PFTs (pulmonary function tests) are noninvasive examinations that demonstrate how effectively the lungs are functioning. The examinations measure lung size, function, flow rates, and gas exchange. Your healthcare professional may use this information to diagnose and treat some lung conditions.

There are two conditions that affect how air enters and exits the lungs:

  • Obstructive: This occurs when airway resistance makes it difficult for air to exit the lungs. Airflow is reduced as a result of this.
  • Restrictive: This occurs when the chest muscles or lung tissue cannot expand sufficiently. Airflow issues result from this, primarily because of reduced lung capacities.

PFT is possible using two techniques. Depending on the data your healthcare professional needs, these 2 approaches may be combined to perform other tests:

  • Spirometry: A mouthpiece-equipped instrument called a spirometer is connected to a small electrical gadget.
  • Plethysmograph: To conduct the tests, you must either sit or stand within an airtight box that resembles a brief, square telephone booth.
  • Gas diffusion study: Your lips will be placed around the mouthpiece, and a medical professional will instruct you on how to inhale and exhale a little, safe amount of carbon monoxide. The spirometer counts the amount of carbon monoxide you exhale while you breathe. This measurement reveals how much gas your lungs were able to take in.
  • Cardiopulmonary exercise test: You'll either use a stationary bike or a treadmill to stroll. Throughout the exam, the equipment will take numerous measurements of your heart, lungs, and muscles.

PFT measures:

  1. Tidal volume (VT). This is the amount of air inhaled or exhaled during normal breathing.
  2. Minute volume (MV). This is the total amount of air exhaled per minute.
  3. Vital capacity (VC). This is the total volume of air that can be exhaled after inhaling as much as you can.
  4. Functional residual capacity (FRC). This is the amount of air left in lungs after exhaling normally.
  5. Residual volume. This is the amount of air left in the lungs after exhaling as much as you can.
  6. Total lung capacity. This is the total volume of the lungs when filled with as much air as possible.
  7. Forced vital capacity (FVC). This is the amount of air exhaled forcefully and quickly after inhaling as much as you can.
  8. Forced expiratory volume (FEV). This is the amount of air expired during the first, second, and third seconds of the FVC test.
  9. Forced expiratory flow (FEF). This is the average rate of flow during the middle half of the FVC test.
  10. Peak expiratory flow rate (PEFR). This is the fastest rate that you can force air out of your lungs.

Normal values for PFTs vary from person to person. The amount of air inhaled and exhaled in your test results are compared to the average for someone of the same age, height, sex, and race. Results are also compared to any of your previous test results. If you have abnormal PFT measurements or if your results have changed, you may need other tests.

To further understand how the test works, watch the video below:

Reference: “Pulmonary Function Tests.” Pulmonary Function Tests | Johns Hopkins Medicine, 19 Nov. 2019,