Tidal Volume

Tidal volume is the volume of air moved into or out of the lungs during a single breath. It is usually abbreviated VT. During quiet breathing at rest, tidal volume represents the air inspired with each normal breath and approximately the same volume subsequently expired. It can increase substantially when breathing becomes deeper, such as during exercise .¹

Tidal volume is one of the two main variables that determine minute ventilation, the total volume of air moved into or out of the lungs each minute. Minute ventilation equals tidal volume multiplied by respiratory rate. This means ventilation can increase because breaths become deeper, more frequent, or both .¹

Not all of each tidal volume reaches or effectively participates in gas-exchanging regions of the lungs. Some air ventilates anatomical or physiological dead space. Alveolar ventilation therefore depends on the portion of each tidal breath remaining after dead-space volume is subtracted. For this reason, deeper and slower breathing can produce a different amount of alveolar ventilation than shallower and faster breathing even when total minute ventilation is the same .^1,2

Tidal volume should not be confused with a lung capacity, such as vital capacity or total lung capacity. Lung capacities are combinations of two or more lung volumes, whereas tidal volume is itself a lung volume describing the amount of air moved during one respiratory cycle .¹