Respiratory Therapy Terms and Definitions

A

AARC – the abbreviation for the American Association for Respiratory Care, a professional organization dedicated to advancing respiratory care through education, advocacy, research, and professional standards.

Accessory Muscles of Breathing – muscles of the neck, chest, and abdomen that assist the diaphragm during increased work of breathing or respiratory distress.

Acid-Base Balance – the process by which the body regulates acids and bases to maintain a stable blood pH and normal physiologic function.

Acute Exacerbation of COPD – a sudden worsening of COPD symptoms that often requires increased medications, additional therapy, or hospitalization.

Acute Respiratory Distress Syndrome (ARDS) – a severe form of acute lung injury characterized by widespread inflammation, impaired gas exchange, and refractory hypoxemia.

Adult Croup – a rare condition in adults involving inflammation of the larynx and trachea, resulting in a barking cough, hoarseness, and airway narrowing.

Advanced Cardiac Life Support (ACLS) – an advanced medical protocol for managing cardiac arrest and other life-threatening cardiovascular emergencies using medications, airway management, and advanced monitoring.

Advance Directive – a legal document that specifies an individual’s preferences for medical treatment if they become unable to communicate or make decisions.

Aerophagia – excessive swallowing of air, often causing abdominal bloating, belching, and gastrointestinal discomfort.

Aerosol Medication – a method of drug delivery in which medication is dispersed into fine particles for inhalation directly into the lungs.

Agonal Breathing – an abnormal, gasping respiratory pattern that occurs during severe hypoxia or cardiac arrest and is not effective for ventilation.

Airborne Particles – microscopic solid or liquid particles suspended in the air that can be inhaled into the respiratory tract.

Airborne Precautions – infection control measures used to prevent the spread of infectious agents transmitted through tiny airborne particles that can remain suspended in the air and travel over long distances.

Air Bronchogram – a radiographic sign in which air-filled bronchi are visible due to surrounding alveoli being filled with fluid or consolidation.

Airway Clearance Therapy – noninvasive techniques used to loosen, mobilize, and remove secretions from the airways to improve ventilation and gas exchange.

Airway Management – the process of maintaining a patent airway and adequate ventilation using positioning, airway devices, or artificial airways.

Airway Obstruction – a partial or complete blockage of an airway that restricts airflow and impairs ventilation.

Airway Pharmacology – the study and use of medications that act on the airways to treat respiratory conditions, often delivered via inhalation.

Airway Pressure Release Ventilation (APRV) – a mode of mechanical ventilation that applies continuous positive airway pressure with brief, timed pressure releases to facilitate ventilation.

Airway Resistance – the opposition to airflow within the respiratory tract during inspiration and expiration.

Airway Suctioning – a procedure that uses negative pressure to remove secretions from the airway through a catheter or suction device.

Albuterol – a short-acting beta-2 agonist bronchodilator used to relieve bronchospasm in conditions such as asthma and COPD.

Alveolar-Arterial Gradient (A-a Gradient) – a calculated measurement that assesses the efficiency of oxygen transfer from the alveoli to the arterial blood.

Alveolar-Capillary Membrane – the thin barrier between the alveoli and pulmonary capillaries where gas exchange occurs.

Alveolar Gas Equation – a formula used to estimate the partial pressure of oxygen in the alveoli.

Alveolar Ventilation – the volume of air reaching the alveoli per minute that is available for gas exchange.

Alveoli – microscopic air sacs in the lungs where oxygen and carbon dioxide are exchanged between air and blood.

Ambulation – the act or ability of a patient to walk, with or without assistance.

Anatomic Dead Space – the portion of the respiratory tract where air does not participate in gas exchange.

Anion Gap – a calculated value used to help identify metabolic acidosis by assessing unmeasured ions in the blood.

Anticholinergic Bronchodilators – medications that block acetylcholine at muscarinic receptors, causing relaxation of airway smooth muscle and bronchodilation.

Antimicrobial Agents – drugs that destroy or inhibit the growth of microorganisms to treat or prevent infections.

Apgar Score – a standardized assessment performed at one and five minutes after birth to evaluate a newborn’s physical condition.

Apnea – a temporary cessation of breathing lasting at least 10 seconds.

Apnea Monitoring – continuous monitoring of respiratory and cardiac activity to detect apnea, bradycardia, or hypoxemia.

Apnea of Prematurity – a condition in premature infants marked by recurrent pauses in breathing due to immature respiratory control.

Apneustic Breathing – an abnormal breathing pattern characterized by prolonged inspiration caused by damage to the upper pons.

Arterial Blood Gas (ABG) – a blood test that measures oxygenation, ventilation, and acid-base status using arterial blood.

Arterial Line – a catheter placed in an artery for continuous blood pressure monitoring and arterial blood sampling.

Artificial Airway – a medical device inserted into the airway to maintain patency and support ventilation.

Assist/Control Mode (A/C) – a ventilator mode in which every breath receives a preset volume or pressure, whether patient- or machine-triggered.

Asthma – a chronic inflammatory airway disease characterized by reversible airflow obstruction and episodic symptoms.

Atelectasis – partial or complete collapse of lung tissue resulting in reduced ventilation.

Auscultation – listening to internal body sounds with a stethoscope to assess organ function.

Automatic External Defibrillator (AED) – a portable device that analyzes heart rhythm and delivers a shock when needed to restore normal cardiac rhythm.

Auto-PEEP – the presence of residual positive pressure in the alveoli at the end of exhalation due to incomplete lung emptying.

B

Barrel Chest – an abnormal increase in the anterior-posterior diameter of the chest, commonly associated with emphysema and chronic lung hyperinflation.

Base Excess (BE) – a value calculated from an arterial blood gas that reflects the amount of excess or deficient base in the blood, used to assess metabolic acid-base status.

Beta-2 Agonist – a medication that stimulates beta-2 adrenergic receptors to relax airway smooth muscle and improve airflow.

Bicarbonate (HCO3-) – a major blood buffer that helps maintain acid-base balance by neutralizing excess hydrogen ions.

Bilevel Positive Airway Pressure (BiPAP) – a form of noninvasive ventilation that delivers two levels of airway pressure to support ventilation and reduce the work of breathing.

Biot’s Respirations – an abnormal breathing pattern marked by irregular respirations with unpredictable periods of apnea, often caused by damage to the medulla.

Bird Flu – a viral infection caused by avian influenza viruses that primarily affects birds but can occasionally infect humans.

Bland Aerosol Therapy – inhalation of sterile water or saline aerosol to humidify the airways and loosen secretions.

Blood Gas Analyzer – a laboratory device that measures blood pH, oxygen, and carbon dioxide levels to evaluate respiratory and metabolic function.

Body Plethysmography – a pulmonary function test that measures lung volumes and airway resistance using pressure changes within an airtight chamber.

Bohr Effect – the shift in hemoglobin’s oxygen dissociation curve caused by increased carbon dioxide or acidity, resulting in decreased oxygen affinity.

Bourdon Gauge – a pressure-measuring device used in oxygen flowmeters that displays gas pressure as a corresponding flow rate.

Bradycardia – a slower-than-normal heart rate, typically defined as fewer than 60 beats per minute in adults.

Bradypnea – an abnormally slow respiratory rate, generally fewer than 12 breaths per minute in adults.

Breathing Pattern – the characteristic rhythm, rate, and depth of a patient’s ventilation over time.

Breathing Reflex – an involuntary neurological response that regulates breathing to protect the airways and maintain adequate ventilation.

Breathing Treatment – inhalation therapy in which medications are delivered to the lungs, commonly using a nebulizer, to relieve or manage respiratory symptoms.

Bronchial Breath Sounds – loud, high-pitched breath sounds with a prolonged expiratory phase, normal over the trachea but abnormal when heard in peripheral lung fields.

Bronchiectasis – a chronic lung disease characterized by permanent dilation and damage of the bronchi due to recurrent infection and inflammation.

