These noninvasive tests measure various lung capacities, volumes, and flow rates, offering crucial insights into respiratory health and identifying abnormalities in lung functionality.
PFTs are integral in assessing both obstructive and restrictive lung diseases, assisting healthcare providers in determining disease severity, evaluating treatment efficacy, and optimizing management strategies.
This article provides a comprehensive overview of pulmonary function testing, discussing the tests commonly performed, the parameters measured, and their clinical application.
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What is Pulmonary Function Testing?
Pulmonary Function Testing (PFT) is a comprehensive set of tests designed to assess lung function and respiratory performance, crucial for diagnosing, managing, and monitoring respiratory diseases. PFTs measure lung volume, capacity, flow rates, and gas exchange, offering vital insights into the presence and severity of pulmonary conditions.
Pulmonary function testing is indicated for various reasons, primarily to evaluate the respiratory system’s function and status.
Some of the primary indications include:
- To assess changes in a patient’s pulmonary function
- To evaluate the effectiveness of treatment
- To diagnose pulmonary diseases
- To assess the progression of pulmonary diseases
- To differentiate between obstruction and restrictive diseases
- To differentiate types of obstructions
- To assess the risk of surgical procedures
- To assess postoperative complications
- To measure the effects of occupational exposure
- To evaluate the patient’s level of fitness
- To evaluate impairment or disability
Note: Each of these indications helps in establishing a diagnosis, guiding therapeutic decision-making, and prognosticating outcomes, ultimately enabling optimized patient-centered care in respiratory medicine.
Pulmonary function testing is a vital tool in respiratory medicine but is contraindicated under certain circumstances due to potential risks.
Some of the primary contraindications include:
- Recent myocardial infarction
- Unstable angina
- Uncontrolled hypertension
- Acute pulmonary embolism
- Acute asthmatic attack
- Acute COPD exacerbation
- Recent cataract surgery
Note: Patient safety is paramount, and therefore, medical practitioners must consider these contraindications to avoid any untoward complications during or after Pulmonary Function Testing.
Types of Pulmonary Function Testing
Pulmonary function testing involves a group of tests that measure different aspects of lung function.
Some of the primary types include:
- Lung volume measurements
- Forced vital capacity (FVC)
- Maximal voluntary ventilation (MVV)
- Maximal inspiratory/expiratory pressures (MIP/MEP)
- Body plethysmography
- Diffusing capacity
- Cardiopulmonary exercise tests
- Bronchoprovocation tests
Note: Each of these tests offers unique insights into pulmonary function and can be selected based on individual patient presentation, suspected diagnosis, and clinical indication to attain a comprehensive evaluation of respiratory health.
Spirometry, a fundamental pulmonary function test, evaluates breathing patterns and lung functionality using a spirometer—a diagnostic tool measuring the volume and velocity of airflow throughout a breathing cycle.
This test is instrumental in diagnosing conditions like chronic obstructive pulmonary disease (COPD) and restrictive lung diseases.
Additionally, it gauges the efficacy of medications for asthma patients, providing insights into the responsiveness and adaptability of the respiratory system to therapeutic interventions.
Lung Volume Measurements
Lung volume measurements are integral to pulmonary function testing and encompass the assessment of:
- Tidal volume
- Inspiratory reserve volume
- Expiratory reserve volume
- Residual volume
These volumes are measured using techniques like nitrogen washout, helium dilution, and body plethysmography, offering a meticulous examination of the lungs’ ability to hold air and aid in defining the nature and extent of pulmonary impairments.
Forced Vital Capacity
Forced Vital Capacity (FVC) measures the total volume of air that a patient can rapidly and forcefully exhale after a maximum inhalation.
This is helpful in determining if the patient has an obstructive or restrictive lung disease.
This highly effort-dependent maneuver requires persistent coaching from a respiratory therapist to ensure the reliability of results, providing an in-depth perspective on lung functionality and respiratory constraints.
Body plethysmography is a test that measures the total amount of air that can be inhaled, as well as the volume of air that remains in the lungs after exhalation (i.e., residual volume).
