A sphygmograph is an instrument consisting of a lever, the short end of which rests on the radial artery at the wrist, and the long end being provided with a stylet that records on a moving ribbon of paper the movements, form, and force of the arterial pulse.
The German physiologist Karl von Vierordt invented the sphygmograph in 1854 after looking for a way to measure arterial pressure non-invasively. Previous apparatuses for measuring arterial pressure required perforating the desired artery to measure the blood pressure directly. Here is a drawing of Vierordt’s sphygmograph:
Here is an animation of Vierordt’s sphygmograph in action:
Here is a photograph of an improved sphygmograph devised by the Scottish homepath Robert Ellis Dudgeon in 1882; the working principles remain the same:
- https://books.google.ae/books?id=ulE_AAAAcAAJ&source=gbs_navlinks_s, pages 284–287.
- https://books.google.ae/books?id=3-4z7ZVJfW0C&source=gbs_navlinks_s, page 210.