Making a sleeping system warmer

[Worth Donaldson]

I made a mistake using the MB #7, Sea to Summit's Thermolite, silk liner and a 3/4-length ZRest pad on a July wilderness canoe trip into the sub-tundra. Historical temperatures indicated it rarely drops below 50 degrees this time of year. Instead, we experienced highs in the mid 40's and rain for 2 weeks straight. I found it difficult staying warm at night. I had to insulate my legs from the cold ground using my life vest. I was able to make it tolerable by wearing a wool hat and multiple layers of fleece and polypro. Upon returning home I purchased the MB's thermal sheet for such occasions. Bottom line, silk liner's contribute very little extra warmth!

[Roman Dial]

Mr Walnut — ooops I mean PJ,

Did you post elsewhere that you are a bivy-bag fan?

You'd want to wear that in our mid to protect yourself from our inability to control our urine streams — actually maybe I'd start using one if you were in my mid and peeing every 15 mins!

[Jay McCombs]

David,

Niacin. It DOES make you feel warm but actually causes heat loss. It causes vasodilation which brings more blood to the skin and allows you to radiate off more heat. Basically works the same way as my Rum and alpine spiced cider powder. I guess if the effect is enough to help you feel warm and fall asleep its so short in nature that you wont freeze to death in your sleep. We all have to pick our poison…some of us are pill poppers, some of us are boozers I suppose

[ROBERT TANGEN]

Does using a full-blown ARC style quilt facilitate using a pee bottle? I've never used one, but I can see you might be able to get up on your knees easier than inside a bag, if the quilt's under-ties were rigged right, and it might be safer from the point of view of keeping the down up high. PS, could you strengthen your igloo with yellow ice?

[Denis Walsh]

another aspect of drinking warm fluid prior to retiring, then getting up to pee is one's body is warming the urine in the bladder to body temp, using calories that could be used keeping the rest of the body warm. IMHO, it's ok to get up and pee. The bag won't get horribly cold before you return, and you no longer have to warm the urine. You're more comfortable post-pee (is that a word?) and it's easy to fall back to sleep.

[Roman Dial]

Robert — what is ARC?

And with a quilt you really don't need to get on your knees — as PJ so aptly described above you just roll over and pee in the same spot.

[Brett .]

Reginald, I would like to hear more about your experience with the MB #7, was it down or synthetic, and how were the condensation problems, if any, and were you in a tent, etc.. I ask because I have a #7 and #3, but never tried the #7 that cold (40F) before and Im wondering how it could be done most effectively. Thanks in advance..

[Michael Martin]

Denis writes:

>> …getting up to pee is one's body is warming the urine in the bladder to body temp, using calories that could be used keeping the rest of the body warm. IMHO, it's ok to get up and pee…you no longer have to warm the urine.

I've read this before — that holding a full bladder will make you cold, but I'm not sure I buy it from a thermodynamic point of view. The heat energy to warm up your pee is the same weather or not you empty your bladder. And, you could argue that any energy spent warming up the fluid actually takes place if/when you ingest food/water that is cooler than your body temp. Except for the miniscule increase in your body's surface area, holding a full bladder of warm pee should not require any additional heat energy. In fact, peeing out the warm pee should be a loss of heat energy unless you pee out ice. ;-)

Roman's comment about the full bladder being tied to vasoconstriction in the extremities is the best explanation I've seen yet for the "holding a full bladder will make you cold" rule. If emptying your bladder results in less blood in your extremities, it should result in less heat loss (albeit at the expense of cold fingers and toes.)

Comments anyone?

[EndoftheTrail]

To me, this is all moot. When Nature calls, I have to answer — else I can't fall asleep. :(

Brett: Did you receive my PM?

[Roger Caffin]

> I've read this before — that holding a full bladder will make you cold, but I'm not sure I buy it from a thermodynamic point of view.
Load of old cobblers actually. Anything inside your body is at body tempeature. Holding it at body temp costs nothing. You're right about the laws of physics.
However, Roman's comment about vasostriction is interesting, and may account for the myth. The obvious solution is to make sure you don't get too cold in bed.

Me, I have a drink after dinner, go for a short walk and then go to bed. I wake up about dawn and get breakfast. Next pit stop is just before I put my pack on, or a little later. But on a LONG-term basis, I drink about 1.5 – 2 litres per day total, so maybe that helps avoid the problem.