It confirms restrictive lung diseases that markedly decrease total lung volume and uniquely measures residual volume, granting a comprehensive view of lung capacity and the repercussions of pulmonary afflictions.
Maximal Voluntary Ventilation
Maximal Voluntary Ventilation (MVV) assesses the maximum volume of air a person can inhale and exhale within a specific timeframe, requiring deep and fast breathing for 12 seconds.
It is pivotal for assessing the comprehensive function of the respiratory system, with decreased MVV indicating the presence of an obstructive lung disease.
Maximal Inspiratory/Expiratory Pressures
Maximal Inspiratory and Expiratory Pressures (MIP/MEP) are crucial for evaluating respiratory muscle strength, gauging the force generated during maximal inhalation and exhalation.
MIP represents the maximal pressure generated during an inhalation against an occluded airway, while MEP denotes the maximum pressure during a maximal exhalation against an occluded airway.
The diffusing capacity for carbon monoxide (DLCO) is a test that evaluates gas exchange in the alveoli of the lungs.
It involves inhaling a mixture of carbon monoxide (CO) and a tracer gas, followed by a 10-second breath-hold maneuver, enabling healthcare providers to determine the patient’s diffusion capacity.
It is frequently used to monitor conditions like pneumoconiosis, evaluate obstructive diseases, and observe changes in lung function.
Cardiopulmonary Exercise Tests
Cardiopulmonary exercise tests, such as the 6-minute walk test (6MWT), assess oxygen uptake, carbon dioxide production, and heart rate during physical exertion, offering insights into the severity of respiratory diseases.
The distance covered in the 6MWT correlates with the clinical outcomes of several pulmonary diseases.
Bronchoprovocation tests, like the methacholine challenge test, assess airway hyperresponsiveness or the narrowing of airways due to triggers like allergens and irritants.
It simulates asthma effects by having patients inhale increasing methacholine concentrations.
Significant changes in FEV1 during this test assist in the definitive diagnosis of asthma.
Types of Lung Diseases
Lung diseases predominantly fall into two main categories:
Note: Distinguishing between these disease types is crucial in pulmonary function testing as it enables healthcare practitioners to administer or advocate for the most suitable treatment modalities based on the identified condition.
Obstructive Lung Diseases
Obstructive lung diseases are characterized by conditions that impede the effortless exhalation of air from the lungs.
This category of diseases leads to shortness of breath, attributed to the constriction of the pulmonary airways, resulting in diminished flow rates.
The mnemonic “CBABE” can aid in remembering the principal obstructive lung diseases, representing:
- Cystic Fibrosis
- Bronchitis (Chronic)
Patients with obstructive diseases usually experience trouble breathing out fully due to airway obstruction, which can be due to inflammation, mucus plugs, or structural changes.
Restrictive Lung Diseases
Restrictive lung diseases comprise conditions that hinder the lungs from fully expanding during inhalation, thereby limiting the lung’s capacity to fill with air.
Essentially, the lung’s ability to expand is restricted, culminating in reduced lung volumes.
By default, pulmonary conditions that do not fall under the classification of obstructive diseases are generally categorized as restrictive lung diseases.
Restrictive lung diseases can be intrinsic, involving conditions like pulmonary fibrosis, or extrinsic, involving conditions such as pleural effusion or obesity, affecting the space around the lungs or the chest wall’s ability to move.
Remember: Discerning the type of lung disease through pulmonary function testing is essential in guiding effective therapeutic interventions for managing respiratory conditions.
Normal Values for Pulmonary Function Testing
The PFT results of individuals with healthy, properly functioning lungs, should generally fall within the following ranges:
- FEV1: > 80% of predicted
- FEV1/FVC%: ≥ 70%
- Forced Vital Capacity (FVC): > 80% of predicted
- Slow Vital Capacity (SVC): > 80% of predicted
- Airway Resistance (RAW): 0.6-2.4 cmH2O/L/sec
- Diffusing Capacity for Carbon Monoxide (DLCO): 20-25 mL/CO/min/mmHg
- Peak Expiratory Flow Rate (PEFR): 10 L/sec
- Exhaled Carbon Monoxide: < 7 for nonsmokers
Note: If a patient’s PFT results fall outside these normal ranges, it can help healthcare practitioners figure out what kind of lung problem they might have, the severity, and the most effective treatment options.
