7th February 2024

Measuring lung volumes

Methods to measure lung volumes include:

• Spirometry
• Body plethysmography
• Helium dilution technique

Spirometry cannot measure residual volume. As a result, we cannot measure functional residual volume and total lung capacity with spirometry. Residual volume can be measured using body plethysmography and helium dilution techniques.

The helium dilution technique may underestimate residual volume as it does not consider smaller airways behind an obstruction (i.e. gas trapping in COPD). Body plethysmography takes smaller airways behind obstruction into account. Hence, it is more accurate compared to the helium dilution technique.