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Respiratory System Function, Testing and Treatment Medical Terminology

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Knowledge of the medical terminology is the first step to understanding respiratory system function. The importance of terms pertaining to testing and treatment follow suit. The net result is improved communication in health care and the promotion of health literacy in this area.


Medical Terminology: Respiratory System Function  

Apnea – The absence of breathing. 

Asphyxia – A state of extreme decrease of oxygen with an accompanying increase of carbon dioxide that results from the restriction or the absence of the ability to breathe.  The end result of it is unconsciousness and death. 

Asphyxiation – The causing of a state of asphyxia. It has the same meaning as suffocation.  

Carbon dioxide (CO2) – It is a colorless, odorless gas resulting from the body’s use of carbon as a source of energy in the presence of oxygen. Tissues form it and the lungs expel it. Before the body can get rid of it though, it must traverse the carbonic-acid bicarbonate buffer system, of which carbonic anhydrase is the catalyst .  

Chemoreceptors – They are the molecular structures on or in cells which are part of a feedback loop that regulates breathing in response to changes in the amount of oxygen (O2), carbon dioxide (CO2) and concentration of hydrogen ions (pH) in the body.  There are two types of chemoreceptors. One is in the periphery and the other is in the central nervous system.  

Peripheral chemoreceptors are located in the aorta and carotid arteries.  They monitor changes in blood O2 and pH and mediate immediate responses in breathing, blood pressure and heart rate to those changes.  They primarily react to hypoxemia but also respond to a lesser degree to changes in blood pH. The effect of CO2 on peripheral receptors is minimal or nonexistent. 

Central chemoreceptors are those believed to be located in the medulla oblongata of the brainstem.  But there precise location is debatable. They trigger responses in breathing, heart rate and blood pressure to chronic changes in the pH of the interstitial fluid of the brain.  According to research, CO2 has only a modest effect on these receptors.

CO2 indirectly stimulates both types of receptors to a significant degree because its effect on pH.  CO2 reacts with water to form carbonic acid.  Carbonic acid dissociates to form H+ which lowers pH. pH is a significant stimulator of peripheral receptors and the main stimulator of central ones.  Thus, CO2 plays a major role in regulating ventilation as a result of its indirect effect on both types of receptors.

Peripheral and central chemoreceptors send messages through afferent nerve fibers to the breathing center in the medulla oblongata and pons of the brainstem.  Nerves in the breathing center in turn transmit impulses down through the spinal cord to efferent nerves that activate the diaphragm and breathing muscles of the chest wall. Additionally there is evidence of some interaction between the central and peripheral receptors.  Based on that interaction each receptor can modify the response of the other under certain conditions. 

Diffusing capacity of the lungs – A measure of how well oxygen and carbon dioxide diffuse between the lungs and blood. 

Exhale – It means to breathe out. 

Exhalation – The breathing out of air. It has the same meaning as expiration. 

Expiration – Means the same as exhalation

Hyperventilation – It is overbreathing.  It includes breathing that is too rapid, too deep, or both. 

Hypoventilation – It is breathing which is too shallow, too slow, or both such that it does not meet the body’s need for gas exchange in the lungs.  By definition, it causes CO2 to rise in the body. 

Inhalation – The breathing and of air. It has the same meaning as inspiration.

Inspiration – Means the same as inhalation.

Hypopnea – Breathing that is shallower, slower, or both, than normal.   

Oxygen (O2) – It is a chemical element essential for sustaining life and respiration in animals and plants.  It makes up 21% of the atmosphere by volume.  It is also necessary for almost all combustion. 

Oxygenation – The passive diffusion of oxygen from alveoli into the bloodstream by means of pulmonary capillaries where it binds to hemoglobin in red blood cells or dissolves in plasma.

Pulmonary shunt – Is a situation in which a portion of the lung has normal blood flow but inadequate or nonexistent oxygen exchange. There are many possible causes, including severe pneumonia and pulmonary edema. It is an extreme V/Q mismatch in which the V/Q ratio is extremely low. Alveolar dead space is at the opposite end of the extreme in which the V/Q ratio is immense.

Respiration – Means the same as ventilation. 

Respiratory acidosis – It is acidosis resulting from the buildup of too much carbon dioxide in the body.  The buildup is the result of the respiratory system’s inability to expel as much CO2 as the body produces.  The increase in CO2 in turn causes an increase in hydrogen ion concentration as it reacts with water to form carbonic acid.  Hypoventilation is the basis of the problem. 

Respiratory alkalosis – It is a state in which CO2 levels in the body are below normal.  Consequently, H+ concentration is below normal and pH is higher than normal. Hyperventilation is the cause.   

Respiratory rate (RR) – Is the number of breaths in and out per minute.  

Ventilation – The movement of air into and out of the lungs. In the normal state it is the process of inhalation and exhalation.    

