Respiratory Capacities (IC, EC, FRC, VC, TLC)
Explains and provides formulae for various lung capacities derived from the combination of different respiratory volumes.
What is Respiratory Capacities (IC, EC, FRC, VC, TLC)?
The maximum amount of air that can be inhaled after a normal expiration.
Key formula / rule: Inspiratory Capacity (IC)
Key points
- Define and differentiate between various respiratory capacities.
- Calculate respiratory capacities using the appropriate formulae.
- Explain the physiological significance of each respiratory capacity.
- Relate respiratory capacities to lung function and health.
Common exam trap
Confusing volumes with capacities.
Definitions
- Term
Inspiratory Capacity (IC)
- Meaning
The maximum amount of air that can be inhaled after a normal expiration.
- Term
Expiratory Capacity (EC)
- Meaning
The maximum amount of air that can be exhaled after a normal inspiration.
- Term
Vital Capacity (VC)
- Meaning
The maximum volume of air a person can expel from the lungs after a maximal inhalation.
- Term
Functional Residual Capacity (FRC)
- Meaning
The volume of air remaining in the lungs after a normal exhalation.
- Term
Total Lung Capacity (TLC)
- Meaning
The total volume of air the lungs can hold at the end of a maximal inhalation.
Learning objectives
Define and differentiate between various respiratory capacities.
Calculate respiratory capacities using the appropriate formulae.
Explain the physiological significance of each respiratory capacity.
Relate respiratory capacities to lung function and health.
Formulae
- Name
Inspiratory Capacity (IC)
- Note
Total volume of air that can be inhaled after a normal expiration.
- Expression
IC = TV + IRV
- Name
Expiratory Capacity (EC)
- Note
Total volume of air that can be exhaled after a normal inspiration.
- Expression
EC = TV + ERV
- Name
Vital Capacity (VC)
- Note
Maximum volume of air that can be expelled from the lungs after maximal inspiration.
- Expression
VC = IRV + TV + ERV
- Name
Functional Residual Capacity (FRC)
- Note
Volume of air remaining in the lungs after a normal exhalation.
- Expression
FRC = ERV + RV
- Name
Total Lung Capacity (TLC)
- Note
Total volume of air accommodated in the lungs at the end of a maximal inspiration.
- Expression
TLC = VC + RV
- Name
Total Lung Capacity (TLC) - Alternative
- Note
Sum of all four lung volumes.
- Expression
TLC = IRV + TV + ERV + RV
Prerequisites
Understanding of Respiratory Volumes (Tidal Volume, Inspiratory Reserve Volume, Expiratory Reserve Volume, Residual Volume).
Common mistakes
Confusing volumes with capacities.
Incorrectly recalling the components of each capacity.
Applying the wrong formula for a specific capacity.
Not understanding the physiological significance of each capacity.
Keywords
Respiratory Capacities
Lung Volumes
Inspiratory Capacity
Vital Capacity
Functional Residual Capacity
Total Lung Capacity
Pulmonary Function Tests
Breathing Mechanics
Practice preview
What is Inspiratory Capacity (IC)?…
easy
Which of the following respiratory capacities represents the volume of air remaining in the lungs after a normal expiration?…
medium
Which of the following represents the Inspiratory Capacity (IC)?…
easy