Respiratory Therapy Terms and Definitions

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Note: The remaining terms and definitions will be added to this page soon. Thank you for your patience.


AARC – the abbreviation for the American Association for Respiratory Care. It’s the primary nonprofit organization that supports respiratory therapists in the United States.

Accessory Muscles of Breathing – muscles of the neck, back, and abdomen that may assist the diaphragm with breathing. When these muscles are in use, it indicates that the patient has an increased work of breathing.

Acute Exacerbation of COPD – a worsening state of COPD that usually indicates that the patient is in need of increased medication dosages or other forms of care.

Advanced Cardiac Life Support (ACLS) – an advanced form of emergency life support for the treatment of cardiac arrest, stroke, myocardial infarction, and other life-threatening cardiovascular emergencies.

Advanced Directive – a legal document that allows a patient to specify what medical care he or she does or does not want to receive if they were no longer able to make decisions on their own. It’s typically in the form of a living will or durable power of attorney.

Aerosol Medications – a medication that can be dispersed as solid or liquid particles in a gas which allows for inhalation into the airways of the respiratory tract.

Air Bronchograms – a pattern on a chest radiograph that shows air-filled bronchi surrounded by areas of consolidation.

Airway Clearance Therapy – a type of therapy that uses noninvasive techniques to help mobilize and remove secretions in order to improve gas exchange.

Airway Management – the process of maintaining ventilation in a patient by using an artificial airway. This ensures that gas exchange can occur by establishing a link between the patient and the ventilator.

Airway Obstruction – a complete or partial blockage of an airway that prevents or limits ventilation and air movement to and from the lungs.

Airway Pharmacology – a term that refers to the deliverance of aerosol medications to the respiratory tract of the lungs.

Airway Pressure Release Ventilation (APRV) – a mode of mechanical ventilation in which two levels of continuous positive airway pressure are applied with an intermittent release phase for spontaneous breaths. This mode is often recommended to improve oxygenation and treat refractory hypoxemia.

Airway Resistance – the measurement of impedance to the movement of air through the respiratory tract during inspiration and expiration.

Airway Suctioning – a method of using negative pressure to remove secretions from a patient’s airway through a collecting tube or catheter.

Albuterol – an inhaled beta-2-agonist bronchodilator that is administered to prevent and treat wheezing, chest tightness, and shortness of breath caused by pulmonary diseases such as asthma and chronic obstructive pulmonary disease (COPD).

Alveolar-Capillary Membrane – a layer of tissue that serves as a barrier through which gas exchange occurs between the alveoli and pulmonary capillaries.

Alveolar Ventilation – the ventilatory process that takes place in the alveoli of the lungs. This is where the body is able to take in oxygen and remove carbon dioxide.

Alveoli – tiny air sacs that are arranged in clusters within the lungs where the gas exchange of oxygen and carbon dioxide molecules takes place

Anticholinergic Bronchodilators – a drug that acts on the parasympathetic nervous system by blocking the mechanism of action of the neurotransmitter acetylcholine (ACh) to promote relaxation of the smooth muscles in the airways of the lungs.

Antimicrobial Agents – a class of drugs that work to eliminate potentially harmful microorganisms and prevents them from growing or spreading in the lungs.

Apgar Score – a system that is used to quickly determine the status of the newborn’s overall condition. It should be obtained one minute and five minutes after birth to determine if treatment is needed for the infant.

Apnea – the absence of spontaneous breathing.

Apnea of Prematurity – a disorder that occurs in preterm infants which results in frequent periods of apnea. It is caused by a physiologically underdeveloped respiratory control center in the brain.

Apneustic Breathing – an abnormal breathing pattern that results from an injury to the upper pons in the brain that results in a prolonged inspiratory time followed by inadequate expiration.

Arterial Blood Gas (ABG) – a test that measures the blood levels of oxygen (PaO2), carbon dioxide (PaCO2), and acid-base balance (pH) in the body that is used to assess how well oxygen is being distributed and how well carbon dioxide is being removed.

