Physiology – Respiratory System 2 Practice Test

Physiological dead space is the portion of each breath that does not participate in gas exchange. It includes air in the conducting airways (anatomical dead space) and air in ventilated but nonperfused alveoli (alveolar dead space). Therefore, physiological dead space equals the sum of anatomical dead space and alveolar dead space. In healthy lungs alveolar dead space is small, so physiological dead space approximates anatomical dead space. The alveolar component increases when perfusion to some alveoli is reduced, raising the physiological dead space. It isn’t just air in the lungs not reaching alveoli (that would be anatomical dead space alone), and it depends on perfusion, since alveolar dead space arises from mismatches between ventilation and perfusion.