Question

A patient presents with the following respiratory volumes and capacities: tidal volume = 500 ml, inspiratory capacity = 2,400 ml and expiratory capacity = 800 ml. What is this patient's vital capacity? Remember to include units in your answer.

Answer 1

Inspiratory capacity is the sum of the tidal volume and the inspiratory reserve volume (maximum volume of air inspired forcefully, after a normal expiration)  

Expiratory capacity is the sum of tidal volume and the Expiratory reserve volume (maximum possible volume expired forcefully, after a normal inspiration)

Vital capacity is given as the sum of Inspiratory Reserve Volume, Tidal Volume, and Expiratory Reserve Volume.

This can be written as: VC= TV+IRV+ERV

So, VC = TV+ (IC-TV) +(EC-TV)  

So, VC = IC + EC - RV

So from the values given, Vital capacity is:

VC =2400+800 - 500 = 2700 ml.

Therefore, Vital capacity in this case is 2.7 litres, or 2700 ml.