brachial artery

What Is the Brachial Artery?

The brachial artery is the major artery of the upper arm, running from the shoulder to the elbow where it bifurcates into the radial and ulnar arteries. In polygraph testing, the brachial artery is the primary anatomical target for the cardiograph cuff, which is typically placed around the upper arm directly over the brachial artery to record the pulse waveform and blood pressure changes during the examination.

Why the Brachial Artery Is Used

The brachial artery is the preferred site for polygraph cardiovascular measurement for several reasons. It is relatively superficial (close to the skin surface), making it accessible to the pressure changes detected by the cuff. It is large enough to produce a strong, clear pulse signal. Its location in the upper arm allows for a standard blood pressure cuff design that does not restrict the examinee's hand movement. The cuff partially inflates to a pressure between systolic and diastolic pressure, allowing the pulsatile expansion and contraction of the brachial artery to modulate the air pressure in the cuff, which is transduced into the cardiovascular tracing.

Cardiovascular Data Recorded

From the brachial artery pulse, the polygraph captures the complete pulse waveform including the anacrotic (ascending) limb, systolic peak, dicrotic notch, and catacrotic (descending) limb. Changes in this waveform — including blood pressure baseline shifts, heart rate changes, and pulse amplitude variations — are the cardiovascular scoring features evaluated during chart analysis.

Cuff Placement Considerations

Proper cuff placement over the brachial artery is essential for data quality. The cuff should be snug but not excessively tight, positioned so that the sensor or bladder is directly over the artery's path. An improperly positioned cuff may produce a weak or distorted signal, degrading the quality of cardiovascular data. The inflation pressure must be set high enough to detect pulsations but not so high as to cause discomfort that could introduce artefacts or affect the examinee's physiological state.

Anatomical Variations

While brachial artery anatomy is relatively consistent across individuals, variations in body habitus (arm size, muscle mass, subcutaneous fat) can affect signal quality. Obese examinees may require larger cuffs to achieve proper contact with the brachial artery. Examiners should verify adequate signal quality during the instrument setup phase before beginning chart collection.