QS Study

Dead Space Air

Definition: The amount of air that enters the respiratory passage but does not take part in the gaseous exchange is called dead space air. Air in the dead space is called dead space air because it is not useful for the gas exchange purpose. Dead space is one reason why taking deeper breaths leads to better ventilation (i.e. higher oxygen perfusion of blood) than breathing faster. This is a normal respiratory system consists of the nose pharynx, larynx, trachea bronchi, bland bronchioles. It can also lo include the alveoli if a pulmonary embolus exists in that area.

Normal value: 1.50 ml

Types of dead space: Two types –

(a) Anatomical dead space: It is the simple volume of all the space of respiratory system besides the alveoli and this other closely related gas exchange areas. It is the airways of the mouth, nose, pharynx, larynx, trachea, bronchi, and bronchioles.


(i) Saturated the inspired air by water vapor before reaching the alveoli.

(ii) Helps in the removing of particles having size more than 2 μ.

Fig: Dead Space Air

(b) Physiological dead space air: Physiological dead space includes anatomical dead space volume and two additional volumes.

  • Inspired gas which ventilates alveoli receives no pulmonary capillary blood flow.
  • The volume of inspired gas which ventilates alveoli in excess of that volume which is required for arterialize the blood in their local pulmonary capillaries.


  • It gives about the condition of lungs.
  • It indicates the ventilation-perfusion ratio.