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Old 08-11-2001, 02:47 PM
Llardball Llardball is offline
Join Date: Jul 1999
Posts: 150
I just jumped in the shower after a long workout in the 93 degree heat. The water that came out of the shower head was of course freezing, which caused me to do the customary quick drawing in of air. Why does this happen? What is the purpose of this reaction?
Old 08-11-2001, 03:00 PM
Finagle Finagle is offline
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Join Date: Sep 1999
Location: Somewhere near Boston
Posts: 9,912
Well, there's obviously no way of knowing for sure (evolution doesn't take notes), but just from a common sense guess, involuntarily taking a deep breath might be a good survival trait if you were falling into water.
Old 08-11-2001, 03:13 PM
warmgun warmgun is offline
Join Date: Aug 2000
Location: California
Posts: 838
Mamalian skin response?
Old 08-11-2001, 03:30 PM
warmgun warmgun is offline
Join Date: Aug 2000
Location: California
Posts: 838
Or 'Mamalian Diving Response' from here.
Not very scientific, but I saw it and had to try posting a link in a real post.

Old 08-11-2001, 04:06 PM
Guinastasia Guinastasia is online now
Join Date: Jul 2000
Location: Pittsburgh, PA
Posts: 51,051
Actually, that's extremely dangerous to go right into a cold shower after being in extreme heat. The abrupt change can cause shock, and has been known to trigger heart attacks.

Next time, be calm and wait for the water to get tepid.
Old 08-11-2001, 04:24 PM
barbitu8 barbitu8 is offline
Join Date: Aug 2000
Location: Charleston, SC
Posts: 5,820
Did you ever jump or dive into the cold sea? Or try swimming in really cold waters. I once swam in Lake Michigan in 55 degree water (in the winter), w/o a wetsuit. It's very difficult to breathe at first. Your chest muscles stay contracted. After a while, as your body warms up a little, it's easier to breathe. I guess it's the same mechanism in play here.
There are 10 kinds of people in this world: those who understand binary numbers and those who don't.
Old 08-11-2001, 10:18 PM
Muffin Muffin is offline
Join Date: Nov 2000
Location: Great White North
Posts: 20,038
I'm wild water instructor with decades of experience in ice-out paddling, so here is my take on it.

It's the mamalian dive reflex. If you are suddenly entering very cold water, the best way to minimize the response is to keep your mouth shut, your chin tucked down, and your shoulders up around your ears, for the worst effect occurs when cold water hits the back of your mouth, and the second worst effect occurs when water hits your neck. The face is particularly susceptable, but there is nothing much you can do about that usually.

For clothing, remember to wear something around your neck and head. In wild water paddling, an ear-covering skull cap under your helmet and a dry top with an extended neck cuff can help.

If you go in the drink and stop breathing, there is not much you can do about it, for odds are that nothing much else is moving either. Just wait for a few seconds and you will usually start both breathing and moving again. I've seen folks immobilized for longer periods, and with them their first breath is often problematic, for once panic sets in, they inhale as soon as possible even if their faces are not clear of the water. Just remember when paddling with bergy bits that you had best stay close to your buddies so that if you dump they can get to you and hold your head out of the water. And remember that part and parcel of this seizure is also a reduced ability to hold your breath.

However, I respectfully disagree that going right into a cold shower from extreme heat is risky. If it were, then saunas would be deadly, for it is quite common to run out of a 200 degree sauna directly into a cold shower, snowbank, or hole in the ice. Not only is there no seizing up, but it takes a few minutes to even realize that the ice water is cold. Last night I finished up with a five minute cold shower but still was sweating for a further ten minutes. Rather, I suggest that if the body is not overheating, then it is more at risk of MDR (including potential heart seizure) than if it is overheating.

Concerning the practical interaction of MDR (the seizing up in very cold water) and hypothermia (a gradual cooling of body temperature), here is part of an email of mine concerning rescue periods which might illustrate the timeframe involved when fishing for popsicles:

A word about the possibility of an on-water demo on xxxxx in mid-April. Coming from someone who has routinely hauled people out of icy water (hundreds over the years), I believe that an on-water xxxxx demo in ice-out conditions would be folly.

Even in xxxxx, the water temperature will be close to freezing in mid-April. If a boat were to dump, which is possible given that there will not be an experienced crew, you can expect most people lose coordination, including the ability to swim or to grasp a rescue rope, within a minute or so due to hypothermia. You can expect one or two of the people (particularly those who take a shot of cold water in the mouth) to seize up upon dumping for about half a minute due to the mammalian dive reflex. Of those who seize up, there is the significant possibility (about 1 in 10) that the seizure might include an inability to breathe for this period, often leading to uncontrollable panic upon return of breathing. A remote possibility exists (and I have witnessed it) that such seizure might include heart failure. Those seizing up will require immediate assistance by those nearest to them to avoid breathing or swallowing water when they begin to recover.

Between the end of the seizure and the beginning of the loss of coordination, there will be about a thirty second window for rescue. Although this is a comfortable margin for one or two swimmers, this is not enough time to rescue a large number of people. Delay in rescue would magnify the risk, for rewarming after a short swim is no big deal, but both rough transportation and external rewarming after the body's core temperature has dropped significantly carry the risk of heart failure as cold blood makes its way back from the limbs to the organs including the heart. Thus highly skilled EMT attention followed by medical centre treatment is necessary. xxxxx popsicles arriving at the xxxxx hospital might not be good for business. xxxxx medical bills being forwarded to us along with negligence claims in American dollars in American courts also would not be good for business.

Wetsuits, drysuits, or layers of polypro under a rainsuit can help against the gradual loss of coordination, but only to the tune of a few minutes. Training can pretty much mitigate the seizure (close mouth and tuck neck and shoulder to help avoid it). This could increase the window for rescue by a couple of minutes. This is still not enough time to rescue a large number of people unless there is a well coordinated rescue by several chase boats, with no one is panicking, and with everyone well trained in cold water rescue. In short, this is not possible for the xxxxx demo.

Might they be interested in simply having a boat moored in the water for walk-on tours or dock paddles rather than an actual excursion? This would limit the potential rescues to one or two individuals at a time beside shore, rather than a boatload offshore.

Richard the Paranoid Paddler
Concerning why we have an MDR, I don't know. I've heard some folks suggest that it shunts blood to the brain, but I have not seen any proof of this in humans. I suppose the sudden reduction in blood flow in the body might help reduce cooling slightly, but if this is so it is a false savings, given the potential for either drowning or heart failure. Along the same line, if one's chance at surviving cold-water near drowning depends on cooling the old grey matter before running out of O2, then I'm not certain that MDR would help. Anyway, IANAD, so take what I say with a grain of salt. For a lead into the research, try starting here: by Dr. Jolie Bookspan, who is an expert in the field of cold water immersion, and highly qualified in the use of "scientific thing-a-ma-bobs".
Old 08-11-2001, 10:21 PM
Muffin Muffin is offline
Join Date: Nov 2000
Location: Great White North
Posts: 20,038
Lets try that link thing again:
Many Are Cold But Few Are Frozen: Another Look at Hypothermia by Dr. Jolie Bookspan, who is an expert in the field of cold water immersion, and highly qualified in the use of "scientific thing-a-ma-bobs".
Old 08-13-2001, 10:43 AM
handy handy is offline
Join Date: Mar 1999
Location: Pacific Grove, Calif
Posts: 17,493
I surf in 52 deg water all year round. I have to agree with Muffin since I wear a wetsuit & hood & gloves & booties I don't get that reflex as the water never hits those important areas that might cause this reflex.


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