Question

Anatomy and Physiology RCT 1

Phenomenon: Marathon Runner Ends up in a Coma

A marathon is a 26.2-mile race. People often train for months leading up to the race in order to successfully complete this type of long-distance running challenge. Sometimes, runners aren’t able to finish the race or runners' collapse. Your challenge is to use your findings from research articles and data sets in order to determine and explain what is causing some marathon runners to collapse.


These days, many amateur athletes participate in marathons. One such amateur athlete -- a 40-year-old woman running a marathon for the first time, runner #0358 -- got very sick and disoriented during the second half of a New York City marathon. She kept running the race, and she even took pictures with her family along the racecourse, but she later had no memory of running the second half of the race! Runner #0358 went home, then became very ill and disoriented, eventually ending up in a coma. While the runner did recover after a while, this event concerned the race organizers. The marathon was held on an unusually hot, humid, and sunny day. The race started at 10:00 AM, but some runners were on the course for 4 or 5 hours. During that time, the temperature got as high as 28◦ C (about 82◦ F), and the sun was out all day. Many runners ended up seeking medical care either at a stop along the racecourse, or at the end of the race.


What could have happened to her to make her so sick? Below is additional information about challenges that athletes may face with strenuous exercise in extreme conditions.


Athletes need more sodium because it is lost while sweating. The amount of sodium excreted in sweat is large and depends on many factors, such as body mass, training level, temperature, clothing, gender, and heat/humidity acclimatization. The level of sodium in your body can become too low or too high based on the amount of water in your body. If the amount of water you consume isn’t equal to the amount you lose, you can become dehydrated (too little water).


Hyponatremia occurs when sweating causes disproportionate sodium loss or an excessive intake of plain water, which dilutes the level of sodium in the blood. This is why it’s imperative to drink sports drinks containing electrolytes and not plain water for any physical activity over an hour.


If your blood sugar drops to a low enough level and you don't elevate it with some sort of fast-acting carbohydrate such as fruit juice or a sports drink, you may begin to experience symptoms of hypoglycemia. Hypoglycemia can cause symptoms such as headache, shakiness or trembling, excessive sweating, mental confusion and heart palpitations.


Exercise is one of the strong factors disturbing the maintenance of body temperature. Some conditions, such as heavy exercise in thermal extremes, could rapidly lead to dangerous internal temperatures. The thermal load posed by the environment or by heavy exercise may be too great for the capacity of the regulators. Or the regulator could be deranged due to extreme temperatures.




Table 1. Marathon Runner. The medical data in the table are from the assessment of four participants, including runner #0358 who had the most negative outcomes.


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*Normal values for Blood Glucose: 135-140 mg/dL

*Normal values for Plasma Sodium: 135-145 mEq/L, <125mEq/L = high mortality

*Normal body temperature: 37◦C= 98.6◦F

* Normal Oxygen Saturation: 95%-100%



(a)

Claim:

Choose the best claim stating why marathon runner #0358 ended up in a coma.

A
She had normal body temperature but was dehydrated.

B
She consumed too many carbohydrates during the race.

C
She had low levels of sodium and glucose.

D
She had elevated levels of sodium and glucose.

Answer 1

Answer: C — She had low levels of sodium and glucose.

Why: The clinical picture (disorientation progressing to coma on a hot humid race day) plus the data in Table 1 point to hyponatremia and hypoglycemia. Severe hyponatremia (plasma Na+ <125 mEq/L) causes cerebral edema, headache, confusion, seizures and coma. Prolonged running in heat also depletes blood glucose (glycogen stores become exhausted), and hypoglycemia produces confusion, sweating, tremor and can progress to unconsciousness. The combination of low Na+ and low glucose explains the neurological collapse better than the other options:

- A (normal temp but dehydrated): dehydration usually raises plasma Na+ (or at least does not produce the low Na+ seen here).
- B (excess carbohydrates): would raise blood glucose, not cause the low glucose/coma seen.
- D (elevated Na+ and glucose): inconsistent with the laboratory values and typical marathon collapse mechanisms.

(Appropriate acute treatment would include careful correction of severe hyponatremia — often hypertonic saline under close monitoring — and prompt correction of hypoglycemia with fast-acting carbohydrate or IV glucose.)