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Pulmonary function testing (PFT) is a complete evaluation of the
respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies g ...
including patient history, physical examinations, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment. Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease. PFTs are normally performed by a pulmonary function technician, respiratory therapist, respiratory physiologist, physiotherapist,
pulmonologist Pulmonology (, , from Latin ''pulmō, -ōnis'' "lung" and the Greek suffix "study of"), pneumology (, built on Greek πνεύμων "lung") or pneumonology () is a medical specialty that deals with diseases involving the respiratory tract.
, or general practitioner.


Indications

Pulmonary function testing is a diagnostic and management tool used for a variety of reasons, such as: * Diagnose lung disease. * Monitor the effect of chronic diseases like
asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
, chronic obstructive lung disease, or
cystic fibrosis Cystic fibrosis (CF) is a rare genetic disorder that affects mostly the lungs, but also the pancreas, liver, kidneys, and intestine. Long-term issues include difficulty breathing and coughing up mucus as a result of frequent lung infections. Ot ...
. * Detect early changes in lung function. * Identify narrowing in the airways. * Evaluate airway bronchodilator reactivity. * Show if environmental factors have harmed the lungs * Preoperative testing


Neuromuscular disorders

Pulmonary function testing in patients with neuromuscular disorders helps to evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis.
Duchenne muscular dystrophy Duchenne muscular dystrophy (DMD) is a severe type of muscular dystrophy that primarily affects boys. Muscle weakness usually begins around the age of four, and worsens quickly. Muscle loss typically occurs first in the thighs and pelvis follow ...
is associated with gradual loss of muscle function over time. Involvement of respiratory muscles results in poor ability to cough and decreased ability to breathe well and leads to collapse of part or all of the lung leading to impaired gas exchange and an overall insufficiency in lung strength.


Tests


Spirometry

Spirometry includes tests of pulmonary mechanics – measurements of FVC, FEV1, FEF values, forced inspiratory flow rates (FIFs), and MVV. Measuring pulmonary mechanics assesses the ability of the lungs to move huge volumes of air quickly through the airways to identify airway obstruction. The measurements taken by the spirometry device are used to generate a pneumotachograph that can help to assess lung conditions such as: asthma, pulmonary fibrosis, cystic fibrosis, and chronic obstructive pulmonary disease.
Physician A physician (American English), medical practitioner (Commonwealth English), medical doctor, or simply doctor, is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through th ...
s may also use the test results to diagnose bronchial hyperresponsiveness to exercise, cold air, or pharmaceutical agents.


Helium Dilution

The helium dilution technique for measuring lung volumes uses a closed, rebreathing circuit. This technique is based on the assumptions that a known volume and concentration of helium in air begin in the closed
spirometer A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. A spirometer measures ventilation, the movement of air into and out of the lungs. The spirogram will identify two different types of abnormal ventilat ...
, that the patient has no helium in their lungs, and that an equilibration of helium can occur between the spirometer and the lungs.


Nitrogen Washout

The nitrogen washout technique uses a non-rebreathing open circuit. The technique is based on the assumptions that the nitrogen concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% oxygen and that the oxygen replaces all of the nitrogen in the lungs.


Plethysmography

The plethysmography technique applies
Boyle's law Boyle's law, also referred to as the Boyle–Mariotte law, or Mariotte's law (especially in France), is an experimental gas law that describes the relationship between pressure and volume of a confined gas. Boyle's law has been stated as: The ...
and uses measurements of volume and pressure changes to determine total lung volume, assuming temperature is constant. There are four lung volumes and four lung capacities. A lung's capacity consists of two or more lung volumes. The lung volumes are
tidal volume Tidal volume (symbol VT or TV) is the volume of air moved into or out of the lungs during a normal breath. In a healthy, young human adult, tidal volume is approximately 500 ml per inspiration or 7 ml/kg of body mass. Mechanical vent ...
(VT),
inspiratory reserve volume Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. Tidal breathing is normal, resting breath ...
(IRV),
expiratory reserve volume Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. Tidal breathing is normal, resting breath ...
(ERV), and residual volume (RV). The four lung capacities are
total lung capacity Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. Tidal breathing is normal, resting breath ...
(TLC), inspiratory capacity (IC),
functional residual capacity Functional residual capacity (FRC) is the volume of air present in the lungs at the end of passive expiration. At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm ...
(FRC) and vital capacity (VC).


Maximal respiratory pressures

Measurement of maximal inspiratory and expiratory pressures is indicated whenever there is an unexplained decrease in vital capacity or respiratory muscle weakness is suspected clinically. Maximal inspiratory pressure (MIP) is the maximal pressure that can be produced by the patient trying to inhale through a blocked mouthpiece. Maximal expiratory pressure (MEP) is the maximal pressure measured during forced expiration (with cheeks bulging) through a blocked mouthpiece after a full inhalation. Repeated measurements of MIP and MEP are useful in following the course of patients with neuromuscular disorders.


