Certified Pulmonary Function Technologist (CPFT) Practice Exam

When is the nitrogen washout test considered complete?

1. When the concentration has decreased to 1.5% for one breath

2. After three consecutive breaths with a concentration of 1.5%

3. When the concentration has decreased to 1.5% for at least 3 consecutive breaths

4. After five total breaths regardless of concentration

The correct answer is: When the concentration has decreased to 1.5% for at least 3 consecutive breaths

The nitrogen washout test is a pulmonary function test used to assess lung function, specifically for measuring functional residual capacity (FRC) and assessing for conditions such as emphysema or other obstructive lung diseases. Completion of the test is determined by the concentration of nitrogen in the exhaled air. The correct understanding is linked to how we assess the nitrogen concentration during the test. When the concentration of nitrogen decreases to 1.5%, this indicates that the test has reached a point where the lungs have effectively cleared nitrogen from the functional residual capacity. To ensure the accuracy and reproducibility of the results, it is important that the concentration remains at or below this level for a measurable duration, specifically three consecutive breaths. This criterion helps confirm that the lower nitrogen concentration observed is consistent and not a fluctuation. Requiring three consecutive breaths with consistent low nitrogen concentration eliminates potential errors or variances that could occur due to inconsistent breathing patterns, which enhances the reliability of the test results. The objective is to solidify the conclusion that the nitrogen has been sufficiently washed out from the lungs, representing a stable and accurate measurement of lung function.