Minute ventilation, also called total ventilation, is the total amount of gas (in liters) expelled from the lungs per minute.  It is equal to the respiratory rate times the tidal volume

Mechanical ventilation is the process of causing gas flow into and out of the lungs via an external means.  There are basically two types. 

Positive pressure mechanical ventilation causes airflow into the lungs as a result of pressure to the airways generated by a machine. 

Negative pressure mechanical ventilation creates negative pressure outside of the chest which transmits to within the thorax.  That negative internal pressure then causes air to flow into the lungs much like during natural breathing.  

Ventilation/perfusion mismatch (V/Q mismatch) – Is an imbalance between the amount of air that reaches the alveoli and pulmonary capillary blood flow. More specifically, it is a state in which some alveoli of the lungs have high V/Q ratios and others have low ones. V stands for ventilation. Q stands for perfusion. The V/Q ratio is a ratio signifying the degree of balance or imbalance in the amount of air entering alveoli and the amount of blood passing through the capillaries within them. The V/Q ratio can be low for two reasons. One reason is normal alveolar blood flow but reduced alveolar air entry. The other is normal air entry, but abnormally high blood flow. Conversely, the V/Q ratio is high when there is normal air entry into a unit but reduced blood flow or if there is increased air entry with normal blood flow. A high V/Q ratio does not adversely affect oxygenation. But the net effect of a low V/Q ratio is hypoxemia, of which a V/Q mismatch is the most common cause. The hypoxemia that occurs with a variety of conditions that cause a V/Q mismatch is due to the low V/Q ratios in the affected region(s).

Medical Terminology: Respiratory System Tests    

A-a gradient – Is the difference in the concentration of oxygen in alveoli (A) and arteries (a).  The measurement of it helps in diagnosing the cause of hypoxemia.

Arterial blood gas (ABG)– The analysis of the partial pressure of oxygen, the partial pressure of carbon dioxide and the acidity of blood from an artery. Its purpose is to assess how well the lungs are functioning in delivering oxygen to and removing carbon dioxide from the body. Unlike most other blood tests, it involves sampling blood from an artery rather than from a vein.

Apnea/hypopnea index (AHI) – The average number of episodes of apnea and hypopnea per hour observed during a sleep study performed on a patient with sleep apnea.  

Atelectasis – An area of partial lung collapse usually due to blockage of an airway or airways. It might cause a decrease in the breath sounds heard with a stethoscope. It can cause a linear opacity or area of whiteness on a chest x-ray.      

Bronchoscopy – Is a procedure for inspecting the air passages of the respiratory tract and obtaining specimen samples for testing. It consists of the passage of a cylindrical lighted scope (bronchoscope) through the mouth, pharynx, larynx, trachea and bronchi. A lung specialist, pulmonologist, performs the procedure. He carefully inspects the trachea and bronchi to determine if there is any evidence of disease such as cancer. Depending on the reason for the procedure he might also obtain samples of secretions or lung tissue for laboratory testing. He would perform brushings or washings to obtain samples of secretions. He would perform a transbronchial biopsy to obtain an actual lung tissue specimen.

Carbon monoxide (CO) – It is an odorless gas which forms from the burning of carbon or organic fuels in a setting of limited oxygen.  It binds irreversibly to hemoglobin which reduces the supply of oxygen to tissues.  Therefore it can cause asphyxiation after prolonged exposure to high levels of it.    

Carbon monoxide diffusing capacity (DLCO) Is a clinical test of lung function which measures the lungs ability to transfer inhaled carbon monoxide to the blood stream.  During the test, patients inhale a mixture of helium (10%) or methane (.3%), carbon monoxide (0.3%), nitrogen (68.7%) and oxygen (21%) then hold their breath for 10 seconds before exhaling.  The test uses the amounts of exhaled carbon monoxide and helium to calculate the DLCO.  The test uses carbon monoxide instead of oxygen to estimate gas transfer because of its greater attraction for the oxygen binding protein and blood (hemoglobin).  Therefore, it is a measure of the diffusing capacity of the lungs. The abbreviation for the test is DLCO.

Hypercapnea – Increased carbon dioxide partial pressure in the blood of an artery, measured by arterial blood gas analysis. The normal partial pressure of carbon dioxide in arterial blood is between 35 and 45 mmHg. It might be higher in obstructive lung disease such as COPD and asthma.  

Hypoxemia – An abnormally low amount of oxygen in the blood, as measured via arterial blood gas analysis and expressed as partial pressure of oxygen. The normal partial pressure of oxygen in arterial blood is between 80 and 100 mmHg. It might be lower in various forms of lung disease.  

Hypoxia – Low oxygen in the tissues and organs of the body. Even though HB determines how much O2 blood can carry per unit volume, it is cardiac output (CO) that determines how much O2 reaches the tissues. Thus, it is possible to hypoxia in the absence of hypoxemia if CO is too low.

