Understanding Vital Capacity: Normal Values, Variations, And Measurements

Understanding Vital Capacity: Normal Values, Variations, And Measurements

Vital capacity. (or) Define vital capacity and give its normal values.
Answer:

• It is the maximum amount of air that can be expelled out forcefully after a deep respiration.
• It includes following lung volumes.

1. Inspiratory reserve volume (IRV):

• It is the maximal volume of air which can be inspired after completing a normal tidal inspiration.

Normal value:

• 2000-3300 ml.

2. Expiratory reserve volume (ERV):

• It is the maximal volume of air which can be expired after completing a normal tidal expiration.

Normal value:

• 750-1000 ml.

3. Tidal volume (TV):

• It is the volume of air breathed in or out of lungs, during quiet respiration.

Normal value:

• 500 ml.

Measurement of Vital Capacity:

• It is measured by spirometry
• Vital capacity = IRV + ERV +TV.
  = 3300 + 1000+ 500 4800 ml.

Variations:

1. Physiological variations:

Sex:

• In males, it is 4.8 litres.
• In females, it is 3.2 litres.

Age:

• It decreases with age due to loss of elasticity of lungs.

Body built:

• It slightly increases in heavily built persons.

Posture:

• It is more in standing position because of.
  • Decrease in venous return.
  • Descend of diaphragm.
  • Decrease in pulmonary blood flow.

Atheletes:

• It is more in athelets.

Pregnancy:

• It decreases in pregnancy.

2. Pathological variations:

• It is reduced in presence of respiratory diseases.

Pathological variations Advantages:

• Provides information about strength of respiratory muscles.
• Provides information about pulmonary functions.