Pulmonary Function Testing (PFT)
Pulmonary function tests measure the lungs' capacity to hold air, to move air in and out, and to exchange oxygen and carbon dioxide. These tests are better at detecting the general type and severity of lung disorder than at defining the specific cause of problems; however, these tests can be used to diagnose some specific disorders, such as asthma.
Lung Volume and Flow Rate Measurements:
The assessment of a lung disorder often involves testing how much air the lungs can hold as well as how much and how quickly air can be exhaled. These measurements are made with a spirometer, which consists of a mouthpiece and tubing connected to a recording device. The person's lips should be held tightly around the mouthpiece, and nose clips should be worn to ensure that all the air inhaled or exhaled goes through the mouth. A person inhales deeply, then exhales forcefully as quickly as possible through the tubing while measurements are taken. The volume of air inhaled and exhaled and the length of time each breath takes are recorded and analyzed. Often, the tests are repeated after a person takes a drug that opens the airways of the lungs (bronchodilator).
A simpler device for measuring how quickly air can be exhaled is the small, hand-held peak flow meter. After inhaling deeply, a person blows into this device as hard as possible.
Lung volume measurements reflect the stiffness or elasticity of the lungs and rib cage as well as the strength of respiratory muscles. The lungs are abnormally stiff in disorders such as pulmonary fibrosis, and the chest wall is abnormally stiff in disorders such as curvature of the spine (scoliosis). Various neuromuscular disorders can cause weakness of the diaphragm and other respiratory muscles, such as myasthenia gravis (see Peripheral Nerve Disorders: Myasthenia Gravis) and Guillain-Barré syndrome (see Peripheral Nerve Disorders: Guillain-Barré Syndrome).
Flow rate measurements reflect the degree of narrowing or obstruction of the airways. The measurements are abnormal in obstructive disorders, such as chronic obstructive pulmonary disease and asthma.
Flow Volume Testing:
Most spirometers can continuously display lung volumes and flow rates during a forced breathing maneuver. These flow rates can be particularly helpful in detecting abnormalities that partially block the voice box (larynx) and windpipe (trachea).
Muscle Strength Assessment:
The strength of the respiratory muscles can be measured by having the person forcibly inhale and exhale against a pressure gauge. Disorders that weaken the muscles, such as muscular dystrophy and amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease), make breathing more difficult and result in low pressures during inhalation and exhalation.
Diffusing Capacity Measurement:
A diffusing capacity test can estimate how efficiently oxygen is transferred from the air sacs of the lungs (alveoli) to the bloodstream. Because the diffusing capacity of oxygen is difficult to measure directly, a person inhales a small amount of carbon monoxide, holds the breath for 10 seconds, and then exhales into a carbon monoxide detector.
If the test shows that carbon monoxide is not well absorbed, oxygen will not be exchanged normally between the lungs and the bloodstream either. The diffusing capacity is characteristically abnormal in people with pulmonary fibrosis, in those with disorders affecting the blood vessels of the lungs, and in some people with chronic obstructive pulmonary disease.
Maximal Voluntary Ventilation (MVV):
MVV measures a person's maximum ability to breathe. This test is done in the sitting position. A person is instructed to breathe as rapidly and deeply as possible through a spirometer for a predetermined period of time, usually 15 to 30 seconds. The volume of air moved over that period of time is measured. This test is dependent upon the ability of a person to cooperate but is useful in certain situations.
Breathing is usually automatic and controlled by centers in the brain that respond to the levels of oxygen and carbon dioxide in the blood. However, in some people, breathing may stop for prolonged periods, especially during sleep—a condition called sleep apnea (see Sleep Apnea). The best test for sleep apnea consists of monitoring brain wave activity (with an electroencephalogram, also called an EEG), the oxygen concentration in the blood (with pulse oximetry, which uses a sensor clipped on a finger or an earlobe), the movement of air during breathing (using a device placed in one nostril), chest wall motion, and sometimes other measurements. Combining all these measurements as part of a single test is called a polysomnogram. Because polysomnography is not always available, other tests are sometimes used during sleep to see whether a person has sleep apnea.
Arterial Blood Gas (ABG) Analysis
Arterial blood gas tests measure the levels of oxygen and carbon dioxide in the arterial blood and determine the acidity (pH) of the blood. Taking a sample from an artery requires skill and may cause a few minutes of discomfort. Usually the sample is taken from an artery in the wrist (radial artery). Oxygen, carbon dioxide, and acidity levels are important indicators of lung function because they reflect how well the lungs are getting oxygen into the blood and getting carbon dioxide out of it.