Bronchitis – inflammation of the bronchial tubes, commonly caused by infection, resulting in cough, mucus production, and airway irritation.

Bronchoalveolar Lavage (BAL) – a procedure performed during bronchoscopy in which saline is instilled and collected to obtain samples from the lower airways.

Bronchoconstriction – narrowing of the airways caused by contraction of bronchial smooth muscle, leading to increased airway resistance.

Bronchodilator – a medication that relaxes airway smooth muscle to widen the airways and improve airflow.

Bronchoprovocation Study – a diagnostic test used to evaluate airway hyperresponsiveness by administering a provoking agent and measuring lung function changes.

Bronchopulmonary Dysplasia (BPD) – a chronic lung disease in premature infants caused by lung immaturity and prolonged oxygen or ventilator exposure.

Bronchoscopy – a procedure that allows direct visualization of the airways using a flexible or rigid bronchoscope for diagnostic or therapeutic purposes.

Bronchovesicular Breath Sounds – medium-pitched breath sounds with equal inspiratory and expiratory phases, normally heard near the sternum and between the scapulae.

Bubble Humidifier – a device that humidifies supplemental oxygen by passing it through water before delivery to the patient.

Bullous Emphysema – a form of emphysema characterized by large air-filled spaces resulting from alveolar destruction, which reduce effective lung tissue and impair breathing.

C

Capillaries – the smallest blood vessels that connect arterioles and venules and allow the exchange of gases, nutrients, and waste products.

Capillary Blood Gas (CBG) – a blood sample obtained from capillary circulation, commonly used in infants and children as an alternative to arterial sampling.

Capnography – the continuous measurement and monitoring of carbon dioxide levels in exhaled gas.

Carbon Dioxide Transport – the process by which carbon dioxide is carried from tissues to the lungs via plasma, bicarbonate ions, and hemoglobin for elimination.

Carbon Monoxide Poisoning – a life-threatening condition caused by inhalation of carbon monoxide, which prevents hemoglobin from effectively transporting oxygen.

Carboxyhemoglobin – hemoglobin bound to carbon monoxide, which significantly reduces the blood’s oxygen-carrying capacity.

Cardiac Electrophysiology – the study of the heart’s electrical system and the diagnosis and treatment of cardiac rhythm disorders.

Cardiac Output – the volume of blood pumped by the heart per minute, calculated as heart rate multiplied by stroke volume.

Cardiac Tamponade – a medical emergency in which rapid fluid accumulation in the pericardial sac compresses the heart and impairs cardiac filling.

Cardiogenic Pulmonary Edema – pulmonary edema caused by elevated cardiac pressures, most commonly associated with left-sided heart failure.

Cardiopulmonary Diseases – conditions affecting the heart and lungs that impair circulation and oxygen delivery.

Cardiopulmonary Rehabilitation – a structured program designed to improve functional capacity, symptoms, and quality of life in patients with heart or lung disease.

Cardiopulmonary Resuscitation (CPR) – an emergency lifesaving technique using chest compressions and ventilation to restore circulation and breathing during cardiac or respiratory arrest.

Cardiovascular Life Support – a group of emergency interventions used to manage acute cardiac and circulatory emergencies.

Cardioversion – a procedure that delivers a controlled electrical shock to restore a normal heart rhythm.

Carina – the cartilaginous ridge at the point where the trachea divides into the right and left mainstem bronchi.

Central Sleep Apnea (CSA) – a sleep disorder characterized by repeated pauses in breathing due to lack of respiratory effort from impaired central nervous system signaling.

Centrilobular Emphysema – a form of emphysema primarily affecting the central portions of the secondary pulmonary lobules, most commonly seen in smokers.

Chest Percussion – a physical examination technique that involves tapping the chest wall to assess underlying lung tissue, air distribution, and the presence of fluid or abnormalities in the thoracic cavity.

Chest Physical Therapy (CPT) – a group of techniques used to mobilize secretions, improve ventilation, and enhance airway clearance.

Chest Radiograph – a diagnostic imaging study that uses x-rays to produce a two-dimensional image of the lungs, heart, and other structures within the thoracic cavity.

Chest Trauma – injury to the chest wall, lungs, or intrathoracic organs resulting from blunt or penetrating force.

Cheyne-Stokes Respiration – an abnormal breathing pattern marked by cyclic increases and decreases in tidal volume followed by periods of apnea.

Chronic Bronchitis – a chronic inflammatory condition defined by productive cough lasting at least three months in two consecutive years.

Chronic Cough – a cough lasting longer than eight weeks in adults or four weeks in children.

Chronic Obstructive Pulmonary Disease (COPD) – a progressive respiratory disease characterized by persistent airflow limitation and chronic inflammation.

Cilia – microscopic hair-like structures lining the airways that move mucus and trapped particles toward the throat for removal.

Clinical Simulation Exam (CSE) – a performance-based examination that assesses a respiratory therapy student’s clinical decision-making and patient management skills using simulated clinical scenarios.

Code of Ethics – a set of professional principles that guide ethical behavior, responsibility, and patient-centered care in respiratory therapy practice.

Committee on Accreditation for Respiratory Care (CoARC) – the accrediting body responsible for establishing educational standards and accrediting respiratory care educational programs.

Complete Blood Count (CBC) – a common laboratory test that evaluates red blood cells, white blood cells, platelets, hemoglobin, and hematocrit to assess overall health and detect disease.

Computed Tomography (CT) – an imaging technique that uses X-rays and computer processing to produce detailed cross-sectional images of internal structures.

Congenital Cardiac Defect – a structural abnormality of the heart present at birth that can affect blood flow and cardiac function.

Congenital Diaphragmatic Hernia (CDH) – a birth defect in which abdominal organs herniate into the chest through an opening in the diaphragm, impairing lung development and causing respiratory distress.

Congestive Heart Failure (CHF) – a condition in which the heart is unable to pump sufficient blood to meet the body’s needs, leading to fluid accumulation, dyspnea, and fatigue.

Contact Precautions – infection control measures used to prevent the spread of diseases transmitted through direct or indirect contact with patients or contaminated surfaces.

Continuous Positive Airway Pressure (CPAP) – a noninvasive therapy that delivers constant positive airway pressure to maintain airway patency and improve oxygenation.

Continuous Mandatory Ventilation (CMV) – a mode of mechanical ventilation in which all breaths are machine-delivered, regardless of patient effort.

COPD – the abbreviation for chronic obstructive pulmonary disease, a progressive condition characterized by persistent airflow limitation.

Cor Pulmonale – right ventricular failure resulting from chronic pulmonary hypertension due to underlying lung disease.

Coronary Artery Bypass Graft (CABG) – a surgical procedure that restores blood flow to the heart by bypassing blocked coronary arteries using grafted vessels.

Coronary Artery Disease (CAD) – a condition caused by atherosclerotic plaque buildup in the coronary arteries, reducing blood flow to the heart muscle.

Coughing Up Mucus – a protective reflex in which mucus is expelled from the airways to remove irritants, pathogens, or excess secretions.

COVID-19 – an infectious respiratory disease caused by the SARS-CoV-2 virus, ranging from mild illness to severe respiratory failure.

CPAP Belly Syndrome – abdominal bloating or discomfort caused by air swallowing during continuous positive airway pressure therapy.

Crackles – discontinuous, popping breath sounds heard during inspiration, often associated with fluid, secretions, or alveolar collapse.

Cricothyrotomy – an emergency airway procedure involving incision of the cricothyroid membrane to establish ventilation when other airway methods fail.

Croup – a viral upper airway infection causing subglottic inflammation, inspiratory stridor, and a barking cough.

Croup Tent – a humidified enclosure used to deliver cool mist therapy to children with croup to reduce airway irritation.

Crowing Breath Sounds – high-pitched inspiratory sounds caused by partial obstruction or narrowing of the upper airway.

CRT – the abbreviation for certified respiratory therapist.

Cyanosis – a bluish discoloration of the skin or mucous membranes resulting from inadequate oxygenation of the blood.

