If 450 ml of fresh air is inspired, the first gas to reach the respiratory zone comes from this anatomical dead space (150 ml). Recall that the conducting airway (anatomical dead space) has a volume of 150 ml. The ratio of physiologic dead space to tidal volume is usually about 1/3. However, because of the anatomical dead space (V D), not all of this entering air is available for exchange with the blood.
Alveolar dead space is the volume of gas within unperfused alveoli (and thus not participating in gas exchange either) it is usually negligible in the healthy, awake patient. In healthy individuals, the anatomic and physiologic dead spaces are roughly equivalent, since all areas of the lung are well perfused. Anatomic dead space is the volume of gas within the conducting zone (as opposed to the transitional and respiratory zones) and includes the trachea, bronchus, bronchioles, and terminal bronchioles it is approximately 2 mL/kg in the upright position. 1- A patient has a dead space of 150 milliliters, FRC of 3 liters, TV of 650 milliliters, ERV of 1.5 liters, TLC of 8 liters, and respiratory rate of 15 breaths/min.
Physiologic or total dead space is the sum of anatomic dead space and alveolar dead space. Dead space is the volume of a breath that does not participate in gas exchange. The main difference between anatomical and physiological dead space is that anatomical dead space is a fixed volume, while physiological dead space is variable and can be affected by disease or injury.
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