Module 4: Physiology of the Respiratory System - Airflow Obstruction: Evaluation of Reversibility.

Airflow Obstruction: Evaluation of Reversibility

Airflow obstruction is evaluated by spirometry as being either reversible or not reversible.

Definition:

• > 200 ml or > 12% change in FEV1, either spontaneously or in response to bronchodilator.
• > 20% change in PEFR.

Beta-2 agonists are the screening test for reversibility: for example, 400 micrograms salbutamol administered by MDI.

• Spirometry is then repeated 15 minutes later.
• Reversibility is present if there is a 12% or > 200 ml improvement.
• This test should be performed in all cases where there is evidence for airflow obstruction (FEV1/FVC < 75%).

The figure on the left illustrates the change that may be observed on a F/V curve before and after bronchodilator. Administration of reversibility using bronchodilator by MDI is specific but not very sensitive. Larger dose of agents (for example, beta-2 agonist +/- anticholinergic by nebuliser) may be used; or a course of oral steroids.