I'd like to get some insights in layering strategies for sleeping gear for winter camping at high altitude (Denali).

I have a bag that's rated to about -6f (-20c). For Denali I'm thinking my bag needs to be at least -20f. Off course I can buy an overbag, but I also have a down jacket (rated to 5f (-15c)) that just fits in the bag. The jacket is much lighter then an overbag and can be part of my clothing system.

For regular camping at low altitude I know it's common practice to wear down clothing inside a bag, to beef up it's rating. What I'd like to know is if there are extra things to take into account when winter-camping at high altitude?

Thanks for your input!

Most ratings for sleeping bags are based on the assumption you are sleeping. Most "rating" of clothing... by it antipodal or marketing lit is typically based on a person being awake. Since you need approx half the insulation which doing light work as compared to sleeping, you should expect high loft clothing to has 1/2 as affective at extending your comfort range compared to your awake experience.

If the jacket is much lighter than an overbag making use of the same materials, then the clothing is going to be less warm. It's hard to beat a minimalist overbag or quilt for warmth / oz. Jackets are more complicated and insulate less efficiently due to the extra weight and inefficiently of arms, pockets, etc.

--Mark

Hi Mark,

thanks, this is the kind of info I was looking for.

The ratings by PHD (who made the jacket) seem to be thought through, I think I can trust them. From their website:
The TOT figure (rating) means that the item is suitable for people heading into situations,
where these are the minimum temperatures likely to be encountered,
for use from short static periods up to medium/low activity.

I'll have to give your reasoning about how efficient the jacket will be some thought,
it seems to make sense!

> if there are extra things to take into account when winter-camping at high altitude?
Technically no, but there is of course a higher risk factor.

Eats lots in the evening, wear a warm head-covering, and try it - and let us know how it goes?

Cheers

I'm no expert, but I've heard that with the lower available oxygen at altitude, the body has a harder time generating heat, since the body uses oxidation to create heat. Of course, since Everst is roughly 9,000 feet higher than Denali / Mt. McKinley, there is more worry climbing Everst.

Oxygen makes up approximately the same 20% of air no matter where you are. The issue is that air pressure is much reduced as you go to higher elevations, so breathing gets tougher. The air pressure on the summit of Everest is approximately 32% of sea level, so it is not a trivial thing.

Mount McKinley has more air pressure, roughly 45%, but then when you add in the cold factor, it gets hard to breathe anyway.

At any of these elevations, due to the air pressure, your blood will be something less than fully oxygenated, even at rest. That contributes to a reduction in the efficiency of digestion, so your whole body function starts to get funky, and the longer that you stay high, the more your body function will deteriorate. Look at the typical Everest climber when he starts and weighs 190 pounds. Then look again when he finishes a month later and weighs only 170 pounds. Something is going on there!

So, climbers are burning up their energy trying to maintain motion, and there isn't so much left for staying warm inside a sleeping bag. Therefore, you want a warmer bag than you would need for an equivalent sea level temperature.

--B.G.--

"For Denali I'm thinking my bag needs to be at least -20f. Off course I can buy an overbag, but I also have a down jacket (rated to 5f (-15c)) that just fits in the bag. The jacket is much lighter then an overbag and can be part of my clothing system."

That might do for your trunk, but you will also need to think about keeping your head, legs and feet warm. If I were you, I would not try to cut corners on your sleeping bag but, rather, would get the bag down to -20 F and have your clothes in reserve in case the temperature falls below -20 F, which can and does happen on Denali. Also, consider taking an insulated bottle of hot chocolate or other carb rich drink into your sleeping bag at night. You can sip on it throughout the night for extra warmth and warmth generating calories. You will find yourself waking up from time to time and, when you do, just take a swig. This will also help you stay hydrated. You will lose a lot of water while sleeping just by breathing, especially at altitude, and drinking during the night can help offset the loss. Every little bit helps.

"What I'd like to know is if there are extra things to take into account when winter-camping at high altitude?"

Your body's water balance gets all screwed up. You are inhaling cold and dry air, and you are exhaling warm and moist breath, so (1) you are losing energy and (2) you are losing moisture with every breath. If you are lucky and healthy, your body will reach a new water balance point within a couple of days of arriving up there, and then you have a better chance of beating the worst of the high altitude illness problems. Still, it is worthy to consider getting prescription Diamox (acetazolamide).

