Anatomical Dead Space

The anatomical dead space may be used to calculate alveolar ventilation by subtracting it from the tidal volume and multiplying the result by the respiratory rate.

What would you expect the normal anatomical dead space to be in a healthy adult male?
A) 50 ml
B) 150 ml
C) 250 ml
D) 350 ml
E) 450 ml

Answer:
B) 150 ml

Discussion: The normal anatomical dead space is approximately 150 ml. If we take tidal volume to be about 500 ml and respiratory rate to be about 15/minute, this gives a normal alveolar ventilation of
(500 – 150) × 15 = 5250 ml/min.
Diseases that cause an additional physiological dead space where parts of lung do not take part
in gas exchange, eg pneumonia, may increase this dead space.