Which of the following would not cause a decrease in minute volume?

• A. Increased tidal volume.
• B. Slight decrease in respiratory rate.
• C. Respirations of 20 breaths/min.
• D. Shallow breathing.

Answer: (A)

Minute volume is the amount of air moved in and out per minute, calculated as tidal volume (air per breath) times respiratory rate (breaths per minute). If tidal volume increases while the rate stays the same, minute volume increases, so this change would not cause a decrease. The other scenarios describe ways to reduce how much air is moved per minute: lowering the rate reduces total air moved per minute, and shallow breathing lowers tidal volume, both leading to a decrease in minute volume. A rate of 20 breaths per minute could increase minute volume if tidal volume remains steady, but the question focuses on factors that would reduce minute volume, and increasing tidal volume by itself does not.