Pulmonary Function Tests

By Robbie Leinweber

(PFTs, Pulmonary Function Studies, Lung Function Studies/Tests, Airflow Assessment)

Procedure Overview

What are pulmonary function tests?

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 physician, 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 into 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) - amount of air inhaled or exhaled during normal breathing

  • Minute volume (MV) - total amount of air exhaled per minute

  • Vital capacity (VC) - total volume of air that can be exhaled after maximum inspiration

  • Functional residual capacity (FRC) - amount of air remaining in lungs after normal expiration

  • Total lung capacity - total volume of lungs when maximally inflated

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

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

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

  • Peak expiratory flow rate (PEFR) - 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.

Some PFTs, such as thoracic gas volume or other lung volume measurements, may be determined by plethysmography. During plethysmography, a person sits or stands inside an air-tight box that resembles a short, square telephone booth to perform the tests.

The normal values for PFTs vary from person to person. The amount of air inhaled and exhaled in your test results are compared to the expected average in someone of the same age, height, sex, and race. In addition, results are compared to your previous test results, if previous testing has been done. If you have abnormal PFT measurements or if your results are different from previous tests, you may be referred for other diagnostic tests to establish a medical diagnosis.

Anatomy of the respiratory system

The respiratory system is made up of the organs involved in the interchanges of gases, and consists of the:

  • Nose

  • Pharynx

  • Larynx

  • Trachea

  • Bronchi

  • Lungs

The upper respiratory tract includes the:

  • Nose

  • Nasal cavity

  • Ethmoidal air cells

  • Frontal sinuses

  • Maxillary sinus

  • Larynx

  • Trachea

The lower respiratory tract includes the lungs, bronchi, and alveoli.

What are the functions of the lungs?

The lungs take in oxygen, which cells need to live and carry out their normal functions. The lungs also get rid of carbon dioxide, a waste product of the body's cells.

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