What is "vital capacity"

Vital \Vi"tal\, a. [F., fr. L. vitalis, fr. vita life; akin to vivere to live. See Vivid.]

1. Belonging or relating to life, either animal or vegetable; as, vital energies; vital functions; vital actions.

2. Contributing to life; necessary to, or supporting, life; as, vital blood.

   Do the heavens afford him vital food?
   --Spenser.

   And vital virtue infused, and vital warmth.
   --Milton.

3. Containing life; living. ``Spirits that live throughout, vital in every part.''
   --Milton.

4. Being the seat of life; being that on which life depends; mortal.

   The dart flew on, and pierced a vital part.
   --Pope.

5. Very necessary; highly important; essential.

   A competence is vital to content.
   --Young.

6. Capable of living; in a state to live; viable. [R.]

   Pythagoras and Hippocrates . . . affirm the birth of the seventh month to be vital.
   --Sir T. Browne.

   Vital air, oxygen gas; -- so called because essential to animal life. [Obs.]

   Vital capacity (Physiol.), the breathing capacity of the lungs; -- expressed by the number of cubic inches of air which can be forcibly exhaled after a full inspiration.

   Vital force. (Biol.) See under Force. The vital forces, according to Cope, are nerve force (neurism), growth force (bathmism), and thought force (phrenism), all under the direction and control of the vital principle. Apart from the phenomena of consciousness, vital actions no longer need to be considered as of a mysterious and unfathomable character, nor vital force as anything other than a form of physical energy derived from, and convertible into, other well-known forces of nature.

   Vital functions (Physiol.), those functions or actions of the body on which life is directly dependent, as the circulation of the blood, digestion, etc.

   Vital principle, an immaterial force, to which the functions peculiar to living beings are ascribed.

   Vital statistics, statistics respecting the duration of life, and the circumstances affecting its duration.

   Vital tripod. (Physiol.) See under Tripod.

   Vital vessels (Bot.), a name for latex tubes, now disused. See Latex.

n. (context biology English) The maximum volume of air that can be discharged from the lungs following maximum inspiration.

n. the maximum amount of air that can be exhaled after a maximum inhalation (usually tested with a spirometer); used to determine the condition of lung tissue

Vital capacity is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.

A person's vital capacity can be measured by a wet or regular spirometer. In combination with other physiological measurements, the vital capacity can help make a diagnosis of underlying lung disease. Furthermore, the vital capacity is used to determine the severity of respiratory muscle involvement in neuromuscular disease, and can guide treatment decisions in Guillain-Barré syndrome and myasthenic crisis.

A normal adult has a vital capacity between 3 and 5 litres. A human's vital capacity depends on age, sex, height, mass, and ethnicity.

Lung volumes and lung capacities refer to the volume of air associated with different phases of the respiratory cycle. Lung volumes are directly measured, whereas lung capacities are inferred from volumes.