Dehydration

This image, of the Italian runner Dorando Pietri staggering across the line at the end of the 1908 Olympic marathon in London, has become a fairly famous sporting image.

Dorando crossed the line first but was later disqualified for receiving assistance. If you watch film of the finish you can see him entering the stadium and turning the wrong way and then collapsing several times.

Why? Was he just out of energy? Hit the proverbial wall? Probably not. Dorando was an accomplished runner but his time (2:55) was positively pedestrian. I can't personally run a marathon this fast but I know a 60 year old who can and there is a 70 year old in Canada who has run a marathon that fast. 2:55 is half an hour short of an Olympic qualifying time now and Dorando would have been about 8 miles behind Sammy Wanjiru, the last Olympic marathon winner, when he crossed the line in Beijing.

So why did he collapse? It was a hot day and early marathon runners were poorly supplied with fluids (if at all). They did receive some solid food but we now know the stomach is poor at digesting these during a race. It is likely that he simply became increasingly dehydrated (possibly also suffering from the effects of the heat). If you exercise vigorously you can easily lose 2.5 pints of water per hour - approximately 2.5 pounds. This is rather conservative, sweat rates vary quite a bit. Men contain about 60% water (by weight). Dorando was a small guy (5'2") and had a slight athletic build so let's guess his weight at 100 pounds, giving us approximately 60 pounds of water. Each hour of vigorous exercise he probably lost approximately 4% of his water.

Medically we know exactly the consequences of such water loss or dehydration:

• 2%-5% - Thirst, fatigue
• 5%-10% - As above plus headache, heart and respiration rate increase (your blood is getting thicker and harder to pump), more severe reduction in performance and nausea
  
• 10%-15% - As above plus decreased skin turgor, vision dimming and delirium
• >15% Risk of death
  

So in barely three hours Dorando went from being a prime specimen of a healthy human to being severely dehydrated. Just three hours. Losing even a few more pounds of water could have been very dangerous.

What does this have to do with disease? Patients with Cholera lose water at about exactly this rate - a couple of pounds per hour (a liter). Losing water at this rate for more than a few hours can easily be fatal. The problem is theoretically easy to fix in both cases - replace the water that is being lost. It's also important, perhaps even more important, to replace the salts that are being lost. However if clean water is not available then we have a serious problem.

I mention this because it is hard to imagine a disease killing you as quickly as Cholera can. It sounds like an exaggeration but it isn't The human body is rather susceptible to dehydration and we can dehydrate very quickly.