[paul johnson]

Roman, the "Mr Walnut" meaning escapes me – please explain (i always enjoy a good laugh, even at my expense). i hope you didn't mind my weak attempts at humor. if i offended you, i sincerely apologize (i never like to have a laugh at another's expense which is why i give others enough ammo to blast me). however, i don't think i did based upon your humor in the post to which i am replying. but, i still don't get the precise meaning of "Mr Walnut" (other than i am a bit 'nuts'). Given my diminutive size "Mr. Peanut" might have been better. In fact (and this is true and not a vain attempt at humor), my Chinese given name, means "peanut", for that very reason.

yes, i am a bivy fan. also, i'll file away that suggested info about bivy use, in case i'm anywhere in AK when you might be camping – that 3+L you drink b/f turnin' in might give you quite a range.

One question, what would be the long term affect of your bad aim on the DWR treatment of my bivy sack?

[Brett .]

Sorry for the delay. Will buy it tomorrow when I get the merino Miguel mentioned..

[John S.]

More than you ever wanted to know…

Medical Aspects of Harsh Environments, Vol 1
http://www.bordeninstitute.army.mil/medaspofharshenvrnmnts/default_index.htm

Medical Aspects of Harsh Environments, Vol 2
http://www.bordeninstitute.army.mil/medaspofharshenvrnmntsvol2/default_index.htm

[Roman Dial]

PJ:

Ditto. my lame attempt at humor — the "walnut" ref was a sad attempt at describing the size of your, ahem, bladder, given your apparent reluctance to drink for fear of peeing in the night.

Please, take no offense…merely trying to join in with you on your fun.

[Robert Burns]

I'm no scientist, and I don't conduct experiments, but one thing I do know is that being a swimmer staying hydrated is important. I drink a fair ammount of fluids at my competitions and I know for a fact that when I have to go but am ignoring it due to other distractions, or occupations such as a heat sheet, etc etc that I will get very much colder. I will not be able to stay warm even in a humid/hot facility with all of my clothes on. I wear a large fleece jacket and pants, with a windbreaker and shoes. After I urinate my body temperature is much warmer and I stay much more loose and comfortable. Not to mention more relaxed and less distracted.

[paul johnson]

Roman, you've got me chuckling, now that i understand "Mr Walnut" – very funny. Thanks for giving "Mr. Walnut" a good chuckle. However, i hate to cut this short, please excuse me, Mr. Walnut needs to go…

[Worth Donaldson]

Brett, I was using the down MB #7 and was sleeping in a BA Seedhouse SL2. I had very little condenstation inside the tent during this particular trip because the tent ventilates almost too with moderate winds. There were a few nights where I almost used my emergency silver reflective mylar emergency bag to protect me from the wind howling through the tent. If you are referring to condensation inside the bag, I have never experienced it.

As you already know, the #7 is light and thin. Although it has allot of loft, I believe my body weight compressed the down; thus, lowering the insulation factor. I lost too much heat the ground.

At this time, I can not recommend using the #7 into the 40's. I have not had the chance to test how low I can go with the MB thermal sheet inside the #7; thus, my recent cold weather excursions have been with a Slumberjack 20 degree bag. I do plan on expermenting with this combination come early spring. Furthermore, I will probably only use the #7 in warm weather when sleeping in my Hennesy Hammock.

[EndoftheTrail]

Reginald:

Changing topic just a bit… you mentioned about winds "howling" through your BA SL2 tent.

I too own the same tent, and my experience is different. One of my early concerns was how much wind (if any) can an all-mesh inner tent stop? I experimented by directing a fan toward it at full force. Sitting inside, I felt almost no wind at all — kind of strange to see the fan blades turning, but feeling almost nothing at all! Combine this with the tent fly, I've found that out in the wilds, the tent blocks substantially all wind.

HOWEVER, another surprise, as much as the tent blocks/deflects strong winds — it allows slow-moving, cool night air to permeate right through! That's why even though the tent's very sturdy structure can qualify it as a 3+ or even 4-season tent, the all-mesh interior makes it too cold to actually use the tent as such.

Anyway, my own findings…

[John S.]

My two cents….When you get cold your body decreases blood flow to the hands and feet. Any resultant increased blood volume in the torso could be handled by the kidneys by increased urine production, if necessary. And that doesn't include all the fluid you drank in the evening. I have never seen studies claiming that cold makes you empty your bladder because it needs room in the torso for extra blood volume.

There are some studies indicating that cold receptors are present in the bladder. It wouldn't surprise me if those cold receptors might be triggered by bladder distension. This topic came up in another forum so someone asked their ER doc what he thought. He theorized that bladder distension triggered cold perception in some manner as the brains way of clueing you in that you needed to empty your bladder. Behavioral control of body temperature is said to be more potent than physiologic mechanisms.

