Alveolar Ventilation

Alveolar ventilation is the volume of fresh air that reaches the gas-exchanging regions of the lungs each minute and is available for the exchange of oxygen and carbon dioxide. It represents the effective portion of total ventilation because not all inhaled air reaches alveoli that participate in gas exchange with pulmonary capillary blood .^1,2

Alveolar ventilation differs from minute ventilation, which is the total volume of air moved into or out of the lungs per minute. Some of each breath ventilates regions that do not participate in gas exchange, collectively represented as physiological dead space. Alveolar ventilation can therefore be expressed as breathing frequency multiplied by the difference between tidal volume, the amount of air moved in one breath, and dead-space volume .¹

This distinction means that two breathing patterns can produce the same minute ventilation but different alveolar ventilation. When tidal volume is small, a larger proportion of each breath may ventilate dead space. Deeper breaths can therefore increase alveolar ventilation more effectively than an equivalent increase in breathing frequency when other factors remain unchanged .¹

Alveolar ventilation is particularly important in regulating carbon dioxide in the blood. At a given rate of carbon dioxide production, arterial carbon dioxide partial pressure is inversely related to alveolar ventilation. If alveolar ventilation falls without a corresponding decrease in carbon dioxide production, arterial carbon dioxide tends to rise. If alveolar ventilation increases disproportionately relative to carbon dioxide production, arterial carbon dioxide tends to fall .²