Diffusing capacity

Measurement of the single-breath diffusing capacity for
carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
(DLCO) is a fast and safe tool in the evaluation of both restrictive and
obstructive lung disease Obstructive lung disease is a category of respiratory disease characterized by airway obstruction. Many obstructive diseases of the lung result from narrowing (obstruction) of the smaller bronchi and larger bronchioles, often because of excessiv ...
.


Bronchodilator responsiveness

When a patient has an obstructive defect, a bronchodilator test is given to evaluate if airway constriction is reversible with a short acting beta-agonist. This is defined as an increase of ≥12% and ≥200 mL in the FEV1 or FVC.


Oxygen desaturation during exercise

The six-minute walk test is a good index of physical function and therapeutic response in patients with
chronic lung disease Chronic lung disease may refer to: * Asthma * Bronchopulmonary dysplasia * Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms ...
, such as
COPD Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...
or idiopathic pulmonary fibrosis.


Arterial blood gases

Arterial blood gas An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe an ...
es (ABGs) are a helpful measurement in pulmonary function testing in selected patients. The primary role of measuring ABGs in individuals that are healthy and stable is to confirm hypoventilation when it is suspected on the basis of medical history, such as respiratory muscle weakness or advanced
COPD Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...
. ABGs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation.


Risks

Pulmonary function testing is a safe procedure; however, there is cause for concern regarding untoward reactions and the value of the test data should be weighed against potential hazards. Some complications include dizziness, shortness of breath, coughing, pneumothorax, and inducing an asthma attack.


Contraindications

There are some indications against a pulmonary function test being done. These include a recent heart attack, stroke, head injury, an aneurysm, or confusion.


Technique


Preparation

Subjects have measurements of height and weight taken before spirometry to determine what their predicted values should be. Additionally, a history of smoking, recent illness, and medications is taken.


Quality control

In order for the forced vital capacity to be considered accurate it has to be conducted three times where the peak is sharp in the flow-volume curve and the exhalation time is longer than 6 seconds. Reproducibility of the PFT is determined by comparing the values of forced vital capacity (FVC) and forced expiratory volume at 1 second (FEV1). The difference between the highest values of two FVCs need to be within 5% or 150 mL. When the FVC is less than 1.0 L, the difference between the highest two values must be within 100 mL. Lastly, the difference between the two highest values of FEV1 should also be within 150 mL. The highest FVC and FEV1 may be used from each different test. Until the results of three tests meet the criteria of reproducibility, the test can be repeated up to eight times. If it is still not possible to get accurate results, the best three tests are used.


Clinical significance

Changes in lung volumes and capacities from normal are generally consistent with the pattern of lung impairment. Spirometry is required for a diagnosis of COPD.


Interpretation of tests

Professional societies such as the
American Thoracic Society The American Thoracic Society (ATS) is a nonprofit organization focused on improving care for pulmonary diseases, critical illnesses and sleep-related breathing disorders. It was established in 1905 as the American Sanatorium Association, and ...
and the
European Respiratory Society The European Respiratory Society, or ERS, is a non-profit organization with offices in Lausanne, Brussels and Sheffield. It was founded in 1990 in the field of respiratory medicine. The organization was formed with the merger of the Societas Euro ...
have published guidelines regarding the conduct and interpretation of pulmonary function testing to ensure standardization and uniformity in performance of tests. The interpretation of tests depends on comparing the patients values to published normals from previous studies. Deviation from guidelines can result in false-positive or false negative test results, even though only a small minority of pulmonary function laboratories followed published guidelines for spirometry, lung volumes and diffusing capacity in 2012.


COPD

The
Global Initiative for Chronic Obstructive Lung Disease The Global Initiative for Chronic Obstructive Lung Disease (GOLD) is a non-profit organization started by the World Health Organization and the US National Heart, Lung, and Blood Institute in 1997 to improve care for chronic obstructive pulmonary di ...
provides guidelines for the diagnosis, severity, and management of
COPD Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...
. To determine obstruction in a patient's lungs, the post-bronchodilator FEV1/FVC needs to be <0.7. Then, the FEV1 percentage of predicted result is used to determine the degree of obstruction where the lower the percent the worse the obstruction.


Maximum respiratory pressures

Several calculations are needed for what a normal maximum inspiratory (MIP) and expiratory pressure (MEP) is. For males this found by: MIP=120-(0.41 \times age) and MEP=174-(0.83 \times age) To find the lower limit of what is acceptable in males the equations are: MIP_=62-(0.15 \times age) and MEP_=117-(0.83 \times age) For females, the equations are slightly different. For the normal values this is used: MIP=108-(0.61 \times age) and MEP=131-(0.86 \times age) For find the lower limit of what it should be without impairment this form of the equations is used: MIP_=62-(0.50 \times age) and MEP_=95-(0.57 \times age) where * MIP = maximum inspiratory pressure in cmH20 * MEP= maximum expiratory pressure in cmH20 * MIP_ = maximum inspiratory pressure lower limit of normal in cmH20 * MEP_ = maximum expiratory pressure lower limit of normal in cmH20 * age = the patient's age in years


References

{{Respiratory system procedures Respiratory therapy Medical tests