Pulmonary functions tests measure how much air you can move in and out of your lungs, how quickly you are are able to move the air and how effectively your lungs give oxygen to your blood and take away its carbon dioxide, (CO2).

Spirometry

The most common testing done is called "spirometry." It uses a machine called a spirometer to see how quickly and easily you can move air in and out of your lungs. This testing is an important tool used for assessing conditions such as asthma, pulmonary fibrosis, cystic fibrosis, and COPD. The values recorded and calculated via spirometry include:

• Forced vital capacity (FVC)- measures the amount of air you can exhale with force after you inhale as deeply as possible
• Peak expiratory flow (PEF)- measures how quickly you can exhale. It is usually measured at the same time as your forced vital capacity (FVC)
• Forced expiratory volume (FEV)- measures the amount of air you can exhale with force in one breath. (The amount of air you exhale may be measured at 1 second (FEV1), 2 seconds (FEV2), or 3 seconds (FEV3) )
• Forced expiratory flow 25% to 75%- measures the air flow halfway through an exhale
• Maximum voluntary ventilation (MVV)- measures the greatest amount of air you can breathe in and out during one minute
• Total lung capacity (TLC)- measures the amount of air in your lungs after you inhale as deeply as possible
• Residual volume (RV)- measures the amount of air in your lungs after you have exhaled completely
• Expiratory reserve volume (ERV)- measures the difference between the amount of air in your lungs after a normal exhale and the amount after you exhale with force
• Maximum voluntary ventilation (MVV)- measures the greatest amount of air you can breathe in and out during one minute

Gas Diffusion Tests

These tests measure the amount of oxygen and other gases that cross the air sacs of the lung into the blood stream per minute, showing how well gases are being absorbed into your blood from your lungs. These tests include:

• Arterial blood gases determine the amount of oxygen and carbon dioxide in your bloodstream as well as the relative acidity/alkalinity of your body's tissues
• Carbon monoxide diffusing capacity (also called transfer factor) measures how well your lungs transfer a small amount of carbon monoxide (CO) into the blood. This provides an estimate of how well a gas like oxygen is able to move from your lungs into your blood

Body Plethysmography

For this test, you sit inside a small airtight room called a plethysmograph booth and breathe through a mouthpiece while pressure and air flow measurements are collected.

This test may be used to measure:

• Total lung capacity (TLC)- the total amount of air your lungs can hold
• Residual volume (RV)- the amount of air left in your lungs after you exhale completely

Pulmonary function tests are done to diagnose the nature of a patient's breathing problems. They are very effective at detecting and measuring the effects of asthma, cystic fibrosis and COPD, and can detect the effect of inhaled substances on lung health, (e.g. occupational exposure to chemicals). PFTs are also used to evaluate lung function prior to surgery and to evaluate the effectiveness of treatments being given for respiratory diseases.

 

A methacholine challenge test (or, bronchial challenge test) is a test that helps in the diagnosis of asthma. The patient is asked to breathe in methacholine (or histamine), which will produce bronchoconstriction, or narrowing of the airways. The degree of narrowing can then be measured using spirometry. People with hyperactive airways, such as asthmatics, will react to lower doses of drug than would others.

In order to assess the reversible the condition is, a bronchodilator may be administered to counteract the effects before repeating the spirometry, ( a "reversibility" test). This type of test can help to distinguish between asthma and COPD.

The bronchial challenge test is physically demanding, and the inhaled drug could stimulate the airway sufficiently to cause violent coughing, making spirometry difficult to perform. This test should not be used in patients with severe airway obstruction since it could worsen the obstruction.

Determining the physical capability of a person with COPD is important to the planning of his clinical treatment. Because many are unable to perform more standard treadmill-based exercise tests, the 6-minute walk test was developed.

This test is generally done at the start of a pulmonary rehabilitation program or to evaluate a patient for lung surgery. It measures the distance a patient can walk quickly on a flat, hard surface in 6 minutes and reflects an individual's ability to perform regular daily activities.

Among the reasons for performing this test are:

• to measure the response to medical intervention in a patient with heart or lung disease
• to provide information about a patient's ability to perform activities of daily living
• to evaluate the response of the heart and lungs to exercise

Most 6-minute walk tests will be done both before and after therapeutic intervention to determine if the patient has seen improvement with the therapy.

Thoracentesis (pleural tap) is a procedure done to remove fluid or air from the pleural space, either to make a diagnosis of illness, or to treat a problem within that space. A cannula is carefully introduced into the chest after placement of local anesthesia. The location that is best for the introduction will vary depending upon the location and nature of the problem.

This procedure is needed when unexplained fluid accumulates in the chest cavity outside the lung. In nearly all cases analysis of fluid removed will provide useful information. If there is a large amount of fluid present, then this procedure may also improve the comfort of the patient comfort and make breathing more efficient.

The most common causes of pleural effusions are cancer, congestive heart failure and lung infection (pneumonia).

Once fluid is removed it is first tested to see if it is a "transudate" or "exudate."

Transudate=

• pleural fluid to serum total protein ratio of less than 0.5
• pleural fluid to serum LDH ratio < 0.6
• absolute pleural fluid LDH < 200 IU

An exudate is any fluid that filters from the circulatory system into lesions or areas of inflammation. Its composition generally includes dissolved solutes of the blood, such as plasma proteins, white blood cells, platelets or red blood cells.

Causes for exudates include:

• hemorrhage
• Inflammation
• cancer
• infection
• connective tissue disease
• endocrine disease

Causes for transudates include:

• congestive heart failure
• low serum protein
• cirrhosis
• atalectasis
• nephrotic syndrome
• superior vena cava syndrome

A high amylase level indicates either acute or chronic pancreatitis, pancreatic pseudocyst that has dissected or ruptured into the pleural space or cancer.

The number of white blood cells can give an indication of infection and specific subtypes of white cells can also give clues as to the type on infection. If the effusion is indeed caused by infection, cultures of the fluid may yield the identity of the infectious organism.

Cytology is an important in identifying effusions produced by malignancy. The most common causes for pleural fluid are lung cancer, mesothelioma, and tumors that have spread from elsewhere.