Q.Distinguish between

These pairs describe different portions and combinations of the air the lungs handle.

• IRV (Inspiratory Reserve Volume) is the extra air that can be forcibly breathed in beyond a normal breath, about 2500 to 3000 mL; ERV (Expiratory Reserve Volume) is the extra air that can be forcibly breathed out beyond a normal breath, about 1000 to 1100 mL.
• Inspiratory Capacity is the total air a person can inspire after a normal expiration, that is tidal volume plus inspiratory reserve volume; Expiratory Capacity is the total air a person can expire after a normal inspiration, that is tidal volume plus expiratory reserve volume. …

The amount of air the lungs move can be broken into a few standard volumes, and adding these together gives the capacities used in clinical work. The three pairs asked about each contrast two of these measures.

(a) IRV and ERV

• Inspiratory Reserve Volume is the additional air a person can take in by breathing in forcibly, over and above a normal breath. Its approximate value is 2500 to 3000 mL.
• Expiratory Reserve Volume is the additional air a person can push out by breathing out forcibly, beyond a normal breath. Its approximate value is 1000 to 1100 mL.
• So both are "reserve" volumes, but one is an inward reserve and the other an outward reserve, and the inspiratory reserve is the larger of the two.

(b) Inspiratory capacity and Expiratory capacity

• Inspiratory Capacity is the total volume of air a person can breathe in after a normal expiration. It is made up of the tidal volume together with the inspiratory reserve volume.
• Expiratory Capacity is the total volume of air a person can breathe out after a normal inspiration. It is made up of the tidal volume together with the expiratory reserve volume.
• Each capacity therefore starts from an ordinary tidal breath, but one then adds the inspiratory reserve and the other adds the expiratory reserve.

(c) Vital capacity and Total lung capacity

• Vital Capacity is the maximum volume of air a person can breathe in after a forced expiration, or breathe out after a forced inspiration. It is the expiratory reserve volume plus the tidal volume plus the inspiratory reserve volume. …

Method: Distinguishing Between Closely Related Respiratory Terms

Use this approach whenever asked to distinguish between two similarly-named volumes or capacities.

Steps

Step 1: Write precise, side-by-side definitions

State each term's definition carefully, noting the direction (inward reserve vs outward reserve) and the starting point (from a normal breath vs from an empty/full lung).

Step 2: Express each as a sum of basic volumes

Writing each capacity as a formula makes the relationship between the pair explicit rather than left as prose.

IC = TV + IRV EC = TV + ERV TLC = VC + RV …