When evaluating phase IV of a single-breath nitrogen test, what is being assessed?

• A. Pure deadspace gases
• B. Closing volume
• C. Mixed deadspace and alveolar gases
• D. Evenness of gas distribution

Answer: (B)

In phase IV of a single-breath nitrogen test, the main focus is on assessing the closing volume of the lungs. This phase occurs as the individual exhales and nitrogen, which has been trapped in the lung's dead space and alveoli, is released. The closing volume reflects the volume of air in the lungs at which the small airways begin to close during expiration.

Understanding closing volume is essential because it can help identify conditions related to lung diseases where airway closure may occur prematurely. It provides valuable insight into the distribution of ventilation within the lungs, particularly in patients with obstructive or restrictive lung diseases.

While deadspace gases and the evenness of gas distribution are important aspects of pulmonary function, they are not the primary focus during phase IV of this test. Therefore, assessing closing volume gives a specific insight into lung function regarding airway closure and can be indicative of various pulmonary conditions.