Anatomical dead space

Anatomical dead space refers to the portion of the respiratory system where gas exchange does not occur. This includes the trachea, bronchi, and bronchioles. Despite the fact that these areas are part of the airway and are ventilated with each breath, they do not participate in the actual process of gas exchange because they do not have alveoli, the tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged.

Definition

The term "anatomical dead space" is used to differentiate this part of the respiratory system from the "physiological dead space," which includes both the anatomical dead space and any areas of the lung that are ventilated but not perfused with blood. The anatomical dead space is typically about 150 ml in humans, or about one-third of the tidal volume (the amount of air inhaled or exhaled in a single breath under resting conditions).

Function

While the anatomical dead space does not participate in gas exchange, it plays a crucial role in the respiratory system. It warms and humidifies the inhaled air, protecting the more delicate structures in the lower respiratory tract. It also acts as a conduit for air to reach the alveoli.

Clinical significance

The size of the anatomical dead space can increase in certain pathological conditions, such as emphysema, where the destruction of alveoli can lead to an increase in areas of the lung that are ventilated but not perfused. This can lead to inefficient gas exchange and symptoms of breathlessness.

Measurement

The volume of the anatomical dead space can be measured using Fowler's method, which involves having the subject breathe in a gas that is not normally present in the air, such as nitrogen, and then measuring the concentration of this gas in the exhaled air.

See also

• Respiratory system
• Gas exchange
• Alveoli
• Emphysema