Dead space

Dead space refers to the portion of the respiratory system where gas exchange does not occur, such as the trachea and bronchi. It is a significant factor in the efficiency of the respiratory system and can be affected by various medical conditions.

Definition

In physiology, dead space is the volume of air which is inhaled that does not take part in the gas exchange, either because it (1) remains in the conducting airways, or (2) reaches alveoli that are not perfused or poorly perfused. In other words, not all the air in each breath is available for the exchange of oxygen and carbon dioxide. Molecules of oxygen, carbon dioxide, and other gases move between the gas in the alveoli and the blood in the surrounding capillaries by diffusion across the alveolar-capillary membrane.

Types of Dead Space

There are three types of dead space: anatomical, alveolar, and physiological.

Anatomical Dead Space

The anatomical dead space is the volume of the conducting airways, which includes the nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles. The volume of this space is about 150 ml in the human adult.

Alveolar Dead Space

The alveolar dead space consists of alveoli that are ventilated but not perfused with blood. This can occur due to a variety of medical conditions, such as pulmonary embolism and certain types of lung disease.

Physiological Dead Space

The physiological dead space is the sum of the anatomical and alveolar dead spaces. It is typically measured using the Bohr equation, which calculates the ratio of carbon dioxide produced by the body to the concentration of carbon dioxide in the exhaled air.

Clinical Significance

The concept of dead space is important in clinical medicine, particularly in the management of patients with respiratory disorders. An increase in dead space can lead to inefficient gas exchange and hypoxia, which can be life-threatening in severe cases. Measurement of dead space can provide valuable information about the severity of a respiratory disorder and the effectiveness of treatment.

See Also

• Respiratory system
• Alveoli
• Pulmonary embolism
• Lung disease

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