Check that you are hydrated enough. The best way is to look at the colour of your urine. It should be straw-coloured. If it isn't you need to drink more water.
Invented by the Russia scientist Rustem Igor Gamow, the Gamow bag is essentially a portable pressurisation chamber. The person gets into the bag before it is sealed and inflated. Pumping the bag full of air effectively increases the pressure inside the bag and so increases the concentration of oxygen molecules, simulating a descent to lower altitudes. In just minutes it can create an atmosphere equivalent to more than 1000 metres lower than the ambient pressure. In a couple of hours the person's body chemistry would have reset to the lower altitude. This lasts for up to 12 hours outside the bag, giving them enough time to descend to lower altitude for natural acclimatisation.
Staying hydrated helps to fight off frostbite and hypothermia because it enables the body to generate heat more efficiently. Drink at least three litres a day and avoid diuretics such as tea and coffee.