Assist/Control Mode (A/C) – a mode of mechanical ventilation in which a minimum number of preset mandatory breaths are delivered by the ventilator but the patient can also trigger assisted breaths. The patient makes an effort to breathe and the ventilator assists in delivering the breath.

Asthma – a chronic, obstructive, and inflammatory respiratory condition characterized by recurring episodes of dyspnea, wheezing, and chest tightness.

Atelectasis – a term that refers to a collapse in the alveoli of the lungs. It could be a total collapse of an entire lung or a partial collapse in one or more lobes.

Auscultation – a non-invasive procedure for listening to the internal sounds of the body using a stethoscope.

Automatic External Defibrillator (AED) – a portable electronic device that can be used outside of the hospital to detect cardiac arrhythmias and perform defibrillation in order to re-establish a normal heart rhythm.

Auto-PEEP – a complication of mechanical ventilation that occurs when a positive pressure remains in the alveoli at the end-exhalation phase of the breathing cycle.


Barotrauma – an injury to lung tissue that results from overexpansion and increased levels of pressure.

Barrel Chest – a term used to describe a patient with an increased anterior-posterior diameter of the chest wall that is often seen in patients with emphysema.

Base Excess (BE) – a value obtained during an Arterial Blood Gas (ABG) analysis that refers to the difference between the normal and actual buffer base in a sample of blood.

Beta-2 Agonist – a type of medication that is administered for the treatment of acute bronchospasm and works by causing relaxation of smooth muscle tissue in the airways.

Bicarbonate (HCO3-) – a byproduct of the body’s metabolism that represents the total carbon dioxide content that is transported in the blood. Once it reaches the lungs, it can be exhaled as carbon dioxide.

Bilevel Positive Airway Pressure (BiPAP) – a form of noninvasive ventilation that distributes two levels of pressure in order to provide ventilatory support and help avoid invasive mechanical ventilation.

Biot Respirations – a breathing pattern characterized by deep breaths that alternate with irregular periods of apnea. It often results from damage to the medulla or pons in the brain.

Bourdon Gauge – a flow meter device that uses a fixed orifice and operates under variable pressures that can be adjusted with a pressure-reducing valve.

Bradycardia – an abnormally decreased heart rate of fewer than 60 beats per minute.

Bradypnea – an abnormal breathing pattern characterized by a respiratory rate that is less than 12 breaths per minute.

Breath Sounds – the sounds that come from the lungs during inhalation and exhalation that can be heard during auscultation. An abnormality in breath sounds is an indication of other health issues.

Breathing Pattern – the ventilatory pattern by a patient over a period of time that accounts for the respiratory rate and amount of air that is cycled.

Bronchiectasis – an obstructive condition that causes irreversible destruction of the bronchial walls of the airways of the lungs that results in an accumulation of copious amounts of bronchial secretions.

Bronchoalveolar Lavage (BAL) – a diagnostic technique that uses a bronchoscope and saline solution to collect specimens from the lower respiratory tract for testing.

Bronchoconstriction – an abnormal contraction of the smooth muscle tissue in the airways of the lungs that results in narrowing and difficulty breathing.

Bronchodilator – a type of medication that relaxes smooth muscle tissue in the airways of the lungs to relieve constriction, increase airflow, and make breathing easier

Bronchoprovocation Study – a test that uses methacholine, a cholinergic drug, to access airway hyperresponsiveness in order to diagnose a patient with asthma.

Bronchopulmonary Dysplasia (BPD) – a chronic respiratory disorder in premature and low birth weight infants characterized by a reduction in the overall surface area for gas exchange.

Bronchoscopy – an endoscopic procedure that involves passing a bronchoscope into the airways of the lungs for diagnostic and therapeutic purposes.


Capnography – a process of measuring and monitoring the amount of carbon dioxide in exhaled air.

Carbon Monoxide Poisoning – the exposure and inhalation of excessive carbon dioxide gas which accumulates in the blood and can cause serious tissue damage.

Carboxyhemoglobin – a compound that refers to the chemical combination of hemoglobin and carbon monoxide.

Cardiac Output – a measurement of the volume of blood that is pumped by the heart per minute.