Cystic Fibrosis – an inherited disorder that causes thick, sticky mucus production, leading to chronic respiratory infections and impaired digestion.

D

Dead Space – the portion of inhaled air that does not participate in gas exchange because it remains in the conducting airways or reaches alveoli that are not perfused.

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

Deep Vein Thrombosis (DVT) – formation of a blood clot in a deep vein, most commonly in the legs, which can lead to serious complications such as pulmonary embolism.

Defibrillation – delivery of an electrical shock to the heart to terminate life-threatening arrhythmias and restore an organized rhythm.

Depth of Respiration – the amount of air inhaled or exhaled with each breath.

Diaphoresis – excessive sweating that is not related to environmental temperature or physical activity and often signals underlying illness or distress.

Diaphragm – a dome-shaped skeletal muscle that separates the thoracic and abdominal cavities and serves as the primary muscle of inspiration.

Diffusing Capacity of the Lungs for Carbon Monoxide (DLCO) – a pulmonary function test that measures the ability of gases to diffuse from the alveoli into the pulmonary capillary blood.

Diminished Breath Sounds – reduced or faint lung sounds caused by decreased airflow or impaired transmission of sound through lung tissue or the chest wall.

Disease X – a placeholder term used by the World Health Organization to represent a hypothetical unknown pathogen with the potential to cause a future epidemic or pandemic.

Diuretic Agents – medications that increase urine output to remove excess fluid and sodium from the body.

DOPE Mnemonic – a troubleshooting tool used for intubated patients to identify Displacement, Obstruction, Pneumothorax, or Equipment failure.

Dorsal Recumbent Position – a body position in which the patient lies on their back with knees flexed and feet flat, commonly used for examinations and procedures.

Droplet Precautions – infection control measures designed to prevent transmission of pathogens spread through respiratory droplets produced by coughing, sneezing, or talking.

Drug Overdose – ingestion or exposure to a drug in an amount greater than recommended or safe, whether accidental or intentional.

Dry Cough – a nonproductive cough that does not produce mucus and is often associated with throat irritation.

Dry Drowning – a condition in which water exposure triggers a laryngospasm that closes the airway and prevents air from entering the lungs, leading to oxygen deprivation without significant water inhalation.

DuoNeb – a combination bronchodilator containing albuterol and ipratropium used to treat bronchospasm in obstructive lung diseases.

Dyspnea – the subjective sensation of difficult or uncomfortable breathing.

E

Elasticity – the ability of a tissue to return to its original shape after being stretched or deformed.

Electrocardiogram (EKG) – a noninvasive test that records the electrical activity of the heart to assess rhythm and cardiac function.

Emphysema – a chronic obstructive lung disease characterized by irreversible destruction of alveolar walls, resulting in reduced gas exchange and airflow limitation.

Endotracheal Tube – an artificial airway inserted into the trachea to maintain airway patency and provide mechanical ventilation.

End-Tidal CO2 Monitoring – a noninvasive method used to measure the partial pressure of carbon dioxide at the end of exhalation, reflecting ventilation status.

Epiglottis – a leaf-shaped structure that covers the airway during swallowing; inflammation of this structure (epiglottitis) can cause severe upper airway obstruction.

Erythrocyte – a red blood cell responsible for transporting oxygen and carbon dioxide.

Esophagus – a muscular tube that connects the pharynx to the stomach and moves food and liquids via peristalsis.

EVALI – e-cigarette or vaping-associated lung injury, a serious condition linked to vaping, often associated with THC-containing products and vitamin E acetate.

Expiratory Reserve Volume (ERV) – the maximum volume of air that can be forcefully exhaled after a normal tidal exhalation.

Extracellular Fluid – all body fluid located outside cells, including plasma and interstitial fluid, involved in nutrient delivery and waste removal.

Extracorporeal Membrane Oxygenation (ECMO) – a form of extracorporeal life support that circulates blood outside the body for oxygenation and carbon dioxide removal.

Extubation – removal of an endotracheal tube once a patient no longer requires mechanical ventilation.

F

Fenestrated Tracheostomy Tube – a tracheostomy tube with an opening (fenestration) that allows airflow through the upper airway, enabling speech when the cuff is deflated.

Fetal Circulation – a specialized circulatory system that allows oxygen, nutrients, and waste exchange between the fetus and placenta, bypassing the lungs.

Fetal Lung Development – a multistage process during gestation in which the lungs mature structurally and functionally to allow postnatal breathing and gas exchange.

FEV1 – the volume of air forcibly exhaled during the first second of a forced vital capacity maneuver.

FEV1/FVC Ratio – the percentage of the forced vital capacity exhaled during the first second, used to assess airflow obstruction.

Fick’s First Law of Diffusion – a principle stating that the rate of gas diffusion across a membrane is directly proportional to surface area, concentration gradient, and permeability, and inversely proportional to membrane thickness.

Flail Chest – a serious chest wall injury in which multiple adjacent ribs are fractured, causing a segment of the chest wall to move independently.

Flexible Bronchoscopy – an endoscopic procedure using a flexible scope to visualize, sample, or treat the airways.

Flowmeter – a device used to regulate and measure the flow of medical gases delivered to a patient.

Flow Rate – the speed at which gas or air moves during inspiration or expiration, typically measured in liters per minute.

Flow-Volume Loop – a graphical display of airflow plotted against lung volume during forced inspiration and expiration.

Flutter Valve – a handheld airway clearance device that combines positive expiratory pressure with oscillations to mobilize secretions.

Forced Expiration Technique (FET) – an airway clearance method that uses controlled breathing and huff coughing to move mucus from the lungs.

Forced Vital Capacity (FVC) – the maximum volume of air that can be forcefully exhaled after a full inspiration.

Fraction of Inspired Oxygen (FiO2) – the proportion or percentage of oxygen in the gas mixture inhaled by a patient.

Functional Residual Capacity (FRC) – the volume of air remaining in the lungs after a normal passive exhalation.

G

Gas Distribution Tests – pulmonary function tests that evaluate how evenly air is distributed throughout the lungs to help assess ventilation abnormalities.

Gas Exchange – the diffusion process by which oxygen moves from the alveoli into the bloodstream and carbon dioxide moves from the blood into the lungs for exhalation.

Glasgow Coma Scale (GCS) – a standardized scoring system used to assess a patient’s level of consciousness based on eye, verbal, and motor responses.

Gastroesophageal Reflux Disease (GERD) – a chronic condition in which stomach contents reflux into the esophagus, causing symptoms such as heartburn, regurgitation, and irritation.

GlideScope – a video laryngoscope that provides an indirect, magnified view of the airway to assist with endotracheal intubation.

Grunting – an abnormal expiratory sound, most commonly seen in infants, produced to maintain airway pressure and indicative of respiratory distress.

Guillain-Barré Syndrome – an acute autoimmune disorder characterized by rapid-onset, ascending muscle weakness due to inflammation and damage of the peripheral nerves.

H

Haldane Effect – the physiological phenomenon in which oxygen binding to hemoglobin in the lungs promotes the release of carbon dioxide, enhancing CO₂ elimination.

Head Trauma – any injury to the head that may affect the scalp, skull, or brain, ranging from mild to severe and potentially impairing brain function.

Heart Rate (HR) – the number of heartbeats per minute.

Heat and Moisture Exchanger (HME) – a passive humidification device that conserves heat and moisture from exhaled gas and returns it during inhalation in mechanically ventilated patients.

Heliox – a mixture of helium and oxygen used to reduce airway resistance and improve airflow in patients with severe airway obstruction.

Hemodynamic Monitoring – the assessment of cardiovascular function through continuous measurement of parameters such as blood pressure, cardiac output, and fluid status.

Hemoglobin – an iron-containing protein in red blood cells responsible for transporting oxygen and carbon dioxide.

Hemoptysis – the expectoration of blood originating from the lower respiratory tract.

Hemothorax – the accumulation of blood within the pleural space, most commonly due to chest trauma.

