Spirometry and Flow-Volume Curves - the Idiot’s Guide. Dr Rod Taylor Consultant Respiratory Physician (part-time). Bob Dylan at 70. Born on the 24 th May 1941. History of Spirometry. 1846 John Hutchinson Defined Vital Capacity Invented the Spirometer 1947 Tiffeneau: FEV 1

Download Presentation

Spirometry and Flow-Volume Curves - the Idiot’s Guide

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

History of Spirometry • 1846John Hutchinson • Defined Vital Capacity • Invented the Spirometer • 1947 Tiffeneau: FEV1 • VEMS: Vol. Expired Maximale, une Seconde • 1959 Wright: Peak Flow Meter

VITAL CAPACITY Hutchinson 1846: “The greatest voluntary expiration, following the deepest inspiration” Simple modern definition: “The biggest breath out, after the biggest breath in”

Brompton Hospital 1852 “Waste of time trying to do spirometry in women and girls: they are simply incapable of doing it.” Of course I can’t blow into it – I’m a woman! I’m pretty useless, too!

ForcedExpiratoryVolume in1second = FEV1 • The volume of air • expelled in the first second • of a maximal forced expiration • starting from full inspiration • i.e. the first 1 second of a FVC

20% either side of Mean 80 – 120% of the mean predicted value For FVC ~ 1 litre either side of mean

Absolute values • e.g. FEV1/FVC = 3.75/4.60 litres • should always be given • Percentage of predicted value • e.g. FEV1 = 67% predicted • Forced expiratory ratio • e.g. FEV1/FVC = 53%

Graphically • As volume-time curve: spirogram • As flow-volume curve • Examples will be shown

The lungs are small • FVC is small • so FEV1 is also reduced • But no obstruction to expiration • so forced expiratory ratio (FEV1/FVC) • is normal – or even increased • becauseelastic recoil increased

Obstructive Defect Definition • FEV1 significantly reduced • to < 80% of predicted value • Forced expiratory ratio 70% or less • FEV1/FVC < 70% NB: Severe airflow obstruction reduces FVC as well as FEV1 , and so increases FER

Forced Expiratory RatioFEV1/FVC • Depends on both FEV1and FVC • Is reduced if • FEV1 is reduced • But goes back up again • if FVC is reduced • by incomplete expiration • or by severe airflow obstruction

Severe airflow obstruction Moderate airflow obstruction Normal FVC FVC FEV1 FVC FEV1 FEV1

Mild airflow obstruction Slightly concave throughout expiration Airflow is reduced at a given lung volume, because the airway is narrower. Sometimes called ‘volume dependent’ reduction in flow.

Bronchodilator Effect Peak flow Before Flow has increased throughout expiration, and peak flow slightly. In this example, there is no increase in FVC. After