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Thursday, October 15, 2009

The PFT Lexicon

These are some of the most common terms regarding spirometry and pulmonary function testing.

Pulmonary Function Test (PFT): Synonym: Spirometry. This is a test where you breath into a mouthpiece to a device called a spirometer. The Spirometer measures your lung function, determines if you have lung disease and if you do how severe your lung disease is.
  • It's a test that uses a spirometer that measures airflow, usually before and 15 minutes after using rescue medicine. The test is not used to diagnose but to determine the type of airway disease a patient has (obstructive or restrictive), the degree or severity of airflow obstruction, and whether it is reversible over the short term.
  • It measures the maximal volume of air forcibly exhaled from the point of maximal inhalation (FVC) and the volume of air exhaled during the first second of this meneuver (FEV1). It is valuable for children greater than 5 years old (some children cannot do it until they are 7).
  • it can help a doctor determine if shortness-of-breath is due to restrictive diseases like obesity, pregnancy, pneumonia, cancer, pleural effusion, etc., or an obstructive
    like COPD and asthma. Also, it can also be used to differentiate COPD from asthma. Thus, if you are considering Asthma or COPD, this is a great test to rule out other disease processes.
  • A test used most often for assessing the risk of future adverse events in asthma and COPD patients. It is the best test for determining severity of obstruction.
  • Patient's perception of airflow obstruction is highly variable, and spirometry sometimes reveals obstruction much more severe than would have been estimated from the history and physical examination.
  • For diagnostic purposes, spirometry is generally recommended over measurement with a peak flow meter, because values for each brand of peak flow meter can be specific to that particular brand. (peak flow meters should be used for patient monitoring only, not diagnosing).
  • Followup spirometrymeasures are indicated as asthma control improves.
Spirometry frequency: Spirometry is recommended at the following frequencies: (1) at the time of initial assessment, (2) after treatment is initiated and symptoms and PEF have stabilized, (3) during periods of progressive or prolonged loss of asthma control, and (4) at least every 1-2 years.
Abnormalities of lung function: Are considered as restrictive or obstructive defects.

Restrictive Diseases:
  • Is indicated by proportianately reduced FVC (or FEV6 in adults) with a normal or increased FEV1/FVC (or FEV1/FEV6) ratio.
  • are caused by anything that decreases the lungs ability to expand and properly ventilate the patient by getting rid of CO2 from the blood and adding O2 to the blood stream. The following are restrictive diseases:Sarcoidosis, pulmonary, fibrosis, pneumonia, cancer, granulomatous disorder, obesity, pregnancy, pneumothorax, pleural effusion, kyphoscoliosis, emphysema (loss of lung tissue), Neuromuscular and neurologic (Guillain-Barre Syndrome, polio myelitis or myasthenia gravis), Pickwickian syndrome, and Pleurisy.
Obstructive Diseases:  a) Is indicated by a reduced ratio of FEV!/FVC or FEV1/FEV6, b) Airway obstruction is anything that causes narrowing or blocking of the Air passages that results in a decreased exhaled airflow. The causes of airway obstruction are as follows:
  • Upper Airway obstruction: Rhinitis/ pharyngitis, Diptheria, Croup,
    Epiglottitis, Obstructive Sleep Apnea, Laryngeal paralysis, Tracheal
    stenosis, Tracheal malacia, Foreign body, Tetanus
  • Lower Airway obstruction: Emhysema, Chronic bronchitis, Asthma, Cystic
    fibrosis, bronchiectasis, Bronchiolitis, Bronchial cmpression (tumor, lymph
    nodes), Endobronchial tumors, Foreign body, and Mucus plugging.
Significant reversibility: Is indicated by an increase in FEV1 of greater than 200 ml and greater than 12% from the baseline measure of inhalation of rescue medicine (Albuterol breathing treatment or 2 puffs Albuterol MDI).
Severity of abnormality of spirometric values: is evaluated by comparison of the patient's results with reference values based on age, height, sex and race.

Impairment: An assessment of the frequency of intensity of symptoms and functional limitations that a patient is experienciencing or has recently experienced.

Risk: is an estimate of the likelihood of either asthma or COPD exacerbations or of progressive loss of pulmonary function over time. Some degree of the risk of exacerbations can be obtained from the medical history and patient assessment. Patients who have had exacerbations requiring ER visits, hospitalization, or ICU admissions, especially in the past year, have a great risk of exacerbations in the future.

Dyspnea tolerance: The inibility of a patient to notice when he or she is dyspneic (feeling like he or she cannot get air in). Patients who perceive the degree of airflow poorly. Usually they are hardluck asthmatics who are short of breath so often they lose the objective means of perceiving degree of dyspnea. Or, patients who have unconsciously accomodated to their symptoms. Spirometry or peak flow monitoring are useful tools in monitoring asthma for these patients.

Percent predicted: This is a formula for determing the predicted normal for a person based on age, height and weight and body mass index. You can find a calculator for finding your percent predicted by clicking here.

