- Respiratory rate (RR): number of breaths per minute
- Tidal volume (VT): the volume of air that is inspired or expired in a single breath
- Minute ventilation (VE)
- Volume of air that a person breathes per minute
- VE = VT x RR
- Physiologic dead space (VD): volume of inspired air that does not participate in gas exchange
- VD is the sum of the anatomic dead space and the alveolar dead space.
- Anatomic dead space: the volume of air in the conducting zone, e.g., mouth, trachea (approx. ⅓ of the resting tidal volume)
- Alveolar dead space: the sum of the volumes of alveoli that do not participate in gas exchange (mainly apex of the lungs); These alveoli are ventilated but not perfused.
- Bohr equation determines the physiologic dead space: VD = VT x (PaCO2 - PeCO2)/(PaCO2)
- In a healthy lung, VD equals the anatomic dead space (normal value: approx. 150 mL/breath).
- Alveolar ventilation (VA)
- Volume of gas that reaches the alveoli each minute
- VA = (VT - VD) x RR