Pulmonary Function Test

Definition

Pulmonary function tests are a group of procedures that measure the function of the lungs, revealing problems in the way a patient breathes. These tests can determine the cause of shortness of breath and may help confirm the diagnosis of lung diseases, such as asthma, chronic bronchitis, or emphysema. The tests may also be performed before any major lung surgery to make sure the person will not be at risk of complications because of reduced lung capacity.

Purpose

Pulmonary function tests can help diagnose a range of respiratory diseases that might not otherwise be obvious to the clinician or the patient. These tests are important, since many kinds of lung problems can be successfully treated if detected early.

The tests are also used to measure how a lung disease is progressing, and how serious the lung disease has become. Pulmonary function tests also can be used to assess a patient's response to different treatments.

If a patient shows signs of decreased lung function relative to the normal values for a person of his or her race, sex, age, height, and weight, that person may suffer from a pulmonary disease. There are two causes of abnormal pulmonary function, obstructive lung diseases and restrictive lung diseases.

Obstructive lung diseases are characterized by a decreased ability to get air out of the lungs. A patient with an obstructive lung disease generally does not experience difficulty getting air into his or her lungs. Obstructive lung diseases are most easily remembered with the acronym CABBE: cystic fibrosis, asthma, brochiectasis, chronic bronchitis, and emphysema.

Restrictive lung diseases are characterized by a decreased capacity to draw air into the lungs. A patient with a restrictive lung disease generally does not experience difficulty getting air out of his or her lungs. The cause of restrictive lung diseases may be either directly related to a dysfunction of the lungs (intrapulmonary) or not related to a dysfunction of the lungs (extrapulmonary). Intrapulmonary restrictive lung diseases include pneumonia, pulmonary fibrosis, and pulmonary edema. Extrapulmonary causes of restrictive lung diseases include rib fractures, head trauma, and neuromuscular disorders.

Precautions

Before any pulmonary function test is performed by a patient, the clinician ordering the test should be aware of any conditions that the patient may have that may affect the reliability of the test results. Also, because pulmonary function testing requires deep breathing, the test itself may aggravate these same conditions.

Conditions in a patient that contraindicate pulmonary function testing include: the coughing-up of blood from the respiratory tract (hemoptysis); a collapsed or partially collapsed lung (pneumothorax); an unstable heart condition, recent heart attack, or blood clot near the lungs; an abnormal localized bulging of a blood vessel (aneurysm) in the chest, abdomen, or head; recent surgery of the chest or abdomen; recent eye surgery; and current nausea or vomiting. If a patient suffers from one or more of these conditions, pulmonary function tests should be postponed until these conditions are resolved.

The patient should not wear clothing that constricts the chest area. Patients should not have eaten a heavy meal three hours or less before the test. Smokers should provide their smoking history and the time of their last cigarette. In order for pulmonary function tests to yield accurate results, the patient must be able to respond to direction; so the tests may not be useful in very young children, uncooperative patients, and physically incapacitated individuals.

Description

One of the most common of the pulmonary function tests is spirometry. This test, which can be given in a hospital or doctor's office, measures how much and how fast the air is moving in and out of the lungs. This test is covered in greater detail in the separate spirometry tests entry.

A peak flow meter can determine how much a patient's airways have narrowed. A test of blood gases is a measurement of the concentration of oxygen and carbon dioxide in the blood, which shows how efficient the gas exchange is in the lungs.

Another lung function test reveals the efficiency of the lungs in absorbing gas from the blood. This efficiency is measured by testing the volume of carbon monoxide a person breathes out after a known volume of the gas has been inhaled.

Preparation

The healthcare provider conducting a pulmonary function test should explain the test and any and all potential side effects to the patient prior to the test being performed. The health care provider should then demonstrate the proper breathing technique for the patient, and the patient should then practice this technique until he or she is able to accurately duplicate the proper technique on two consecutive trials. The health care provider should also indicate that while most side effects of pulmonary function tests are extremely rare, the patient should stop the test if he or she becomes extremely uncomfortable or feels intense pain in the head, eye, chest, or abdomen.

Prior to the test, the age, race, and sex of the patient should be recorded, along with a height measurement in stocking feet and a weight measurement. This information will allow each individual's results to be compared to normal values for people in the same demographic category.

Aftercare

There is usually no patient care required after the administration of a pulmonary function test. If a patient feels lightheaded or dizzy, he or she should lie down until the symptoms subside. In rare cases, oxygen may have to be administered to prevent pneumothorax or to restore normal breathing patterns.

Complications

In general, pulmonary function tests are safe procedures that simply require deep breathing. In very rare instances complications can occur. These include pneumothorax; increased fluid pressure between the bones of the skull and the brain (increased intracranial pressure); loss of consciousness, dizziness, and/or lightheadedness; chest pain; uncontrollable coughing; and contraction of an infection from the test equipment.

Results

Normal results

Normal test results are based on a person's age, height, weight, race, and gender. Normal results are expressed as a percentage of the predicted lung capacity for a person of the same age, height, weight, race, and sex. Any measurement within 20% of the predicted value is considered a normal result.

Abnormal results

Abnormal results mean that the person's lung capacity is less than 80% of the predicted value. Such findings usually mean that there is some degree of chest or lung disease.

Health care team roles

Pulmonary function tests are generally ordered by a primary care doctor (M.D. or D.O.) or advanced practice nurse, and performed either by a physician, nurse, or respiratory technician under the direction of a doctor specifically trained in pulmonary function testing. When the results of pulmonary function testing are inaccurate, the most frequent reason is inadequate patient education and/or technician training. It is recommended that personnel conducting pulmonary function testing have one of the following credentials: certified respiratory therapy technician (CRTT); registered respiratory therapist (RRT); certified pulmonary function technologist (CPFT); or registered pulmonary function technologist (RPFT). A doctor specializing in diseases of the lungs (pulmonologist) may be consulted to examine abnormal pulmonary function test results.