There are 3 main pulmonary function tests that measure how well the lungs take in and exhale air and how efficiently they transfer oxygen into the blood. Anchor Health Centers Pulmonary Medicine offers spirometry, lung volume measurement and diffusion capacity testing. Each of these tests provides different information about the health and functioning of the lungs and aids in the diagnosis and monitoring of respiratory diseases.
Spirometry
This test assesses how well the lungs exhale. When you breathe into a mouthpiece connected to an instrument called a spirometer, the spirometer measures the amount of air your lungs inhale and exhale over a specified time. Spirometry is especially useful for the evaluation of obstructive lung diseases such as asthma and chronic obstructive pulmonary disease (COPD).
The amount of air you exhale during a forced breath (called the “forced expiratory volume,” or FEV) and the total amount of air you exhale during the test (called the “forced vital capacity,” or FVC) are important measures that your physician will use to help diagnose your condition and monitor your response to treatment.
Lung Volume Measurement (Plethysmography)
Plethysmography is a painless procedure that measures total lung capacity. This type of test is especially helpful in evaluating restrictive lung diseases, in which a person cannot inhale a normal volume of air. Restrictive lung diseases may be caused by inflammation or scarring of lung tissue or by abnormalities in the muscles or skeleton of the chest wall.
During plethysmography, you will sit in an airtight chamber, insert a breathing tube into your mouth, and inhale and exhale a measured volume of air. Then a shutter will close off the breathing tube, and you will be directed to breathe against the shutter’s resistance. This will cause your chest volume to expand, and this increase in chest volume will slightly reduce the volume in the airtight chamber. In turn, the pressure inside the box will change, and these changes will allow a determination of your total lung volume.
Diffusion Capacity Testing (DLCO)
To determine how efficiently your lungs transfer oxygen from the air into your bloodstream, your physician may order a diffusion capacity test (also called DLCO, which stands for “diffusing capacity of the lung for carbon monoxide”).
Diffusion capacity is measured when you breathe carbon monoxide for a very short period, often just 1 breath. When you exhale, the concentration of carbon monoxide is measured. The difference in the amount inhaled and the amount exhaled allows your physician to estimate how rapidly gas (oxygen) can travel from your lungs into your blood. Reduced diffusion capacity may indicate interstitial pulmonary disease and fibrosis.
VO2 Max Test
The VO2 max (also called “oxygen uptake”) refers to the maximum volume of oxygen that you are able to metabolize during exercise. The higher your VO2 max, the longer you are able to exercise. VO2 max is measured by having you exercise on a treadmill or stationary bicycle while breathing through a 2-way valve system. Air will come in through the room but will be expired through sensors that measure the volume and oxygen concentration. The intensity of your exercise will be increased gradually by changing the speed or incline of the treadmill or the resistance on the bicycle. As the intensity of your workload increases, so will your oxygen consumption, until it reaches a peak. That peak is your VO2 max.
Anaerobic Threshold Test
The anaerobic threshold is the point at which your muscles are using more oxygen than your heart and lungs can deliver. When you reach this point, lactate starts to accumulate in your bloodstream. As with VO2 max, the higher your anaerobic threshold, the longer you are able to exercise. Measuring the anaerobic threshold involves taking blood samples (usually a pinprick to the thumb) during an exercise test while the intensity is progressively increased.
Oximetry Studies
Oximetry is a painless and noninvasive method for measuring the amount of oxygen in the blood. Usually it involves a clip placed on the ear or finger. The clip is attached to a device (the oximeter) that transmits a beam of light through the blood vessels and measures how much light is absorbed by oxygenated and deoxygenated blood.
A technologist may monitor your blood readings for several minutes while you are seated in order to evaluate your oxygen levels at rest, without supplemental oxygen. Then, if necessary, supplemental oxygen may be administered to bring your oxygenation to the level your physician has recommended.
Six-minute Walk Test
Your physician may also want to observe your oxygen levels in response to exertion. In this case, the technologist will have you walk with an oximetry sensor clip in place for 6 minutes. If your oxygen level falls, you may be asked to repeat the test with supplemental oxygen. This process may be repeated with increasing amounts of oxygen until your levels are sufficient.
Nocturnal Oximetry
Nocturnal oximetry is the measurement of blood oxygen levels during sleep. In some cases, this procedure may be done at home using a small, portable oximeter equipped with a memory module that can record a full night of oxygen and pulse rate data. Your physician may use this information to help diagnose pulmonary problems, sleep apnea, and other sleep-related disturbances.
Arterial Blood Gas with Co-Oximetry
Arterial blood gas is a common blood sample test that measures levels of oxygen and carbon dioxide in the blood to determine how well your lungs are working. An arterial blood gas test uses blood drawn from an artery, usually from the pulse site at the wrist. In addition to measuring the oxygen level and carbon dioxide in your blood, this test will measure the blood pH and bicarbonate levels. Abnormal values for oxygen, carbon dioxide and pH may indicate changes in lung function, heart and circulation function, kidney function, or other problems.
Co-Oximetry
Co-oximetry measures levels of compounds called carboxyhemoglobin and oxyhemoglobin in the blood. The purpose of co-oximetry is to detect oxygen deficiency at the level of the tissues (hypoxia). To perform this test, a painless co-oximeter clip will be placed on your finger and a beam of light will be transmitted through the blood.
Bronchial Provocation Test
Bronchial provocation testing is used to evaluate how sensitive the airways in your lungs are. In the first part of this procedure, you will undergo pulmonary function tests (usually spirometry) to measure how much air you can breathe in and out and how quickly you can breathe. Then you will inhale a spray compound called methacholine, followed by a repeat of the pulmonary function tests. The before-and-after results will be compared to determine what changes there are in your breathing.
Radiography
Radiography (X-ray) of the chest is the most commonly performed diagnostic X-ray. A chest X-ray is helpful for the evaluation of the lungs, heart and chest wall and can be used to aid in the diagnosis or monitoring of emphysema, pneumonia, heart disease, lung cancer, and a number of other medical conditions.
Computed Tomography (CT)
A computed tomography (CT) scan takes more detailed pictures than a typical X-ray. During a CT scan, cross-sectional images are generated of the thoracic structures in your body, including your lungs, heart, and the bones and tissues around these areas.
Blood Allergy Testing
An allergy is an abnormal immune response to certain substances called allergens. Common allergy symptoms include congestion, wheezing, coughing, itching, sneezing, shortness of breath, and runny nose. Allergies are linked to several respiratory illnesses, including sinusitis and asthma. A blood allergy test requires the collection of a small sample of blood, which is exposed to an allergen and then measured for a specific antibody response. Types of blood allergy tests performed may include enzyme-linked immunosorbent assay (ELISA), in vitro basophil histamine release assay, and radioallergosorbent test (RAST). The results of these tests may help your physician determine the cause of your symptoms.
Serologies for Interstitial Lung Disease
Interstitial lung disease (ILD) is a general term that includes more than 130 chronic lung diseases. Underlying symptoms of these individual diseases are often similar, so your physician may order serology (blood) testing to help diagnose a specific lung disease.