PFT Pre and Post

Pulmonary function tests fall into two main categories: spirometry and full lung function testing. Spirometry assesses airflow and obstruction using measures like FEV1 and FVC. Full lung function tests measure lung volumes (via body plethysmography or gas dilution) and gas transfer (diffusing capacity/DLCO), helping detect restrictive disease and quantify gas-exchange impairment.

Do not smoke for at least an hour before the test; avoid vigorous exercise for 30 minutes; don’t use bronchodilator inhalers or other respiratory medications unless your clinic has told you to continue (follow their instructions); avoid heavy meals and alcohol beforehand; and don’t wear tight clothing that restricts breathing. Arrive rested and bring a list of current medications.

Pre-bronchodilator measurement is the spirometry (lung function) reading taken before giving a bronchodilator. Post-bronchodilator is the repeat measurement taken after inhaling a bronchodilator (usually 10–15 minutes later). Comparing the two assesses reversibility of airflow obstruction; a significant rise in FEV1 (generally ≥12% and ≥200 mL) suggests reversible airway disease such as asthma.

Pulmonary function normal ranges vary by age, sex, height and ethnicity. Typical cutoffs: FEV1 and FVC ≥80% of predicted, FEV1/FVC ratio ≥70% (or above the lower limit of normal for age), total lung capacity (TLC) 80–120% predicted, and diffusing capacity for carbon monoxide (DLCO) 80–120% predicted. Values outside these ranges suggest obstructive, restrictive, or gas-exchange impairment.

Four main pulmonary function tests are: 1) Spirometry — measures airflow and volumes (FEV1, FVC). 2) Lung volumes — measured by body plethysmography or gas dilution to assess total lung capacity and residual volume. 3) Diffusing capacity (DLCO) — evaluates gas transfer across the alveolar membrane. 4) Gas-exchange tests — pulse oximetry and arterial blood gas analysis assess oxygenation and CO2 elimination.

Pulmonary function testing has two main components: spirometry and lung volume/gas‑transfer assessment. Spirometry measures airflow and volumes (e.g., FEV1, FVC, flow–volume loops) to identify obstruction or restriction. The second component measures lung volumes (often by plethysmography) and diffusion capacity (DLCO) to evaluate hyperinflation, restrictive defects and efficiency of gas exchange across the alveolar membrane.