroke or postural hypotension or something else. If the individual does indeed have a rectal temperature at or above 42 C (107.6 F), then active cooling in the form of ice-water immersion must take place, and even when it does it is possible that some tissue damage might have occurred and the person might require further monitoring.

However the signs and symptoms of "dehydration" and another condition, hyponatremia, are similar, and one can and often has been mistaken for the other. These include nausea, vomiting, and headache, among others. Hyponatremia is worthy of a post on its own, and we promise we will do one very soon. In short, it is caused by ingesting too much fluid, which causes the concentration of sodium in the blood to fall. Therefore it is a problem of fluid balance in which there is too much fluid, and not a problem of sodium balance as many people argue.

So whether or not the runners who remained in hospital were being treated due to heat stroke or hyponatremia is to us a crucial question, primarily because the race has been railed for not supplying enough water, which many people think is the cause of the hopsitalizations. We were fortunate to have access to the admission details of one of the hospitalized runners, and it is telling.

One case from Chicago

This runner began feeling bad at 20 miles, but did finish the race. They had a fainting episode sometime after the finish, the importantance of which is that this runner collapsed after they had stopped running. The athlete was admitted approximately one hour after the finish with the following results (normal values in brackets):
  • Serum sodium concentration - 130 (135-145)
  • Troponin - 0.11 (less than 0.1)
  • Creatine Kinase or CK - 4102 (35-232)
  • CK MB - 82.9 (5.1)
  • Rectal temperature - 37.1 C
First, a quick explanation. . .

This is a substance used to help confirm the diagnosis of a heart attack, which means this runner suffered a heart attack? Not quite. Prolonged endurance exercise can elevate the levels of this substance in the absence of any cardiac abnormalities.

CK and CKMB:
In the clinical setting, also a measure of cardiac damage. However, in exercise physiology we use this enzyme as a marker of muscle damage. CK, for example, is an enzyme found in the muscle , and the only way it gets into the blood is if the muscle is damaged. As you will know, this happens during marathon running. Many scientists are interested in muscle damage and repair, and this is an objective method to quantify the degree of muscle damage. Plenty of scientific evidence exists showing that after marathon running CK levels are vastly elevated.

Rectal temperature:
Ummm. . .ok, we all know what this one is! But seriously, the normal exercising range for the rectal temperature is 37-41+ C. Most people do not reach 40+ C, but in trained athletes rectal temperatures above 41 C have been documented, and more importantly they have been measured in the absence of any signs and or symptoms of "heat illness" or heat stroke. But in any case, this runner's rectal temperature approximately one hour after the marathon was totally normal, and in fact it was at a resting value.

Serum sodium concentration:
This measure reflects how diluted or concentrated the blood is. Most people finish marathons (and longer races) within the normal range, and furthermore the normal response is to maintain or even increase slightly. It is not normal for this value to fall during exercise. When an athlete presents with such a low sodium concentration it is a clear indication that they have ingested too much fluid. The tricky part is that "too much" is a relative amount and does not necessarily mean gallons and gallons----although fluid ingestion on that scale has been documented during endurance exercise.

The problem is that sometimes the body inappropriately secretes a hormone that promotes water retention. When you ingest too much fluid, this hormone quietly goes away until you need it. . .however, some of the stresses that occur during exercise can perhaps trigger its release, and that is why some athletes present with hyponatremia even when they ingest apparently modest volumes of fluid during their race.

Granted that is an entirely simplified explanation of hyponatremia, and we will follow with a full series of this condition and why and how it came about. However the take home message here is that this runner, and we suspect more than a few others, remained in the hospital on Monday not because of a heat-related problem, but because of a fluid-related problem---namely, hyponatremia---and this fluid problem was not a lack of fluid but rather a gross excess of fluid.

So be sure to come back later for the follow up posts on this and other runners as we obtain information, or even better, subscribe to The Science of Sport and get the posts delivered directly to your inbox.

Thanks for reading!

Read more insight from the Chicago Marathon in our post on heat stroke and running HERE


Luke said...

More great myth busting, guys. Perhaps you could put together an essay and submit it to either paper's commentary pages. People need to read this.

Uninformed runners and observers have been unfairly calling for the organizers' heads all weeks. In my eyes they did absolutely nothing wrong. The only failure may have been volunteers not being able to pour fast enough to keep up with the runners' unsound consumption. If cups weren't poured, all runners had to do was wait. If you're running a 6-hour marathon, are you really in that much of a hurry?

Yet can you imagine the mob's reaction if the organizers were to come out and say: "We have recognized what we did wrong. Therefore, for your safety there will be less water available next year"?

Hung-Kwong Ng said...

Hello again. I posted anonymously a comment in a previous post about the 2 runners who were running under 8 minutes that lead to the call to cancel the race.

My understanding of dehydration and hyponatremia is slightly different. Dehydration is simply the percentage loss in bodyweight due to fluid losses. Hyponatremia and hypernatremia is the concentration of sodium in your blood. You can be both dehydrated (loss in bodyweight) and hyponatremic. You can also gain weight and be hypernatremic.

I actually gained weight this weekend from running the St George and Chicago marathon. Accordingly to my Tanita scale, my body water went up from 59.5 to 62 percent. The home gadget may not be a precise tool but I am confident its measurements are in the right direction. I had little time to eat properly - so I ate french fries and took an electrolyte capsule between marathons. I believe I was retaining water from the excess sodium. After 4 days, my weight is now lower than when before the 2 marathons. I atttribute that to some fat burn in the 52 miles of running.

Ross Tucker and Jonathan Dugas said...

Hi Hung-Kwong, and thanks so much for visiting The Science of Sport and for commenting on our blog.

It has been reported that some athletes lose weight and are still hyponatremic. It has also been shown that some people gain weight and maintain or elevate their sodium concentration.

Our current hypothesis on why this happens has to do with one's ability to regulate the sodium concentration. It is a very complicated physiological explanation, but the gist of it is that when the sodium concentration falls, you can respond to it by activating sodium stores in the body that are osmotically inactive (and therefore not contributing to the sodium concentration). It would seem that people who gain fluid and still maintain their sodium concentration have a larger capacity to activate these stores, and therefore even when they axpand their plasma volume (via over drinking) they still maintain their sodium concentration.

Sorry for the mumbo-jumbo, but it is really quite a complicated thing to explain in short and easy words!

The take home message, though, is that losing weight during endurance exercise is normal. In addition, drinking too much fluid will almost certainly lead to hyponatremia. Further, drinking more than to your thirst is entirely unnecessary and is not proven to be of any significant benefit to health or performance.

Thanks again for visiting, and we hope you enjoy the rest of the posts on this topic. Good luck with your future ultra-running---pretty soon you will be ready for Comrades!

Kind Regards,