Equipment for Pulmonary Function Testing
Performing pulmonary function tests requires the use of a variety of specialized tools and devices, such as:
- Peak flowmeter
- Body plethysmograph
- Pulmonary gas analyzer
- Oxygen analyzer
- Gas-conditioning device
- Blood gas analyzer
- Silverman pneumotachometer
With advancements in technology, the incorporation of new and improved PFT equipment into clinical practices is a continual process.
The devices listed above are some of the most prevalent examples used in pulmonary function testing.
Pulmonary Function Testing Practice Questions
1. What is the purpose of pulmonary function testing?
To identify pulmonary impairment and quantify the severity.
2. What is a spirometer?
A device that measures volume and flow.
3. What are the three categories of pulmonary function tests?
1) Dynamic flow rates of gases through the airways, 2) Lung volumes and capacities, and 3) The ability of the lungs to diffuse gases.
4. What are the three components of pulmonary function testing?
1) Performing spirometry for measuring airway mechanics, 2) Measuring lung volumes and capacities, and 3) Measuring the diffusing capacity of the lung.
5. What are the two general types of measuring instruments?
Instruments that measure gas volumes, and instruments that measure gas flow.
6. What are the two major categories of pulmonary diseases?
Obstructive and restrictive pulmonary diseases.
7. What can disqualify a forced vital capacity trial?
A cough, an inspiration, a Valsalva maneuver, a leak, or an obstructed mouthpiece.
8. What does an FEV1/FVC ratio of less than 70% indicate?
An obstructive impairment.
9. What is airway resistance (Raw)?
The difference in pressure between the ends of the airways divided by the flow rate of gas moving through the airway.
10. What is the most commonly measured lung volume?
11. What is the most commonly performed test in pulmonary mechanics?
Forced vital capacity (FVC)
12. What is the normal tidal volume amount for an adult?
500 to 700 mL
13. What is the normal value for ERV?
14. What is the normal value for IRV?
15. What is the normal value for peak expiratory flow?
16. What is the normal value for RV?
17. What is the normal value for TLC?
18. What is the normal value for VC?
19. What is the normal value of FRC?
20. What is the normal value of inspiratory capacity?
21. What is the predicted normal FEV1 for a 20-year-old man?
22. What is the predicted normal FVC for a 20-year-old man?
23. What is the primary problem in obstructive lung diseases?
Increased airway resistance
24. What is the primary problem in restrictive lung diseases?
Reduced lung compliance, thoracic compliance, or both.
25. What makes up the functional residual capacity (FRC)?
Expiratory reserve volume (ERV) and the residual volume (RV)
26. What pulmonary function test poses the greatest risk for fainting?
27. What test is used to measure FRC?
A lung diffusion test
28. What type of gas is used in a diffusion test?
29. When a patient performs an FVC maneuver, how much volume in % should be exhaled in the first second?
30. When are flow rates measured?
Flow rates are usually measured during expiration.
31. When performing pulmonary function testing, what establishes test validity?
The test should strictly follow testing procedures, it must ensure patient effort and performance, and you must ensure equipment accuracy and calibration.
32. When is bronchial provocation indicated?
When the patient’s history suggests episodic symptoms of hyperactive airways and airway obstruction, such as seasonal or exercise-induced wheezing.
33. Why is vital capacity reduced in restrictive lung diseases?
Because the patient’s inhaled volume is reduced.
34. When will an airway collapse most likely occur?
During forced exhalation
35. What is an example of a combined obstructive/restrictive disease?
36. What is the FEV1?
The volume of gas expired in 1 second.