Oxygenation of the blood can be monitored using a sensor placed on a finger or an earlobe—a procedure called pulse oximetry. When a doctor also needs a carbon dioxide or blood acidity measurement (for example, in certain people who are seriously ill), an arterial blood gas measurement is needed.
Chest x-rays are routinely taken from the back to front. Usually a view from the side is taken also. Chest x-rays provide a good outline of the heart and major blood vessels and usually can reveal a serious disorder in the lungs, the adjacent spaces, or the chest wall, including the ribs. For example, chest x-rays can clearly show most pneumonias, lung tumors, chronic obstructive pulmonary disease, a collapsed lung (atelectasis), and air (pneumothorax) or fluid (pleural effusion) in the pleural space. Although chest x-rays seldom give enough information to determine the exact cause of the abnormality, they can help a doctor determine whether and which other tests are needed to make a diagnosis.
Computed tomography (CT—see Common Imaging Tests: Computed Tomography) of the chest provides more detail than a plain x-ray. With CT, a series of x-rays is analyzed by a computer, which then provides several views in different planes, such as longitudinal and cross-sectional views. During CT, a radiopaque dye may be injected into the bloodstream or given by mouth to help clarify certain abnormalities in the chest.
Magnetic resonance imaging (MRI—see Common Imaging Tests: Magnetic Resonance Imaging) also produces highly detailed pictures that are especially useful when a doctor suspects blood vessel abnormalities in the chest, such as an aortic aneurysm. Unlike CT, MRI does not use radiation.
Ultrasonography (see Common Imaging Tests: Ultrasonography) creates a picture from the reflection of sound waves in the body. Ultrasonography is often used to detect fluid in the pleural space (the space between the two layers of pleura covering the lung and inner chest wall). Ultrasonography can also be used for guidance when using a needle to remove the fluid.
Nuclear lung scanning (see Common Imaging Tests: Radionuclide Scanning) is particularly useful in detecting blood clots in the lungs (pulmonary emboli); it also may be used during the preoperative evaluation of people who have lung cancer. This type of imaging uses minute amounts of short-lived radioactive materials to depict the flow of air and blood through the lungs. Usually, the test is done in two stages. In the first stage (lung perfusion scan), a radioactive substance is injected into a vein, and a scanner creates a picture of how it is distributed throughout the blood vessels of the lung. If the perfusion scan is abnormal, a second stage is necessary (lung ventilation scan); the person inhales a radioactive gas, and a scanner creates a picture of how the gas is distributed throughout the lungs.
Pulmonary artery angiography (also called pulmonary artery arteriography) is done by injecting a radiopaque dye into the pulmonary artery and using conventional x-rays to view the dye in the lungs (see Common Imaging Tests: Angiography). Angiography is used most often when pulmonary embolism is suspected, usually on the basis of abnormal lung scan results, and is considered the best test for diagnosing or excluding pulmonary embolism. Increasingly, angiography of the pulmonary arteries is being done instead with pictures obtained from CT (CT angiography). CT angiography is less invasive, because in this procedure, radiopaque dye is injected into a small peripheral vein rather than a central pulmonary artery.
Positron emission tomography (PET—see Common Imaging Tests: Positron Emission Tomography) scanning may be used when cancer is suspected. This radiographic imaging technique relies on different metabolic rates of malignant (cancerous) compared with benign (noncancerous) tissues. Glucose molecules are combined with a compound that is visible using PET. These molecules are injected intravenously, where they accumulate in rapidly metabolizing tissue (such as in cancerous lymph nodes), making these tissues visible on PET scans. Benign growths usually do not accumulate enough molecules to be visible.
In thoracentesis, fluid that has collected abnormally in the pleural space (pleural effusion—see Pleural and Mediastinal Disorders: Pleural Effusion) is removed. The two principal reasons to perform thoracentesis are to obtain a fluid sample for diagnostic testing or to relieve shortness of breath caused by fluid compressing lung tissue.
During the procedure, the person sits comfortably and leans forward, resting the arms on supports. A small area of skin on the back is cleaned and numbed with a local anesthetic. Then a doctor inserts a needle between two ribs into the chest cavity, but not into the lung, and withdraws some fluid into a syringe. Sometimes the doctor uses ultrasound for guidance (to determine where to insert the needle). The collected fluid is analyzed to assess its chemical makeup and to determine whether bacteria or cancerous cells are present.
