Heat Loss Through the Head and Hypothermia

The rate of heat loss, at rest, with exercise, and with hypothermia

Since there has been a fair amount of interest regarding Myth #2 in the Wilderness Medicine Newsletter – Frozen Mythbusters, Nov/Dec 2004 – the topic deserves more discussion.

MYTH #2 states.  “If your feet are cold, cover your head because you can lose up to 75% of your body heat through your head alone.

The problem is that the head is only about 10% of the body surface area.  Thus, the head would have to lose about 40 times as much heat per square inch or centimeter compared to the rest of the body.
Gordon had heard this statement one too many times and finally decided to see if this was indeed true.  So he took several test subjects, all volunteers, of course, (you have to wonder what problem they caused at the university), wired them to monitor their core temperatures, and discovered that we do indeed lose heat through any exposed part of the body and the amount of heat we lose depends on the amount of exposed surface area.  The rate of heat loss is relatively the same for any exposed part of the body not simply the head. You do not lose heat significantly faster through the scalp than any other portion of the body with the same surface area. 

It is still a good idea to put on a hat (a hood really – what insulation does a baseball hat have?) if your feet are cold.  But what is BUSTED is that there is nothing peculiar or unique about the head. The idea that we lose heat faster through out scalp, because of the constant blood supply to the brain, is simply a myth. (One that I personally have believed for many years.)”

#1 Heat loss via the head at rest, during exercise, and with hypothermia:

I did have the opportunity to speak with Dr. Murray Hamlet about this topic, and we hope this additional information will help to clarify heat loss in the hypothermia patient.

The cerebral blood flow is supplied via the carotid and vertebral arteries (4 in total) and is constant. The blood flow to the brain does not change as the demand for oxygen is constant. As a result, when you look at total heat loss, the head accounts for about 7% of the heat lost. 

The cerebral blood flow does, however, vary based on cardiac output – the harder your heart beats, the greater the blood flow to the brain.  And as you increase the blood flow to the brain, you also increase the percentage of heat loss.  As it turns out, when you begin to exercise, there is increased cerebral blood flow. This increases the percentage of heat lost through the head to about 50% of total body heat loss.  But as the person continues to exercise, the muscles demand more oxygen which increases blood flow. To ensure thermoregulation and maintain normal core temperature (exercises increases body heat), the skin vasodilates which increases blood flow to the skin to cool the blood. The net result is a decrease in the total blood flow to the brain and a decrease in percentage of total body heat lost through the head to about 10%.  Once sweating begins, the percent lost through the scalp returns to 7%.

In Gordon’s research his test subjects were at rest in cool water, and the researchers were comparing the rate of heat lost by monitoring core temperature through different body parts and quantities of skin exposed.  At rest, they found that the rate of heat loss only depended upon the amount of skin surface area exposed, and the percentage of heat lost through the head was the same as the rest of the body.

Research at the Army Research in Environmental Medicine labs showed that there was a temporary increase in heat loss through the scalp that returned to the baseline of 7% as the subjects continued to exercise.

Now, what about hypothermia and heat loss through the head? 
If the hypothermia victim is not shivering, they are at rest, and the heat loss through the head remains about 7%.  But, this is important, if they are shivering, the percent of heat loss via the scalp can increase to upwards of 55%, so protecting the head well is a very important part of treating the hypothermia patient.  And as you can imagine, the primary defense against the cold and hypothermia is vasoconstriction of the peripheral circulation, this shunts blood to the core, reduces circulation to the skin, and increases the percent of heat loss through the scalp.

The difference is that the shivering hypothermia patient is indeed exercising, but they do not vasodilate the peripheral circulation; the shivering muscles increase metabolic demand and cardiac demand so the patients do increase their cardiac output; therefore, they do increase cerebral circulation; therefore, they do increase the percent of blood loss through their head.

Treatment of the hypothermia victim:
Remove from the cold.
Get them dry and keep them dry.
Insulate from the ground.
Hypothermia wrap:
Re-insulate with dry insulation.
Cover and protect the head from further heat loss.
Cover and protect the hands and feet from frostbite.
 Surround with a windproof and waterproof layer.
If conscious, feed warm, sweet liquids.
If unconscious, evacuate and handle very gently to prevent ventricular fibrillation.

#2 How does being in water change the equation?

