Dead Space
All of the air we breathe in fills our lungs. Only a fraction of it ends up in the alveoli.
The volume of the conducting passageways – the air that is in the trachea, bronchi and bronchioles – makes up anatomical dead space, a volume of ~150ml.
- If the tidal volume is ~500ml, and ~150m of that is tied up in dead space, that means only ~350ml of each breath we breathe is utilized.
Alveolar dead space is the volume in alveoli that have ceased to function. This could be due to collapse (lack of surfactant) or obstruction by mucus (cystic fibrosis).
Anatomical dead space plus alveolar dead space equals total dead space.