Respiratory Terms

A-VO2 difference

difference between oxygen content in arterial blood and the venous blood

Alveolar gas equation

equation that described the relationship between the concentration of inspired oxygen, PACO2, and PAO2; used to calculate the partial pressure of oxygen within the ideal alveolus

Functional Residual Capacity (FRC)

- the volume of the lungs at the end of a normal, relaxed exhalation. At the FRC, the inward or deflating force of the lungs is balanced by the outward or expanding force of the chest wall

Total lung capacity (TLC)

- volume of air in the lungs at the end of the maximal inspiration. The TLC is the sum of the residual volume and vital capacity.

Alveolar ventilation (VA)

- volume of air per minute that enters (or exits) alveoli that are perfused. This air is able to participate in gas exchange.

Dead space ventilation (VD)

- volume of air that enters (or exits) the parts of the lung that do not participate in gas exchange.

Alveolar dead space

- volume of the alveoli that are not being perfused (about 20 - 50 ml in the average person)

Anatomic dead space

- volume of the conducting (non-gas-exchange) airways of the lungs (approx. 150 ml in the avg. person)

Residual volume (RV)

- volume remaining in the lungs at the end of a maximal expiration

Transitional zone

- zone making the transition between the conducting airways and alveoli; consists of the respiratory bronchioles

Forced expiratory volume in 1 second (FEV1)

- the volume of gas that is exhaled in the first second of a forced vital capacity maneuver. People who have obstructive lung diseases such as emphysema and chronic bronchitis typically have an abnormally FEV1

Tidal volume (VT)

- Volume of air inspired or expired in a normal breath. In an avg. person at rest, normal tidal volume is approx. 450-500 mL.

Physiologic dead space

- all of the parts of the lungs (including the conducting airways) that receive air but do not participate in gas exchange. Physiological dead space is the sum of the anatomical dead space and alveolar dead space and it is about 175 ml in the avg. person

Dyspnea

- breathing discomfort

Hypoxemia

- condition in which the PO2 of the arterial blood is below normal

Hypoxia

- condition in which the level of oxygen in inspired gases or tissues is below normal.

Hypoventilation

- decreased ventilation to a level less than that required to meet metabolic needs, as reflected in carbon dioxide production or decreased alveolar ventilation relative to metabolic carbon dioxide production. If a person is hypoventilating, it means that his or her PaCO2 is greater than normal, or greater than about 42 mm Hg.

Ventilation/Perfusion (V/Q) mismatch

- imbalance between alveolar ventilation & pulmonary capillary blood flow. Many disease states, including pneumonia, heart failure, asthma, and emphysema can increase ventilation/perfusion mismatch and lead to impaired gas exchange

Hyperventilation

- increased ventilation that is greater than that required to meet metabolic needs, as reflected in the production of carbon dioxide, or increased alveolar ventilation relative to metabolic carbon dioxide production. If a person is hyperventilating, it means his or her PaCO2 is less than normal or less than about 38 mm Hg.

Hyperpnea

- increased ventilation that meets the metabolic needs of the body, as reflected in the production of carbon dioxide. If ventilation is increasing in proportion to increases in carbon dioxide production, PaCO2 remains normal

Vital Capacity (VC)

- maximal amount of air that can be moved into or out of the lungs in a single breath. The VC is the difference between the total lung capacity & the residual volume

Expiratory Reserve Volume

- maximal volume of air that can be expelled from lungs after a normal expiration; the difference in volume between the functional residual capacity and the residual volume

Inspiratory capacity

- maximal volume of air that can be inspired after a normal expiration. The inspiratory capacity is the sum of the tidal volume and inspiratory reserve volume

Ventilation (V)

- movement of air into and out of the lungs/per minute. There is relatively more ventilation than perfusion at the lung apices. Total ventilation (VE) is the sum of the alveolar ventilation & the dead space ventilation.

Equal pressure point (EPP)

- point at which transmural pressure of the airway is 0, that is the pressure inside and outside are the same. When EEP is reached in peripheral unsupported airways, further increases in pleural pressure do not result in increased flow. This is the flow limitation.

Respiratory zone

- portion of lungs containing alveoli

Tachypnea

- rapid breathing; an increase in the respiratory rate above the normal value (usually refers to ≥ 20 breaths/min).

Oxygen consumption (VO2)

- rate at which oxygen is used by the body; a measure of metabolic activity and often given in mL O2/min. VO2 can be expressed as the difference between the amount of O2 inhaled and the amount of O2 exhaled

Respiratory bronchioles

- smallest bronchioles; they connect the terminal bronchioles to the alveolar ducts. The respiratory bronchioles have alveoli sporadically originating from their walls and are therefore the first site of gas exchange as air travels distally in the lungs

Oxygen content

- the sum of the oxygen bound to hemoglobin and dissolved in blood

Forced Vital Capacity (FVC)

- the vital capacity measured with the subject exhaling as rapidly as possible

Acidosis

a process that leads to the production of excess acid

Bradypenea

abnormally slow breathing; a decrease in respiratory rate below the normal range (usually refers to <10 breaths/min)

Alkalemia

condition in which the pH of the blood is above normal

Acidemia

condition inwhich the pH of the blood is below normal

Alkalosis

process that leads to the production of excess base

Dead space

regions of the lungs (the conducting airways) that receive air butdo not participate in gas exchange; also referred to as "anatomical dead space".

Conducting airways

respiratory passages through which air flows but no gas exchange takes place. Consists of region from trachea to terminal bronchioles

Arterial blood gas

test in which a sample of arterial blood is analyzed todetermine PaO2, PaCO2, and pH of blood