Measuring Lung Capacity

Lung capacity can be measured by:A peak flow meter. This measures the rate at which air can be expelled from the lungs. People who have asthma can use this to check how well their lungs are working.Vitalographs. This also measures the rate at which air can be expelled.The subject breathes out through a mouthpiece and the vitalograph produces a graph of the amount of air breathed out and how quickly the air is breathed out.This is called the forced expiratory volume in 1 second.A spirometer. Different aspects of breathing can be measured using a spirometer. The nose is occluded with a nose clip and the person breathes in and out through a mouthpiece.The spirometer is a tank of water with an air-filled chamber suspended in the water.Adding air to the chamber makes the lid of the chamber rise in the water, and removing air makes it fall.Movements of the chamber are recorded using a pen writing on a rotating drum.The apparatus can be calibrated so that the movement of the lid corresponds to a given volume.A canister containing soda lime is inserted between the mouthpiece and the floating chamber.This absorbs the carbon dioxide that the subject exhales.