37. What is the FEV3?
The volume of gas expired in 3 seconds.
38. What is a description of obstructive lung diseases?
They have decreased flows and increased airway resistance.
39. What is a hallmark sign of restrictive lung diseases?
They have decreased volumes.
40. What is the main purpose of pulmonary function testing?
To differentiate between obstructive or restrictive diseases.
41. What is a description of restrictive lung diseases?
They have decreased volumes and decreased lung compliance.
42. What tests are used to determine FRC and RV?
Nitrogen washout, helium dilution, and the “body box.”
43. What values will remain normal in restrictive lung diseases?
Tidal volume, FEV1, FEF200, and PEFR.
44. What is a lung capacity?
A combination of two or more lung volumes.
45. What correlation exists between the measurement of pulmonary mechanics and age?
A negative correlation
46. What correlation exists between the measurement of pulmonary mechanics and height?
A positive correlation
47. What is the diffusing capacity of the lung?
The number of milliliters of gas that transfer from the lungs to the pulmonary blood per minute for each 1 mmHg partial pressure difference between the alveoli and pulmonary capillary blood.
48. What is the diffusing capacity of the lung for carbon monoxide (DLCO)?
The difference between the volume of carbon monoxide inhaled and the volume of carbon monoxide exhaled, considering the partial pressure of carbon monoxide in the lungs at the time of measurement.
49. An exhalation of how long is acceptable for children younger than 10 years old?
50. What is the expiratory reserve volume (ERV)?
The total amount of gas that can be exhaled from the lung after a quiet exhalation.
51. What is extrapolated volume?
The volume exhaled before the zero time point.
52. The FEF 25% to 75% is a measurement of what?
The flow during the middle portion of an FVC maneuver, or the time necessary to exhale the middle 50%.
53. The Fleisch pneumotachometer measures what?
It measures the changes in pressure as gas flows through a minimal, constant resistance.
54. Flow measuring devices are commonly called what?
55. For baseline testing, patients should temporarily abstain from what?
Bronchodilator medications, short-acting bronchodilators, long-acting beta-agonist bronchodilators, and oral therapy with aminophylline should be stopped for 12 hours.
56. What four general principles should be considered during pulmonary function testing?
Test specificity, sensitivity, validity, and reliability.
57. For volume measurements, standard reference values are provided by what?
By a graduated 3.0 L calibration syringe.
58. FVC is an effort-dependent maneuver that requires what?
It requires careful patient instruction, understanding, coordination, and cooperation.
59. How many attempts must be performed to indicate that an FVC is valid?
60. How often should a PFT machine be calibrated?
At least daily, although the best practice in many labs is to verify accuracy before each test subject.
61. How to calculate minute ventilation?
Respiration rate x Tidal volume
62. How to calculate the % of error?
% error = mean measured value – reference value ÷ reference value x 100
63. What do you use to calibrate a PFT machine?
3.0 L calibration syringe
64. How can you measure residual volume?
When the FRC is known, RV can be calculated as the difference between FRC and ERV.
65. What does it mean when a person cannot exhale at least 70% of their VC in 1 second?
They have an airway obstruction.
66. What is the inspiratory capacity (IC)?
The maximum amount of air that can be inhaled from the resting end-expiratory level or FRC. It is the sum of the tidal volume and inspiratory reserve volume.
67. What is the inspiratory reserve volume (IRV)?
The maximum volume of air that can be inhaled after normal quiet inspiration.
68. In what patients may the validity of measuring the forced vital capacity be hindered?
Acutely ill patients or those who have recently smoked a cigarette.
69. Is tidal volume alone a valid indicator of the type of lung disease?
70. Is the TLC increased or decreased in an obstructive lung disease?
71. Is the TLC increased or decreased in a restrictive lung disease?
72. What is maximal voluntary ventilation (MVV)?
An effort-dependent test for which the patient is asked to breathe as deeply and as rapidly as possible for at least 12 seconds. It’s a test that reflects patient cooperation and effort, the ability of the diaphragm and thoracic muscles to expand the thorax and lungs, and airway patency.
