There are different ways to express the rate a person is breathing. In respiratory physiology, these include Minute Ventilation and Alveolar Ventilation.
Minute ventilation is equal to the Tidal Volume times the Breaths per minute.
MV = tidal volume x Breaths/minute
Alveolar Ventilation is equal to Tidal Volume minus Dead Space times the breaths per minute.
AV = (tidal volume – dead space) x Breaths/minute
To get the Dead Space (for using in the alveolar ventilation equation), you can use the following formula:
Dead space = Tidal Volume x (PCO2 arterial – PCO2 expired air) / PCO2 arterial
This formula measures the physiological dead space.