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Cardiovascular
Polygraphs record relative blood pressure using a standard blood pressure cuff. During testing the polygraph examiner will inflate the cuff with a small amount of air so that it fits snugly against the upper arm. The cuff detects the pressure wave of the heartbeat along with increases in blood pressure. Increases in blood pressure often accompany attempts at deception. When the blood pressure rises with the same question every time it is presented during the test, it can signal that the person has withheld information about that question. The diagram below shows a blood pressure response suggesting truthfulness (A) and deception (B). This channel is also sensitive to muscular movements, and when an examinee attempts to defeat the test by moving it can be readily identified by the unusual pattern it makes.
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