It is then implied that V/VT represents the portion of a tidal volume that does not participate in gas exchange :ĭead space has particular significance in the concept of ventilation (V) and perfusion (Q) in the lung, represented by the V/Q ratio. Total ventilation (VE) is, therefore, the sum of alveolar ventilation (Valv) and VD:Įnghoff's equation compiles these variables with PaCO2, tidal volume (TV), and expired CO2 (PECO2). Thus:ĭead space ventilation (VD) is then calculated by multiplying VD-Phys by the respiratory rate (RR): Physiologic dead space (VD-Phys) is the sum of the anatomic (VD-Ana) and alveolar (VD-Alv) dead space. On the other hand, alveolar dead space refers to the volume of air in alveoli that are ventilated but not perfused, and thus gas exchange does not take place. These segments of the respiratory tract include the upper airways, trachea, bronchi, and terminal bronchioles. Īnatomic dead space specifically refers to the volume of air located in the respiratory tract segments that are responsible for conducting air to the alveoli and respiratory bronchioles but do not take part in the process of gas exchange itself. This is comprised of two segments: the anatomic dead space (parts of the airway that are not alveolar exchange membranes) and the alveolar dead space (alveoli that are ventilated but not perfused with pulmonary capillary blood flow).

ĭead space of the respiratory system refers to the volume of inspired air in a given breath in which oxygen (O2) and carbon dioxide (CO2) gasses are not exchanged across the alveolar membrane in the respiratory tract.

However, differences in the exact way of measuring this space result in clinically significant different results and, therefore, debate remains about the true value of this measured parameter. Indeed, it may serve as a prognostic factor in patients with acute repository distress syndrome (ARDS) who require ventilation. This phenomenon has clinical significance because, both in healthy and impaired lungs, properly calculating and accounting for this non-physiological space is important for the proper respiratory care of ventilated patients. This is therefore termed anatomical dead space as it serves no respiratory function. Anatomic dead space is an important phenomenon in respiratory physiology whereby, owing to the fact that upper airways do not function as locations for gas exchange, and because of the tidal nature of ventilation, there is always a fraction of the inspired air that does not perform a physiologic function of exchanging carbon dioxide for oxygen.

Physiologic vs pathologic dead space