FVC: The maximum volume (in liters) of air that you can exhale after taking in as deep a breath as you can. FEV1 and FEV6 are both calculated from the FVC. In severe cases where airway obstruction is present (asthma, COPD) the FVC may be reduced due to air trapping of air in the lungs.


  1. A measurement made during a spirometry test which measures the amount of exhaled air during the first second of FVC. One is considered to have "airflow obstruction" when this value is low in comparison to patient predicted. This measurement is considered the best way of diagnosing obstructive disorders because it cannot be faked.
  2. The post bronchodilator FEV1 can be used to determine lung growth paterns over time.
  3. A low FEV1 indicates current obstruction and risk for future exacerbation.
  4. A baseline FEV1 (before using bronchodilator) that is lower than normal but that increases by at least 12-15% 15 minutes after inhaling rescue medicine (Albuterol) is indicitive of airflow obstruction that is reversible. This appears to be a useful measure indicating risk of exacerbations.
  5. Normal FEV1 is 80% of the predicted value. The predicted value is based on a formula using age, weight and height.

FEV1/FEV6: A measurement made during a spirometry test which measures the amount of exhaled air during the first six second of the meneuver. This test is used as a substitute for FEV1 in adults who have significant air trapping and who get "light headed" while trying to forcibly do spirometry.

FEV1/FVC: FEV1 expressed as a percent of the predicted value or as a proportion of the forced vital capacity. This appears to be a more sensitive measure of severity in the impairment domain, especially in children. It may be more reliable in assessing asthma severity in children as opposed to FEV1 because it is more sensitive.

FEV0.5: Used instead of FEV1 in children because some asthmatic children have a hard time exhaling for a full second.

FEV 0.75: Used instead of FEV1 in children because some asthmatic children have a hard time exhaling for a full second.

Percent change: This is used to determine how much a patient's lungs improve following a bronchodilator. % change =(post-test FEV1 - Pretest FEV1/ Pretest FEV1 X 100. An increase in expiratory flow greater than 15% indicates beneficial effects of the medication.

Peak flow meter: This is a device used to determine "how well your lungs are functioning," according to National Jewish Health. This is recommended as part of the asthma action plan for children and anyone who has difficulty perceiving asthma symptoms. It should be noted that peak flows are a great tool for monitoring asthma status, but should not be used to diagnose.

Diffusion capacity: The surface area of the lung where oxygen can 'get in' to the body is very limited in people with COPD. For example, in patients with emphysema, both the small air sacs (alveoli) and the small blood vessels (capillaries) that run past them are destroyed, leaving a smaller area for oxygen to come in contact with the oxygen-carrying proteins in the blood (hemoglobin).

"Diffusing capacity" refers to the capacity of the lung to release carbon dioxide and take in fresh oxygen. This lung function test measures the amount of area of the lung where oxygen can move into the blood vessels. It is performed much like the spirometry test, except that during this test, you breathe in a small amount of carbon monoxide gas. Carbon monoxide is used because it binds very quickly and well with hemoglobin and the amount is easily measured.

The test is usually performed during a single breath. To measure the diffusing capacity, you have to have certain minimal lung volumes and be able to hold your breath for a brief period of time. Also since diffusing capacity varies with the concentration of hemoglobin in the blood, the values obtained need to be revised if your hemoglobin level is not normal. (Definition by

Severity of obstruction: How severe is your asthma? How severe is your COPD? This can be determined by your pre-bronchodilator percent of predicted FEV1. Degree of severity:
  • Normal: FEV1 80% of predicted value or greater
  • Mild: FEV1 65-79% of predicted value
  • Moderate: FEV1 50-64% of predicted value
  • Severe: 35-49% of predicted value
  • Very severe: FEV1 below 35% of predicted value
Degree of Reversibility: (as determined by pre and post bronchodilator FEV1):
  • Slight: 15-25% change
  • Moderate: 25-50% change
  • Marked: Greater than 50% change


Steve said...

Green, non purulent secretions could also indicate dehydration.

Thanks for the refresher course. No wonder I don't miss my job:-)

Anonymous said...

hey thanx! What about all the doctors ordering PFTs prior to loading patients with Amiodarone? I really should look it up because all my patients that are going to be on Amiodarone the MDs want to know the PFT results first. It is like a pulmonary MD versus cardiology MD. (with pulm wanting the PFTs done before the cardio loads the amio)

Anonymous said...

An increase in FEV1 and/or FVC of greater than 200 ml and greater than 12% from the baseline is considered a significant response..... you forgot to add the and/or FVC... For seejanenurse- Amiodarone can cause pulmonary toxicity. It was a little more common when they were using much higher doses awhile back. The docs are looking to get a baseline DLCO (lung diffusion of carbon monoxide) before they start amiodarone. If the patient begins to have any pulmonary symptons the they should have the DLCO checked again.

Christy said...

can you please tell me how to figure an FEF 25-75 and MVV using predicted and observed values?