# Ventilation (physiology)

In respiratory physiology, ventilation is the movement of air between the environment and the lungs via inhalation and exhalation. Thus, for organisms with lungs, it is synonymous with breathing. Ventilation usually happens in a rhythmic pattern, and the frequency of that pattern is called the ventilation rate (or, by long-standing convention, the respiratory rate, even though in precise usage ventilation is a hyponym, not a synonym, of respiration).

Ventilation volumes and rates are categorized under the following definitions:

 Measurement Symbol Equation Description Minute ventilation $\dot{V}_E$ = tidal volume * respiratory rate[1][2] the total volume of gas entering the lungs per minute. Alveolar ventilation $\dot{V}_A$ = (tidal volume - dead space) * respiratory rate [1] the volume of gas per unit time that reaches the alveoli, the respiratory portions of the lungs where gas exchange occurs. Dead space ventilation $\dot{V}_D$ = dead space * respiratory rate[3] is the volume of gas per unit time that does not reach these respiratory portions, but instead remains in the airways (trachea, bronchi, etc.).

## Sample values

Measure Sample value at rest Sample value moderate exercise[4]
Tidal volume 0.5 L 3.0 L
Respiratory rate 12 breaths/minute 30 breaths/minute
Minute ventilation 6.0 L/min 90 L/min
Dead space 0.15 L 0.15 L
Dead space ventilation 1.8 L/min 4.5 L/min
Alveolar ventilation 4.2 L/min 85.5 L/min
Functional residual capacity (FRC) 2.5 L 2.5 L
Specific Ventilation (Tidal volume / FRC) 0.2 L

Pulmonary ventilation may be evaluated using a breathing tube or spirometer, measuring the movement of the chest and abdominal walls using respiratory inductance plethysmography or by isolating the subject in an enclosed metabolic chamber (body plethysmography).