What Is a Cardioactivity Monitor?
A cardioactivity monitor (CAM) is a supplementary cardiovascular sensor used in some polygraph instrument configurations to provide additional cardiac data beyond what the standard cardiograph cuff records. The CAM typically measures pulse rate, Amplitude">pulse amplitude, and pulse timing from peripheral sites (such as the fingertip) using photoplethysmographic or piezoelectric technology, complementing the blood pressure waveform data captured by the arm cuff.
How the CAM Differs from the Standard Cuff
The standard polygraph cardio cuff, placed on the upper arm over the brachial artery, captures a blood pressure waveform that includes information about systolic and diastolic pressure changes, heart rate, and pulse amplitude. The CAM provides complementary data from a different vascular site, typically recording blood volume pulse (BVP) from the fingertip. Because the fingertip vasculature is richly innervated by the sympathetic nervous system, finger pulse data can be particularly sensitive to vasoconstriction responses associated with arousal.
Diagnostic Value
The CAM provides several types of data that may enhance cardiovascular scoring. Pulse amplitude changes at the fingertip can reflect sympathetic vasoconstriction more sensitively than arm cuff data, because the finger’s vasculature is more responsive to autonomic commands. Pulse transit time — the delay between the heartbeat and the arrival of the pulse wave at the fingertip — provides information about vascular tone. Heart rate timing derived from the CAM signal can complement or verify the heart rate data from the arm cuff.
Integration with Scoring Systems
Some computerised scoring algorithms incorporate CAM data as additional features alongside the standard three-channel data. The additional cardiovascular information can improve the signal-to-noise ratio of the cardiovascular channel and provide redundancy if the arm cuff data is compromised by movement or improper fit. However, the primary validated scoring features remain those derived from the standard channel configuration, and CAM data is supplementary.
Modern Implementations
Current polygraph systems from manufacturers such as Lafayette and Limestone offer integrated CAM capabilities, typically using a fingertip plethysmograph sensor. The sensor is small, non-invasive, and does not cause discomfort that might produce artefacts in the recording.