Certified Pulmonary Function Technologist (CPFT) Practice Exam

What happens to the helium concentration during a prolonged He dilution test?

1. It consistently decreases

2. It levels off and then begins to rise again

3. It remains constant throughout

4. It fluctuates wildly

The correct answer is: It levels off and then begins to rise again

During a prolonged helium dilution test, the concentration of helium in the lungs can level off and then begin to rise again due to several factors at play. Initially, when a patient inhales a gas mixture containing helium, the concentration will decrease as helium is absorbed into the alveoli and dispersed throughout the lungs. However, over time, if the patient continues to breathe this mixture, the helium may become less concentrated due to ventilation changes, diffusion, or possibly even the patient’s dynamic lung function altering the distribution of the gas. The leveling off of the helium concentration indicates that the rate of diffusion is becoming equal to the rate of ventilation in the lungs. If there is a disruption in this balance, such as changes in lung volumes or increased airway resistance, the helium concentration may then rise again as a response to the alterations in pulmonary mechanics. This dynamic change showcases how diffusion of gases can be affected by physiological variables and the patient's respiratory effort. Therefore, the correct answer reflects the understanding that helium concentration is influenced by both the physiological state of the lungs and the ventilation process during the test, leading to a scenario where the concentration can level off and potentially rise again.