High-Flow Nasal Cannula (HFNC) – an oxygen delivery system that provides heated, humidified oxygen at high flow rates to improve oxygenation and reduce work of breathing.

High-Frequency Chest Wall Compression (HFCW) – an airway clearance technique that uses an inflatable vest to generate chest wall oscillations and mobilize pulmonary secretions.

High-Frequency Oscillatory Ventilation (HFOV) – a mechanical ventilation mode that delivers very small tidal volumes at very high frequencies to reduce the risk of ventilator-induced lung injury.

History of Respiratory Care – the evolution of respiratory care practices, technologies, and professional roles used to assess and treat pulmonary disease.

Humidification Therapy – the administration of moisture to inhaled gases to maintain airway hydration and normal mucociliary function.

Hypercapnia – an abnormally elevated level of carbon dioxide in the blood.

Hyperoxia – an excessive level of oxygen in the blood or tissues, often due to prolonged high-concentration oxygen therapy.

Hyperpnea – increased depth and rate of breathing that results in increased ventilation, often in response to metabolic demand.

Hypertension – persistently elevated arterial blood pressure.

Hyperventilation – increased ventilation that leads to abnormally low arterial carbon dioxide levels.

Hypocapnia – abnormally low levels of carbon dioxide in the blood, commonly caused by hyperventilation.

Hypokalemia – a condition marked by low serum potassium levels that can disrupt neuromuscular and cardiac function.

Hypotension – abnormally low blood pressure.

Hypoventilation – inadequate ventilation resulting in elevated arterial carbon dioxide levels.

Hypoxemia – a condition characterized by low oxygen levels in arterial blood.

Hypoxia – insufficient oxygen supply at the tissue level.

I

Incentive Spirometry – a lung expansion therapy that encourages sustained deep inhalation to promote alveolar inflation and reduce the risk of atelectasis.

Indoor Air Quality – the condition of air within enclosed environments as it relates to occupant health, comfort, and exposure to pollutants.

Inhaled Anti-Infective Agents – medications delivered via inhalation to treat or prevent respiratory infections by targeting pathogenic microorganisms in the airways.

Inhaled Corticosteroids – anti-inflammatory medications used for long-term control of airway inflammation in conditions such as asthma.

Inhaled Nitric Oxide (iNO) – a selective pulmonary vasodilator that relaxes vascular smooth muscle, improving ventilation–perfusion matching and oxygenation.

Inhaled Pulmonary Vasodilators – medications administered by inhalation to dilate pulmonary blood vessels, reduce pulmonary vascular resistance, and improve oxygenation.

Inspiratory Capacity (IC) – the maximum volume of air that can be inhaled following a normal passive exhalation.

Inspiratory Flow Rate – the rate at which air enters the lungs during inspiration, commonly measured in liters per minute.

Inspiratory Pressure – the pressure applied during the inspiratory phase of ventilation to deliver airflow into the lungs.

Inspiratory-to-Expiratory Ratio (I:E Ratio) – the ratio comparing the duration of inspiration to expiration during a single respiratory cycle.

Inspiratory Reserve Volume (IRV) – the additional volume of air that can be forcibly inhaled after a normal tidal inspiration.

Intercostal Muscles – groups of skeletal muscles located between the ribs that assist with breathing by stabilizing and moving the chest wall during ventilation.

Intercostal Space – the anatomical area between two adjacent ribs that contains muscles, nerves, and blood vessels that support breathing and chest wall function.

Intermittent Positive Pressure Breathing (IPPB) – a patient-triggered, pressure-limited therapy used to assist lung expansion and improve ventilation.

Interstitial Fluid – the portion of extracellular fluid that surrounds tissue cells and facilitates the exchange of nutrients and waste products.

Interstitial Lung Disease (ILD) – a group of disorders characterized by inflammation and fibrosis of the lung interstitium, leading to impaired gas exchange.

Intrapulmonary Percussive Ventilation (IPV) – an airway clearance therapy that delivers rapid, small-volume bursts of gas to mobilize secretions and improve ventilation.

Intrapulmonary Shunt – the passage of blood through the lungs without exposure to ventilated alveoli, resulting in impaired oxygenation.

Intubation – placement of a tube into the trachea to secure the airway and provide mechanical ventilatory support.

Inverse Ratio Ventilation – a ventilator strategy that prolongs inspiratory time relative to expiratory time to improve oxygenation.

Iron Lung – an early negative-pressure ventilator developed in the 1920s, historically used to support breathing in patients with poliomyelitis.

J

Joint Commission – a nonprofit organization that accredits and certifies hospitals and healthcare organizations in the United States to ensure quality and patient safety standards.

Jugular Venous Distention – visible distention of the jugular vein above the sternal angle, indicating elevated central venous pressure and often associated with right-sided heart failure or fluid overload.

K

Kerley B Lines – thin, horizontal lines seen near the lung periphery on chest X-ray that indicate interstitial edema caused by increased pulmonary capillary pressure.

Kussmaul Respiration – a deep, rapid, and labored breathing pattern associated with severe metabolic acidosis, most commonly diabetic ketoacidosis.

Kyphoscoliosis – a spinal deformity involving abnormal curvature in both the sagittal (kyphosis) and coronal (scoliosis) planes, which can restrict chest wall movement and impair ventilation.

L

Laminar Flow – a type of fluid flow in which particles move smoothly in parallel layers with minimal mixing, in contrast to turbulent flow.

Laryngopharyngeal Reflux – a condition in which gastric contents reflux into the larynx and pharynx, causing throat irritation, hoarseness, chronic cough, or throat clearing.

Laryngopharynx – the lower portion of the pharynx located behind the larynx that directs air to the lungs and food to the esophagus while helping protect the airway.

Laryngoscope – a medical device used to visualize the larynx and vocal cords, commonly for airway assessment and endotracheal intubation.

Larynx – a cartilaginous structure in the upper airway responsible for voice production, airway protection, and passage of air into the trachea.

Leukocyte – a white blood cell involved in immune defense and response to infection.

Lobar Atelectasis – collapse of an entire lung lobe, commonly caused by airway obstruction or external compression.

Lung Adenocarcinoma – the most common subtype of non–small cell lung cancer, arising from glandular cells and typically located in the peripheral lung tissue.

Lung Cancer – uncontrolled growth of abnormal cells in the lungs that can form tumors and metastasize to other parts of the body.

Lung Capacity – the total volume of air the lungs are capable of holding during full inhalation and exhalation.

Lung Compliance – a measure of the lung’s ability to stretch and expand in response to applied pressure.

Lung Consolidation – a condition in which alveoli are filled with fluid, pus, blood, or cells, replacing air and causing lung tissue to appear solid on imaging.

Lung Damage – injury to lung tissue that impairs normal respiratory function and may lead to chronic or acute breathing problems.

Lung Expansion Therapy – techniques used to increase lung volume, improve ventilation, and prevent or treat atelectasis.

Lung Fissure – a natural anatomical groove that separates the lobes of each lung.

Lung Health – the overall condition of the lungs, reflecting effective ventilation, gas exchange, and absence of disease or obstruction.

Lung Infection – invasion of lung tissue by infectious organisms, resulting in inflammation and impaired respiratory function.

Lung Infiltrates – abnormal substances within the lung parenchyma that appear as increased density on imaging and suggest infection, inflammation, or other pathology.

Lung Lobe – a distinct anatomical division of the lung separated by fissures, each containing its own bronchial and vascular structures.

Lung Nodule – a small, well-defined mass in the lung, usually detected incidentally and often benign, though occasionally malignant.

Lung Parenchyma – the functional tissue of the lung responsible for gas exchange, including alveoli, alveolar ducts, and capillaries.

Lung Sounds – sounds generated by airflow through the airways and lungs, assessed by auscultation with a stethoscope.

Lymph – a clear fluid of the lymphatic system that contains white blood cells and helps maintain fluid balance and immune function.

M

Magnetic Resonance Imaging (MRI) – an imaging modality that uses strong magnetic fields and radio waves to produce detailed images of internal organs and soft tissues.

