Vital Capacity - QS Study
QS Study

Vital Capacity

The maximum volume of air that a person can expire forcefully after the forceful inspiration is called vital capacity. It is the maximum amount of air a person can expel from the lungs after a maximum inhalation. A person’s vital capacity can be measured by a wet or regular spirometer.

Volume: 4600 ml (male) and 3100 ml (female).

Fig: Vital Capacity

Factors affecting vital capacity

  1. Force of contraction of the respiratory muscle.
  2. Elastic recoil tendency of lungs.
  3. Airway resistance.

Others

  • Age: It is more in young due to increased muscular strength.
  • Sex: 10% less in female due to (a) Short thoracic cage, (b) Less surface area, (c) Less muscular effort.
  • Posture: More in erect posture than lying posture.
  • Surface area: Vital capacity is proportional to surface area. It is usually 2.6L/m2 of surface area in male and 2.4 L/m2 in the female.
  • Anatomical built of the chest: Decrease in some thorasic cage deformity, such as- Pigeon chest.
  • Disease of lungs and pleura: Decrease the vital capacity such disease as – Emphysema, Poliomyeletis, Respiratory obstruction, Edema etc.
  • Left heart failure: It causes pulmonary vascular congestion and oedema cause decrease lung compliance and subsequently vital capacity.
  • Reduced in pregnancy and ascites
  • Increased in swimmers & divers.

Importance of vital capacity

  1. It is an important lung function test.
  2. It indicates the efficiency of the lungs in act of.
  3. It indicates the condition of lungs.
  4. It is important for the assessment of the different pulmonary fibrotic diseases such TB, emphysema, asthma etc.

Measurement of vital capacity

Vital capacity can be measured by a spirometer. A typical basic spirometer consists of a drum inverted over a chamber of water, with the drum counterbalance by a weigh. In the drum is a breathing gas, usually air or oxygen, a tube connects the mouth to the gas chamber. When one breathes into & out of the chamber, the drum rises and falls and an appropriate recording is made on a moving sheet of paper.