The word polygraph means many recordings. The polygraph instrument
records the physiological changes that occur within the human
body. The polygraph is comprised of at least three components.
The first component of the polygraph instrument is the cardio
sphygmograph component.
This section records the examinee’s pulse
wave amplitude, pulse rate, relative blood pressure, and changes
in each of these variables through the use of a blood pressure
cuff and bladder. The examiner determines the examinee’s
normal cardiovascular activity, and monitors the changes that
occur in response to structured questions.
The second section of the polygraph is the pneumograph. This
component is made up of two corrugated rubber tubes that wrap
around the examinee’s lower and upper chest area. This
section of the instrument records respiratory movements, the
examinee’s breathing rate and inhalation / exhalation
pattern.
The examinee’s normal breathing pattern
and respiratory movements are analyzed throughout the examination,
and changes that occur during the structured examination are
reviewed by the examiner.
The third section of the polygraph instrument is the galvanograph.
In 1791, an Italian physiologist and physician, Luigi Galvani
discovered that current or galvanic electricity flowed through
animal tissue. In the late 1800’s and early 1900’s,
the body’s response to electricity was measured and found
to be an indicator of deception due to changes that occur within
the body when a person is deceptive.
The human body’s resistance to and conductance
of electrical current fluctuates, and these fluctuations that
occur during structured question techniques are recorded by
the polygraph instrument through the use of two components that
attach to the pointer and index fingers of the examinee. There
is no electrical shock experienced during the use of this instrument,
and nothing is felt by the examinee other than the feeling of
two small metal plates attached to the two finger tips with
Velcro.