Mallampati Score – a clinical classification used to assess airway anatomy and predict the difficulty of endotracheal intubation.

Mandatory Breath – a ventilator-delivered breath that is initiated and controlled entirely by the machine.

Mandatory Minute Ventilation (MMV) – a ventilator mode that ensures a minimum minute ventilation by increasing mandatory breaths when spontaneous ventilation is insufficient.

Mean Airway Pressure – the average pressure applied to the airway throughout the entire respiratory cycle during mechanical ventilation.

Mechanical Insufflation-Exsufflation – an airway clearance therapy that simulates a cough by alternating positive and negative airway pressures to mobilize secretions.

Mechanical Ventilation – the use of a machine to provide positive pressure ventilation for patients who are unable to maintain adequate spontaneous breathing.

Mechanical Ventilation Monitoring – ongoing assessment of ventilator performance and patient response to ensure effective and safe ventilatory support.

Mechanical Ventilator – a device that delivers controlled or assisted breaths to support or replace spontaneous breathing.

Meconium Aspiration Syndrome – a neonatal condition caused by inhalation of meconium-stained amniotic fluid, leading to airway obstruction and respiratory distress.

Medical Gas Therapy – the therapeutic administration of medical gases such as oxygen, heliox, or nitric oxide to treat respiratory disorders.

Metabolic Acidosis – an acid-base disturbance caused by non-respiratory processes that result in decreased blood bicarbonate levels.

Metabolic Alkalosis – an acid-base disturbance caused by non-respiratory processes that result in elevated blood bicarbonate levels.

MetaNeb – a therapeutic device that combines lung expansion, secretion clearance, and aerosol delivery to improve respiratory function.

Methacholine Challenge Test – a diagnostic test used to evaluate airway hyperresponsiveness by measuring lung function after inhaled methacholine.

Methylxanthine – a class of bronchodilator drugs used to manage asthma and other obstructive lung diseases by relaxing airway smooth muscle.

Military Respiratory Therapist – a respiratory care professional who provides diagnostic, therapeutic, and emergency respiratory services within military healthcare systems.

Minute Ventilation – the total volume of air inhaled or exhaled from the lungs per minute.

Mixed Acid-Base Disorders – occur when two or more independent primary disturbances affect the body’s pH balance at the same time, rather than one system simply compensating for the other.

Mixed Venous Oxygen Saturation (SvO2) – the percentage of hemoglobin saturated with oxygen in mixed venous blood, reflecting the balance between oxygen delivery and consumption.

Modified Allen Test – a bedside test used to assess collateral circulation of the hand prior to radial artery puncture.

Modified Borg Dyspnea Scale (MBS) – a numerical scale ranging from 0 to 10 used to quantify a patient’s perceived level of breathlessness.

Morning Cough – a cough that occurs primarily upon waking, often associated with chronic lung disease, postnasal drip, or smoking.

Mucolytic Agents – medications that thin and loosen thick respiratory secretions to improve airway clearance.

Mucus – a viscous secretion produced by mucous membranes that traps pathogens, moistens airways, and protects epithelial surfaces.

Mucus Disorders – conditions involving abnormal production, consistency, or clearance of mucus, commonly affecting the respiratory system.

Mucus Plug – a thick accumulation of mucus that obstructs an airway and impairs ventilation.

Muscular Dystrophy – a group of inherited disorders characterized by progressive muscle weakness, often affecting respiratory muscles.

Myasthenia Gravis – an autoimmune neuromuscular disorder causing fluctuating muscle weakness, often involving facial, bulbar, and respiratory muscles.

Myocardial Infarction – a medical emergency caused by interruption of coronary blood flow, resulting in ischemia and death of heart muscle tissue.

N

Narcan – the brand name for naloxone, a fast-acting medication that reverses opioid overdose by restoring normal respiration.

Nasal Cannula – a low-flow oxygen delivery device that administers supplemental oxygen through small prongs placed in the nostrils.

Nasal Flaring – outward widening of the nostrils during breathing, commonly seen as a sign of increased work of breathing or respiratory distress.

Nasopharynx – the upper portion of the pharynx located behind the nasal cavity that serves as an airway for nasal breathing.

National Board for Respiratory Care (NBRC) – a nonprofit organization in the United States that administers credentialing examinations and maintains credentials for respiratory therapists.

Near Drowning – a life-threatening event in which a person survives a drowning incident long enough to receive medical care but experiences respiratory impairment from water exposure.

Nebulizer – a device that converts liquid medication into an aerosol for inhalation into the lungs.

Negative Pressure Ventilation – a form of mechanical ventilation that uses sub-atmospheric pressure around the chest to draw air into the lungs, mimicking normal spontaneous breathing.

Neonatal Mechanical Ventilation – ventilatory support provided to newborns who cannot adequately breathe on their own, using specialized equipment and settings.

Neonatal/Pediatric Patient Assessment – a focused evaluation of infants and children that accounts for age-specific anatomy, physiology, and clinical presentation.

Neonatal Respiratory Distress Syndrome (NRDS) – a condition in premature infants caused by surfactant deficiency, leading to alveolar collapse and respiratory distress.

Neuromuscular Blocking Agents – medications that produce skeletal muscle paralysis by inhibiting acetylcholine at the neuromuscular junction.

Newborn Grunting – an expiratory sound produced by infants to maintain airway pressure, commonly indicating respiratory distress.

Nic Sick – a collection of symptoms such as nausea, dizziness, headache, and tachycardia caused by excessive nicotine exposure.

Noninvasive Positive Pressure Ventilation (NPPV) – delivery of positive airway pressure through a mask or similar interface without the use of an artificial airway.

Noninvasive Ventilation – mechanical ventilatory support provided without endotracheal intubation.

Nonsteroidal Anti-Asthma Agents – medications used primarily for prevention and long-term control of mild persistent asthma.

Normal Breathing – effortless, rhythmic ventilation sufficient to meet metabolic oxygen demands and eliminate carbon dioxide.

Nosocomial Pneumonia – pneumonia acquired in a hospital setting at least 48 hours after admission.

Nutrition Assessment – a systematic evaluation of nutritional intake, status, and needs used to guide clinical care.

O

Obstructive Lung Diseases – respiratory disorders characterized by airflow limitation due to narrowed, inflamed, or obstructed airways, particularly during exhalation.

Obstructive Sleep Apnea (OSA) – a sleep-related breathing disorder caused by recurrent upper airway collapse during sleep, resulting in repeated pauses in breathing.

Oropharynx – the middle portion of the pharynx located behind the oral cavity that serves as a shared pathway for air, food, and liquids.

Orthopnea – shortness of breath that occurs when lying flat and improves when sitting or standing upright.

Over-the-Counter Oxygen – non-prescription oxygen products sold in small canisters for short-term, recreational, or altitude-related use, not intended for medical oxygen therapy.

Oxygenation – the process by which oxygen diffuses from the alveoli into the bloodstream.

Oxygen Concentrator – a medical device that filters nitrogen from ambient air to deliver concentrated oxygen for supplemental therapy.

Oxygen Extraction Ratio – the fraction of delivered oxygen that is removed from the blood by body tissues for metabolic use.

Oxygen Face Tent – an oxygen delivery device that fits loosely around the face, often used when masks or nasal cannulas are poorly tolerated.

Oxygen Therapy – the administration of supplemental oxygen to treat or prevent hypoxemia.

Oxygen Toxicity – lung or systemic injury resulting from prolonged exposure to elevated concentrations of oxygen.

Oxygen Transport – the movement of oxygen from the lungs to body tissues, primarily bound to hemoglobin within red blood cells.

P

Pack Years – a measure of smoking exposure calculated by multiplying the number of cigarette packs smoked per day by the total number of years smoked.

Paradoxical Breathing – an abnormal breathing pattern in which the chest wall moves inward during inspiration and outward during expiration, indicating impaired respiratory mechanics.

