Which intrathoracic pressure is generated during recoil with the impedance threshold device?

• A. Positive intrathoracic pressure
• B. Zero intrathoracic pressure
• C. Negative intrathoracic pressure
• D. Variable intrathoracic pressure

Answer: (C)

The device works by creating a negative pressure in the chest during the recoil (decompression) phase of CPR. As the chest springs back after a compression, the impedance threshold device delays airflow into the lungs, which lowers intrathoracic pressure below atmospheric pressure. This negative intrathoracic pressure pulls more blood back toward the heart, increasing venous return and improving coronary perfusion during CPR. Because this mechanism relies on generating a transient negative pressure to boost blood flow, negative intrathoracic pressure is the correct description. Positive or zero pressure would not enhance venous return the way this device is designed to, and it wouldn’t align with how recoil with an ITD augments perfusion.