Karl Vierordt was a German physiologist and invented an instrument called sphygmograph which allowed the monitoring of arterial pulsation using a non-invasive approach. Vierordt's work was published in an article in 1854, which was then expanded into a book in 1855.
Vierordt used Ludwig's kymograph as a model to construct his new instrument. This instrument functioned on the principle that indirect estimation of blood pressure could be obtained by measuring the counter-pressure necessary to obliterate the radial arterial pulsation.
This was the first instrument, a spring mounted lever attached to a revolving drum, with which a tracing of human pulse could be recorded.
Vierordt's Sphygmograph was used for the measurement of blood pressure and for the radial arterial pulse recording.
This device was, however, very cumbersome and was not used routinely in clinical practice. In addition, the recordings were not very accurate. Despite all these limitations, that was a significant progress in graphic recordings of physiologic events.
In 1860, Etienne Jules Marey improved significantly the technique of sphygmograph allowing the physicians to obtain recording of arterial pulsation with fine detail.