Question 1
Multiple choiceEasy1 markA student records a spirometer trace. Which statements correctly identify lung volumes from the trace?
I. Tidal volume is 0.5 dm³. II. Inspiratory reserve volume is 2.0 dm³. III. Vital capacity is 4.0 dm³.
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Answer: D. Tidal volume is the change between ordinary expiration and inspiration; inspiratory reserve volume is measured from ordinary inspiration to maximum inspiration; vital capacity is the difference between maximum inspiration and maximum expiration.
- Ordinary breaths range from 2.5 to 3.0 dm³, so tidal volume is 0.5 dm³.
- Inspiratory reserve volume is 5.0 − 3.0 = 2.0 dm³.
- Vital capacity is 5.0 − 1.0 = 4.0 dm³.
A: Confusing inspiratory reserve volume with vital capacity makes the 2.0 dm³ reserve seem to be the capacity. B: Measuring inspiratory reserve from ordinary expiration gives 5.0 − 2.5 = 2.5 dm³. C: Reading the ordinary inspiration peak as tidal volume gives 3.0 dm³ instead of subtracting the expiration level.
Remember: Reserve volumes are measured from the appropriate level of ordinary breathing to a forced maximum.