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In the world of pulmonary diagnostics, precision matters — in testing, interpretation, and communication. Whether you're onboarding new technicians, refreshing your clinical knowledge, or exploring the latest advancements in cardiopulmonary testing, having a clear understanding of key terminology is essential.
To support clinicians, respiratory therapists, lab directors, and exercise physiologists, we’ve assembled this comprehensive glossary of common pulmonary terms. Think of it as a quick‑reference companion for your PFT and CPET workflows — written with clarity, accuracy, and everyday usability in mind.
Pulmonary Terms You Should Know
A
Airflow Limitation
A decrease in the ability of air to move freely through the airways, commonly associated with conditions like asthma and COPD. It’s often identified through reduced FEV1 or FEV1/FVC ratios.
Air Trapping
Occurs when air remains in the lungs at the end of exhalation due to incomplete emptying. Often linked with obstructive lung diseases.
Airway Resistance (Raw)
This represents the frictional opposition to gas flow through the respiratory tract. The higher the resistance, the harder it is to move air in and out of the lungs.
Alveolar-arterial Gradient
Measures the difference between alveolar and arterial oxygen, and is used to determine if hypoxemia is caused by lung disease or other factors.
Alveolar Volume (VA)
Represents the total volume of gas in the lungs that is actively involved in gas exchange.
Alveoli
The small, balloon‑like air sacs where oxygen and carbon dioxide exchange occur. Healthy alveoli are essential for proper oxygenation.
Asthma
A chronic respiratory disease characterized by inflammation, swelling, and narrowing of the airways, along with increased mucus production.
ATS/ERS Standards
Guidelines created by the American Thoracic Society and European Respiratory Society that define best practices for performing and interpreting pulmonary function tests (PFTs). These standards guide everything from spirometry testing technique to quality grading.
B
Breath‑by‑Breath Analysis
Measurement of gas exchange parameters (like VO₂ and VCO₂) for every individual breath. This technique is foundational in cardiopulmonary exercise testing (CPET).
Bronchial Challenge Test (Bronchoprovocation)
A diagnostic procedure using medication, cold air or exercise that is used to evaluate airway hyperresponsiveness by measuring how easily a patient’s airways constrict, commonly diagnosing asthma.
Bronchodilator Response (BDR)
A change in PFT values — especially FEV1 — following administration of a bronchodilator medication, used to assess reversibility of airway obstruction.
Bronchoconstriction
Tightening of the airway muscles, often triggered by allergens, exercise, or irritants. Leads to reduced airflow and increased work of breathing.
C
Cardiopulmonary Exercise Testing (CPET)
A powerful diagnostic tool that evaluates the combined performance of the heart, lungs, and muscles during exercise. CPET identifies causes of exercise limitation and provides insight beyond what resting tests can show.
Calibration
The process of verifying that diagnostic equipment is measuring accurately using known reference values. Regular calibration is essential for reproducible, high‑quality results.
Chronic Obstructive Pulmonary Disease (COPD)
A group of progressive lung diseases — including chronic bronchitis and emphysema — characterized by persistent airflow limitation.
Cystic Fibrosis
An inherited, chronic disease caused by a genetic mutation that leads to the production of thick, sticky mucus, severely affecting the lungs, pancreas, and other organs. This mucus causes airway blockages, chronic infections, and, in many cases, significant difficulty absorbing nutrients from food.
D
Diffusing Capacity (DLCO)
A measurement of how efficiently gases move from the lungs into the bloodstream. DLCO helps identify conditions like emphysema, pulmonary hypertension, or interstitial lung disease.
Dead Space
Portion of each breath that does not participate in gas exchange. Can be anatomical (airways) or physiological (non‑functioning alveoli).
Dilutional Lung Volumes
The measurement of lung volumes using inert gas techniques—specifically helium dilution or nitrogen washout—to determine the volume of gas within the lungs that communicates with the airways.
Direct Fick
Technique for measuring cardiac output by directly measuring total oxygen consumption, and oxygen content in both arterial and mixed venous blood.
