Dead space and its measurement

Dead space is the volume of ventilated air that does not participate in gas exchange.

Anatomical dead space is the volume of air that fills the conducting zone, about 150 mL (~30% of normal tidal volume).

Alveolar dead space includes those parts of the respiratory zone that do not participate in gas exchange. In the ideal healthy adult, this is zero.

Physiological dead space is the sum of the anatomical dead space and the alveolar dead space. It cannot be measured directly but is calculated by