1854

Karl Vierordt introduces the sphygmograph, which produced pulse training by connecting pen and revolving drum device to an artery noninvasively, via a spring pressed on the artery; it was refined and rendered usable in 1860 by Etienne-Jules Marey, which greatly simplified Vierordt’s design via a level with one end resting on a pulsating artery and the other connected to a pen that left tracings on a rotating drum (Reiser, 101-102).