What is the Difference Between Anatomical and Physiological Dead Space?

Anatomical dead space and physiological dead space are two different ways of defining the lung dead space, which refers to the volume of ventilated air that does not participate in gas exchange.

Anatomical dead space represents the volume of air that fills the conducting zone of the trachea and bronchi, but does not penetrate the gas exchange regions of the lung. This volume is considered to be 30% of normal tidal volume (500 mL), resulting in a value of 150 mL for anatomical dead space.

Physiological dead space, on the other hand, is the sum of all parts of the tidal volume that does not participate in gas exchange. It is equal to the anatomical dead space plus the alveolar dead space, which is the volume of ventilated air in the alveoli that do not participate in gas exchange. In a healthy adult, alveolar dead space can be considered negligible, making the physiological dead space equivalent to the anatomical dead space. However, the value of physiological dead space can increase in lung disease states where the alveolar dead space becomes significant.

In summary, the key difference between anatomical and physiological dead space lies in the fact that anatomical dead space only considers the volume of air in the conducting airways, while physiological dead space includes both the anatomical dead space and the alveolar dead space.

Comparative Table: Anatomical vs Physiological Dead Space

Here is a table comparing anatomical and physiological dead space:

Anatomical dead space refers to the air-filled volume in the conducting airways, such as the trachea and bronchi, which does not participate in gas exchange. In contrast, physiological dead space includes both anatomical dead space and the portion of the tidal volume that does not participate in gas exchange in the alveoli. In a healthy individual, alveolar dead space is negligible, and physiological dead space is equal to anatomical dead space. However, in lung disease states, alveolar dead space can have a value, making physiological dead space larger than anatomical dead space.