Happy Christmas to everyone who reads my blog!
I hope you all have splendid New Year's in 2009.
Take care and see you next year.
Jon
Wednesday, 24 December 2008
Heat loss from head - continued!
Well, I've looked into this a bit more and found some interesting stuff. Bear with the biology lesson, it's worth it.
Under normal circumstances the blood flow to the brain doesn't change because the demand for oxygen is constant. This being the case then the head accounts for about 7% of total heat loss. So far so good and pretty much what I said in the previous post.
Blood flow to the brain however does vary according to cardiac output. This means the faster your heart beats, then more blood flows to your head. This increase in blood flow causes an increase in heat loss. So when you start to exercise, more blood flows to your brain. This increases the heat loss from the head to about 50%! But, as you continue to exercise, muscles demand more oxygen and more blood. In order for your body to maintain its core temperature it now needs to shunt blood to other parts of the body eg blood vessels in the skin vasodilate to help cool the body.
This means that blood flow to the brain decreases causing the total heat loss from the head to decrease back down to about 10%. Once sweating starts this will drop back down to about 7%. Cool eh!
There is a big implication here for victims of hypothermia. Someone who is hypothermic but not shivering will be losing about 7% of total body heat through there head (see above). However, as soon as they start shivering, they are, in effect, exercising and so heat loss can rise to 50% or more through their head. So it is important to protect a hypothermia victim's head from the cold especially if they are shivering.
heat loss, hypothermia
Under normal circumstances the blood flow to the brain doesn't change because the demand for oxygen is constant. This being the case then the head accounts for about 7% of total heat loss. So far so good and pretty much what I said in the previous post.
Blood flow to the brain however does vary according to cardiac output. This means the faster your heart beats, then more blood flows to your head. This increase in blood flow causes an increase in heat loss. So when you start to exercise, more blood flows to your brain. This increases the heat loss from the head to about 50%! But, as you continue to exercise, muscles demand more oxygen and more blood. In order for your body to maintain its core temperature it now needs to shunt blood to other parts of the body eg blood vessels in the skin vasodilate to help cool the body.
This means that blood flow to the brain decreases causing the total heat loss from the head to decrease back down to about 10%. Once sweating starts this will drop back down to about 7%. Cool eh!
There is a big implication here for victims of hypothermia. Someone who is hypothermic but not shivering will be losing about 7% of total body heat through there head (see above). However, as soon as they start shivering, they are, in effect, exercising and so heat loss can rise to 50% or more through their head. So it is important to protect a hypothermia victim's head from the cold especially if they are shivering.
heat loss, hypothermia
Friday, 19 December 2008
If you want to get ahead, get a hat!
Recently, scientists have decided to bust some myths. One of them is how much heat is lost through the head. It would seem that many of us having been labouring under the misapprehension that we lose anywhere between 20% and 50% of our body heat through our heads (Guardian article).
This would appear to be total rubbish that has come about from some flawed research done by American scientists in the 1950's. Scientists, eh! Anyway, the upshot is that the amount of heat loss from any exposed skin is about the same no matter where on the body that skin is. The heat loss is proportional to the amount of exposed skin. Pretty logical really. The head accounts for about 10% of our body's surface area, so, in order for it to lose 40% of our heat, the skin on our heads would have to lose 40 % more heat, per square inch, than any other skin on our bodies. Not likely, is it?
The skin on our neck and head is more sensitive to temperature which is why wearing a hat is so cosy on a brisk winter's day. It just feels like it is stopping more heat loss rather than actually doing so.
I find this interesting so will probably look into it in more detail and post something else about it later.
Have fun!
heat loss
This would appear to be total rubbish that has come about from some flawed research done by American scientists in the 1950's. Scientists, eh! Anyway, the upshot is that the amount of heat loss from any exposed skin is about the same no matter where on the body that skin is. The heat loss is proportional to the amount of exposed skin. Pretty logical really. The head accounts for about 10% of our body's surface area, so, in order for it to lose 40% of our heat, the skin on our heads would have to lose 40 % more heat, per square inch, than any other skin on our bodies. Not likely, is it?
The skin on our neck and head is more sensitive to temperature which is why wearing a hat is so cosy on a brisk winter's day. It just feels like it is stopping more heat loss rather than actually doing so.
I find this interesting so will probably look into it in more detail and post something else about it later.
Have fun!
heat loss
Thursday, 4 December 2008
Radio gaga
Well on Monday this week I was on an informal discussion panel on local BBC Somerset Radio.
It was good fun and lasted for an hour and we talked about local and national news. I enjoyed it so much I hope to be invited back in a few weeks time to have another go! It was also a good way to get myself some publicity.
I'll keep you posted when I'm on again.
It was good fun and lasted for an hour and we talked about local and national news. I enjoyed it so much I hope to be invited back in a few weeks time to have another go! It was also a good way to get myself some publicity.
I'll keep you posted when I'm on again.
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