Dyspnea
Clinical term for shortness of breath. A common symptom evaluated during CPET and pulmonary function testing.
E
End‑Tidal CO₂ (ETCO₂)
The level of carbon dioxide measured at the end of exhalation. ETCO₂ is used during metabolic testing and can provide insight into ventilation and perfusion.
Electrocardiogram (ECG or EKG)
A noninvasive test that records the electrical signals of your heart to check for heart disease, arrhythmias, and other issues. By placing electrodes on the chest, arms, and legs, it measures the heart's electrical activity, rate, and rhythm to help diagnose heart attacks or structural issues.
Emphysema
A chronic, progressive lung disease and a form of COPD (chronic obstructive pulmonary disease) that destroys the alveoli (air sacs) in the lungs, making it difficult to breathe.
Exercise-induced Asthma
A condition where physical activity triggers temporary narrowing of the airways, causing coughing, wheezing, and chest tightness.
Exercise Limitation
A reduced ability to perform physical activity due to pulmonary, cardiac, or muscular factors — identified most precisely through CPET.
F
FEV₁ (Forced Expiratory Volume in 1 Second)
The volume of air expelled in the first second of a forceful exhalation. A cornerstone measurement in diagnosing obstructive lung diseases.
Flow-Volume Curve (Loop)
A noninvasive spirometry test plotting maximum airflow rate (y-axis) against lung volume (x-axis) during forced inspiration and expiration.
Forced Oscillation Technique (FOT)
A non-invasive, effort-independent lung function test that measures respiratory mechanics (resistance and reactance). It is used to assess airway obstruction without requiring forced maneuvers
FVC (Forced Vital Capacity)
The total amount of air exhaled during a complete forced breath. Compared to FEV1 to assess airflow patterns.
FEV₁/FVC Ratio
A key indicator used to differentiate obstructive from restrictive lung patterns.
G
Gas Exchange
Movement of oxygen and carbon dioxide between the lungs and bloodstream — essential for assessing both pulmonary and metabolic function.
Gas Analyzer
A component of metabolic and CPET systems that measures breath gases. Accuracy is critical for reliable VO₂ and VCO₂ data.
Global Lung Initiative (GLI)
A part of the European Respiratory Society (ERS), and is an international collaboration that provides standardized, globally applicable reference values for lung function tests.
H
High Altitude Simulation Test (HAST)
A diagnostic procedure that determines if patients with chronic lung or heart conditions require supplemental oxygen during air travel or at high altitudes.
Hyperinflation
An increase in lung volumes due to air trapping or loss of elasticity. Often seen in emphysema.
Hypoxemia
Low levels of oxygen in the blood. Pulse oximetry or blood gases can detect it.
I
Inspiratory Capacity (IC)
The maximum amount of air that can be inhaled after a normal exhalation. Helpful in evaluating hyperinflation.
Indirect Calorimetry
A method of measuring metabolic rate through oxygen consumption and carbon dioxide production — valuable in clinical nutrition and ICU care.
Impulse Oscillometry (IOS)
A noninvasive technique measuring airway resistance using sound waves during tidal breathing.
L
Lower Limit of Normal (LLN)
A threshold used in medical testing to identify the lowest value (5th percentile) of a healthy reference population, indicating the point below which results are considered abnormal.
Lung Clearance Index (LCI)
A non-invasive lung function measurement derived from a "multiple-breath washout" (MBW) test, indicating the number of lung volume turnovers required to clear an inert tracer gas from the lungs. It measures ventilation inhomogeneity — how evenly air moves throughout the lungs.
Lung Compliance
A measure of lung expandability. Reduced compliance indicates stiff lungs, often seen in restrictive diseases.
Lung Volumes
Measurements such as Total Lung Capacity (TLC), Residual Volume (RV), and Vital Capacity (VC), which help diagnose restrictive and obstructive patterns.
M
Maximal Expiratory Pressure (MEP)
The maximum pressure generated by the respiratory muscles during forced expiration.
Maximal Inspiratory Pressure (MIP)
The maximum pressure generated by the respiratory muscles during forced inspiration.
