Evaluating the credibility of testimony is a highly complex task that continually challenges the boundaries of psychology and forensic technology. Despite significant scientific advances in the field of forensic psychophysiology, polygraph tests, one of the best-known tools for assessing truthfulness, achieve maximum reliability only under ideal conditions.
These optimal conditions are not limited solely to the technology used or the methodology of the test but also involve critical human and environmental factors. The experience and training of the examiner are fundamental, as a trained professional is essential to properly administer the test, accurately interpret the results, and handle unforeseen situations that may arise during the session.
Environmental conditions where the examination is conducted also play a crucial role. Factors such as appropriate temperature, the absence of noise and distractions, and a controlled and neutral environment are essential to prevent external influences that may affect the subject during the test. The psychophysical state of the individual being evaluated is equally critical; any alteration, whether due to stress, fatigue, or the consumption of psychoactive substances, can result in atypical physiological responses that lead to false positives or negatives.
Therefore, the reliability of the polygraph results intrinsically depends on these conditions. Ensuring their compliance is indispensable to guarantee the integrity and accuracy of the credibility assessment of the testimony, thus reflecting a commitment to justice and procedural truth.
This document establishes the exclusion criteria for individuals who are not considered suitable for undergoing polygraph tests, based on their physical and mental health, age, specific psychiatric diagnoses, and recent consumption of psychoactive substances. These criteria are designed to ensure the integrity and reliability of the polygraph test results and to guarantee the safety and well-being of the examinees.

Exclusion Criteria
Age: Individuals under the age of 12 will not be considered suitable for the polygraph test due to the cognitive and emotional immaturity that may affect the reliability of their responses during the examination.
Physical Health Conditions: Individuals suffering from medical conditions that may interfere with their ability to respond consistently during the test or that may jeopardize their health during the process. This includes, but is not limited to:

Acute Respiratory Conditions
Significant acute or chronic respiratory diseases can profoundly affect a subject’s ability to undergo a polygraph test. These conditions can alter the normal respiratory pattern, which is crucial for accurate measurement in polygraph examinations. In particular, the following conditions are considered exclusion criteria:
Respiratory Failure: Characterized by the respiratory system’s inability to maintain adequate levels of oxygen and carbon dioxide in the blood. This condition can cause variations in breathing frequency and depth that may be misinterpreted as physiological responses on a polygraph, affecting the validity of the results.
Asthma: Asthma is an inflammatory disease of the airways that causes episodes of wheezing, shortness of breath, chest tightness, and coughing. During an asthma attack, the respiratory pattern is significantly altered, which can complicate the interpretation of the respiratory charts in a polygraph examination.
Chronic Obstructive Pulmonary Diseases (COPD): Includes diseases such as chronic bronchitis and emphysema, which reduce the lungs’ ability to expel air. Fluctuations in breathing due to COPD can lead to inaccurate polygraph results due to irregularities in the recording of pneumographs.

2.2 Impact of Respiratory Diseases on Polygraph Testing
Polygraph pneumographs are sensitive to variations in respiratory volume and cycle. In subjects with acute respiratory conditions, these patterns can vary unpredictably and may not accurately reflect reactions to specific stimuli, but rather the fluctuations caused by their medical condition. This could result in a high incidence of false positives or negatives, compromising the reliability of the test.
Additionally, the emotional and psychological stress of participating in a polygraph examination can exacerbate these respiratory disorders, putting the health of the examinee at risk and further complicating the accurate interpretation of the data collected.

3. Severe Cardiovascular Diseases
3.1 General Considerations: Severe cardiovascular conditions such as the use of pacemakers, history of heart attacks, and severe hypertension can compromise an individual’s ability to safely and effectively undergo a polygraph test. These conditions not only pose a potential health risk to the individual during the test but can also directly affect the measurements of the cardio channel and plethysmograph of the polygraph, which are essential for assessing physiological responses.
3.2 Use of Pacemakers: Devices like pacemakers can interfere with the electrical signals recorded in the polygraph’s cardio channel. These devices regulate heartbeats and can alter the measurement of heart rate and the electrical conductivity of the heart, producing readings that do not accurately reflect the examinee’s natural physiological responses to interrogation stimuli.
3.3 History of Heart Attacks: Patients with a history of heart attacks may have compromised cardiac function. During a polygraph examination, emotional stress can induce changes in cardiac activity that may not only complicate the interpretation of the results but also put the individual’s health at risk, potentially triggering another adverse cardiac event.
3.4 Severe Hypertension: Hypertension can affect the measurements of the plethysmograph, which assesses fluctuations in blood volume in the extremities. Elevated blood pressure can alter these volumes, affecting the accuracy of plethysmograph measurements. Moreover, the anxiety and stress associated with the test can exacerbate hypertension, leading to variations in blood pressure that can confuse the collected data and increase the risk of complications such as a cerebrovascular event.
3.5 Impact of Cardiovascular Diseases on the Polygraph: The cardio channel and plethysmograph of the polygraph are fundamental for detecting changes in cardiac activity and peripheral blood volume, respectively. In the presence of severe cardiovascular diseases, these measurements may not be representative of emotional or cognitive reactions to interrogation but rather manifestations of the underlying disease or the effect of medical devices.
Given the significant influence that severe cardiovascular diseases can have on polygraph measurements and the potential health risks to the examinee, it is prudent to exclude individuals with these conditions from polygraph tests.
In cases of uncertainty about health conditions, a detailed medical evaluation should be performed before considering a candidate suitable for the test, ensuring the individual’s safety and the integrity of the polygraph results.

