ASTHMA sufferers unable to tell if their inhalers are empty should be shown the 'flotation test', says Mark Rickenbach, a GP from Eastleigh, Hampshire. He has found that an inhaler placed in water takes up one of four positions, depending how full it is. A canister on its side with the corner exposed, for example, is less than 15 per cent full. Knowing the different positions could reduce the risk of asthmatics running out of drugs, he argues in the British Journal of Gen eral Practice.