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April 2008
April 7, 2008
DEHYDRATION AND COLD WEATHER
Dehydration in a cold environment
is a far greater risk to humans than when it occurs in a temperate
environment. When you are generating sweat from work or play when
the weather is warm the body’s normal mechanism is a chain reaction
to the sweating. The body sweats, causing the blood volume to decrease
(water leaves the blood); this triggers the hypothalamus (the brain’s
thirst center), which then triggers the brain to send out a demand
for an increase in fluids (water), which we normally feel as thirst
sensation or a dry mouth. In cold weather our body’s react in
a completely different way. People do not feel as thirsty when the
weather is cold; when they don’t feel thirsty, they don’t
drink as much, and this can cause dehydration. During cold exposure
vasoconstriction takes place--- the body decreases blood flow to the
periphery (skin surface) of the body to decrease heat loss. As a result
blood flow to the body’s core increases (the blood is moving
through fewer blood vessels as a result of vasoconstriction); the
brain does not detect the decreased blood volume (the amount of water
in the blood that has become sweat, which leaves the body). Thus a
hormone AVP (argentine vasopressin) which is a fluid-regulating hormone
is not secreted at the same increased rate, despite elevated blood
sodium. The kidneys get a diminished signal to conserve fluid, and
the thirst sensation is reduced by up to 40 percent. In November 1995
when I was lost in the Fossil Ridge Wilderness near Gunnison, Colorado
during a blizzard whenever I came to a stream I gorged myself with
water. I only knew I needed to consume the water to keep from dehydrating;
I did not know the technical reasons until now.
The published report “Human
Fluid Balance and Dehydration during Cold Weather Military Operations.” The
publication date is December 1994 from the U.S. Army Research Institute
of Environmental Medicine (USARAEM), Natick, MA. What I find interesting
is that the USARAEM apparently commissioned this study; however, they
have a disclaimer in the publication or so that is how I interpret
the following; “The views, opinions and findings contained in
this report are those of the authors and should not be construed as
an official Department of the Army position, policy or decision unless
so designated by other official documentation.”
To quickly summarize the report; it identifies all
of the basic information I had previously read in other dehydration and cold
weather studies at such places as the University of New Hampshire, Mayo Clinic,
and several web sites such as suite101.com.
Everyone who is active during the cold weather months
(when temperature are +32 degrees F and colder) will try to dress with adequate
layers of clothing so they stay warm and do not retain moisture (sweat) that
they know they will be generating and which they also know will be a problem.
There is no clothing system that will allow the moisture to evaporate through
its layers equal to the rate it is being generated. However, as I will show
later in the article you can help yourself significantly. To believe the “hype” published
by companies that make fabric or those companies who use the fabric to make
garments is very foolish. They “all of them” are for all intents
and purposes lying about the wondrous “properties or capabilities” of
their materials or garments. It is my opinion that these garments have never
been put through field testing to verify conclusively that they perform as
advertised or they have and the results are not fit for publication. I have
spent more time in the field testing garments than all of the “creative
geniuses (?)” in the employ of these companies put together. When I was
selling the polyester fiberfill insulation to all of the skiwear and many general
outerwear manufacturers in the USA in the 1960’s and early 70’s
I would take winter vacations and field test what these manufacturers garments
that were made with insulations they purchased from me. If you wanted to then
or want to now stay warm you need (ed) bulk and without quilt stitching for
uniform loft and expect to sweat when you are very active. However, do not
expect that the sweat will leave the garment if you are wearing a first layer
of clothing that is standard knit underwear made with synthetic or natural
fiber. Expect that the amount of sweat generated in a cold region will be of
a greater volume than if you were expending the same amount of energy when
the temperature is +70 degrees or higher.
In the report done for USARAEM
it states “If clothing is not carefully matched to metabolic
rate, significant heat storage and sweating can (emphasis
added) occur. [All evidence says it does occur.] A person
dressed in the U.S. Army Extended Cold Weather Clothing System (ECWCS)
produces little sweat while resting in the cold. However, if this
person performed moderate or heavy exercise in that uniform, it is
estimated that nearly 2 liters per hour of sweat would be lost. Since
this clothing system allows for little evaporation, [the outer layer
garment of the ECWCS is made from either Gore-Tex or EVENT laminated
fabric. Each of which is a PTFE (Teflon) film laminated to the nylon
shell material. Neither of which will actually allow for the vapor
present inside of the garment to escape] the uniform might (emphasis
added)become soaked. [If the moisture does not
get out then obviously it will be absorbed by the materials underneath
the last layer of the system.] A wet uniform has serious
implications for heat loss and subsequent cold injury susceptibility.
If the cold weather clothing system is altered to reduce total insulation,
sweating would be reduced five fold to about 0.4 liters per hour.
