Lung volumes and capacities, Functional residual capacity Helium dilution method By Prof Dr Samia Jawed Student spirometer. • THE GRAPHICAL RELATIONSHIP AMONG VARIOUS LUNG VOLUME AND CAPACITIES. Spirogram • What are the advantages of residual volume, FRC, dead space air? • Clinical measurements of specific volumes and capacities provide insights into lung function and origin of disease processes. •These tests are screening and not diagnostic. • The VC is the maximum volume of air that an individual can move in a single breath. • The most useful assessment of VC is to expire as quickly and forcefully as possible. • This way we get timed vital capacity or forced vital capacity.(FVC). • During the FVC maneuver ,volume of air exhaled in the first second is FEV1. • From 0-20 years vital capacity increases • From 20 -60 years it remains stable if there is no pathology • With more aging elasticity of lungs decreases and residual volume increases • Pathology affects vital capacity • Like neuromuscular disorders,lower motor neuron diseases,myasthenia gravis, kyphosis, scoliosis, • Lung infections, collapse, pleural effusion, bronchial Asthma, emphysema, chronic Brochitis etc. • Males have more VC.Why? • VC decreases in pregnancy and while lying down. Flow volume curves in different conditions Helium dilution method FRC and its measurement. • What is the difference between hyperventilation, hyperpnoea, tachypnoea?