Monthly Archives: August 2013

Whitewater safety

It’s been a rough week in southeast Tennessee.  Two people died in two days on Grumpy’s rapid past Ocoee Dam No. 2. Just how common is death due to whitewater rafting?

Wilson et al reviewed 16 articles in the primary literature to determine the specific types of injuries that occur from whitewater rafting and paddling.  They found that the rate on injury is low, and that specific injuries occur with each sport.  Paddling (including kayaking and canoeing) had mostly upper extremity injuries while in the boat.  Lower limb injuries occurred during the hike in or out, or while in the water apart from the boat.  Rafting injuries generally occurred while “swimming” (ie fell out of the boat), and were typically from collision trauma.  Paddling injury rates are roughly 4.5 per 1000 days for novice paddlers, and rafting rates are 26.3 per 100,000 participants (different measures theirs, not mine). There was likely reporting bias for minor injuries, as people not seeking treatment were not reported.

Mildly relevant to the news article, fatality rates from commercial whitewater rafting in New Zealand to range from 0.16-0.27 per 100,000 participants per year. Drowning was indicated in 94% of the fatalities.  Paddling death rates were much higher, at 2.9 per 100,000 participants per year.  The authors attribute this to the fact that most paddling is done with commercial groups, as well as the fact that it is easier to sink a canoe than an 8 person raft.

Perhaps it was simply bad luck, as the death rates in this sport are fairly low. Perhaps more can be done to prevent drowning beyond the required helmets and life jackets. Better epidemiological studies may tease out this. In the meantime, be safe out there.

Injuries, Ill-Health and Fatalities in White Water Rafting and White Water Paddling
http://www.ncbi.nlm.nih.gov/pubmed/23315757

The brain wants oxygen

It goes without saying that the body is designed to work aerobically.  The mind therefore, follows the same pattern.  This essay by Rodway shows historical data and research about the changes in cognition as one goes further up into thin air.  This is important, because they conjecture that many of the problems climbers face are so serious that they have life or death implications, and thus the brain cannot process them as it should, leading to fatal errors.

“Mountaineers have often observed a lack of clarity in their mental state at high altitudes; it is difficult for the stupid mind to observe how stupid it is.”               George Leigh Mallory 1922

He further explains how this is likely a combination of sleeplessness due to periodic breathing as well as hypoxia due to the altitude.  Interestingly, one of the references (Richalet) showed that psychomotor performance and mental efficiency declined progressively with altitudes above 5500m, but differences did not reach statistical significance until 8000m.  Another reference (Waters) in the same paper describes the neuropsychological effects of sleep loss. They include: sleep loss effects both cognitive functions as well brain regions that support cognitive performance; decreased processing speed is most reliable finding after sleep loss; and peformance decreases appear in a dose dependent manner with sleep debt accumulation.

Thus, be aware (and self aware as best as possible) to the problems associated with cognitive function with high altitude climbing. You wouldn’t let a drunk drive you home, don’t let one hold the rope that keeps you alive.

“Decision making at extreme altitude: Has anyone seen my executive function lately?”
http://www.ncbi.nlm.nih.gov/pubmed/22633144

Don’t pet the sweaty stuff

Tech shirts.  All of the major companies make them now.  Mostly polyester, they were designed originally to increase evaporation to provide a “cool” feeling and decrease the amount of sweat present in the clothing after a workout.  They were popular with military in the Middle East until they were banned due to the injuries they cause when burned. Living in south Texas, I’m infinitely familiar with clothing soaked with sweat.

This article took 3 different kinds of synthetic shirts and 1 ordinary cotton shirt (Fruit of the Loom!) and compared them.  The methods section makes me never want to be friends with these guys, as they made them start at 7 kph, going up 1kph per minute up to 14 kph.  Then inclination was increased by 1 degree per minute until exhaustion. This was to determine peak oxygen uptake.  Then for each individual fabric test they made them perform at 70% of that maximum uptake for 30 minutes, then increased the inclination to exhaustion again.  At least there was a fan blowing on them from the front.  Temperature was controlled at 31.7C and relative humidity was kept at 42%.

During testing, they measured

  • Temperatures (ambient, skin, body, and core)
  • Relative humidity (ambient, chest, and back)
  • Blood lactate (from the ear)
  • Ratings of
    • perceived exertion on a 6-20 scale
    • thermal sensation on a 1-9 scale
    • wettedness sensation on a 1-4 scale
    • shivering and sweating sensation on a 1-7 scale
  • Heart rate
  • Respiratory exchange ratio
  • Ventilation
  • Oxygen uptake
They found that 2 of the 3 synthetic shirts did lower body temperatures, decreased relative humidity, and made the runners “feel cooler” during exercise.  They did not demonstrate any increase in performance ability.  Thus, it is likely that this kind of shirt may make you feel less wet, but is unlikely to make you an Olympic athlete right out of the box.  Certainly they aren’t worth a huge premium over regular shirts.
Exercising in a Hot Environment: Which T-shirt to Wear?

See you later, alligator.

Alligators can be found from Florida to Texas, and north into North Carolina and possibly even Tennessee.  3 species are present, with the American alligator being predominant, followed by the American crocodile in southern Florida, and the caiman is an exotic species present in southern Florida.  

There have been 24 documented deaths from crocodilians in the United States.  This is in addition to the 567 reported adverse encounters in the same time frame (1928-2009).  The encounters are predominantly caused by human encroachment into alligator territory. All reported attacks are limited to the American alligator. 

This article gives some pointers on alligator attacks.  These include:

  • Don’t go to Florida.  91.6% of fatalities and 90.8% of documented attacks occur there.
  • Males represent 85.4% of attacks.
  • Most bites (81%) are single bites.
  • 80.8% of bites are on the hand or arm.
  • 26.5% of bites occur while handling alligators (shocking, I tell you). Wading and swimming combined make up 30%.
  • Noon to 6pm is the highest incidence of bites.
  • May to August are the worst months for alligator bites.
  • 54.8% of the bites were felt to be unprovoked, and 33% were felt to be provoked.
  • 29.2% of the cases were consistent with the alligators treating humans as prey.
  • Most fatal attacks involve alligators greater than 8ft in length, so avoid the big ones.
  • 38 bacteria and 20 fungal species have been cultured from alligator mouths, and overwhelming sepsis has been a cause of death after an attack.
  • Alcohol wasn’t reported commonly.
Sadly, no advice is given on how to survive an attack once it starts, and treatment descriptions are lacking. But the article does help reinforce common sense when it comes to animals that hunt humans. One last thing, don’t run away in a zig zag pattern. That’s a myth. Just run straight away as fast as you can.

Adverse Encounters With Alligators in the United States: An Update
http://www.ncbi.nlm.nih.gov/pubmed/20591380