As far as a full bladder using up energy, I agree with Michael and Roger that little or no extra energy is needed to heat urine which is formed at body temperature.

Cold perception seems to not be fully understood. In the camping setting, I think there are many factors to a person feeling cold, from environmental (not enough insulation) to individual physiology.

[David Olsen]

A friend who teaches survival to the army in Alaska said
of all the soldiers who came in with frostbite to the med
facility, all were very dehydrated. He thought that staying
hydrated fended off frost bite, but also said it may be
that frost bite could be causing the dehydration. He taught
his troops to drink lots in any case.

[Roman Dial]

"When you get cold your body decreases blood flow to the hands and feet. Any resultant increased blood volume in the torso could be handled by the kidneys by increased urine production, if necessary. And that doesn't include all the fluid you drank in the evening. I have never seen studies claiming that cold makes you empty your bladder because it needs room in the torso for extra blood volume."

John, are you saying that the kidneys increase urine production but the bladder does not fill with the urine? Or are you describing the method that the bladder fills with urine?

Also, with regard to psychological response to cold: some people without much exposure to cold are afraid of the cold, and their physical response is exagerated: their hands freeze because they have "told" their body it's cold. These are people whose hands feel cold to the touch in spite of wearing gloves.

Others with a signiifcant experience to the cold actually have hand temps that increase when exposed to cold. The "hunter's response" of flushing blood into extremities to counteract the hand's environmental coldness. This presupposes the "hunter" is warm otherwise. These are people who can work in the cold without gloves and when you feel their hands they are warm.

[Worth Donaldson]

On one particular cold, windy trip I observed that I began to urinate every 15 – 30 minutes for several hours. My paddling buddy even noticed it. I had never heard of this being a sign of hypothermia thus I spoke with one of our physicians when we arrived home. He told me that my body was trying to keep its core warm by shunting blood away from my extremities. This process increased blood volume in my abdomen and thus raised my blood pressure. My body recognized the increased blood pressure and attempted to lower it through diuresis. Diuresis causes the kidneys to remove fluid from the blood (shrinks blood volume) and lowers blood pressure through increased urine production which ultimately fills the bladder prompting one to urinate. This cycle repeats itself until blood pressure returns to normal.

Thus, it is my speculation that dehydration occurs from frequent urination and the lack of replacing the fluids. Frostbite eventually occurs because the body shuts off blood flow into the extremities that keep them warm. I now believe frequent urination is a symptom of mild hypothermia.

[John S.]

Roman, I'd be theorizing peripheral vasoconstriction –> increased blood volume –> increased urine production by kidney –> filling bladder –> cold perception by autonomic nervous system.

Chapter 11 of that military medicine post I put up says this:
"Cold-induced diuresis is one of the early consequences of exposure to the cold, and it becomes prominent even before core temperature has decreased. The mechanisms for this cold-induced diuresis remain controversial. One school of thought suggests that cold-induced diuresis is an autoregulatory response of the kidney to a relative central hypervolemia induced by peripheral vasoconstriction. Owing to a volume overload, the release of antidiuretic hormone is suppressed. The subsequent cold-induced diuresis decreases the blood volume so that progressive hemoconcentration develops."

This is all the same as what Reginald said.

[paul johnson]

I might put it this way "The reason the body wants to pee when it's cold, is that when you get cold, your body shuts off blood to the extremities to reduce the blood's exposure to heat loss by reducing surface area to volume ratio of the vascular system and hence heat loss rate. In other words your hands and feet get cold to save the brain and organs some heat. To bring the heat/blood into the trunk requires that your body make room for the blood. So your body empties the bladder."

However, if i did, i'd be stealing Roman Dial's words. For this is exactly what he stated on 12/13/2006 12:30:25 MST.

Sounds to me like Roman is saying the same thing as Reginald and John.

I think Roman's last questions are being misunderstood.

Am i misreading any of this?

[John S.]

The part I was debating was "To bring the heat/blood into the trunk requires that your body make room for the blood. So your body empties the bladder."

Roman's statement seems to imply cold –> vasoconstriction –> bladder empying –> room for blood

Reginalds doc, the military paper and I are saying cold –> vasoconstriction –> increased abdominal blood volume and/or blood pressure –> room for blood –> body senses higher blood volume or pressure –> increased urine production –> bladder filling –> bladder emptying

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