Question

The volume of anatomical dead space air is normally
a. 230 ml
b. 210 ml
c. 190 ml
d. 150 ml

Answer 1

Hint: Physiologic dead space involves all the non-respiratory parts of the bronchial tree involved in anatomic dead space, but also factors in alveoli which are well-ventilated but weakly perfuse and are thus less resourceful at exchanging gas with the blood. Since atmospheric $PCO_2$ is almost zero, all the $CO_2$ expired in-breath can be supposed to come from the communicating alveoli and nothing from the dead space.

Complete answer:
Dead space is the segment of the respiratory tract which does not involve gaseous exchange. Air that gets amassed in dead space never plays any function in the gaseous exchange; it means oxygen which comes to that portion is of no use for the body.

There are two diverse ways to define dead space- anatomic and physiologic. Anatomic dead space is the sum volume of the passing airways from the nose or mouth to the stage of the tertiary bronchioles and is about 150 ml on the standard in humans. The anatomic dead space fills with inspired air at the ending of each inspiration, but this air is exhaled unaffected.

As a result, assuming a normal tidal volume of 500 ml, about 30% of this air is "shattered" in the sense that it does not contribute to gas exchange.

Hence, the correct answer is option (D).

Note: Dead space can be boosted by breathing via a long tube, such as a snorkel. Despite the fact, one end of the snorkel is open to the air, when the wearer breathes in; they intake a major quantity of air that remained in the snorkel from the earlier exhalation. Thus, a snorkel amplifies the person's dead space by adding even more "airway" that doesn't contribute to gas exchange.