shiato storm
Suspended / Banned
- Messages
- 1,756
- Edit My Images
- No
I thought it would be useful to impart some basic physiology that I picked up a few years back concerning heat stress and the like as I was doing an MSc project down on the naval medical centre in Gosport, this involves effective cooling mechanisms currently employed by the MoD (how ever much we trust them, or not, this is science and does actually work).
Very roughly; your body thermoregulates with its environment by either pushing blood flow to the skin or pulling it back into your core. no prizes for guessing that when its hot blood flow to the extremities is high - conversly its why our fingers and toes go blue when we're cold. The general concensous is that the controlling mechanism for this vasoconstriction/vasodilation is a balance between the skin temperature and core temperature. So if you got really cold on the inside your blood vessels in the skin would constrict to keep the warm blood around your vital organs - too hot, and it goes to the skin to radiate some of the heat off. similarly you can immerse your self in cold water whilst your core is still at a comfortable 37C (standard normal body temp) and your blood vessels would clamp shut sending blood towards the core - incidentally this is a very common cause of death in the water known as cold shock, the rapid immersion in cold water suddenly loads the heart with returning blood flow and pphhfft! it goes into arrest and you sink. happens a lot in overweight people on holiday.
Now, it gets a little tricky when someone is in extreme conditions such as hypothermia where your core cools to 35 degrees or below - simply slapping them in a shower doesn't work as their core is still too cold - requires heating from the inside like a hot chocolate of similar. Deep divers using helium (derekM might be able to offer more info on this specifically) may suffer the bizaare situation in that compressed air cools as it is released (squirt a can of deodorant for a couple of secs and see what I mean), this coold the diver from the core, but no deep diver travels without his heated suit that warms his skin up. a point may be reached where they have the heat up to 38/39C on the suit but they're technically hypothermic due to the chill in their core!
The MoD carried out a series of experiments (quite humanely) to see what is the most effective way of cooling a human in high temperatures, they looked at whole body cooling, head cooling, chest cooling and extremity cooling (my heart goes out to the control subject who had no cooling afforded to them). What they found was whole body cooling actually initiated a vasoconstriction response preventing further heat loss regardless of the high core temperature, head cooling and chest cooling produced minimal rsults whilst the cooling of extremities produced a remarkable and amazing result.
Subject who placed their hands and feet - up to the wrists and ankles and no further - in chilled water actually lost heat from the core so rapidly it virtually returned to 'normal' (whilst still at a high environmental temperature, test was done in a climate chamber). What was happening was the blood vessels were remaining open on account of a high core temperature and the surface of skin mmersed in cold water was not enough to cause a vasoconstriction response - therefore much like a radiator in your average car the flow of warm blood was cooled whilst going through the hands and feet and returned to the core to bring the temperature down.
So, on a hot day stick your wrists under a cold tap or in the sink for a few mins to help cool you down. better yet fill a bucket and dunk your feet in...and even better find a river bank and dangle you feet in. Dont go for the whole body immersion/cold shower approach - it really doesn't do much good and takes far far longer cause it prevents the hot blood from reaching areas where it can be cooled.
/physiology lesson over!
p.s. KEEP DRINKING FLUIDS, its surprising how much water you lose through sweat, and if you lose too much then you can, in extreme cases, rapidly over heat the body and sometimes dangerously!
Very roughly; your body thermoregulates with its environment by either pushing blood flow to the skin or pulling it back into your core. no prizes for guessing that when its hot blood flow to the extremities is high - conversly its why our fingers and toes go blue when we're cold. The general concensous is that the controlling mechanism for this vasoconstriction/vasodilation is a balance between the skin temperature and core temperature. So if you got really cold on the inside your blood vessels in the skin would constrict to keep the warm blood around your vital organs - too hot, and it goes to the skin to radiate some of the heat off. similarly you can immerse your self in cold water whilst your core is still at a comfortable 37C (standard normal body temp) and your blood vessels would clamp shut sending blood towards the core - incidentally this is a very common cause of death in the water known as cold shock, the rapid immersion in cold water suddenly loads the heart with returning blood flow and pphhfft! it goes into arrest and you sink. happens a lot in overweight people on holiday.
Now, it gets a little tricky when someone is in extreme conditions such as hypothermia where your core cools to 35 degrees or below - simply slapping them in a shower doesn't work as their core is still too cold - requires heating from the inside like a hot chocolate of similar. Deep divers using helium (derekM might be able to offer more info on this specifically) may suffer the bizaare situation in that compressed air cools as it is released (squirt a can of deodorant for a couple of secs and see what I mean), this coold the diver from the core, but no deep diver travels without his heated suit that warms his skin up. a point may be reached where they have the heat up to 38/39C on the suit but they're technically hypothermic due to the chill in their core!
The MoD carried out a series of experiments (quite humanely) to see what is the most effective way of cooling a human in high temperatures, they looked at whole body cooling, head cooling, chest cooling and extremity cooling (my heart goes out to the control subject who had no cooling afforded to them). What they found was whole body cooling actually initiated a vasoconstriction response preventing further heat loss regardless of the high core temperature, head cooling and chest cooling produced minimal rsults whilst the cooling of extremities produced a remarkable and amazing result.
Subject who placed their hands and feet - up to the wrists and ankles and no further - in chilled water actually lost heat from the core so rapidly it virtually returned to 'normal' (whilst still at a high environmental temperature, test was done in a climate chamber). What was happening was the blood vessels were remaining open on account of a high core temperature and the surface of skin mmersed in cold water was not enough to cause a vasoconstriction response - therefore much like a radiator in your average car the flow of warm blood was cooled whilst going through the hands and feet and returned to the core to bring the temperature down.
So, on a hot day stick your wrists under a cold tap or in the sink for a few mins to help cool you down. better yet fill a bucket and dunk your feet in...and even better find a river bank and dangle you feet in. Dont go for the whole body immersion/cold shower approach - it really doesn't do much good and takes far far longer cause it prevents the hot blood from reaching areas where it can be cooled.
/physiology lesson over!
p.s. KEEP DRINKING FLUIDS, its surprising how much water you lose through sweat, and if you lose too much then you can, in extreme cases, rapidly over heat the body and sometimes dangerously!
- Paul
