What is the Normal respiratory dead space ratio?

The normal respiratory dead space ratio (VD/VT) is typically around 0.2 to 0.4, meaning that 20% to 40% of the tidal volume (VT) may not participate in gas exchange due to being in non-perfused areas of the lungs. This dead space includes both anatomical dead space (the conducting airways) and physiological dead space (areas where ventilation exceeds perfusion). The exact ratio can vary based on factors like age, body position, and underlying lung conditions.