Distinguish between IRV and ERV.

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Hint: We breathe in and out the air. Even after maximum inhalation or exhalation, there are some residues of the air left in the lungs. The spirometer is used to calculate these volumes. The total lung capacity of an average person is 4-6 litres.

Complete answer: We inhale oxygen and breathe out carbon dioxide. The alveoli in our lungs do this purification process. The lungs can hold the volume of air that has to be inhaled or exhaled.
 There are some terms related to these capacities.
1. Tidal volume- the amount of air breathed or exhaled during normal breathing.
2. Residual volume- the volume of air that remains in the lungs even after the maximum exhalation.
3. Vital capacity- the volume of air breathed out after the maximum inhalation
Some more terms- IRV and ERV are related to the volume of air in the lungs.

Inspiratory reserve volume(IRV)Expiratory reserve volume(ERV)
1. It is the maximum amount of air that can be inhaled after a normal inhalation.1. It is the maximum amount of air that can be exhaled out after a normal exhalation.
2. 2500-3500 ml of air can be inhaled after a normal inhalation.2. 1000-1100 ml of air can be exhaled after the normal exhalation.

Note: Spirometer is an instrument in which when we breathe through its mouthpiece, we can know of any respiratory malfunction in our body. Spirometry measures airflow, that is how much air we inhale or exhale and how quickly it is done. An average person breathes about 13 pints of air in a minute.