Question

The volume of inhaled air where there is no exchange of gases with the pulmonary capillaries is called the:

A. Residual Volume
B. Functional Residual Capacity
C. Inspiratory Volume
D. Dead Space
E. Vital Capacity

Answer 1

Answer is option D.

Dead space is the volume of inhaled air that does not take part in gas exchange. In adults it is in about 150 ml.

■Anatomic dead space is the total volume of conducting airways from nose to level of terminal bronchioles. This dead space fills with inspired air after each inspiration but air is exhaled without any change.

■Alveolar dead space is the sum of volumes of alveoli where perfusion is absent but are ventilated. It is of negligible value.

■Physiologic dead space is the total of anatomic and alveolar dead space.

●Advantages of dead space

-Humidification of inspired air.

-Removal of foreign bodies

-Formation of bicarbonate buffered blood by retention of CO2.

-Bringing inhaled air to body temperature

♢Formula for calculating Dead space =

Vd/Vt = (PaCO2 -PeCO2)/PaCO2

Here, Vd is dead space volume .Vt is tidal volume. PaCO2 is the partial pressure of CO2 .PeCO2 is partial pressure of CO2 (exhaled air).