John is trying to identify how strong his lungs are. In order to do so he finds out his TV is 450 ml, IRV is 2.6 L, ERV is 900 mL. What is his vital capacity

Vital capacity can be defined as the maximum volume of air a person can breathe in after a forced expiration. It is equivalent to the sum of expiratory reserve volume (ERV), tidal volume (TV) and inspiratory reserve volume (IRV).

Expiratory reserve volume (ERV) : It refers to the volume of air a person can exhale by forcible expiration or air exhaled from the end-expiratory position. Tidal volume (TV) : It is a volume of air inhaled or exhaled during a normal respiration. Inspiratory reserve volume (IRV) : Maximum volume of air a person can inhale from the end-respiratory position.

Now, the vital capacity of John would be = 450 + 2600 + 900 ml

= 3950 ml or 3.95 L.