Background information respiration | Physiology | Definitions | Lung volume and capacities

Volumes and capacities describing ventilation

Ventilation is characterised by different volumes and capacities, which are measures of combined volume values:

  1. Tidal volume – volume inhaled and exhaled during normal breathing
  2. Inspiratory reserve volume – volume which can be inhaled additionally after normal inspiration
  3. Expiratory reserve volume – volume which can be exhaled additionally after normal expiration
  4. Residual volume – volume remaining in the lungs after maximal expiration
  5. Vital capacity – volume which can be exhaled after maximal inspiration (sum of 1, 2 and 3)
  6. Inspiratory capacity – volume that can be inhaled additionally after normal expiration (sum of 1 and 2)
  7. Functional residual capacity – volume remaining in the lung after the end of a normal expiration (sum of 3 and 4)
  8. Total capacity – volume filling the lung after maximal inspiration (sum of 1, 2, 3 and 4)

All pulmonary volumes and capacities are about 20 to 25 percent smaller in women than in men. In large and athletic people the values obtained exceed those of small and asthenic subjects.

The flow-volume curve during a normal inspiration and expiration (‘tidal loop’), and subsequently recorded during forced in- and expirations serve to demonstrate the considerable ventilatory reserves available to a healthy subject. During exercise the level of ventilation can be increased by greater inspiratory and expiratory flows, as well as by increasing tidal volume and respiratory rate. In general in exercising healthy subjects the end-expiratory lung volume remains by and large the same.

Literature:

Klinke R, Silbernagel S. Lehrbuch der Physiologie. 2001. Thieme: Stuttgart

Shier D, Butler J, Lewis R. Hole’s human anatomy and physiology. 2004. McGraw Hill: New York

Lung volumes and capacities