Cardiac Tamponade – a medical condition characterized by the accumulation of blood, fluid, or gas in the pericardial sac of the heart.

Cardiogenic Pulmonary Edema – a type of pulmonary edema that is caused by increased pressures in the heart and is associated with congestive heart failure.

Cardiopulmonary Rehabilitation – an organized program that is designed to improve the status of patients with conditions of the heart and lungs with a goal to improve their overall quality of life.

Cardiopulmonary Resuscitation (CPR) – an emergency medical procedure for life support that involves repeated chest compressions and artificial ventilation in an effort to restore spontaneous breathing and blood circulation in a patient who is in cardiac or respiratory arrest.

Cardioversion – a medical procedure that uses an electrical shock to restore an abnormal heart rhythm back to normal.

Carina – the bifurcation of the trachea that separates into the right and left mainstem bronchi.

Central Sleep Apnea – a disorder characterized by the absence of breathing while asleep that is caused by a medullary depression that inhibits an inspiratory effort.

Chest Physical Therapy (CPT) – a form of therapy that is designed to help clear secretions, improve ventilation, and strengthen the respiratory muscles of breathing.

Chest Radiograph – a radiographic imaging technique used for the assessment of the heart, lungs, and structures within the thoracic cavity.

Chest Trauma – any type of trauma or injury to the chest wall.

Cheyne-Stokes Respiration – an abnormal breathing pattern characterized by gradual periods of deep and shallow breaths with a period of apnea.

Chronic Bronchitis – a type of COPD that is characterized by increased mucus production in the trachea and bronchi that results in a productive cough that occurs for at least three months of the year for more than two consecutive years.

Cilia – microscopic hairlike structures that line the cells within the airways of the lungs that help mobilize mucus and secretions.

Committee on Accreditation for Respiratory Care (CoARC) – an accrediting committee that establishes education standards and oversees the approval of respiratory care programs.

Complete Blood Count – a group of medical laboratory tests for screening and diagnostic purposes that analyzes the counts of red blood cells, white blood cells, and platelets, as well as the concentration of hemoglobin and hematocrit.

Computed Tomography (CT) – a radiographic imaging technique that generates cross-sectional images of an organ or tissue structure.

Congenital Cardiac Defect – a condition of the heart that develops before an infant is born.

Congenital Diaphragmatic Hernia – a developmental birth defect characterized by a hole in the diaphragm of a fetus that results in severe respiratory distress.

Congestive Heart Failure (CHF) – a chronic condition that affects the ability of the heart to pump blood adequately and often results in pulmonary edema.

Contact Precautions – safety measures used to reduce the risk of transmitting infectious diseases and microorganisms that can be spread by direct or indirect contact.

Continuous Positive Airway Pressure (CPAP) – a mode of ventilatory support in which a continuous pressure that is above atmospheric pressure is maintained throughout the breathing cycle.

Control Mode Ventilation (CMV) – a mode of mechanical ventilation where the machine delivers a preset tidal volume at a set time-triggered frequency.

COPD – an abbreviation that stands for chronic obstructive pulmonary disease; it’s a chronic disease that causes progressive airway obstruction that results in breathing-related problems.

Cor Pulmonale – a condition that causes failure of the right ventricle and often results from pulmonary hypertension.

Coronary Artery Bypass Graft (CABG) – a surgical procedure that aims to improve blood flow to the heart and is often performed on patients with coronary artery disease.

Coronary Artery Disease – a disease that develops when there is narrowing or a blockage of the coronary arteries. It is usually caused by plaque build-up that results in decreased blood flow to the heart.

Crackles – also known as rales, are abnormal sounds that are heard as air moves through secretions in the small or middle airways of the lungs.

Cricothyrotomy – an emergency surgical procedure where an incision is made through the skin and cricothyroid membrane in order to access the trachea so that ventilation can occur.

Croup – a viral infection of the upper airway that results in subglottic swelling and an obstruction below the vocal cords.

CRT – the abbreviation that stands for Certified Respiratory Therapist.

Cyanosis – an abnormal bluish discoloration of the skin that is an indication of hypoxemia or inadequate oxygenation.

