What is the typical physiologic dead space fraction range?

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What is the typical physiologic dead space fraction range?

Physiologic dead space fraction (VD/VT) is the portion of each breath that does not participate in gas exchange, combining air in the conducting airways (anatomic dead space) and any ventilated but poorly perfused alveoli (alveolar dead space). In a healthy adult, the anatomical dead space is about 150 mL and the typical tidal volume is around 500 mL, giving a VD/VT near 0.3. Because normal variation usually places this ratio between roughly 0.2 and 0.4, that range is considered typical. Values higher than this can occur with increased dead space from certain lung diseases or ventilation-perfusion mismatch, while much lower values would imply less wasted ventilation. Therefore, 0.20–0.40 best reflects the normal physiologic range.

Physiologic dead space fraction (VD/VT) is the portion of each breath that does not participate in gas exchange, combining air in the conducting airways (anatomic dead space) and any ventilated but poorly perfused alveoli (alveolar dead space). In a healthy adult, the anatomical dead space is about 150 mL and the typical tidal volume is around 500 mL, giving a VD/VT near 0.3. Because normal variation usually places this ratio between roughly 0.2 and 0.4, that range is considered typical. Values higher than this can occur with increased dead space from certain lung diseases or ventilation-perfusion mismatch, while much lower values would imply less wasted ventilation. Therefore, 0.20–0.40 best reflects the normal physiologic range.

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