Elements necessary to measure PWV if done by tonometry coupled with electrocardiography (EKG). Elements necessary to measure PWV if done by tonometry coupled with electrocardiography (EKG). Distance from sternal notch to carotid pulse site (red) and distance from sternal notch to umbilicus and then to groin (in blue) are measured as shown. The probe captures the wave form at the carotid and femoral sites, and the time elapsed between the tip of the QRS complex and the onset, or “foot,” of the pulse wave is calculated. Generally, 10 s worth of data are captured, yielding six to 11 beats, which are averaged for the elapsed time at the carotid and femoral sites. The distance divided by time generates the velocity. Because the distances are in millimeters and the times are in milliseconds, the “milli” cancels out, leaving units of m/s. Stephanie S. DeLoach, and Raymond R. Townsend CJASN 2008;3:184-192 ©2008 by American Society of Nephrology