Infiltrate – An abnormal collection of matter, usually including fluid, in the lung, which causes a corresponding area of whiteness seen on a chest x-ray. Causes include pneumonia and cancer. Atelectasis may appear as an infiltrate.

Lung plethysmography – Is a lung function test that measures total lung capacity and functional residual capacity. The machine that performs the test is a plethysmograph. It consists of a large airtight box or booth which enables the determination of lung volumes based on pressure changes within the box. 

Oxygen desaturation – It is a drop in the amount of oxygen the blood.  

Oxygen saturation (O2 sat) – A measure of how much oxygen the blood is carrying as a percentage of its maximum capacity. Since hemoglobin is the substance in blood that carries oxygen, the degree to which it is saturated is the percentage of the maximum capacity. Normal oxygen saturation is between 95% and 100%. 

Peak flow meter – It is a handheld device for patients to use at home.  It measures the maximum speed at which air can be exhaled air from the lungs following a maximum deep breath. The measurement termed the peak flow rate (PFR). It provides a measure of the severity of asthma or other obstructive lung disease. Doctors also sometimes use the measurements to tailor treatment. 

Polysomnography – An overnight series of test to evaluate sleep disorders. It commonly confirms the diagnosis of sleep apnea. It consists of various observations and measurements of physical and electrical events while a patient is in the sleep state. The testing takes place in a sleep laboratory.  

Polysomnogram – The recorded physiologic functions obtained during polysomnography.    

PPD (Purified protein derivative) – Is a skin test for determining if one has been previously exposed to tuberculosis. It does not distinguish between exposure and active disease.  

Pulmonary arteriogram (pulmonary angiogram) – Is a special x-ray study of the pulmonary arteries using a special dye (contrast medium). Its purpose is to determine if there is blockage to blood flow. It can diagnose or rule out a pulmonary embolus, a blood clot to the lung.    

Pulmonary function test (PFT) – A group of test procedures performed in a pulmonary function respiratory system functionlaboratory. Its purpose is to detect if there are any problems in one’s breathing as a result of lung disease affecting either the breathing process or flow through the airways. There are 3 types. They are spirometry, lung plethysmography and DLCO.    

Pulse oximetry – The measurement of O2 saturation with a device attached to the skin. The name of the device is a pulse oximeter. The point of attachment is usually a fingertip or earlobe.      

Spirometry – A specific pulmonary function test which measures the amount and rate of airflow in and out of the lungs as one is breathing. The most important measurements are FEV1 and FVC.

FEV1 is the volume of air that one can forcefully exhale from the lungs in one second after a deep as possible breath in. Forced vital capacity (FVC) is the greatest volume of air expelled from the lungs after taking a maximum deep breath and exhaling with maximum effort and speed.

Thoracentesis – A procedure consisting of the placement of a needle in the pleural space for the removal of fluid from the space. Its purpose is to diagnose the cause of the fluid collection or to remove the fluid to alleviate shortness of breath caused by it.  

Transbronchial biopsy – Is the part of a bronchoscopy in which the pulmonologist obtains a piece of lung tissue by passing a tiny forceps through a channel of a bronchoscope into the lung.

Medical Terminology: Respiratory System Treatment  

BiPAP (bilevel positive airway pressure) – Is a form of continuous airway pressure used for treating sleep apnea. It differs from CPAP in that the amount of pressure delivered differs during inspiration and expiration. It is a form of treatment for sleep apnea patients who have difficulty exhaling against the static amount of positive pressure encountered with CPAP.      

Bronchodilator – Is a class of medications which temporarily partially or totally relieves obstruction of bronchi and bronchioles by causing smooth muscle relaxation. A beta agonist is a bronchodilator that works by binding to protein subunits (receptors) of the airways.  The most commonly used beta agonists are for inhalation but there are some oral forms.  A short acting beta agonist (saba) has duration of action for between 4 to 6 hours.  Because it quickly relieves symptoms when they occur it is labeled rescue medication. Albuterol is most commonly used. A long acting beta agonist (laba) has duration of action of 12 hours or more and is used primary to prevent airway obstruction symptoms.    

CPAP (Continuous positive airway pressure) – Is a common nonsurgical method of treating sleep apnea. A CPAP device is a mask connected to a machine which delivers continuous pressure to a patient’s airways in order to keep them open.  

Fraction of inspired oxygen (FiO2) – Is the percentage of oxygen in inspired air.  It in particular refers to supplemental O2 for treatment.  The FiO2 of air in the atmosphere is 21%. 

Lobectomy – Surgical removal of a lobe of the lung.  

Pneumonectomy – Surgical removal of an entire lung.  

Tracheostomy – It is a surgical opening in the trachea created for the purpose of inserting a tube to allow air entry into the lungs.

























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