Kymograph

Kymograph
Ludwigs kymograph. One limb of the manometer is connected to a stylus which writes on the kymograph. Below: kymograph recording
MeSH	D007734

A kymograph (from Greek κῦμα, swell or wave + γραφή, writing; also called a kymographion) is an analog device that draws a graphical representation of spatial position over time. The graphical representation is a graph in which the y axis shows position and the x axis shows time. A kymograph consists of a revolving drum wrapped in paper on which a stylus draws to record measured changes of phenomena such as motion or pressure.^[1][2]

The kymograph was initially a mechanical and hydraulic device, invented by German physiologist Carl Ludwig in the 1840s, and found its first use as a means to monitor blood pressure. The blood pressure was conveyed by hydraulics and levers to move a stylus that scratched a white trace into soot-covered paper on the revolving drum. Time is represented by the drum's rotation rate, and was recorded by a second stylus driven by a clock or tuning fork. The kymograph almost immediately became the central instrument in physiology and physiology education. Throughout the nineteenth and twentieth centuries, researchers and technicians devised many improvements to the device, plus numerous new sensory components to measure a wide range of physiological phenomena such as breathing, muscle movement, and speech. New detection and registration systems included electrical and electronic methods, and plotted in ink.^[3]

Kymographs were also used outside medical science to measure atmospheric pressure, tuning fork vibrations, the functioning of steam engines, animal habits, and the movement of molecules in cells.