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Lung Volumes and Capacities Overview

Sep 16, 2025

Overview

This lecture reviews lung volumes and capacities, their definitions, normal values, and how they are measured, focusing on key concepts for spirometry.

Total Lung Capacity (TLC)

  • TLC is the total amount of gas in the lungs after a maximal inspiration.
  • Normal TLC is 6 liters for adult males and 4.2 liters for adult females.

Vital Capacity (VC) and Residual Volume (RV)

  • VC is the amount of gas exhaled after a maximal inspiration.
  • RV is the amount of gas remaining in the lungs after a maximal expiration, making up about 20% of TLC.
  • VC plus RV equals TLC.

Tidal Volume (TV)

  • TV is the amount of gas inspired or expired during normal quiet breathing.
  • TV is about 7–8% of TLC.

Inspiratory and Expiratory Reserve Volume

  • Inspiratory Reserve Volume (IRV) is the amount inhaled above a tidal inspiration, normally 60% of TLC.
  • Expiratory Reserve Volume (ERV) is the amount exhaled beyond a tidal expiration, normally 20% of TLC.
  • TV + IRV + ERV equals VC.

Functional Residual Capacity (FRC) and Inspiratory Capacity (IC)

  • FRC is the amount of gas remaining after a tidal expiration, normally 40% of TLC.
  • FRC includes ERV and RV.
  • FRC cannot be measured directly by spirometry due to RV; measured indirectly via helium dilution or nitrogen washout.
  • Inspiratory Capacity (IC) is the amount inhaled starting at a tidal expiration (TV + IRV), usually 60% of TLC.

Types of Lung Capacities

  • Major capacities: Inspiratory Capacity (IC), Functional Residual Capacity (FRC), Vital Capacity (VC), and Total Lung Capacity (TLC).

Key Terms & Definitions

  • Total Lung Capacity (TLC) — total volume after maximal inspiration.
  • Vital Capacity (VC) — gas exhaled after maximal inspiration.
  • Residual Volume (RV) — gas left after maximal expiration.
  • Tidal Volume (TV) — gas shifted in/out during normal breathing.
  • Inspiratory Reserve Volume (IRV) — extra air inhaled after normal inspiration.
  • Expiratory Reserve Volume (ERV) — extra air exhaled after normal expiration.
  • Functional Residual Capacity (FRC) — gas left after normal exhalation.
  • Inspiratory Capacity (IC) — maximum air inhaled after normal exhalation.

Action Items / Next Steps

  • Review lung volume and capacity definitions for understanding.
  • Practice identifying which lung volumes/capacities can be measured by spirometry.
  • Remember the formulas and percentage values associated with each lung volume and capacity.

Full transcript