Diagnosis
A doctor usually can tell whether a person has a lung or airway disorder based on the medical history and physical examination. Diagnostic procedures are used to confirm the diagnosis, determine the extent and severity of the disease, and help in planning treatment.
Medical History and Physical Examination
A doctor first asks the person about symptoms. Chest pain, shortness of breath (dyspnea), cough, coughing up of blood (hemoptysis), wheezing, and a crowing sound while breathing (stridor) suggest lung or airway disease. Other, more general symptoms, such as fever, weakness, fatigue, and a general feeling of illness or discomfort (malaise), may also point to lung or airway disease.
Next, the doctor asks the person about past infections; previous exposure to chemicals; use of drugs, alcohol, and tobacco; home and work environments; travels; and recreational activities. A doctor also asks the person about whether family members have had lung or airway disease and any other diseases that may affect the lungs or airways.
During the physical examination, a doctor notes the person's weight and overall appearance. The person's general mood and feeling of wellbeing, which also may be affected by lung or airway disease, are also noted. A doctor may ask a person to walk around or climb a flight of stairs to see if either activity causes shortness of breath.
Assessing skin color is important because pallor or cyanosis may indicate anemia or poor blood flow. These findings can indicate that the skin is receiving inadequate oxygen from the blood because of lung or airway disease. Fingers are examined for evidence of clubbing.
A doctor observes the chest to determine if the breathing rate and movements are normal. By tapping (percussing) the chest, a doctor can determine if the lungs are filled with air, which is normal, or if they contain fluid, which is abnormal. Using a stethoscope, a doctor also listens to the breath sounds to determine whether airflow is normal or obstructed and whether the lungs contain fluid as a result of respiratory failure or pneumonia. In addition to examination of the chest, a complete physical examination may be needed, because many disorders not related to the lungs first present with evidence of lung problems (for example, the presence of pleural fluid, which may represent metastasis from an abdominal tumor).
Pulmonary Function Testing
Tests for lung disease are designed to give an accurate assessment of how well the lungs are working. Each test assesses a different aspect of lung function.
One group of tests, called 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 type and severity of lung disorders than at defining the specific cause of problems. The tests are used to diagnose some diseases, however, including asthma. Pulmonary function tests include lung volumes and flow rate measurements, flow volume testing, muscle strength assessment, and diffusing capacity measurement.
Lung Volume and Flow Rate Measurements: The assessment of lung disease 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. A person inhales deeply, then exhales forcefully as quickly as possible through the tubing while measurements are taken. The volume of air inhaled or 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).
See the figure Using a Spirometer.
A simpler device for measuring how quickly air can be exhaled is the peak flow meter. After inhaling deeply, a person blows into a small, handheld device as hard as possible. This inexpensive device helps people who have asthma or other lung diseases monitor the severity of their disease and the effectiveness of treatment at home.
Lung volume measurements reflect the stiffness or elasticity of the lungs and rib cage as well as the strength of respiratory muscles. The measurements are abnormally low in disorders such as pulmonary fibrosis, curvature of the spine (scoliosis), and a variety of neuromuscular disorders that cause weakness of the diaphragm and other respiratory muscles, such as myasthenia gravis (see Section 6, Chapter 95) and Guillain-Barré syndrome (see Section 6, Chapter 95).
Flow rate measurements reflect the degree of narrowing or obstruction of the airways. The measurements are abnormal in obstructive disorders, such as bronchitis, emphysema, and asthma.
Flow Volume Testing: Most newer 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. A disease that weakens the muscles, such as muscular dystrophy, makes breathing more difficult and results in low pressures during inhalation and exhalation. This test also helps predict whether a person on a ventilator will be able to breathe independently after being taken off it.
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, emphysema, and disorders affecting the blood vessels of the lungs.
Sleep Studies
Breathing is usually automatic and controlled by centers in the brain that respond to the levels of oxygen and carbon dioxide in the blood. If this control is abnormal, breathing may stop for prolonged periods, especially during sleep--a condition called sleep apnea (see Section 6, Chapter 81). The 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 utilizes an electrode clipped on a finger or an earlobe), the movement of air during breathing (using a device placed in one nostril), and chest wall motion. Combining all these measurements as part of a single test is called a polysomnogram.
Arterial Blood Gas Analysis
Arterial blood gas tests measure the levels of oxygen and carbon dioxide in the arterial blood. A sample from a vein cannot be used. Taking a sample from an artery requires skill and may cause a few minutes of discomfort for the person. Usually the sample is taken from an artery in the wrist (radial artery). Oxygen and carbon dioxide 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.
Oxygen concentrations can be monitored using an electrode placed on a finger or an earlobe--a procedure called oximetry. When a person is seriously ill or a doctor also needs a carbon dioxide and blood acidity measurement, an arterial sample is needed.
Chest Imaging
Routinely, chest x-rays are taken from the back to front, but sometimes doctors supplement this view with a side view. Chest x-rays provide a good outline of the heart and major blood vessels and usually can reveal a serious disease in the lungs, the adjacent spaces, and the chest wall, including the ribs. For example, chest x-rays can clearly show pneumonia, lung tumors, emphysema, 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 which other tests are needed to make a diagnosis.
Computed tomography (CT) 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 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) 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.
