anatomic dead space
Summary
Anatomic dead space refers to the portion of the respiratory system where no gas exchange occurs, including the conducting airways from the nose/mouth to the terminal bronchioles. It typically accounts for approximately 150 mL or 2.2 mL/kg of body weight in healthy adults.
Detail
Anatomic dead space encompasses all airways that conduct air but do not participate in gas exchange, extending from the nose and mouth through the trachea, bronchi, and bronchioles down to the terminal bronchioles. This represents the first 16 generations of airway branching. During ventilation, the air in this space is 'wasted' ventilation since it doesn't contribute to alveolar gas exchange. The volume remains relatively constant regardless of tidal volume changes. Clinically, anatomic dead space becomes significant in respiratory pathology calculations and mechanical ventilation settings. It's distinguished from physiologic dead space, which includes anatomic dead space plus any alveolar dead space (alveoli that are ventilated but not perfused). Factors that can effectively increase dead space include shallow breathing patterns, where a larger proportion of each breath remains in the conducting airways, and certain disease states affecting ventilation-perfusion matching.
Sources
- Guyton and Hall Textbook of Medical Physiology
- West's Respiratory Physiology
- First Aid for the USMLE Step 1
- Costanzo Physiology
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