Cystic Fibrosis – a genetic disease that is characterized by abnormally large amounts of thick secretions and pancreatic insufficiency that causes lung infections and difficulty breathing over time.


Dead Space – the volume of ventilated air that does not participate in gas exchange.

Dead Space/Tidal Volume Ratio (VD/VT) – a ratio that shows the percentage of each breath that does not participate in gas exchange.

Defibrillation – the act of delivering an electrical shock to the heart for the treatment of a life-threatening cardiac arrhythmia.

Diaphoresis – a medical term characterized by abnormal, excessive sweating.

Diaphragm – a muscle of respiration located below the lungs that continually contracts and assists with ventilation.

Diminished Breath Sounds – a type of lung sounds that are heard (or not heard) when there is decreased air movement in the lungs.

Diuretic Agents – a class of medication that stimulates urine production to promote the excretion of excess water and sodium in patients who are fluid overloaded.

DLCO Test – a pulmonary function test that is performed to assess the extent to which carbon monoxide can diffuse from air into the bloodstream.

Droplet Precautions – safety measures used to reduce the risk of transmitting infectious diseases and microorganisms that can be spread by droplet particles in the air after coughing, sneezing, or talking.

Drug Overdose – when a person takes too much of a medication that is more than the recommended medical dose. The medication could be prescription, over-the-counter, or illegal. It could be intentional or accidental.

Dyspnea – a term that refers to shortness of breath or difficulty breathing as perceived by the patient.


Electrocardiogram (ECG)
Endobronchial Intubation
Endotracheal Tube
Extracorporeal Membrane Oxygenation (ECMO)


Fenestrated Tracheostomy Tube
Fetal Lung Development
FEV1/FVC Ratio
Flail Chest
Flexible Bronchoscopy
Flow Rate
Forced Expiratory Volume in 1 Second (FEV1)
Forced Vital Capacity (FVC)
Fraction of Inspired Oxygen (FiO2)
Frequency/Tidal Volume Ratio (f/VT)
Full Ventilatory Support
Functional Residual Capacity (FRC)


Gas Exchange – the physiological process of diffusion where oxygen moves from the lungs to the bloodstream during inhalation and carbon dioxide moves from the blood to the lungs for removal during exhalation.

Glasgow Coma Scale (GCS) – a scoring system used to classify a patient’s level of consciousness after a brain injury.

Grunting – a noisy, irregular breathing pattern in infants that serves as an indication of respiratory distress.

Guillain-Barré Syndrome – a rapid-onset disease characterized by ascending paralysis in which the patient’s autoimmune system attacks and causes inflammation and deterioration of the peripheral nervous system.


Head Trauma
Heart Rate (HR)
Heat and Moisture Exchanger (HME)
High-Flow Nasal Cannula (HFNC)
High-Frequency Chest Wall Compression (HFCW)
High-Frequency Oscillatory Ventilation (HFOV)
Hoover Sign
Huff Cough
Hyperbaric Oxygen Therapy
Hypertonic Saline
Hypoxemic Respiratory Failure


Inhaled Corticosteroids
Inhaled Anti-Infective Agents
Inhaled Nitric Oxide (INO)
Inspiratory Capacity (IC)
Inspiratory-to-Expiratory Ratio (I:E Ratio)
Inspiratory Positive Airway Pressure (IPAP)
Inspiratory Reserve Volume (IRV)
Intermittent Positive Pressure Breathing (IPPB)
Interstitial Fluid
Interstitial Lung Disease (ILD)
Intrapulmonary Percussive Ventilation (IPV)
Inverse Ratio Ventilation (IRV)
Iron Lung


Joint Commission – a nonprofit organization that is responsible for the accreditation and certification of hospitals and healthcare organizations in the United States.

Jugular Venous Distention – the abnormal bulging of the jugular veins in a patient’s neck that is often a sign of heart failure.


Kerley B Lines – the thin lines that can be seen on a chest x-ray near the pleural edge of the lungs that are caused by increased pulmonary capillary pressures.

Kussmaul Respiration – an abnormal breathing pattern characterized by an increased respiratory rate and depth of breathing with an irregular rhythm.

