Tutorial – Lung Function Testing

Lung Function in Obstructive/Restrictive Disease VC VC VC TLC VT RV VOLUME (litres) NormalCOPD VT ERV RV TLC Restricted VT ERV RVTLC Restriction Normal Obstruction

4 Volumes: Inspiratory Reserve Volume Tidal Volume Expiratory Reserve Volume Residual Volume 2 or more Volumes  a Capacity 4 Capacities: Vital Capacity Inspiratory Capacity Functional Residual Capacity Total Lung Capacity Lung Volumes and Capacities

“Spirometry is a medical test that measures the volume of air an individual inhales or exhales as a function of time. (ATS, 1994)” A spirometer can be used to measure the following: FVC and its derivatives (such as FEV 1, FEF 25-75%) Forced Inspiratory Vital Capacity (FIVC) Peak Expiratory Flow Rate (PEF) Maximum Voluntary Ventilation (MVV) Slow VC IC, IRV and ERV Pre- and post-bronchodilator tests Spirometry

Two ways to record/display results… Volume as a function of time Flow rate as a function of volume (expiration & inhalation) Flow-Volume Curves

FVC – the maximum volume exhaled FEV 1 – the volume exhaled during the first second of the FVC manoeuvre FEV 1 % – the ratio of FEV 1 to FVC expressed as a percentage A reduction is specific for obstructive rather than restrictive diseases FEF 25-75% – the mean expiratory flow rate during the middle half of an FVC manoeuvre Reflects flow through the small (<2mm diameter) airways Measurement Definitions

Estimate FEV 1 % and FEF 25-75% Measurement Definitions

Prediction Nomograms (>=80% is ‘normal’)

A plot of inspiratory/expiratory flow (y-axis) vs volume (x-axis) during maximal, forced manoeuvres Flow-Volume Loop

PEF reduced (max height of the loop) Airflow reduces rapidly post-PEF  concave loop Reversed with bronchodilator treatment (Irreversible in COPD) Obstructive Lung Disease - Asthma

Airways collapse during forced expiration Destruction of supporting lung tissue  reduced flow at low lung volume ‘dog-leg’ curve Obstructive Lung Disease - Emphysema

Full lung expansion prevented by fibrotic tissue Typically, reduced FVC (shown) But PEF may be preserved/increased (not shown) Restrictive Lung Disease

Normal vs. Obstructive vs. Restrictive

Obstructive Disorders FVC  or↓ FEV 1 ↓ FEF 25-75% ↓ FEV 1 /FVC ↓ TLC  or ↑ Obstructive vs. Restrictive Defect Restrictive Disorders FVC ↓ FEV 1 ↓ FEF 25-75%  to ↓ FEV 1 /FVC  to ↑ TLC ↓

Cannot measure TLC, FRC, RV Limits of Spirometry

Fully enclosed rigid box Breathe through mouthpiece connected via shutter to the internal volume of the box Breathe against the shutter Pressure in lungs changes Pressure in the box changes (opposite direction) Application of Boyle’s Law  lung volumes Including parts of lungs not in communication with bronchial tree Body Plethysmography