What is the net effect of using an impedance threshold device during CPR?

• A. Improved venous return due to negative intrathoracic pressure.
• B. Increased intrathoracic pressure during recoil.
• C. No change in blood flow.
• D. Decreased blood return to the heart.

Answer: (A)

The key idea is that an impedance threshold device boosts blood flow during CPR by changing the pressure inside the chest. By limiting air entry during chest recoil, the device creates more negative intrathoracic pressure, which acts like a vacuum that pulls venous blood back into the right atrium. That increases venous return to the heart, improving preload and thereby enhancing overall blood flow and perfusion during CPR. So the net effect is improved venous return due to negative intrathoracic pressure. The other ideas describe opposite effects or no change, which don’t match how the ITD works.