Pulmonary Function Testing

Pulmonary function tests (PFTs) are noninvasive diagnostic tests that provide measurable feedback about the function of the lungs. By assessing lung volumes, capacities, rates of flow, and gas exchange, PFTs provide information that, when evaluated by your doctor, can help diagnosis certain lung disorders.

A normally-functioning pulmonary system operates on many different levels to ensure adequate balance. One of the primary functions of the pulmonary system is ventilation, the movement of air into and out of the lungs.

Some medical conditions may interfere with ventilation. These conditions may lead to chronic lung disease. Conditions that interfere with normal ventilation are categorized as restrictive or obstructive. An obstructive condition occurs when air has difficulty flowing out of the lungs due to resistance, causing a decreased flow of air. A restrictive condition occurs when the chest muscles are unable to expand adequately, creating a disruption in air flow.

Pulmonary function tests may be indicated to determine the presence, location, cause, and characteristics of the problem, and to guide treatment.

Pulmonary function tests is an inclusive term that refers to several different procedures that measure lung function in different ways. Some of the more common values that may be measured during pulmonary function testing include:

  • Tidal volume (VT). This is the amount of air inhaled or exhaled during normal breathing.

  • Minute volume (MV). This is the total amount of air exhaled per minute.

  • Vital capacity (VC). This is the total volume of air that can be exhaled after maximum inspiration.

  • Functional residual capacity (FRC). This is the amount of air remaining in lungs after normal expiration.

  • Total lung capacity. This is the total volume of lungs when maximally inflated.

  • Forced vital capacity (FVC). This is the amount of air exhaled forcefully and quickly after maximum inspiration.

  • Forced expiratory volume (FEV). This is the volume of air expired during the first, second, and third seconds of the FVC test.

  • Forced expiratory flow (FEF). This is the average rate of flow during the middle half of the FVC test.

  • Peak expiratory flow rate (PEFR). This is the maximum volume during forced expiration.

Some PFTs involve the use of a spirometer.


The spirometer is an instrument that measures the amount of air breathed in and/or out and how quickly the air is inhaled and expelled from the lungs while breathing through a mouthpiece. The measurements are recorded on a device called a spirograph.

Other test results are derived from calculations based on the results of certain spirometry procedures. In addition to measuring the amount and rate of air inhaled and exhaled, these tests can also indicate how well oxygen and carbon dioxide are being exchanged in the alveoli.



Generally PFTs do not require any prior preparation. In some cases you may be asked to cease the use of inhalers/preventors several hours before the test - your doctor or a QE Specialist Centre staff member will be able to clarify this for you. If you are a smoker you may also be asked to refrain from smoking a few hours before the test, too.



  • Faintness or light-headedness due to hyperventilation

  • Asthmatic episode precipitated by deep inhalation exercises