VPB 121: Veterinary Physiology - II (2+1)

PULMONARY VOLUMES AND CAPACITIES

• Pulmonary volumes and capacities are recorded by Spirometer.The recordings are known as Spirogram. It shows the following:
  • Tidal Volume (VT) - the volume of air entering or leaving the nose or mouth per breath. It accounts 70% of the total lung capacity. If an animal inhales more forcefully, it can increase the volume of air entering the lungs above normal tidal volume.
  • Inspiratory Reserve Volume (IRV) - the volume of gas inhaled into the lungs during a maximal forced inspiration starting at the end of a normal tidal inspiration.
  • Residual Volume (RV) - the volume of gas left in the lungs after a maximal forced expiration. Determined by the force generated by the muscles of expiration and the inward elastic recoil of the lungs as they oppose the outward elastic recoil of the chest wall. Dynamic compression of the airways during the forced expiratory effort is also an important determinant of the residual volume - as airway collapse occurs gas is trapped in the alveoli.
  • Total Lung Capacity (TLC) - the volume of air in the lungs after a maximal inspiratory effort. Determined by the strength of contraction of the inspiratory muscles in opposition to the inward elastic recoil of the lungs and chest wall.
  • Inspiratory Capacity (IC) - the volume of air inhaled into the lungs during a maximal inspiratory effort that begins at the end of a normal tidal expiration.
  • Functional Residual Capacity (FRC) - the volume of gas remaining in the lungs at the end of a normal tidal expiration. Balance point between the inward elastic recoil of the lungs and the outward elastic recoil of the chest wall.
  • Vital Capacity (VC) - the volume of air expelled from the lungs during a maximal forced expiration starting after a maximal forced inspiration. About 4.5 liters.
  • Expiratory Reserve Volume (ERV) - the volume of gas expelled from the lungs during a maximal forced expiration that starts at the end of normal tidal expiration.