Which calculation will determine inspiratory capacity (IC)?

Inspiratory capacity (IC) is defined as the maximum amount of air a person can inspire after a normal expiration. It can be calculated by adding the tidal volume (VT) and the inspiratory reserve volume (IRV). Therefore, mathematically, IC is expressed as:

IC = IRV + VT

However, this calculation isn't directly provided in the choices, and the closest alternative involves total lung capacity (TLC) and functional residual capacity (FRC).

Functional residual capacity (FRC) is the volume of air remaining in the lungs after a normal expiration, and it can be calculated as:

FRC = ERV + RV

Thus, the equation to calculate inspiratory capacity can be rearranged when looking at total lung capacity. Since total lung capacity is the sum of inspiratory capacity and functional residual capacity, the equation becomes:

TLC = IC + FRC

To isolate inspiratory capacity, we can rearrange this equation to:

IC = TLC - FRC

This matches the choice indicating TLC minus FRC, confirming that this option correctly represents the calculation for inspiratory capacity.

Understanding these definitions and relationships between the lung volumes is essential for respiratory therapists as they assess lung function and determine treatment options based on lung capacity measurements