Why Is AIx Normalized to 75 bpm?

Heart rate affects the timing of both the forward pressure wave and its reflection by altering the duration of systole. At higher heart rates, systole is shorter, causing the reflected wave to return later relative to systole and thus reducing its augmentation effect on central systolic pressure.

Because AIx is strongly dependent on heart rate, it is normalized to a standard heart rate of 75 beats per minute (bpm) to allow meaningful comparisons between individuals and across measurement sessions.