The impedance threshold device (itd) may improve circulation during active compression-decompression cpr by: select one: a. maximizing the amount of air in the lungs following chest recoil, which hyperinflates the lungs and forces more blood from the ventricle during each compression. b. limiting the amount of air that enters the lungs during the recoil phase between chest compressions, which results in negative intrathoracic pressure and improved cardiac filling. c. maintaining increased intrathoracic pressure during the downward stroke of each chest compression, which forces more blood from both of the ventricles. d. drawing all of the air out of the lungs in between chest compressions, which causes positive intrathoracic pressure and a reduction of blood return to the right side of the heart.