If a large volume of fluid has accumulated, it may need to be removed through a plastic catheter and it may be necessary to use a fluid container that is larger than a syringe. The fluid may need to be drained over several days, in which case a larger tube (chest tube or drainage catheter) is left in the chest and suctioned continuously.
The risk of complications during and after thoracentesis is low. A person may feel some pain as the lung fills with air and expands against the chest wall or may feel the need to cough. Also, a person may briefly feel light-headed and short of breath. Other possible complications include puncture of the lung with leakage of air into the pleural space (pneumothorax), bleeding into the pleural space or chest wall, fainting, infection, puncture of the spleen or liver, and, if a large amount of fluid that has been present for weeks to months is withdrawn rapidly, accumulation of fluid within the lung itself (pulmonary edema). A chest x-ray may be performed after the procedure to determine whether any of these complications has occurred.
Needle Biopsy of the Pleura or Lung
If thoracentesis does not uncover the cause of a pleural effusion (a fluid buildup in the space between the two layers of the pleura), a doctor may do a pleural biopsy. First, the skin is cleaned and anesthetized as for thoracentesis. Then using a larger cutting needle, a doctor takes a small sample of tissue from the pleura and sends it to a laboratory to be examined for signs of disorders, such as cancer or tuberculosis. About 80 to 90% of the time, a pleural biopsy is accurate in diagnosing tuberculosis, but it is less accurate for diagnosing cancer and other disorders.
If a tissue specimen needs to be obtained from a lung tumor, a doctor may do a needle biopsy. After anesthetizing the skin, a doctor, often using chest computed tomography (CT) for guidance, directs a biopsy needle into a tumor and obtains cells or a small piece of tissue to be sent to the laboratory for analysis. If a lung infection is suspected, tissue can also be sent for culture (a procedure in which a tissue sample is placed in a container containing nutrients and the container is observed to detect bacterial growth). Complications of pleural and lung biopsies are similar to those for thoracentesis.
Bronchoscopy is a direct visual examination of the voice box (larynx) and airways through a flexible viewing tube (a bronchoscope). A bronchoscope has a light at the end that allows a doctor to look down through the larger airways (bronchi) into the lungs.
A bronchoscope can be used to investigate the source of bleeding in the lungs. If a doctor suspects lung cancer, the airways can be examined and specimens can be taken from any areas that look cancerous. Bronchoscopy can be used for collecting the organisms causing pneumonia that are difficult to collect and identify in other ways. Bronchoscopy is especially helpful for obtaining specimens from the lungs in people who have AIDS and other immune deficiencies. When people have been burned or have inhaled smoke, bronchoscopy helps doctors assess for burns and smoke injury of the larynx and airways. Bronchoscopy can help a doctor treat certain conditions. For example, the bronchoscope can also be used to remove secretions, blood, pus, and foreign bodies; to place drugs in specific areas of the lung; and as a guide over which a tube can be inserted to assist breathing (tracheal intubation).
For at least 4 hours before bronchoscopy, the person should not eat or drink. A sedative is often given to ease anxiety, and atropine may be given to reduce the risks of spasm of the voice box and slowing of the heart rate, which sometimes occur during the procedure. The throat and nasal passage are sprayed with an anesthetic, and the bronchoscope is passed through a nostril and into the airways of the lungs.
Bronchoalveolar lavage is a procedure doctors can use to collect specimens from the smaller airways and alveoli that cannot be seen through the bronchoscope. After wedging the bronchoscope into a small airway, a doctor instills salt water (saline) through the instrument. The fluid is then suctioned back into the bronchoscope, bringing cells and any bacteria with it. Examination of the material under the microscope helps in diagnosing infections and cancers. The fluid can also be placed into containers containing special nutrients and left alone for a period of time to see if bacteria grow (culturing), which is a better way to diagnose infections.
Transbronchial lung biopsy involves obtaining a specimen (pieces) of lung tissue by using forceps passed through a bronchoscope. The forceps is threaded through a channel in the bronchoscope into progressively smaller airways until reaching the area of concern. A doctor may use a fluoroscope (an imaging device that uses x-rays to show internal body structures on a screen) for guidance in identifying the area of concern. Such guidance can also decrease the risk of accidentally perforating the lung and causing leakage of air into the pleural space (pneumothorax—see Pleural and Mediastinal Disorders: Pneumothorax). Although transbronchial lung biopsy increases the risk of complications during bronchoscopy, it provides additional diagnostic information and may make major surgery unnecessary.
