Lesson 12

Lesson 12: Closing Volume and Capacity

• Closing Volume: Volume above residual volume where small airways begin to close during expiration.

• Closing Capacity (CC): Sum of closing volume and residual volume (CC = Closing Volume + Residual Volume).

Factors Increasing Closing Volume

• Conditions (CLOSE-P):

  • COPD

  • Left ventricular (LV) failure

  • Obesity

  • Surgery

  • Extremes of age

  • Pregnancy

Implications of Closing Capacity

• Airway closure occurs during tidal breathing when CC > FRC, leading to intrapulmonary shunting and hypoxemia.

• CC increases with age:

  • Age 30: CC ~ FRC under general anesthesia.

  • Age 44: CC ~ FRC in supine position.

  • Age 66: CC ~ FRC in standing position.

Age-Related Changes in Lung Volumes

• As age increases:

  • FRC increases

  • Closing capacity increases

  • Residual volume increases

  • Vital capacity decreases

Impact of Anesthesia

• Age and anesthesia affect closing capacity:

  • Age 30: CC ~ FRC under anesthesia.

  • Age 44: CC ~ FRC in supine.

  • Age 66: CC ~ FRC in standing.

Measurement of Closing Volume and Capacity

• Limitations of Spirometry: Cannot measure closing volume or capacity as it does not assess residual volume.

• Best Measurement Technique: Washout of tracer gas (e.g., nitrogen or xenon-133) inhaled at residual volume and measured as exhaled from total lung capacity.