Arterial Blood Pressure Sensor and Polygraph

Among polygraph examiners, the arterial blood pressure sensor is traditionally called a pneumatic cuff fixed on the respondent's shoulder, into which air is injected during the research.

The procedure for measuring arterial blood pressure in traditional medicine is presented below.

Note that to measure arterial blood pressure in brachial artery, the air in the cuff should be injected an average of 75 to 125 mm Hg.

Contrary to the classical procedure for measuring arterial blood pressure, when conducting researches on a polygraph it is recommended to inject pressure in the cuff from 30 to 60 mm Hg. As a result, a reasonable question arises, pressure of which arterial blood-vessels is monitored during polygraph examinations? To clarify the situation, one should refer to the classification of human blood-vessels.

As can be seen in the range of pink color, allocated for pressure from 30 to 60 mm Hg., there are no large arteries, which include the brachial artery.

Objective conclusion - with the help of a pneumatic cuff, the dynamics of blood filling of arterioles, terminal arteries and capillaries are monitored during the polygraph researches. As is known, plethysmography is a method of studying the terminal arteries and capillaries. Plethysmographs are classified as follows:

1. Mechanical;
2. Mechanoelectric;
3. Electrical;
4. Photovoltaic;
5. Occlusal.

In polygraph researches mechano-electric, photovolvatic, and occlusal plethysmographs are used.

Occlusal plethysmograph registers increase in the volume of a part of a body (or organ) after creation of its venous occlusion (compression), which violates the venous outflow from the organ. Sensors of polygraphs working on this principle include a cuff that is fixed on the shoulder, on the forearm or on the finger for violation of venous outflow.

In addition, occlusal plethysmographs also include a piezoelectric sensor when it is fixed on the shoulder or forearm.

Mechanoelectric plethysmograph converts mechanical vibrations into electrical vibrations. In cases when piezoelectric sensor is located on the palmar surface of one of the fingers or on the head of the respondent, there is no need for occlusion (compression of the venous vessels). It should be noted that at the present time there is no such a technical solution that would allow to compete with piezoelectric sensor on the quality of the recorded information with photoelectric sensors or with a pneumatic cuff.

Photoelectric plethysmograph registers optical density of the tissue (organ) being examined. The test area of the tissue is illuminated by infrared light, which falls on the photoconverter after reflection or diffusion. The intensity of light of reflected or scattered by the examined tissue (organ) site is determined by the amount of blood contained in it. The sensors of polygraphs working on this principle include the PPG sensor.

As an example of the identity of the data obtained by means of a pneumatic cuff and photoplethysmographic sensor, a fragment of recorded reactograms is shown (at the top - cuff, at the bottom - PPG).

If both types of polygraph sensors allow obtaining data that provide almost identical information, then which one should be optimally used? Apparently the one that has practical advantages when carrying out research on polygraph.

The PPG sensor should be optimally fixed on the palmar surface of the terminal (distal) phalanx of one of the fingers of the hand in an average degree of tension. Moreover, during the research it is not necessary to change its location and / or the degree of tension of the sensor. The concomitant factor is the respondent's sense of comfort and lack of attention to the sensor from the specialist.

The "Cuff" sensor is traditionally recommended to fix on the middle third of the forearm. Before and after each test, polygraph examiner should increase and lower the pressure in the cuff accordingly. Consequently, during each test lasting a few minutes, the cuff puts pressure upon the tissue of the respondent's forearm.

Disadvantages of occlusal plethysmography when used for a long time are obvious - the respondent's discomfort caused by squeezing the tissues of the hand, as well as the additional intellectual and physical load of the polygraph examiner.

Contraindications for the use of pneumatic cuff:

1. Reduced pain threshold (causes increased psycho-emotional stress);
2. Increased blood clotting ability (provokes the formation of blood clots);
3. Increased permeability of the vessel walls (causes bruising);
4. Pathology of the cardiovascular system (factor of exacerbation of venous diseases, hypertension, ischemia, arthritis and so on).

Perhaps, it is for these reasons that some polygraph manufacturers duplicate the "cuff" by another kind of plethysmograph.

We hope that the objective analysis given above will help every specialist who uses polygraph in his professional activity, to make the best choice in what type of sensor (kind of plethysmography) is optimal for fixing the dynamics of cardiovascular activity.

As a rule, as a result of this choice, the specialist should change not only the model, but also the manufacturer of the polygraph. This problem is absent when purchasing RUBICON polygraph because the P-02 model, which selling starts in Fall 2017, provides  the variability of 1-2 ways of registering physiological activity for each channel, as well as the variability of the number of registration channels from 5 to 7 items.