Dead space is the volume of air which is inhaled but does not take part in gas exchange either because it remains in the conducting airways or in alveoli that are poorly perfused i.e. not all the air in each breath is able to be used for the exchange of oxygen and carbon dioxide.
The total dead space (also known as physiological dead space) is the sum of the anatomical dead space plus the alveolar dead space.
The total dead space (also known as physiological dead space) is the sum of the anatomical dead space plus the alveolar dead space.
Anatomic dead space
Approx one-third tidal volume ~150mL in a healthy adult.Alveolar dead space
- Sum of the volumes of alveoli which have little or no blood flowing through their adjacent pulmonary capillaries i.e., alveoli that are ventilated but not perfused, and where, as a result, no gas exchange can occur.
- Alveolar dead space is negligible in healthy individuals, but can increase dramatically in some lung diseases due to ventilation-perfusion mismatch.
References
- http://en.wikipedia.org/wiki/Dead_space_(physiology)
- http://www.paramedicine.com/pmc/End_Tidal_CO2.html