pulmonary function test

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. The tests can determine the cause of shortness of breath and may help confirm lung diseases, such as asthma, bronchitis or emphysema. The tests also are performed before any major lung surgery to make sure the person won't be disabled by having a reduced lung capacity.

Purpose

Pulmonary function tests can help a doctor diagnose a range of respiratory diseases which might not otherwise be obvious to the doctor or the patient. The 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 how a patient is responding to different treatments.

One of the most common of the pulmonary function tests is spirometry (from the Greco-Latin term meaning "to measure breathing"). 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. Specific measurements taken during the test include the volume of air from start to finish, the fastest flow that is achieved, and the volume of air exhaled in the first second of the test.

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 how efficient the lungs are in absorbing gas from the blood. This is measured by testing the volume of carbon monoxide a person breathes out after a known volume of the gas has been inhaled.

Precautions

Pulmonary function tests shouldn't be given to patients who have had a recent heart attack, or who have certain other types of heart disease. It is crucial that the patient cooperate with the health care team if accurate results are to be obtained.

Description

The patient places a clip over the nose and breathes through the mouth into a tube connected to a machine known as a spirometer. First the patient breathes in deeply, and then exhales as quickly and forcefully as possible into the tube. The exhale must last at least six seconds for the machine to work properly. Usually the patient repeats this test three times, and the best of the three results is considered to be the measure of the lung function. The results will help a doctor figure out which type of treatment to pursue.

Preparation

The patient should not eat a heavy meal before the test, nor smoke for four to six hours beforehand. The patient's doctor will issue specific instructions about whether or not to use specific medications, including bronchodilators or inhalers, before the test. Sometimes, medication may be administered as part of the test.

Risks

The risk is minimal for most people, although the test carries a slight risk of a collapsed lung in some patients with lung disease.

Normal results

Normal results are based on a person's age, height, and gender. Normal results are expressed as a percentage of the predicted lung capacity. The prediction takes into account the patient's age, height, and sex.

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.

Resources

Books

Ruppel, Gregg L. Manual of Pulmonary Function Testing. St. Louis: Mosby, 1997.

Key terms

Emphysema — A disease in which the small air sacs in the lungs become damaged, causing shortness of breath. In severe cases it can lead to respiratory or heart failure.

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pulmonary function test

n. Abbr. PFT

Any of several breathing tests that measure the function of the lungs, including the rate of air flow and the volume of exhaled air, performed to assess lung function and to detect the presence of respiratory disease.

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pulmonary function test (PFT),

a procedure for determining the capacity of the lungs to exchange oxygen and carbon dioxide efficiently. There are two general kinds of respiratory function tests. One measures ventilation, or the ability of the bellows action of the chest and lungs to move gas in and out of alveoli. The other kind measures the diffusion of gas across the alveolar capillary membrane and the perfusion of the lungs by blood. Efficient gas exchange in the lungs requires a balanced ventilation-perfusion ratio, with areas receiving ventilation well perfused and areas receiving blood flow capable of ventilation. Basic ventilation studies are performed with a spirometer and recording device as the patient breathes through a mouthpiece and connecting tube; a nose clip prevents nasal breathing. Measurements or calculations are made of the tidal volume (TV), or gas inspired and expired in a normal breath; the inspiratory reserve volume (IRV), or the maximal volume that can be inspired after a normal respiration; the expiratory reserve volume (ERV), or the maximal volume that can be expired forcefully after a normal expiration; the residual volume (RV), or the gas remaining in the lungs after maximal expiration; and the minute volume, or the gas inspired and expired in 1 minute of normal breathing. The vital capacity of the lungs is equal to TV + IRV + ERV, and the total lung capacity to TV + IRV + ERV + RV. Bronchospirometric measurements of the ventilation and oxygen consumption of each lung separately are performed by using a specially constructed double-lumen catheter with two balloons. One balloon is inflated to seal off the contralateral lung when the other lung is tested. Arterial blood gas studies, including determinations of the acidity, partial pressure of carbon dioxide and of oxygen, and oxyhemoglobin saturation, provide information on the diffusion of gas across the alveolar capillary membrane and the adequacy of oxygenation of tissues. See also blood gas determination, forced expiratory volume, maximum breathing capacity.

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pulmonary function test

Any technique and maneuver–eg, spirometry, ventilation and perfusion scans, measurement of lung volumes, airway resistance, strength of respiratory efforts, efficiency of gas exchange, carbon monoxide diffusing capacity and arterial blood gases–that provide objective and quantifiable data of pulmonary function, and may be combined with endoscopy-bronchoscopy, mediastinoscopy and various forms of imaging–chest films, CT, MRI to evaluate morphologic abnormalities–eg, an abscess or tumor. See Lung volumes, Pulmonary panel, Spirometry.