Kyphoscoliosis – a condition characterized by an abnormal curvature of the sagittal and coronal planes of the spine.


Lobar Atelectasis
Low-Flow System


Magnetic Resonance Imaging (MRI)
Mallampati Score
Mandatory Breath
Mandatory Minute Ventilation (MMV)
Maximum Expiratory Pressure (MEP)
Maximum Inspiratory Pressure (MIP)
Maximum Voluntary Ventilation (MVV)
Mean Airway Pressure
Mechanical Insufflation-Exsufflation
Mechanical Ventilation
Mechanical Ventilator
Meconium Aspiration Syndrome
Metabolic Acidosis
Metabolic Alkalosis
Methacholine Challenge Test
Methylxanthine Medication
Minute Ventilation
Modified Allen Test
Mucous Plugging
Muscular Dystrophy
Myasthenia Gravis
Myocardial Infarction


Nasal Flaring
National Board for Respiratory Care (NBRC)
Negative-Pressure Ventilation
Neonatal Respiratory Distress Syndrome (NRDS)
Neuromuscular Blocking Agents
Newborn Grunting
Noninvasive Positive Pressure Ventilation (NPPV)
Noninvasive Ventilation
Nonsteroidal Anti-Asthma Agents
Nosocomial Pneumonia


Obstructive Sleep Apnea (OSA)
Oxygen Therapy


Patient-Ventilator Asynchrony
Peak Expiratory Flow Rate (PEFR)
Pediatric Advanced Life Support (PALS)
Persistent Pulmonary Hypertension of the Newborn (PPHN)
P/F Ratio (PaO2/FiO2)
Plateau Pressure
Pleural Effusion
Pleural Friction Rub
Positive End Expiratory Pressure (PEEP)
Positive Expiratory Pressure (PEP)
Positron Emission Tomography (PET Scan)
Pressure Controlled Ventilation (PCV)
Pressure Support Ventilation (PSV)
Prone Positioning
Pulmonary Edema
Pulmonary Embolism
Pulmonary Function Testing (PFT)
Pulmonary Rehabilitation
Pulmonary Surfactant
Pulsus Alternans
Pulsus Paradoxus


Quality Assurance
Quality Control


Rapid Shallow Breathing Index (f/VT)
Reducing Valve
Refractory Hypoxemia
Residual Volume (RV)
Respiratory Acidosis
Respiratory Care Plan
Respiratory Care Practitioner
Respiratory Care Protocol
Respiratory Distress Syndrome (RDS)
Respiratory Rate
Respiratory Therapist (RT)
Restrictive Lung Disease
Retinopathy of Prematurity (ROP)
Rhonchal Fremitus


Silverman Score
Spontaneous Breathing Trial (SBT)
Standard Precautions
Status Asthmaticus
Strain-Gauge Pressure Transducers
Stroke Volume
Subcutaneous Emphysema
Sudden Infant Death Syndrome (SIDS)
Supplemental Oxygen
Swan-Ganz Catheter
Synchronous Intermittent Mandatory Ventilation (SIMV)


Tamponade (Cardiac)
Tension Pneumothorax
Tetralogy of Fallot
Thoracic Flap or Flail Chest
Tidal Volume
Total Lung Capacity (TLC)
Tracheoesophageal Fistula
Tracheostomy Tube
Transient Tachypnea of the Newborn (TTN):
Traumatic Brain Injury


Ultrasonic Nebulizer – a type of nebulizer that uses an electrical signal and high-frequency vibrations to break a drug solution into aerosol particles for inhalation.

Ultrasound – an imaging test that uses high-frequency sound waves to create a visual of the organs and structures of the body for assessment.

Upper Airway Stimulation – a technique for treating obstructive sleep apnea that involves the implantation of a device that can monitor breathing patterns and provide stimulation to maintain an open airway.


Vagus Nerve – a cranial nerve in the brain that is part of the autonomic nervous system which controls involuntary bodily functions.

Vallecula – an anatomic depression behind the base of the tongue that serves as an important reference landmark during intubation.