Maximum Voluntary Ventilation (MVV)
Measures the maximum volume of air a person can inhale and exhale over 12–15 seconds, often extrapolated to one minute. This test evaluates respiratory muscle strength, endurance, and chest wall integrity.
Metabolic Cart
Equipment used to analyze gases during rest or exercise — essential for CPET and indirect calorimetry.
Minute Ventilation (VE)
The total amount of air inhaled or exhaled per minute.
Multiple Breath Nitrogen Washout
A non-invasive, pulmonary function test that assesses ventilation distribution inhomogeneity and measures functional residual capacity (FRC) by having the subject inhale 100% oxygen for approximately 7 minutes.
O
Obstructive Lung Disease
Conditions that limit airflow due to narrowed or inflamed airways.
Oxygen Consumption (VO₂)
Measures how much oxygen the body uses per minute. Peak VO₂ during CPET is a gold‑standard indicator of aerobic capacity.
P
Peak VO₂
The highest rate of oxygen consumption during maximal exercise — a key CPET parameter for evaluating fitness and disease severity.
Plethysmograph
A diagnostic, airtight chamber (or "body box") used in pulmonary function testing to accurately measure lung volumes, including residual volume and total lung capacity.
Provocative Dose (PD20)
The specific, measured amount of a substance (drug, allergen, or chemical) administered during a challenge test to intentionally trigger a controlled, reproducible, and observable reaction.
Pulmonary Function Test (PFT)
A series of tests assessing lung function, including spirometry, lung volumes, and diffusing capacity.
Pulse Oximetry (SpO₂)
Noninvasive monitoring of blood oxygen saturation.
Q
Quality Control (QC)
A process of inspecting, testing, and reviewing test data to ensure they meet established, predefined standards. It focuses on identifying defects or variations in the final output.
R
Residual Volume (RV)
Air remaining in the lungs after maximum exhalation.
Restrictive Lung Disease
Conditions that limit lung expansion, resulting in reduced lung volumes.
Respiratory Exchange Ratio (RER)
The ratio of carbon dioxide production to oxygen consumption — used to assess metabolic intensity during CPET.
Respiratory Quotient (RQ)
The ratio of carbon dioxide production to oxygen consumption — used in indirect calorimetry to determine which macronutrients (carbohydrates, fats, or proteins) the body is using for energy.
S
Shunt Study (Pulmonary)
A diagnostic procedure that measures the amount of blood bypassing ventilated alveoli in the lungs, causing low blood oxygen (hypoxemia) that does not improve with oxygen therapy.
Six Minute Walk Test (6MWT)
A submaximal exercise test that measures the maximum distance a person can walk on a flat, hard, surface in six minutes.
Slow Vital Capacity (SVC)
The maximum volume of air that can be exhaled slowly and completely after a maximum inhalation.
Spirometry
A fundamental PFT that determines how well your lungs are working by measuring the volume and speed of the air you can inhale and exhale.
Static Lung Volumes
Volumes measured without forced breathing maneuvers, often determined via plethysmography.
Static Compliance
Measures the elasticity of the lungs and chest wall when there is no airflow, typically during an inspiratory pause.
Submaximal Exercise Testing
Exercise testing performed below maximal levels; often used when full CPET isn’t indicated.
T
Tidal Volume (VT)
The amount of air inhaled or exhaled during relaxed, normal breathing.
Total Lung Capacity (TLC)
The maximum volume of air the lungs can hold.
Thoracic Gas Volume (TGV)
Measured during body plethysmography to assess lung volume at a specific point in the breathing cycle.
V
Ventilation (VE)
The total air moved in and out of the lungs per minute.
Ventilatory Threshold (VT1/VT2)
Points during exercise where ventilation increases disproportionately to the workload; key markers in CPET.
Vital Capacity (VC)
The total amount of air exhaled after a full inhalation.
Why This Glossary Matters
Clear communication leads to clearer diagnoses, better workflows, and more confident clinical decision‑making. Whether you're onboarding new staff or educating patients, this glossary helps ensure consistency and accuracy across your lab.
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