Dead Space

Dead Space

What are two types of dead space? How it is determined?
Answer:

Dead Space Definition:

• It is the amount of air in the respiratory passage which does not take part in exchange of gases.

Dead Space Types:

1. Anatomical dead space:

• It is the volume of air present in the `conducting zone’ of the respiratory passage.
• It exists from nose and mouth upto terminal bronchiole where exchange of gases does not take place.

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2. Physiological dead space:

• It includes anatomical dead space plus volume of air in the alveoli which does not take part in exchange of gases.
• It includes.
  • Air in the non-functioning alveoli.
  • Air in the alveoli which do not receive adequate blood flow.

Dead Space Normal value:

• The volume of normal dead space is 150 ml.

Determination of dead space:

• The dead space is determined by single breath nitrogen washout method.
• The subject is asked to take a deep breath of pure oxygen and expire steadily into a nitrogen meter.
• The concentration of nitrogen in the expired air is recorded continuously.
• The first portion of expired air comes from upper part of respiratory tract contains only oxygen.
• The next portion of expired air comes from the alveoli containing nitrogen.
• The nitrogen concentration in expired air increases continuously.
• The graph obtained is as follows.

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