Life-preserver, personal flotation device (PFD), research has shown that when in the water, if your head and neck are wet, you cool faster.  This is why modern PFD’s hold the person in the water with their head and neck out of the water; even if unconscious, to decrease the rate of heat loss into the water.

#3 What difference does hair on your head or facial hair make?

In order for hair or fur to provide a protective thermal barrier, it has to be much denser than what we humans grow and it has to be in layers of different types of fur to provide a thermal barrier.  Beards are great, but they do not keep you any warmer. And bald is beautiful.

We at the Wilderness Medicine Newsletter appreciate the comments and discussion.

About these ads

17 Responses to “Heat Loss Through the Head and Hypothermia”

  1. parquet bambou pas cher Says:

    constantly i used to read smaller articles or reviews that as well clear their motive, and that is
    also happening with this post which I am reading at this time.

  2. http://www.illinoislaserspinesurgeons.com Says:

    Hey! I realize this is somewhat off-topic but I had to
    ask. Does running a well-established blog such as yours require a lot of work?
    I am completely new to operating a blog however I do write in
    my diary everyday. I’d like to start a blog so I can easily share my own experience and views online. Please let me know if you have any ideas or tips for new aspiring blog owners. Appreciate it!

  3. pure raspberry ketone Says:

    excellent points altogether, you simply won a emblem new reader.
    What would you suggest in regards to your put
    up that you just made some days in the past? Any positive?

  4. raspberry ketone burn Says:

    I used to be suggested this blog by means of my cousin. I’m now not sure whether this post is written by means of him as no one else recognize such specific about my problem. You’re incredible!
    Thank you!

  5. pure raspberry ketones made in usa Says:

    Definitely believe that which you stated. Your favorite justification appeared
    to be on the internet the simplest thing to be aware of.
    I say to you, I certainly get annoyed while people consider worries that they just do not
    know about. You managed to hit the nail upon the top as well as defined
    out the whole thing without having side-effects , people could take a
    signal. Will probably be back to get more. Thanks

  6. raspberry ketones Says:

    I’m very pleased to discover this website. I wanted to thank you for your time due to this fantastic read!! I definitely loved every little bit of it and i also have you bookmarked to check out new stuff in your site.

  7. green coffee bean extract drops Says:

    Your way of telling all in this post is genuinely nice, all can simply
    know it, Thanks a lot.

  8. dermology hair removal Says:

    Hey there, You’ve done a great job. I’ll definitely digg it and personally
    recommend to my friends. I am confident they’ll be benefited from this web site.

  9. Carroll Says:

    Highly descriptive article, I liked that bit.

    Will there be a part 2?

  10. norske spilleautomater på nett Says:

    Konsoll og kunstige intelligensen spilleautomater virker bedre human det ble ogs flere som pekte p gjeng spillere var hrreisende.
    For peterborough norgesautomat hente andre kjpbevegelse.

  11. garcinia cambogia 1500mg with calcium and potassium Says:

    It can speed the recovery of the body from the toxins of the cigarette.
    Garcinia cambogia has the capacity to decrease lipid quantities.
    They will want to eat less and thus decrease the amount they consume.

  12. spelautomater Says:

    Inte vinner ver dem om forst du inte to keep customers onside man behver skert borra helt manuella idag
    har det slags slots online online casino siffrorna.
    Du maste reservera r den intemin vrld.

  13. seiko メカニカル Says:

    seiko レディース 人気

  14. Ralph Says:

    I think the final point is overstated. Facial hair may foster a fluid boundary layer. Scalp hair provides insulation. The effect is small but noticeable. Certainly, in my experience, after a short haircut, the head is more sensitive to cool air.

  15. Enduring Cold Weather in Style: Three Essential Pieces | Image Coach for Success Says:

    […] True?  or False?   Possibly true for an infant, NOT true for an adult says results of  a Wilderness Medicine […]

  16. www.squidoo.com Says:

    Hi there, I enjoy reading all of your post.
    I like to write a little comment to support you.

  17. rescue from heights Says:

    It is not easy to keep from shedding a tear
    or two when you see a photo of a firefighter rescuing a person or even sharing an oxygen mask with a family’s beloved pet after making a rescue.
    Write 3- 5 sentences in your discussion and then give a hyperlink where people can read the full story.
    So, getting back to the email, I opened it up to see an application
    for adoption of a boxer we have been fostering for

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


Get every new post delivered to your Inbox.

Join 27 other followers

%d bloggers like this: