Alveolar dead space

Alveolar dead space refers to the portion of the alveoli in the lungs that are ventilated but not perfused with blood, and therefore do not participate in gas exchange. It is a component of the total physiological dead space in the respiratory system.

Physiology

The respiratory system is designed to facilitate gas exchange, specifically the intake of oxygen and the expulsion of carbon dioxide. This process primarily occurs in the alveoli, tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged between the air and the blood.

However, not all alveoli are involved in this process. Some are ventilated, meaning they receive air, but are not perfused, or supplied with blood. This lack of perfusion can be due to a variety of factors, including disease, injury, or normal variation in blood flow. The air in these alveoli is referred to as the alveolar dead space.

Measurement

The volume of the alveolar dead space can be measured using the Bohr equation, which calculates physiological dead space as the difference between tidal volume (the volume of air moved in or out of the lungs during a normal breath) and alveolar volume (the volume of air that reaches the alveoli and is involved in gas exchange).

Clinical significance

An increase in alveolar dead space can be a sign of various lung diseases, such as pulmonary embolism, pulmonary hypertension, and chronic obstructive pulmonary disease (COPD). It can also occur in healthy individuals at high altitudes, where the lower air pressure reduces blood flow to the alveoli.

See also

• Anatomical dead space
• Ventilation (physiology)
• Pulmonary circulation

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