What is meant by Dead space?

It is actually meant to describe the airway space inside our body that is not useful for the body to get the oxygen that could be used to nourish the millions and millions of cells inside our body( or rather making our body).

There are  mainly 2 types of dead spaces that are to be understood viz.,

1.Anatomical dead space 

2. Physiological dead space.

1. Anatomical dead space:

 This is the volume of the conducting airways, and can some extent be referring to the upper respiratory tract where there are no alveoli and functional system that could be leveraged for the gaseous exchange.

 The approximate volume of this dead space is around 150cc

So, how do we measure the anatomical dead space?

There are some techniques that could be used to  measure or to be precise, calculate the anatomical dead space which are,

1) Single breath nitrogen washout method(Fowler's method)

2) Radford's formula( according to which, normally the volume of dead space is equal to the body weight in pounds, with units of "cc")

3) Single breath CO₂ method.

It is to be noted that the ratio between dead space and the tidal volume( which is nothing but the volume of air inspired and expired during normal quiet respiration)  will be 0.3( i.e 150mL:500mL).

2.Physiological dead space:

This term itself describes that it is related to physiology or rather functional.

Physiological dead space is the volume of the airways in the respiratory tract, not participating or cannot participate in the wonderful mechanism of gaseous exchange ( delivering oxygen and getting CO2 for the normal physiological process).

This tricky type of dead space can be determined by an equation called " Bohr's Mixing equation", using the values of tidal volume and the CO2 concentration in the alveolar and the mixed expired air.

Take home message: 

As far as a healthy individual is concerned, both of the above dead spaces are pretty much equal in values.