Respiratory Equations

Question 1

Ventilation (V)

Answer 1

The rate at which gas is passing through the lungs

Question 2

Perfusion (Q)

Answer 2

The rate at which blood is passing through the lungs

Question 3

V/Q Ratio

Answer 3

Low (<0.8): obstructive airway disease e.g. asthma
High (>0.8): not enough blood reaching alveoli e.g. pulmonary embolism

Question 4

Tidal Volume (TV)

Answer 4

the volume of air inspired/expired during a single breath
(IRV-ERV)

Question 5

Residual Volume (RV)

Answer 5

the volume of air remaining in the lungs after maximal expiration
(FRC-ERV)

Question 6

Inspiratory Reserve Volume (IRV)

Answer 6

the additional volume of air that can be inspired after a normal inspiration
(TLC-TV-FRC)

Question 7

Expiratory Reserve Volume (ERV)

Answer 7

the additional volume of air that can be expired after a normal expiration
(FRC-RV)

Question 8

Functional Residual Capacity (FRC)

Answer 8

the volume of air remaining in the lungs after normal expiration
(ERV+RV)

Question 9

Vital Capacity (VC)

Answer 9

maximum amount of air that can be expelled after maximal inspiration
(IRV+TV+ERV)

Question 10

Total Lung Capacity (TLC)

Answer 10

the volume of air in the lungs after maximal inspiration
(IRV+TV+ERV+RV)