Time between the Q wave of the electrocardiogram and the B wave of the impedance cardiogram for the same pulse. It is the period between when the ventricular contraction occurs and the semilunar valves open ejecting blood into the aorta. Shorter periods are thought to correlate with sympathetic nervous system arousal. The sensors for the production of the PEP phenomenon are relatively noninvasive, and if future research validates it as a diagnostic measure, the PEP could be added as an alternate PDD channel.