Define closing volume (CV) and closing capacity (CC). What is the normal value of CV?
Answer:
CC is the lung volume at which the small airways in the dependent parts of the lung begin to close. CC is the sum of CV and RV. CV is the volume above the RV at which small airways begin to close during expiration. It can be measured during the single-breath nitrogen test (Fig. 1.3) or with an inert tracer gas such as helium, xenon, or argon.
In healthy young people, CV is approximately 10% of the VC, or 400 to 500 mL. CV and CC increase with age. CV is increased in patients with small airway disease and in chronic smokers.
Reference(s):
- Gropper MA, Cohen NH, Eriksson LI, et al, eds. Miller’s Anesthesia. 9th ed. Philadelphia, PA: Elsevier; 2020:362.
- Lumb AB. Nunn’s Applied Respiratory Physiology. 8th ed. Philadelphia, PA: Elsevier; 2017:26-29.