Abstract
Polygraph instruments rely heavily on cardiovascular and respiratory activity to assess physiological changes associated with deception. Both systems are regulated by the autonomic nervous system and can be influenced by medical conditions, physical discomfort, or environmental factors. Understanding how these elements affect signal quality and interpretation is essential for producing valid and defensible polygraph results.
1. Introduction
The cardiovascular and respiratory channels provide two of the three primary physiological measures in modern polygraphy.
- The cardiovascular component reflects changes in blood pressure and heart rate through the sphygmomanometer or cardio-sensor.
- The respiratory component records thoracic and abdominal movement via pneumograph tubes.
Both parameters represent direct outputs of autonomic nervous system (ANS) modulation. Consequently, any abnormality within these systems—whether pathological or situational—can distort the recorded tracings and influence data interpretation.
2. Cardiovascular System and Polygraph Measurement
2.1 Physiological Basis
During the test, cardiovascular reactivity (blood pressure, pulse amplitude, and rate) responds to sympathetic activation. When an examinee experiences cognitive or emotional arousal, vasoconstriction and heart rate acceleration occur through norepinephrine release.
2.2 Common Interfering Factors
| Category | Effect on Chart | Examiner Consideration |
|---|---|---|
| Hypertension / hypotension | Elevated or unstable baseline | Confirm medication, avoid overinflation of cuff |
| Cardiac arrhythmia | Irregular pulse wave, loss of rhythmicity | May render cardio tracing non-diagnostic |
| Beta-blockers | Reduced heart rate and pressure variation | Lower overall cardio reactivity |
| Caffeine or stimulants | Increased amplitude, tremor-like oscillations | Record caffeine intake before test |
| Pain or discomfort | False sympathetic activation | Reposition cuff or postpone test |
2.3 Instrumental Considerations
The cardio cuff is typically inflated to 60–70 mmHg. Excessive pressure or prolonged inflation can cause discomfort and sympathetic arousal unrelated to question stimuli.
Examiners should also monitor artifacts caused by hand or arm movement, especially when using laptops or digital scoring algorithms sensitive to vibration.
3. Respiratory System and Polygraph Measurement
3.1 Physiological Basis
Two pneumograph sensors—thoracic and abdominal—measure respiration rate, amplitude, and synchronicity.
When individuals experience emotional or cognitive stress, respiratory suppression or irregularity often occurs due to cortical modulation of the medullary respiratory centers.
3.2 Typical Response Patterns
Deceptive or significant responses may involve:
- transient apnea or respiratory inhibition,
- reduced amplitude following question stimulus,
- desynchronization between chest and abdomen movements.
These patterns, when consistent with other channels, contribute to diagnostic scoring.
3.3 Factors Affecting Respiratory Validity
| Factor | Impact | Notes |
|---|---|---|
| Asthma, COPD, or emphysema | Irregular waveform, shortness of breath | May cause noise or inconsistent baseline |
| Respiratory infection | Coughing, shallow breathing | Pause or reschedule test |
| Chest or abdominal pain | Restricted movement | Limited pneumograph expansion |
| Anxiety-induced hyperventilation | Excessive amplitude, irregular rhythm | Manage with pre-test breathing normalization |
| Sedatives / opioids | Depressed rate and amplitude | Verify medication timing |
3.4 Examiner Controls
- Instruct examinees to breathe normally; avoid deep, forced breaths.
- Observe for voluntary control or countermeasures (e.g., holding breath, subtle manipulation).
- Ensure pneumograph tubes are snug but not restrictive.
- Re-calibrate baseline after each chart segment if respiration drifts significantly.
4. Interaction Between Cardiovascular and Respiratory Channels
These two systems are interdependent.
Respiratory Sinus Arrhythmia (RSA) causes cyclic variations in heart rate with each breath — inhalation accelerates the heart rate, exhalation slows it.
Consequently, irregular breathing patterns can mimic cardiovascular reactions if not interpreted in context.
For this reason, advanced scoring algorithms and trained examiners interpret both channels jointly to distinguish true autonomic arousal from normal physiological coupling.
5. Clinical and Ethical Considerations
- Subjects with cardiac instability, uncontrolled hypertension, or recent thoracic surgery should not undergo testing.
- Examiners must document all medications, caffeine, nicotine, and respiratory conditions in the case file.
- Continuous observation during the acquaintance test helps identify abnormal baseline variability before the data collection phase.
Ethically, the examiner bears responsibility for suspending or postponing the test if medical risk or physiological instability is evident.
6. Technical Best Practices
- Use digital polygraph instruments with high-resolution cardio and respiration sampling rates (≥ 20 Hz).
- Maintain consistent room temperature to avoid vasomotor fluctuations.
- Ensure the cuff and pneumographs are positioned correctly and free of tension artifacts.
- Apply filter settings judiciously — over-filtering may mask micro-responses, while under-filtering increases noise.
- Note any movement or coughing artifacts directly on the chart for later review.
7. Conclusion
Cardiovascular and respiratory responses remain central to the diagnostic integrity of polygraph examinations.
However, they are susceptible to physiological variability caused by health conditions, medications, and improper instrumentation.
Through careful pre-test screening, controlled environmental conditions, and correct data interpretation, examiners can minimize distortions and preserve the evidentiary value of the polygraph chart.
References
- Raskin, D.C., & Kircher, J.C. (2014). Computerized Polygraph Data Analysis: Principles and Practice.
- Matte, J.A. (1996). Forensic Psychophysiology Using the Polygraph.
- Handler, M. et al. (2013). Best Practices for Polygraph Examiners. American Polygraph Association.
- Meijer, E., & Verschuere, B. (2019). Autonomic Physiology and Deception Detection. Journal of Forensic Psychophysiology.
- ASTM E2031-17. Standard Practice for Examination of Physiological Responses to Psychological Stress.