Parietal Pleura – the outer pleural membrane that lines the inner surface of the thoracic cavity, diaphragm, and chest wall.

Partial Pressure of Carbon Dioxide (PaCO2) – the arterial blood measurement of carbon dioxide that reflects the adequacy of ventilation.

Partial Pressure of Oxygen (PaO2) – the arterial blood measurement of oxygen that reflects the effectiveness of oxygenation.

Patient Assessment – a systematic evaluation of a patient’s health status using medical history, physical examination, and diagnostic data.

Patient-Ventilator Asynchrony – a mismatch between the patient’s spontaneous breathing efforts and the timing or delivery of ventilator-supported breaths.

Peak Expiratory Flow Rate (PEFR) – the maximum flow achieved during a forceful exhalation after full inspiration, commonly used to monitor asthma severity.

Peak Inspiratory Pressure (PIP) – the highest level of pressure applied to the lungs during inspiration on mechanical ventilation.

Pectus Carinatum – a congenital chest wall deformity in which the sternum protrudes outward, producing a pigeon-shaped chest.

Pectus Excavatum – a congenital chest wall deformity characterized by a sunken or depressed sternum.

Pediatric Advanced Life Support (PALS) – an advanced emergency care program focused on the management of critically ill or injured infants and children with cardiac or respiratory emergencies.

Penetrating Chest Trauma – a chest injury involving a puncture of the thoracic cavity, most commonly caused by stab wounds or gunshot injuries.

Peripheral Cyanosis – bluish discoloration of the extremities caused by reduced blood flow or oxygen delivery to peripheral tissues.

Persistent Pulmonary Hypertension of the Newborn (PPHN) – a neonatal condition marked by elevated pulmonary vascular resistance due to failure of normal circulatory transition after birth.

Personal Protective Equipment (PPE) – specialized clothing and equipment worn to reduce exposure to infectious agents and workplace hazards.

P/F Ratio (PaO2/FiO2) – an index used to evaluate oxygenation efficiency and the severity of hypoxemia by dividing PaO2 by FiO2.

PFT Equipment – devices used in pulmonary function testing to measure lung volumes, airflow, capacities, and gas exchange.

Pharynx – a muscular passageway that connects the nasal cavity and mouth to the larynx and esophagus, playing a role in breathing and swallowing.

Phlegm – thick mucus produced in the lower respiratory tract that helps trap and expel irritants and pathogens.

Pin-indexed Safety System (PISS) – a gas cylinder safety system that prevents incorrect gas connections by using uniquely arranged pins for each gas type.

Plateau Pressure – the pressure measured during an inspiratory hold that reflects alveolar pressure and lung compliance.

Pleural Diseases – disorders affecting the pleura that may result from infection, inflammation, trauma, or malignancy.

Pleural Effusion – the abnormal accumulation of fluid within the pleural space.

Pleural Friction Rub – a coarse, grating sound heard on auscultation when inflamed pleural surfaces rub together during respiration.

Pleurisy – inflammation of the pleura that causes sharp chest pain, often worsened by breathing or coughing.

Pneumonia – a lung infection that causes inflammation of the alveoli, often leading to fluid or pus accumulation, fever, cough, and difficulty breathing.

Pneumothorax – the presence of air in the pleural space that causes partial or complete collapse of the lung.

Positive End Expiratory Pressure (PEEP) – positive pressure maintained in the lungs at the end of expiration to prevent alveolar collapse and improve oxygenation.

Positive Expiratory Pressure (PEP) – an airway clearance technique in which exhalation against resistance helps mobilize secretions toward the central airways for removal.

Positron Emission Tomography (PET) – an imaging study that uses radioactive tracers to evaluate metabolic and functional activity within tissues.

Postnasal Drip – excessive mucus drainage from the nasal passages into the throat, often causing throat clearing, cough, or irritation.

Postural Drainage – an airway clearance method that uses gravity-assisted positioning to move secretions from peripheral lung segments to the central airways.

Pressure-Controlled Ventilation – a ventilator mode in which inspiratory pressure and time are set, resulting in variable tidal volumes based on lung compliance and resistance.

Pressure Support Ventilation (PSV) – a spontaneous mode of ventilation that augments each patient-initiated breath with a preset level of inspiratory pressure.

Principles of Respiratory Care – the foundational physical and physiological concepts governing ventilation, airflow, pressure, and gas exchange.

PRN – an abbreviation for pro re nata, meaning “as needed,” indicating medication use based on symptoms rather than a fixed schedule.

Prone Positioning – a patient position in which the individual lies face down, commonly used to improve oxygenation in severe respiratory failure.

Proportional Assist Ventilation (PAV) – a ventilator mode that delivers pressure in proportion to the patient’s inspiratory effort, improving synchrony and reducing work of breathing.

Pulmonary Artery Pressure (PAP) – the pressure within the pulmonary artery, used to evaluate pulmonary circulation and right ventricular function.

Pulmonary Barotrauma – lung injury caused by excessive airway pressures, potentially resulting in alveolar rupture and air leaks.

Pulmonary Capillary Wedge Pressure (PCWP) – an indirect measurement of left atrial pressure used to assess left-sided cardiac function.

Pulmonary Diffusion – the transfer of oxygen and carbon dioxide across the alveolar-capillary membrane.

Pulmonary Edema – accumulation of fluid within the alveoli that interferes with gas exchange and causes respiratory distress.

Pulmonary Embolism – obstruction of one or more pulmonary arteries by a blood clot, resulting in impaired perfusion and oxygenation.

Pulmonary Fibrosis – a chronic lung disease marked by progressive scarring of lung tissue, leading to reduced lung compliance and impaired gas exchange.

Pulmonary Function Testing (PFT) – a group of noninvasive tests used to evaluate lung volumes, airflow, and gas exchange.

Pulmonary Hypertension – elevated pressure within the pulmonary arteries that increases right ventricular workload and limits pulmonary blood flow.

Pulmonary Rehabilitation – a comprehensive program combining exercise training, education, and breathing strategies to improve quality of life in chronic lung disease.

Pulmonary Vascular Disease – disorders affecting the pulmonary blood vessels that impair circulation and gas exchange.

Pulse Oximetry – a noninvasive method for measuring arterial oxygen saturation using a sensor placed on the skin.

Pulsus Paradoxus – an exaggerated decrease in systolic blood pressure during inspiration, often associated with severe airway obstruction or cardiac tamponade.

Q

Quality Assurance – an ongoing, proactive program that focuses on evaluating processes, policies, and outcomes to ensure consistent delivery of safe, effective, and high-quality patient care.

Quality Control – a reactive process that involves monitoring, testing, and correcting specific aspects of care or equipment to ensure they meet established standards and performance requirements.

R

Radiograph – an image produced using X-ray radiation to visualize internal body structures.

Radiolucent – a term describing substances that allow X-rays to pass through and therefore appear dark or black on radiographic images.

Radiopaque – a term describing substances that block X-ray penetration and therefore appear white or light on radiographic images.

Rales – abnormal breath sounds, also known as crackles, produced when air passes through fluid-filled or collapsed small airways.

Rare Lung Disease – an uncommon respiratory disorder that is often difficult to diagnose and may require specialized evaluation and treatment.

Red Blood Cells – specialized blood cells that transport oxygen from the lungs to body tissues and carry carbon dioxide back to the lungs for removal.

Refractory Hypoxemia – severe hypoxemia that persists despite high levels of supplemental oxygen, typically defined as inadequate PaO₂ with FiO₂ greater than 0.50.

Regulation of Breathing – the neurologic control of ventilation by the brainstem and peripheral receptors to maintain normal oxygen and carbon dioxide levels.

Renal Insufficiency – a condition in which the kidneys have a reduced ability to filter waste products and regulate fluid and electrolyte balance.

Residual Volume (RV) – the volume of air remaining in the lungs after a maximal forced exhalation that cannot be voluntarily expelled.

Respiration – the cellular metabolic process by which oxygen is used to produce energy, with carbon dioxide generated as a byproduct.

