Question

What are the dead space volume and the residual volume? Why do we have them? How, if at all, do they benefit us and/or impede our getting oxygen and getting rid of carbon dioxide?

Answer 1

*Dead space volume refers to the volume of space in which O2 and CO2 gases are not exchanged across the alveolar membrane in the respiratory tract. It is about 150ml in an average man.

Anatomic dead space is the volume of air located in the segments of respiratory tract that are responsible for conducting air to the alveoli and respiratory bronchioles but do not take part in the gas exchange. This include the upper airways,trachea,bronchi and terminal bronchioles.

Alveolar dead space refers to the volume of air in alveoli that are ventilated but not perfused, and thus gas exchange does not take place in it.

Physiologic dead space = Anatomic dead space + Alveolar dead space

The following are the advantages of having dead space:

1.CO2 is retained, this making a bicarbonate-bufferes blood and interstitium possible.

2.Inspired air is humidified, thus improving the quality of mucus in the airway

3.Inspired air is brought to body temperature which increases the affinity of hemoglobin for O2 thus improving O2 uptake

*Residual volume is the amount of air that remains in a person's lung after full exhalation. It is the volume of air that cannot be expelled from the lungs.Normal adult value is 1200ml.

The presence of residual volume prevents lungs from collapsing.It keeps the alveoli open even after maximum expiration.

In healthy lungs,it allows continous gas exchange to occur between the breaths.