Ultrasound creates a picture on a monitor from the reflection of sound waves in the body. Ultrasound 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). Ultrasound can also be used for guidance when using a needle to aspirate the fluid.
Nuclear lung scanning 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 ventilation scan), a person inhales a radioactive gas, and a scanner creates a picture of how the gas is distributed throughout the airways and the alveoli. In the second 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. This type of imaging is particularly useful in detecting blood clots in the lungs (pulmonary emboli); it also may be used during the preoperative assessment of people who have lung cancer.
Angiography accurately shows the blood supply to the lungs. Radiopaque dye, which can be seen on x-rays, is injected into a blood vessel, and pictures are taken of the arteries and veins in the lungs. Angiography is used most often when pulmonary embolism is suspected, usually on the basis of abnormal lung scan results. Pulmonary artery angiography is considered the definitive test for diagnosing and for ruling out pulmonary embolism.
Positron Emission Tomography
Positron emission tomography (PET) scanning is a radiographic imaging technique that relies on the different metabolic rates of malignant (cancerous) versus benign (noncancerous) tissues. This procedure may be used when a cancer is suspected. Glucose molecules that are tagged with a tracer are injected intravenously; these molecules accumulate in rapidly metabolizing tissue (such as in malignant lymph nodes) and can be detected using PET. Benign growths usually do not accumulate enough activity to be detected.
Thoracentesis
In thoracentesis, fluid that has collected abnormally in the pleural space (pleural effusion (see Section 4, Chapter 52)) is removed with a needle and syringe, so it can be analyzed. The two principal reasons to perform thoracentesis are to relieve shortness of breath caused by lung tissue compression or to obtain a fluid sample for diagnostic testing.
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 and withdraws some fluid into a syringe. Sometimes the doctor uses ultrasound for guidance while inserting 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. During thoracentesis, a doctor can also instill substances, such as doxycycline (an antibiotic derived from tetracycline) into the pleural space to prevent a reaccumulation of fluid.
The risk of complications during and after thoracentesis is low. Occasionally, a person may feel some pain as the lung fills with air and expands against the chest wall. 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 very rarely, accidental entry of air bubbles into the bloodstream (air emboli). A chest x-ray may be performed after the procedure to ensure that none 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 perform a pleural biopsy. First, the skin is 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 cancer or tuberculosis. About 85 to 90% of the time, a pleural biopsy is accurate in diagnosing these diseases.
If a tissue specimen needs to be obtained from a lung tumor, a doctor may perform 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. Tissue can also be sent for culture if a lung infection is suspected. Complications of pleural and lung biopsies are similar to those for thoracentesis.
Bronchoscopy
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.
See the figure Understanding Bronchoscopy.
Bronchoscopy can help a doctor make a diagnosis and treat certain conditions. A flexible bronchoscope can be used to remove secretions, blood, pus, and foreign bodies; to place drugs in specific areas of the lung; and to investigate the source of bleeding. If a doctor suspects lung cancer, the airways can be examined and specimens can be taken from any suspicious areas. Bronchoscopy is used for collecting the organisms causing pneumonia and 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.
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 flexible 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; culturing the fluid is a better way to diagnose infections. Bronchoalveolar lavage can also be used to treat pulmonary alveolar proteinosis (see Section 4, Chapter 50) and other conditions.
Transbronchial lung biopsy involves obtaining a specimen of lung tissue through the bronchial wall. A doctor removes pieces of tissue from a suspicious area by passing a biopsy instrument through a channel in the bronchoscope and then through the wall of a small airway and into the suspicious area of lung. A doctor may use a fluoroscope for guidance in identifying the suspicious area. Such guidance can also decrease the risk of accidentally perforating the lung and causing leakage of air into the pleural space (pneumothorax (see Section 4, Chapter 52)). Although transbronchial lung biopsy increases the risk of complications, it often provides additional diagnostic information and may make major surgery unnecessary.
Transbronchial needle aspiration is sometimes performed. In this procedure, a needle is passed through the bronchoscope into the bronchial wall. A doctor may be able to extract cells from suspicious lymph nodes to sample.
After bronchoscopy, the person is observed for several hours. If a tissue specimen was removed, the doctor takes chest x-rays to check for complications, such as bleeding.
Thoracoscopy
Thoracoscopy is the visual examination of the lung surfaces and pleural space through a viewing tube (a thoracoscope). Thoracoscopy is the most common means for obtaining a sample of lung tissue for a biopsy. 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 and 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 and general anesthesia.
Mediastinoscopy
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 or to evaluate how far lung cancer has spread before chest surgery (thoracotomy) is performed.
Mediastinoscopy is performed 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, allowing the doctor to observe all the contents of the mediastinum and to obtain specimens for diagnostic tests if necessary. Complications are similar to those for thoracentesis and needle biopsy of the pleura.
Thoracotomy
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 diseases of the lungs, heart, or major arteries.
Although thoracotomy is the most accurate means of assessing lung diseases, it 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 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 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 air leak.
Suctioning
Suctioning is used to obtain secretions and cells from the trachea and large bronchi. It is used to obtain specimens for microscopic examination or a sputum 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 an artificial opening directly into the trachea (tracheostomy), the tube can be inserted directly into the trachea.
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