A kymograph is a device that graphically records changes in position over time, and is most commonly used to record changes in pressure or motion. The kymograph consists of a drum to which a stylus is attached. The stylus records the changes on a paper wrapped around the drum as the drum revolves. Since its invention in the 1800s, the kymograph has been used most commonly in the field of medicine to study various physiological and muscular processes, for example blood pressure, respiration and muscle contractions. It has also been used to analyze other phenomena like atmospheric pressure, speech sounds, and tuning fork vibrations.
The term kymograph comes from Latin and translates as "wave writer," referring to the graphical record produced by the instrument, where the stylus traces a pattern of the changes as they occur. This record provides a representation of changes over time, with time intervals usually marked on the paper. The graphic record generated by the kymograph instrument is commonly translated into a graph, showing changes in pressure or motion on the horizontal x-axis, and time elapsed on the vertical y-axis.
This instrument was invented in the 1840s by German physiologist Carl Ludwig, who primarily used it to study changes in blood pressure. Ludwig also used it to study speech sounds. As a person read words out loud, the vibrations of the sound waves would be recorded by the kymograph, making it possible to study sound duration, intensity and pitch. In the 1800s, kymographs were also used for a variety of other purposes, like studying the influence of drugs on various organs and the function of steam engines.
Today kymographs have been replaced by more recently invented instruments for many purposes, but kymograph analysis is still used for certain phenomena. For example, kymographs can be used to study moving organelles and to describe their motion in detail. This instrument is also commonly used in physiological and biological experiments, and in some pharmacological testing, to record mechanical activities of animal tissues and to study how muscular tissue reacts to drugs and other stimuli.
A kymograph can be either horizontal or vertical, depending on the orientation of the drum. A clockwork or electric motor drives the drum, rotating it slowly while the stylus traces a graphic record on a piece of paper wrapped around the drum. Today, plain paper is commonly used for this purpose, but in the past, smoked paper that had been treated by holding it over the fumes from a petroleum lantern, was often used.