Question

About 1500 ml of air left in the lungs is called
A) Tidal volume
B) Inspiratory reserve volume
C) Residual volume
D) Vital capacity

Answer 1

It is the only lung volume that is not decreased with respiratory muscle weakness. However, it can be unchanged despite expiratory muscle weakness.

Complete step by step answer:
The volume of air inspired or expired during normal breathing is known as tidal volume (TV). The value of the tidal volume is approximately 500ml. This value of the tidal volume is lowest among all types of respiratory volumes. A healthy man can inspire or expire approximately 6000ml to 8000ml of air/min but the values will be altered in disease conditions.
During forceful inspiration, the additional or extra volume of air inspired by a person is known as inspiratory reserve volume (IRV). The average value of IRV is 2500ml to 3000ml. During forceful expiration, the additional or extra volume of air expired by a person is known as expiratory reserve volume (ERV). This volume averages between 1000ml to 1100ml. In the lungs, even after forceful expiration some amount of air remains and that is the residual volume (RV). The value of RV is about 1500ml. Respiratory capacity is the sum of two or more respiratory volumes. When Inspiratory reserve volume (IRV) is added with tidal volume (TV), then Inspiratory capacity (IC) is formed. When Expiratory reserve volume (ERV) is added with tidal volume (TV), then Expiratory capacity (EC) is formed.
The addition of Inspiratory capacity (IC) with Expiratory capacity (EC) leads to the formation of vital capacity. It can be defined as the maximum volume of air a person can breathe in after a forceful expiration or the maximum volume of air a person can breathe out after forceful inspiration.
Hence, the correct answer to the given question is option C.

Note: The volume of air remains in the lungs after a normal expiration is known as functional residual capacity (FRC). FRC is the addition of expiratory reserve volume (ERV) and Residual volume (RV). All other respiratory capacities can be measured by a simple spirometer with the exception of FRC, RV and total lung capacity (TLC).