Pulmonary Function Tests

Pulmonary Function Tests or “PFTs” are just one of the convenient “on site” services offered to our patients. These tests can be very useful in the initial assessment of a number of medical conditions which affect the lungs and the long term follow-up of these conditions. PFTs generally consist of three main parts but it is not always necessary to perform all parts in every situation.

The precise tests performed will depend upon the specific information that your healthcare provider requires to diagnose or treat you. For example, “shortness of breath” may result from a number of medical conditions, including an inability to get adequate air into the lungs (restrictive lung disease), a diminished ability to get air out of the lungs (obstructive lung disease) or a diminished ability to transfer the oxygen contained in the air that we breathe into our circulation so that it may be delivered to the body tissues. Each separate component of the PFT is designed to assess each of these possibilities.

Below is a brief explanation of each PFT component and what to expect during the test:


This is by far the most common type of PFT performed and it is often performed in isolation. During this test, you will be asked to wear nose clips and to breathe in and out through your mouth while your lips are sealed tightly around a disposable mouthpiece which has a built-in filter. (If you prefer, you may simply pinch your nostrils with your fingers rather than wearing nose clips.) After you become accustomed to breathing in and out through your mouth, the technician will ask you to inhale as deeply as you can and then to blow the air out as quickly and completely as you can for a specified period of time.

A device called a “flow sensor” will determine how much air your lungs can blow out and how quickly your lungs can empty themselves. Diseases such as asthma and COPD (i.e. emphysema and chronic bronchitis) can result in incomplete or slowly emptying lungs due to reversible (asthma) or fixed (COPD) changes in the airways and/or lung tissue which obstruct the flow of air out of the lungs. Hence the name “chronic obstructive pulmonary disease.”

During this test, you may be given a “bronchodilator” medication such as albuterol to see if there is any improvement in the air flow. If you normally take bronchodilator type medication (inhalers or nebulizer), you will be asked to withhold these medications for a certain period of time before testing. Please ask us how long you should withhold these bronchodilator (inhaled or nebulized) medications prior to testing. This will vary depending on the specific medications that you take. In addition, you should not consume caffeine containing food or beverages within 24 hours of testing.

In addition, spirometry can also be used to help diagnose various other conditions such as upper airway (“voice box”) or tracheal (“windpipe”) abnormalities that can interfere with airflow into and/or out of the lungs.

Lung Volumes

Through the measurement of various lung volumes and lung capacities, this test will help to determine if you are able to get adequate volumes of (oxygen-carrying) air into the lungs. Certain medical conditions or environmental toxins can cause injury to the lungs which result in scarring or “fibrosis” that can make it more difficult to fully expand the lungs and this scarring can lead to smaller lung volumes.

Many diverse disorders, originating both within and outside the lung itself, can result in   “restrictive” defects on pulmonary function testing and can cause symptoms such as shortness of breath. Lung volumes can be measured a number of different ways. We use a technique called “Nitrogen washout” or Fowler’s Method to measure lung volume. You will breathe in 100% oxygen and then the amount of nitrogen in your expired air will be measured to determine your lung volumes.

Diffusion Capacity

This part of the test measures the ability of the lungs to efficiently transfer the oxygen in the air that you breathe into the bloodstream. You will breathe in a harmless “tracer gas” and the ability of the lungs to transfer this gas across the “alveolar membrane” in your lungs will be measured. During this test, you will be asked to take a deep breath and hold it for a set period of time during this test. Most patients are able to hold their breath for this short period of time without much difficulty. It is VERY important that you do NOT smoke prior to this test as this can interfere with the test results.