Respiratory Abbreviations – standardized shortened terms used in respiratory care to improve efficiency and clarity in clinical communication.

Respiratory Acidosis – an acid-base disorder caused by hypoventilation resulting in carbon dioxide retention and decreased blood pH.

Respiratory Alkalosis – an acid-base disorder caused by hyperventilation resulting in excessive carbon dioxide elimination and increased blood pH.

Respiratory Calculations – mathematical formulas used to assess ventilation, oxygenation, and pulmonary function.

Respiratory Care in Alternative Settings – the delivery of respiratory services in non-acute care environments such as long-term care facilities, rehabilitation centers, home care, and subacute settings.

Respiratory Care Plan – a structured plan outlining respiratory assessments, interventions, goals, and evaluations for managing a patient’s pulmonary condition.

Respiratory Care Practitioner – a licensed healthcare professional who provides diagnostic, therapeutic, and preventive care for patients with cardiopulmonary disorders.

Respiratory Care Research – scientific investigation focused on improving the diagnosis, treatment, and management of respiratory diseases.

Respiratory Care Week – an annual event recognizing respiratory therapists and promoting awareness of respiratory health.

Respiratory Exchange Ratio (RER) – the ratio of carbon dioxide produced to oxygen consumed during metabolism.

Respiratory Failure – a life-threatening condition in which the lungs cannot adequately oxygenate blood or remove carbon dioxide.

Respiratory Management – the coordinated use of therapies and interventions to support or restore effective breathing and gas exchange.

Respiratory Quotient (RQ) – a metabolic measurement calculated as the ratio of carbon dioxide produced to oxygen consumed.

Respiratory Rate – the number of breaths taken per minute.

Respiratory System – the group of organs responsible for ventilation and gas exchange, supplying oxygen to the body and removing carbon dioxide.

Respiratory System Laws – physical and gas laws that explain airflow, pressure, volume, and gas exchange in the respiratory system.

Respiratory Therapy Examination – a standardized examination used to assess competency for CRT and RRT credentialing.

Respiratory Zone – the portion of the lungs where gas exchange occurs, including the respiratory bronchioles, alveolar ducts, and alveoli.

Restrictive Lung Diseases – disorders that limit lung expansion and reduce lung volumes.

Reverse Trendelenburg Position – a patient position in which the head is elevated above the feet to improve ventilation and reduce aspiration risk.

Rhonchi – low-pitched, coarse breath sounds caused by airflow through mucus-filled airways, often clearing with coughing.

Rhonchal Fremitus – palpable chest wall vibrations produced by secretions within the airways during respiration.

Rigid Bronchoscopy – a procedure using a rigid bronchoscope to access the airways for therapeutic interventions.

S

Safety Indexed Connector Systems – standardized gas-specific connection systems used for high- and low-pressure medical gases to prevent misconnections and delivery of the wrong gas to a patient.

Sarcoidosis – an inflammatory disease marked by the formation of granulomas, most commonly affecting the lungs and lymph nodes.

Saturation of Arterial Oxygen (SaO2) – the percentage of hemoglobin molecules bound with oxygen in arterial blood, commonly estimated by pulse oximetry or measured by blood gas analysis.

Sensitivity – a ventilator setting that determines the amount of patient effort, measured as pressure or flow, required to trigger a machine-delivered breath.

Severe Epidemic Enterovirus Respiratory Syndrome (SEERS) – a hypothetical respiratory illness attributed to a novel enterovirus strain, characterized by rapid spread and severe respiratory symptoms.

Shock – a life-threatening condition caused by inadequate tissue perfusion and oxygen delivery, resulting in cellular and organ dysfunction.

Shunt – a condition in which blood passes through the lungs without participating in gas exchange, resulting in hypoxemia.

Sickle Cell Anemia – a genetic blood disorder in which abnormally shaped red blood cells impair oxygen transport and undergo premature destruction.

Silicosis – an occupational lung disease caused by inhalation of crystalline silica dust, leading to chronic inflammation, fibrosis, and reduced lung function.

Silverman Score – a clinical scoring system used to assess the severity of respiratory distress in newborns by evaluating chest movement, retractions, nasal flaring, and grunting.

Simple Face Mask – an oxygen delivery device that covers the nose and mouth and provides moderate concentrations of supplemental oxygen.

Sinusitis – inflammation of the mucous membranes lining the paranasal sinuses, resulting in nasal congestion, facial pain, pressure, and drainage.

Sleep Apnea – a sleep disorder characterized by repeated episodes of airflow cessation lasting 10 seconds or longer during sleep.

Sleep Disorder – a condition involving disruption of normal sleep patterns that negatively affects health, alertness, and daily functioning.

Sleep Physiology – the study of the biological mechanisms and stages of sleep and their role in maintaining normal body function.

Sleep Study – a diagnostic evaluation, also known as polysomnography, that records physiologic parameters during sleep to diagnose sleep disorders.

Small Particle Aerosol Generator (SPAG) – a large-volume jet nebulizer specifically designed for aerosolized administration of ribavirin.

Smoking Cessation – the process of stopping tobacco use to improve overall health and reduce disease risk.

Sphygmomanometer – a device used to measure arterial blood pressure using an inflatable cuff, pressure gauge, and auscultation or electronic detection of blood flow.

Spirometer – a diagnostic device used in pulmonary function testing to measure the volume of air inhaled and exhaled by the lungs.

Spirometry – a pulmonary function test that measures the volume and flow of air during inhalation and exhalation to assess lung function.

Spontaneous Breathing Trial (SBT) – a clinical assessment used to evaluate a mechanically ventilated patient’s readiness for weaning by allowing spontaneous breathing with minimal support.

Spontaneous Pneumothorax – the sudden collapse of a lung caused by air entering the pleural space without trauma or an obvious external cause.

Sputum – mucus expectorated from the lower respiratory tract, often analyzed to diagnose or monitor lung disease.

Standard Precautions – infection control practices used with all patients to prevent the spread of microorganisms through contact with blood, body fluids, secretions, excretions, contaminated surfaces, and medical equipment.

Status Asthmaticus – a severe, life-threatening asthma exacerbation that does not respond adequately to standard bronchodilator therapy.

Sternal Rub – a painful stimulus applied to the sternum to assess a patient’s level of consciousness.

Sternum – a flat bone located at the center of the chest that connects to the ribs and helps protect the heart and lungs.

Stethoscope – a medical instrument used during auscultation to listen to internal body sounds, such as heart and lung sounds.

Stridor – a high-pitched, harsh breath sound caused by turbulent airflow through a narrowed upper airway, usually heard during inspiration.

Stroke – a medical emergency that occurs when blood flow to part of the brain is interrupted or reduced, resulting in brain tissue injury.

Stroke Volume – the amount of blood ejected by the left ventricle with each heartbeat.

Subcutaneous Emphysema – the presence of air within subcutaneous tissues, often producing swelling and crepitus, and commonly associated with trauma or air leaks.

Supplemental Oxygen – oxygen administered at concentrations greater than 21% for therapeutic purposes.

Surfactant – a substance that lines the alveoli and reduces surface tension, helping prevent alveolar collapse during exhalation.

Surfactant Replacement Therapy – administration of exogenous surfactant, primarily in premature infants, to improve lung compliance and alveolar expansion.

Swan-Ganz Catheter – a pulmonary artery catheter used to measure intracardiac pressures and assess cardiac and pulmonary hemodynamics.

Synchronized Intermittent Mandatory Ventilation (SIMV) – a mode of mechanical ventilation that delivers a set number of mandatory breaths while allowing spontaneous breathing between them.

T

Tachycardia – a condition in which the heart beats faster than normal, typically defined as a resting heart rate greater than 100 beats per minute in adults.

Tachypnea – an abnormally rapid respiratory rate, generally defined as more than 20 breaths per minute in adults at rest.

Tension Pneumothorax – a life-threatening condition in which trapped air in the pleural space causes lung collapse and shifts mediastinal structures, impairing cardiac output.

