A primary DECREASE in arterial CO2 (hypocapnia) will lead to which respiratory effect?

Correct answer: A. Decreased ventilatory drive (decreased tidal volume/rate)

• A. Correct. CO2 is the main stimulus to breathe; LOW CO2 reduces the drive from central/peripheral chemoreceptors, decreasing tidal volume and rate until CO2 rises again.
• B. Increased tidal volume occurs with INCREASED CO2 (hypercapnia), not a decrease.
• C. Chemoreceptors respond to CO2 changes; there is a change in ventilation.
• D. A simple hypocapnia reduces drive but does not classically cause apnea-then-hyperventilation.

Note: The source key ('increased tidal volume') is physiologically reversed — it describes the response to INCREASED CO2. A decrease in CO2 reduces ventilatory drive.