Oxygen Shunting Effects in ASD

Steps:

• In a normal heart, the left atrium receives oxygenated blood from lungs, while the right atrium receives deoxygenated blood from the body.
• ASD creates an opening allowing blood to shunt from left to right atrium due to higher left-side pressure.
• This mixes oxygenated blood into the right atrium, increasing oxygen levels in pulmonary circulation.
• Systemic circulation gets slightly less oxygenated blood as some is recirculated to lungs instead of body.

Why C is correct:

• Left-to-right shunt in ASD delivers more oxygen to pulmonary circulation while causing mild systemic desaturation, per cardiac physiology.

Why the others are wrong:

• A: Right atrium oxygen increases, not decreases; systemic is not unchanged.
• B: Systemic oxygen decreases slightly, not stays the same; pulmonary oxygen rises above normal.
• D: Systemic oxygen does not increase; it mildly decreases.

Final answer: C