73. Measuring pulmonary mechanics is essentially assessing what?
The ability of the lungs to move large volumes of air quickly through the airways in order to identify an airway obstruction.
74. Measuring what can identify the destruction of alveolar tissue or the loss of functioning alveolar surface area?
The diffusing capacity of the lungs for carbon monoxide (DLCO).
75. What is peak expiratory flow rate (PEFR)?
The maximum expiratory flow rate in L/sec.
76. Plethysmography techniques apply what law?
77. What do pneumotachometers measure?
78. Residual volume represents how much of the TLC?
79. What is residual volume?
The volume of gas remaining in the lungs after a complete exhalation.
80. What is a restrictive pulmonary disease?
A broad category of disorders with widely variable etiologies but all resulting in a reduction in lung volumes, particularly the inspiratory and vital capacities; categorized according to origin skeletal/thoracic, neuromuscular, pleural, interstitial, and alveolar.
81. The severity of pulmonary impairment is based on what?
A comparison of each patient’s measurement with the predicted normal value for the patient.
82. The speed of lung expansion represents what?
The flow rate
83. To ensure validity, each patient must perform a minimum of how many acceptable FVC maneuvers?
84. What is total lung capacity (TLC)?
The total amount of gas in the lungs after a maximum inspiration.
85. The validity of MVV depends on what?
The duration of the maneuver, which should be at least 12 seconds; the breathing frequency, which should be at least 90/min; and the average volume, which should be at least 50% of FVC.
FAQs About Pulmonary Function Testing
What is Pulmonary Function Testing Used for?
Pulmonary Function Testing (PFT) is instrumental in evaluating numerous respiratory conditions, encompassing obstructive and restrictive lung diseases. It serves to monitor the evolution of diseases and ascertain the efficacy of administered treatments.
Typical pulmonary function tests encompass spirometry, measurement of lung volumes and capacities, maximal voluntary ventilation, MIP/MEP, and body plethysmography.
What is the Purpose of Pulmonary Function Testing?
Pulmonary function testing primarily aims to yield a comprehensive analysis of an individual’s respiratory health, facilitating the diagnosis and surveillance of diverse respiratory ailments.
By scrutinizing lung functionality and the responsiveness of airways, medical professionals can devise precise diagnoses and formulate optimal treatment plans tailored to individual patients.
Moreover, PFTs are pivotal in monitoring the trajectory of diseases and assessing the response to different therapeutic interventions.
What is DLCO in Pulmonary Function Testing?
DLCO, denoting the diffusing capacity for carbon monoxide, is a pivotal component of pulmonary function testing, evaluating the rate of gas exchange across the alveolar-capillary membrane.
It is indispensable for diagnosing a spectrum of lung diseases and for tracking alterations in disease states over time.
How Do You Read Spirometry or PFT Results?
Spirometry or PFT results are generally conveyed via graphs or tables, with values juxtaposed against normative ranges based on age, sex, height, and other pertinent parameters.
Conventionally, subnormal values are indicative of compromised lung function, whereas elevated values might signify air trapping in the lungs or augmented effort in breathing.
A pulmonologist or a respiratory therapist typically undertakes the interpretation of spirometry or PFT results to ensure accuracy and appropriateness in diagnosis and treatment planning.
Pulmonary Function Testing (PFT) remains an essential component of respiratory care, offering a comprehensive overview of lung function and aiding in the accurate diagnosis, management, and treatment of a plethora of respiratory conditions.
These tests are invaluable for discerning the intricacies of pulmonary diseases, providing a framework for tailored therapeutic interventions, and understanding the longitudinal impacts of respiratory diseases.
The continued advancements and refinements in PFT methodology are paramount for enhancing our knowledge of respiratory pathology and refining treatment approaches, thereby contributing to improved respiratory health outcomes and quality of life for affected individuals.
John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.
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- Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
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- Heckman EJ, O’Connor GT. Pulmonary function tests for diagnosing lung disease. JAMA. 2015.