Terminal Bronchiole – the smallest conducting airway that leads to the respiratory bronchioles and marks the end of the conducting zone.

Tetanus – a serious bacterial infection that affects the nervous system, causing painful muscle spasms and potentially life-threatening respiratory complications.

Theophylline – a methylxanthine bronchodilator used in the management of asthma and COPD.

Thoracentesis – a procedure involving needle insertion into the pleural space to remove fluid or air for diagnostic or therapeutic purposes.

Thoracic Imaging – a diagnostic field focused on imaging the chest to evaluate the lungs, heart, and surrounding structures.

Thorax – the anatomical region that encloses the thoracic cavity, composed of the ribs, sternum, and thoracic vertebrae.

Thorpe Tube – a variable-area flowmeter attached to a 50-psig gas source that allows precise oxygen flow adjustments measured in liters per minute.

Tidal Volume – the volume of air inhaled or exhaled during a normal, quiet breath.

TMC Exam – a standardized examination that assesses foundational respiratory therapy knowledge and serves as the entry-level credentialing exam for respiratory therapists.

Total Lung Capacity (TLC) – the maximum volume of air the lungs can hold after a maximal inspiration.

Trachea – a rigid, cartilaginous airway that conducts air between the larynx and bronchi.

Tracheal Disorder – any condition affecting the trachea that may impair airflow or respiratory function.

Tracheobronchial Tree – the branching airway system extending from the trachea to the bronchioles, responsible for conducting air to the alveoli.

Tracheostomy – a surgically created opening in the trachea that provides an alternate airway for breathing.

Tracheostomy Tube – an artificial airway inserted into a tracheostomy to maintain airway patency and facilitate ventilation.

Transairway Pressure – the pressure gradient between the airway opening and the alveoli that drives airflow.

Transtracheal Catheter – a small catheter inserted directly into the trachea through the neck to deliver supplemental oxygen.

Trigger – the amount of patient effort required to initiate a ventilator-assisted breath, typically measured by pressure or flow changes.

Tuberculosis – a contagious bacterial infection caused by Mycobacterium tuberculosis that primarily affects the lungs.

Turbulent Flow – a pattern of airflow characterized by chaotic motion, increased resistance, and irregular pressure changes, commonly seen in narrowed or obstructed airways.

U

Ultrasonic Nebulizer – a type of nebulizer that uses high-frequency sound vibrations generated by an electrical signal to convert liquid medication into an aerosol for inhalation.

Ultrasound – a diagnostic imaging technique that uses high-frequency sound waves to produce real-time images of internal organs and body structures.

Upper Airway Stimulation – a treatment for obstructive sleep apnea that involves an implanted device designed to sense breathing patterns and deliver mild electrical stimulation to upper airway muscles to maintain airway patency during sleep.

Upper Respiratory Infection – an acute infectious illness affecting the upper airway structures, including the nose, sinuses, pharynx, or larynx.

V

Vagus Nerve – the tenth cranial nerve that carries parasympathetic motor and sensory signals between the brain and major organs, helping regulate breathing, heart rate, and airway function.

Vallecula – an anatomic depression between the base of the tongue and the epiglottis that serves as a key landmark during endotracheal intubation.

Ventilation – the movement of air in and out of the lungs to facilitate the removal of carbon dioxide and delivery of oxygen.

Ventilation-Perfusion (V/Q) Ratio – the relationship between alveolar ventilation and pulmonary blood flow, used to assess gas exchange efficiency.

Ventilator Alarms – safety features on mechanical ventilators that alert clinicians to changes in patient status, circuit integrity, or ventilator performance.

Ventilator-Associated Pneumonia (VAP) – a lung infection that develops 48 hours or more after endotracheal intubation and initiation of mechanical ventilation.

Ventilator-Induced Lung Injury (VILI) – lung damage that occurs as a result of mechanical ventilation due to excessive pressure, volume, or repetitive alveolar collapse.

Ventilator Management – the ongoing assessment and adjustment of ventilator settings to optimize gas exchange, patient comfort, and lung protection.

Ventilator Mode – a classification that defines how a ventilator delivers breaths, including the control variable, breath triggering, and cycling mechanisms.

Ventilator Settings – adjustable parameters on a mechanical ventilator that determine the level and type of respiratory support provided.

Ventilator Weaning – the gradual reduction of ventilatory support as a patient demonstrates improved respiratory function and readiness for independent breathing.

Ventilatory Response – the physiological adjustment of breathing rate and depth in response to changes in oxygen, carbon dioxide, or pH levels.

Ventilatory Threshold – the point during increasing exercise intensity at which ventilation rises disproportionately to oxygen consumption due to increased anaerobic metabolism.

Ventricular Fibrillation – a life-threatening cardiac arrhythmia characterized by chaotic ventricular electrical activity that results in no effective cardiac output.

Ventricular Tachycardia – a potentially life-threatening arrhythmia marked by a rapid heart rate originating from the ventricles.

Vesicular Breath Sounds – soft, low-pitched lung sounds heard over peripheral lung fields with a longer inspiratory phase than expiratory phase.

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

Volume-Controlled Ventilation – a ventilator mode in which a preset tidal volume is delivered with each breath, while airway pressure varies based on lung compliance and resistance.

Volume Support – a spontaneous mode of ventilation that provides pressure support adjusted to achieve a target tidal volume, commonly used during weaning.

Volutrauma – lung injury caused by excessive alveolar overdistension during mechanical ventilation.

V/Q Scan – a nuclear imaging study that evaluates pulmonary ventilation and perfusion, most commonly used to assess for pulmonary embolism.

W

Water Vapor Pressure – the pressure exerted by water molecules when water is in equilibrium with its gaseous (vapor) state, influencing gas exchange and humidity in the respiratory system.

Weaning Parameters – clinical measurements used to assess a patient’s readiness to transition from mechanical ventilation to spontaneous breathing.

Wet Drowning – a condition in which water is inhaled into the lungs, causing surfactant washout, alveolar collapse, impaired gas exchange, and oxygen deprivation.

Wheezing – a high-pitched, whistling breath sound typically caused by narrowed or obstructed airways.

Whispered Pectoriloquy – a physical examination technique in which a patient whispers words while the clinician auscultates the chest to detect abnormal sound transmission.

White Blood Cell – an immune system cell responsible for defending the body against infections, foreign substances, and abnormal cells.

Winter Cough – a persistent cough that occurs during colder months, often related to viral infections, dry indoor air, or seasonal allergens.

Winters’ Formula – an equation used to calculate the expected PaCO₂ in metabolic acidosis to determine whether respiratory compensation is appropriate.

World Lung Day – an annual global observance on September 25th dedicated to raising awareness of lung health and promoting prevention, research, and treatment of lung diseases.

Work of Breathing (WOB) – the amount of energy and effort required to inhale and exhale air, reflecting respiratory muscle workload and airway resistance.

X

Xanthine Drugs – a class of bronchodilator medications that relax airway smooth muscle to improve airflow, commonly used in the treatment of asthma and COPD.

Xiphoid Process – the small, cartilaginous structure at the inferior end of the sternum that serves as an anatomical landmark and attachment point for muscles.

Xopenex – an inhaled short-acting beta-2 agonist bronchodilator used to provide rapid relief of acute, reversible airflow obstruction in patients with asthma or COPD.

Y

Yankauer – a rigid, hard-plastic oral suction catheter with an angled tip, designed for suctioning secretions from the mouth and oropharynx.

Y-connector – an adapter in a mechanical ventilator circuit that joins the inspiratory and expiratory limbs and connects them to the patient interface.

Z

Zafirlukast – an oral antileukotriene medication used for the long-term management of chronic asthma by blocking leukotriene-mediated airway inflammation and bronchoconstriction.

Zone Valve – a control valve in a hospital’s medical gas pipeline system that allows oxygen, air, and vacuum services to be shut off or isolated to a specific clinical area for maintenance or emergency purposes.