Ventilation – a term that refers to the molecular exchange of oxygen and carbon dioxide in the body. Carbon dioxide is transported through veins to the lungs where it can be exhaled.

Ventilation/Perfusion (V/Q) Ratio – a ratio that refers to the amount of air that reaches the alveoli per minute compared to the amount of blood that reaches the alveoli per minute.

Ventilator Alarms – a safety mechanism on a mechanical ventilator that uses set parameters to provide alerts whenever there is a potential problem related to the patient-ventilator interaction.

Ventilator-Associated Pneumonia (VAP) – a lung infection that develops 48 hours or more after a patient has been intubated and placed on the ventilator.

Ventilator Mode – a way of describing how a mechanical ventilator assists a patient with inspiration. The characteristics of a particular mode essentially control how the ventilator functions.

Ventilator Settings – the controls on a mechanical ventilator that can be set or adjusted in order to determine the amount of support that is delivered to the patient.

Ventricular Fibrillation – a life-threatening cardiac arrhythmia that results in a rapid heart rate due to erratic quivering of the muscles of the ventricles.

Ventricular Tachycardia – a cardiac arrhythmia that results in an abnormally fast heart rate due to improper electrical activity in the ventricles.

Vesicular Breath Sounds – a term that refers to the normal breath sounds that you would expect to hear as air flows through an open airway.

Vital Capacity (VC) – the total amount of air that can be exhaled from the lungs after a maximum inhalation.

Volume-Controlled Ventilation – a mode of mechanical ventilation in which a specific tidal volume can be set and delivered.

Volume Support – a mode of mechanical ventilation in which the ventilator delivers a supported breath to help the patient reach a set tidal volume. This mode is commonly used to wean patients from anesthesia.

V/Q Scan – an imaging test that uses a radiographic substance to assess the ventilation and perfusion of the lungs. It’s typically indicated to check for a pulmonary embolism.


Water Vapor Pressure – the pressure at which water is in equilibrium with its gaseous state.

Wet Drowning – a type of drowning that occurs due to the inhalation of a large amount of water into the lungs.

Wheezes – high-pitched abnormal breath sounds that are heard as air flows through a narrowed airway.

Work Of Breathing (WOB) – the energy and force that is required in order to inhale a volume of gas into the lungs.


Xiphoid Process – the section of the lower end of the sternum that sits just above the diaphragm.

Xopenex – an inhaled short-acting Beta-2 agonist bronchodilator that is administered to provide relief for acute reversible airflow obstructions as seen in patients with asthma or COPD.


Yankauer – an oral catheter made of hard plastic with an angled head that is designed for suctioning the mouth and throat.

Y-connector – an adapter in the circuit of a mechanical ventilator that connects the inspiratory and expiratory limbs together


Zafirlukast – an orally administered antileukotriene agent that is used for the treatment of chronic asthma and is effective in inhibiting episodes that are caused by certain triggers.

Zone Valve – a valve that controls the medical gas distribution of the central piping system to a specific zone of the hospital that typically contains an on/off switch for oxygen, air, and vacuum.


The following are the sources that were used while doing research for this article:

  • Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020. [Link]
  • Clinical Application of Mechanical Ventilation. 4th ed., Cengage Learning, 2013. [Link]
  • Pilbeam’s Mechanical Ventilation: Physiological and Clinical Applications. 6th ed., Mosby, 2015. [Link]
  • Mosby’s Respiratory Care Equipment. 10th ed., Mosby, 2017. [Link]
  • Rau’s Respiratory Care Pharmacology. 10th ed., Mosby, 2019. [Link]
  • Wilkins’ Clinical Assessment in Respiratory Care. 8th ed., Mosby, 2017. [Link]
  • Cardiopulmonary Anatomy & Physiology: Essentials of Respiratory Care. 7th ed., Cengage Learning, 2019. [Link]
  • Clinical Manifestations and Assessment of Respiratory Disease. 8th ed., Mosby, 2019. [Link]
  • Ruppel’s Manual of Pulmonary Function Testing. 11th ed., Mosby, 2017. [Link]
  • Neonatal and Pediatric Respiratory Care. 5th ed., Saunders, 2018. [Link]