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Pulmonary dead space
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Not all of the air that comes in with a breath is used to exchange gases. The part that is not is called dead space: the share of each breath that stays in the airway and never reaches the lung's deepest part.
There are two ways to count it. Anatomical dead space is the air left in the conducting zone, the path the air only passes through: the nose, the trachea and the bronchi. That comes to about 150 milliliters, close to 30 percent of what comes in with a normal breath.
Physiological dead space is the anatomical part plus the alveolar part, which is air that does reach the alveoli, the little sacs at the end, but does not exchange anything there either. In a healthy adult the alveolar part is so small that it can be ignored.
That changes with some lung diseases, where dead space goes up: either because the movement of gases in the alveolus is impaired, or because air and blood stop arriving at the same places.
In brief
Dead space is ventilated air that takes no part in gas exchange.
The part of each breath that stays in the tube and never reaches the bottom.
The anatomical kind fills the conducting zone, the nose, trachea and bronchi: about 150 milliliters, or 30 percent of a normal breath.
Physiological dead space is the anatomical part plus the alveolar part; in healthy adults the alveolar part is negligible.
Some lung diseases raise it, through impaired alveolar diffusion or a mismatch between ventilation and perfusion.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Lung Dead Space, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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