Transbronchial needle aspiration is sometimes done. In this procedure, a needle is passed through the bronchoscope into the bronchial wall. The needle may be passed through the wall of a large airway under direct visualization or through the wall of a small airway using an x-ray machine for visualization. A doctor may be able to extract cells from suspicious lymph nodes to examine under a microscope.
After bronchoscopy, the person is observed for several hours. If a tissue specimen was removed, a chest x-ray may be taken to check for complications, such as bleeding or leakage of air into the pleural space (pneumothorax).
Thoracoscopy is the visual examination of the lung surfaces and pleural space through a viewing tube (a thoracoscope). The most common means for obtaining a sample of lung tissue for a biopsy is with a thoracoscope. A thoracoscope also may be used in treating accumulations of fluid in the pleural space (pleural effusions).
The person usually is given general anesthesia for this procedure. Then a surgeon makes up to three small incisions in the chest wall and passes a thoracoscope into the pleural space; this allows air to enter, collapsing the lung. Besides being able to view the lung surface and pleura, a doctor may take samples of tissue for microscopic examination and culture. In certain cases, the doctor may give drugs through the thoracoscope to prevent a reaccumulation of fluid in the pleural space. After the thoracoscope is removed, a chest tube is inserted to remove air that entered the pleural space during the procedure, enabling the collapsed lung to reinflate.
Complications are similar to those for thoracentesis and needle biopsy of the pleura. However, this procedure is more invasive, leaves a small wound, and requires hospitalization.
Mediastinoscopy is the direct visual examination of the area of the chest between the two lungs (the mediastinum) through a viewing tube (mediastinoscope). The mediastinum contains the heart, trachea, esophagus, thymus, and lymph nodes. Nearly all mediastinoscopies are used to diagnose the cause of enlarged lymph nodes deep in the chest or to evaluate how far lung cancer has spread before chest surgery (thoracotomy) is done.
Mediastinoscopy is done in an operating room with the person under general anesthesia. A small incision is made in the notch just above the breastbone (sternum). The instrument then is passed down into the chest in front of the windpipe, allowing the doctor to observe the contents of the mediastinum next to the windpipe and to obtain specimens for diagnostic tests if necessary. Complications are similar to those for thoracentesis and needle biopsy of the pleura.
Thoracotomy is an operation in which the chest wall is opened to view the internal chest organs, to obtain samples of tissue for laboratory examination, and to treat disorders of the lungs, heart, or major arteries.
Thoracotomy is a major operation and therefore is used less often than other diagnostic techniques. Thoracotomy is used when procedures such as thoracentesis, bronchoscopy, or mediastinoscopy fail to provide adequate information. The lung problem is identified in more than 90% of people who undergo this operation because the sample site can be seen and selected and because large tissue samples can be taken. Thoracotomy is also often used when cancerous tissue is to be removed from the lung. Thoracotomy allows a surgeon to see and remove all involved tissue.
Thoracotomy requires general anesthesia in an operating room. An incision is made in the chest wall, and tissue samples of the lung are removed for microscopic examination. If specimens are to be taken from areas in both lungs, the breastbone is often split. If necessary, a lung segment, a lung lobe, or an entire lung can be removed.
A chest tube is inserted into the pleural cavity and left in place for 24 to 48 hours afterward. The person usually stays in the hospital for several days. Complications include infection, persistent bleeding, and a persistent leakage of air into the pleural space (pneumothorax).
Suctioning is used to obtain secretions and cells from the trachea and large bronchi. It is used to obtain specimens for microscopic examination or culture and to help clear secretions from the airways when cough is inadequate.
One end of a long, flexible, clear plastic tube is attached to a suction pump; the other end is passed through a nostril or the mouth and into the trachea. When the tube is in position, suction is applied in intermittent bursts lasting 2 to 5 seconds. With people who have a tube in the neck that leads to the trachea (tracheostomy) or a tube in the nose or mouth that leads to the trachea (endotracheal tube), the suctioning tube can be inserted directly into the tube that leads to the trachea. Sometimes inserting some salt water into the tube that leads to the trachea eases removal of secretions and cells via suctioning.
Last full review/revision November 2006 by James H. Fisher, MD