[Now how do they know that the sweating will be decreased
by any percentage, my opinion they don’t know.]Therefore,
it is important that persons in cold climates dress in layers, allowing
insulation to be matched to their metabolic rate. Clothing can be
added when work rates decrease and removed when work rates and metabolic
heat production are increased.” AND PIGS CAN FLY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
The Army and Marine Corps have apparently been utilizing
this way of thinking for the past two or three years now. They have been working
on a multilayer clothing system that has at least seven layers. The organization
that each of these two military groups work with is located within the confines
of the U.S. Army Natick Laboratories. The people employed at Natick it is now
clear to me are acting upon the report from the USARAEM. Unfortunately the
grunts that will be issued these ensembles; unfortunately in my opinion will
discover they will not work as the writers of the report apparently believe.
The dehydration problem in their minds (?) if in fact they have ever given
it thought will not be changed in a positive way when wearing these clothing
systems, but rather in a negative manner. Since the body is programmed to function
in a particular manner as we have learned the way they think one should be
clothed will not be effective. In my experience the best way to address the
problem is to have a first layer; fishnets on to allow the sweat produced to
move away from the skin surface. The last layer should be very capable of keeping
one warm at a temperature 20 degrees lower than the temperature one is operating
in. this would mean whatever is worn between these two layers would be limited
to fewer layers. Fewer layers mean greater ease of mobility. When you start
to overheat open the zipper at the neckline. The larger opening will now allow
the moist warm air to easily escape. Keep in mind that your movements create
a bellows action which forces the moist warm air up (heat rises) and out of
the clothing you are wearing at the neckline. In this manner you are better
controlling the immediate environment around your body; the environment inside
your clothing.
You will successfully remove the excess moisture as
well which will prevent getting a chill. The fact that your skin surface is
continuing to receive its normal supply of blood means that the brain’s
thirst center the hypothalamus will know to trigger the proper response telling
you it is time to get a drink of water. Also, if the clothing is made properly
utilizing an insulating material that is proven to work at extremely low temperatures
and is light in weight as well as completely un-affected by water in any of
its forms you will be capable of doing your work for a longer period of time.
Of course that insulation already exists and has proven itself time and time
again; it is Lamilite. Wearing a Lamilite parka will mean you are wearing fewer
layers which means less restriction of movement. It also means not carrying
additional layers of clothing which would be cumbersome to say the least as
well as take up space that would be necessary for needed supplies such as extra water.
If you are wearing multiple layers as is suggested
by the USARAEM report a dehydration situation is likely to develop. The Generation
III clothing system contains a first layer that is traditional knitted polyester
underwear. When you sweat the fabric does not wick away the moisture,
so it stays against the skin. Then each of the ensuing layers is also made
of polyester fiber fabrics which are knitted. Did you ever layer knitted fabrics
over one another? They mesh together and bind, now do that with two or three
more layers as is directed to increase the level of protection against the
cold and see how easily you are able to move. Because movement will be restricted
(I can assure of that) you will generate a significant amount of sweat. You
will get a chill once your activity level is decreased to a resting state and
your “periphery” will go into a vasoconstriction phase and all
negative bodily actions will occur as has previously been noted; the end result
will be dehydration. In order to have the best chance of thermoregulation of
your body, it is necessary that you not fool it.
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If you wear lose fitting clothing over the fishnets
almost all of the sweat you generate will get away from your periphery (skin
surface). It is also very important that one and all layers of the clothing
you are wearing including the outer most layer be made from materials that
are vapor permeable, you do not want any coated fabrics at any level
of the clothing especially the last or outer most layer.
Below is a picture of Rudy Rudibaugh and myself when
we arrived back at base camp about 9 hours after he found me on Fossil Ridge.
We are each wearing the first two Fossil Ridge parkas I made. Rudy had been
out looking for me for several hours while I had been in the field for three
days. Until he found me I was on foot in snow waist deep. I was walking and
obviously generating sweat. As is visible since it was about -20 F all of the
sweat that I generated migrated through the insulation and fabric only to condense
and freeze on the exterior of my parka. When I was allowed off of my horse
so I could go into the cooks tent and take off my parka I found that my skin
surface was bone dry as was my cotton plaid shirt. With proper ventilation
wearing a layer of cotton that does not come in contact with your skin surface
is not problematic. I am living proof of that fact.
CONCLUSION: As I see it, it is irrelevant what the
reason or circumstances are that causes you to be out when it is cold;
soldier or hunter, you need to wear what will be of the greatest benefit
to you. My personal experience and that of thousands of my customers
bears out the performance of Lamilite insulation. If you want the
best chance of not suffering dehydration look no further than Wiggy’s
clothing.
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