However, your body will tend to be warm during the day while you are active, and then it cools down at night. As a result, your body's blood volume changes. That is why it is common to feel the need to urinate at night. Due to the extreme cold and elevation, you will find it most practical to use a dedicated pee bottle within the tent. Most climbers using this idea do not want to make the mistake of grabbing the wrong bottle, so they typically decorate it with a Capital P or something unmistakable, along with your initials. Plus, you and your tentmates need to set a protocol for which direction from the tent door is used for gathering clean snow to melt, and which direction is used for dumping the pee bottles.

Anecdote: While climbing a very high peak, these two old guys were sharing a tent, and they knew about the need for a pee bottle, so each had one. On one night, one guy could not find his own pee bottle, so he used the other guy's pee bottle. That brought on the first argument. On the next night, the same guy could not find either pee bottle, so he used the common cook pot. That brought on the ultimate argument.

--B.G.--

Thank you all for your input.
I have been a few times to high altitude (~6000m and ~7000m), so while new to Denali (and it's temperatures) I'm not totally new to altitude.
First trip I didn't know yet about pee-bottles, which made me bring one the second trip ;-) I use one in a different shape from my drinking bottles.
I usually don't drink that much during the night, as it makes me pee even more.

Your input makes me think very seriously about getting an overbag for my sleeping-bag. I am bringing other insulation off course (hands, legs, feet) but if that brings me to my req. minimum temperature, I have no back-up.

"I usually don't drink that much during the night, as it makes me pee even more."

You missed my point. Your body has a normal blood volume during the day while you are active. Then at night, it cools down, and the blood volume is reduced. When that happens, the excess water goes through the kidneys and into the bladder. So, even though you are not consuming more liquids during the night, your bladder still fills.

--B.G.--

Hi Bob

> Your body has a normal blood volume during the day while you are active. Then
> at night, it cools down, and the blood volume is reduced. When that happens,
> the excess water goes through the kidneys and into the bladder.

Sounds good on the surface, but I have major problems with it in detail. The details sound medically very unlikely. Sorry, but such claims do require some proof.

* First of all, I am not sure the body will change in temperature by very much - not even by 1 degree I suspect.

* Second, a change in blood temperature of a few degrees, which is far more than expected, will result in a microscopic change in volume relative to the volume of the fairly elastic human body.

* The idea that reduction in blood volume will cause any excess water to go through the kidneys into the bladder seems counter-intuitive to me. IF there is to be any effect, I would have thought the 'excess water' would have gone into the blood to make up the volume.

* If instead the 'reduction in blood volume' is meant to be a 'reduction in artery/vein volume', then I remain unconvinced that there will any significant reduction happening due to any (very small) change in body temperature.

Do you have any (published) references on this subject?

Cheers

PS: at 10,000' camped on snow, who goes outside the tent in a storm at 3 am anyhow???? Large space deep in the snow in (under) the vestibule ...

"* First of all, I am not sure the body will change in temperature by very much - not even by 1 degree I suspect."

Not unless something has gone seriously awry. Stable body temperature is a core principle of mammalian physiology.

"* Second, a change in blood temperature of a few degrees, which is far more than expected, will result in a microscopic change in volume relative to the volume of the fairly elastic human body."

A change in blood temperature of a few degrees is an indicator that something has, in fact, gone seriously awry. A temperature of 101, +2.4 degrees, degrees F indicates a fever or hyperthermia; a temperature of 96 degrees F, -2.6 degrees, indicates onset of hypothermia. Both of these conditions point to a potentially life threatening situation.

Roger and Tom, I have only printed notes from a Mountain Medicine Seminar that I attended. It was held on Treasure Island near San Francisco, and it was intended for medical professionals, park rangers, SAR people, and people who lead group outdoor trips. Attendees received continuing educational credit, so it wasn't like it was a bunch of hogwash.

During an active day in the mountains, your blood pressure is high and blood volume expands somewhat as the circulatory system is busy delivering maximum blood to the muscles. Typically in the evening you are not so active, and there is less blood delivery. Also during the active day, often your body temperature goes slightly high, but not by much. Then in the evening it drops back to normal.

