Basic concepts what is Polygraphy?

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Forensic Polygraphy

  1. Continued research and development of the polygraph. In 1949, he invented the Keeler Polygraph with components that simultaneously recorded changes in blood pressure, pulse and respiration, as well as the newly developed galvanic skin reflex.

  2. He devised the chart roll paper, a better method of questioning, and incorporated the kymograh.

  3. He also devised a metal bellows.

THE KEELER POLYGRAPH - In 1925, Keeler developed a compact portal instrument using a modification of the Erlanger pressure reducer that permitted the blood pressure changes to be recorded over a greater range. He later made further improvement by substituting metal bellows or diaphragm capsules in place of the Erlanger type pressure reducer. The instrument is housed in a steel case with wrinkle finish and chromium trim. The cover is attached to case by means of slip hinges and can be removed when the instrument is to be used. Opening of the cover permits hinged doors at each end of the case to open outward for access to the chart at one end and the accessories at the other. All connections to the instrument are made directly under the right end of the panel, which include the hose connection for the cuff inflation bulb, the tube from the blood pressure cuff, a connector for the hand electrodes of the electro dermal recording unit, an extension cord, and a tube from the pneumograph. Space is provided directly below the attachments for storage of the accessories, and they may be stored without disconnecting the accessories form the instrument.



  1. Successfully detected deception with a pneumograph, an instrument that graphically measures an examinee’s inhalation and exhalation.

  2. He demonstrated that changes in breathing patterns accompany deception.

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