Pulmonary Ventilation

Pulmonary ventilation is the movement of air into and out of the lungs. During inspiration, air flows from the atmosphere through the conducting airways into the lungs. During expiration, air moves in the opposite direction. Ventilation brings fresh gas into the respiratory system and removes gas containing carbon dioxide, making it an essential part of pulmonary gas exchange .^1,2

Pulmonary ventilation is commonly quantified as minute ventilation, the total volume of air moved into or out of the lungs each minute. Minute ventilation equals tidal volume, the volume moved with each breath, multiplied by respiratory rate, the number of breaths per minute. It can therefore increase through deeper breaths, more frequent breaths, or both .²

Air moves because pressure differences develop between the atmosphere and the lungs. During spontaneous inspiration, contraction of the diaphragm and other inspiratory muscles expands the chest and lungs, lowering alveolar pressure below atmospheric pressure and drawing air inward. During quiet expiration, relaxation of these muscles and elastic recoil reduce lung volume, increasing alveolar pressure and driving air outward .²

Pulmonary ventilation should be distinguished from alveolar ventilation. Minute ventilation includes all air moved during breathing, including air that ventilates physiological dead space and does not participate in gas exchange. Alveolar ventilation accounts for this dead space and represents the volume of fresh air reaching gas-exchanging regions each minute. Ventilation is also distinct from pulmonary perfusion, which refers to blood flow through the pulmonary circulation .^1,2