During the less active period, and as the body becomes the least bit hypotherimic, the body reduces the blood flow to the extremities in order to maintain the core temperature.

During the less active period, your arterial volume drops slightly due to reduced demand, and since the blood fills that volume, the blood volume drops. The kidneys allow the excess fluid to pass to the bladder, and that is often why a cold camper feels the need to urinate during a cold night. If the kidneys did not do this, it would raise the blood pressure during the night. Most people tend to have lowered blood pressure at night.

So, I don't think the daytime/nighttime changes are due to temperature alone.

--B.G.--

Hi Bob

> I have only printed notes from a Mountain Medicine Seminar that I attended.
Ah, right. I wonder what the qualifications were for the teachers?

> During the less active period, and as the body becomes the least bit hypotherimic,
Um ... and how many bodies do become slightly hypothermic at night in the mountains? I suspect you would be shivering rather noticeably.
Me, I sleep just fine, and do not get at all hypothermic at night.

> Most people tend to have lowered blood pressure at night.
Well, yes, of course. If your body is resting there is not a *high* demand for ATP and oxygen in the muscles, so the heart pumps less vigorously. (May take a little while to clear out the lactic acid of course.) Yes, that may mean that the volume of the arteries could drop slightly. I am yet to be convinced however that this alone would cause the kidneys to suck water out of the blood supply.

I suspect the water which accumulates in the bladder overnight is actually extracted from the stomach. Many walkers drink a huge amount of water during the day under the mistaken impression that a slightly dry mouth means they are dehydrated. That water has to be excreted.

But if you only drink in moderation you can remain fully hydrated to the extent your body really needs, and not have to get up several times in the night. Fwiiw, I haven't needed to get up in the night for ... 30+ years? And yet, my urine remains a very pale yellow.

However, the myth of 'hydration' is persistent, helped along by the bladder vendors, and I doubt I have any chance of influencing that.

Cheers

i don't think needing to pee during the night is a result of dropped blood pressure/volume and the body getting rid of that liquid. Even while awake your bladder fills, and this i would think is from excess water in the stomach and water that is accompanying waste, which could be from the bloodstream.

"I wonder what the qualifications were for the teachers?"

Primarily, they were physicians. The ones teaching the sessions on high altitude physiology and hypothermia were all military and related physicians, Navy and Coast Guard. Around Treasure Island (where the seminars were held), there is a high population of Navy and Coast Guard people, so they didn't have to go far to teach their sessions to us. The National Park Service representative had less of the physiological mechanism to explain, and more post-rescue statistics.

As far as I know, there is no mechanism for fluid from the stomach to be extracted out into the bladder. It all has to be absorbed into the blood stream first, then via kidneys to the bladder.

When you state that you do not have to get up during the night, I believe you. I'll give you a few more years, and then tell us how that is doing.

Where I operate mostly (the Sierra Nevada Range of California), dehydration is a very real problem for backpackers, especially for those in the initial few days of arrival at high elevation (say, 9,000' to 14,000'). On trips elsewhere where we went significantly higher, the dehydration problem remained real. However, the trips elsewhere tend to be longer, and you only have to go through the adaptation cycle once per trip.

--B.G.--

a little more...

Apparently this is called Cold Diuresis.

Even though your body tries to do a good job of keeping the internal core body temperature steady in cold weather, it does this by vasoconstriction to the extremities. In essence, the blood vessels are narrowed slightly, which would cause an increase in blood pressure if there were no other mechanism at work. Liquid is diverted to the kidneys and to the bladder to solve it.

Now, if you are the type of person who does not need to urinate in the middle of the night when snow camping, that suggests that you are a warm-blooded person (high metabolic rate) who stays plenty warm enough in the sleeping bag.

--B.G.--

Here's another piece I found floating out there in cyber-space:

"High-altitude diuresis occurs at altitudes above 10,000 ft and is a desirable indicator of adaptation to high altitudes. Mountaineers who are adapting well to high altitudes experience this type of diuresis. Urine output is thus an important indicator of adaptation to altitude (or lack thereof). Persons who produce less urine even in the presence of adequate fluid intake probably are not adapting well to altitude."

--B.G.--