4. Neurological Issues Affecting Comprehension and Communication
4.1 General Considerations: Neurological disorders that compromise cognitive, comprehension, or communication abilities can render an individual unfit for polygraph tests, as these conditions can significantly affect the ability to interpret and respond to questions coherently and accurately. Specific disorders include:
4.2 Schizophrenia: This disorder is characterized by thoughts or experiences that seem disconnected from reality, persistent delusions, hallucinations (such as hearing voices), and disorganized thinking. Subjects with schizophrenia may have significant difficulties in following questions and responding coherently during a polygraph, as their perceptions and beliefs may not correspond with reality.
4.3 Delusional Disorder (Paranoid Type): This disorder involves the presence of persistent delusions, often of a persecutory or grandiose nature, without significant hallucinations. Individuals with delusional disorder may misinterpret questions and situations during a polygraph, responding based on their delusions rather than objective facts.
4.4 Schizophreniform Disorder: Similar to schizophrenia, this disorder presents psychotic symptoms that last less than six months. During this period, the individual may experience episodes of confusion, delusions, and hallucinations, which can complicate the conduct of a polygraph, as their ability to process and respond appropriately to questions may be severely compromised.
4.5 Schizoaffective Disorder: This disorder combines symptoms of mood disorders, such as depression or bipolar disorder, with symptoms of schizophrenia. The fluctuation of moods and psychotic symptoms can deeply affect the individual’s ability to maintain coherent and logical thought, necessary for providing accurate and reliable responses on a polygraph.
4.6 Impact of Neurological Problems on the Polygraph Test
The efficacy of a polygraph test critically depends on the examinee’s ability to understand the questions and respond in a coherent and deliberate manner. The disorders described compromise this process by distorting the individual’s perception of reality and affecting their communication ability. Responses may be impulsive, incongruent, or based on distorted realities, resulting in polygraph readings that are difficult to interpret and potentially misleading.
Given the complexity of these disorders and their significant impact on cognition and perception, individuals diagnosed with these conditions are not suitable candidates for polygraph tests. It is crucial to exclude these individuals to ensure the integrity of the test results and to protect the well-being of the affected individuals, avoiding placing them in situations that could be exacerbated by the stress of the examination.

5. Influence of Psychoactive Substances on Polygraph Test Results
5.1 General Overview: The consumption of psychoactive substances significantly affects the reliability of polygraph tests. Substances such as alcohol and illicit drugs alter the body’s physiological responses, which are precisely what the polygraph measures to assess the veracity of an individual’s responses. Individuals under the effects of alcohol or drugs are not considered suitable for testing. Alcohol, as a depressant, can alter breathing and heart rate, directly affecting the reliability of polygraph measurements. Conversely, stimulant drugs like cocaine increase alertness and physical response, producing contrary effects that also compromise the accuracy of the polygraph results. The presence of these substances can significantly distort the physiological responses that the polygraph attempts to measure.
A detailed evaluation of the medical and psychological history of all candidates is required before conducting a polygraph test to confirm their eligibility according to the criteria established in this document.
5.2 Alcohol: As a central nervous system depressant, alcohol reduces brain functions, relaxes muscles, and alters emotional and physical responses. In the context of a polygraph, alcohol can affect breathing and heart rate, as well as reduce blood pressure, which is reflected in the readings of pneumographs and cardiographs of the device. It can also alter the individual’s reaction time to questions, making their responses slower and less precise, which could be misinterpreted as signs of deception.
5.3 Fentanyl: This potent synthetic opioid has extremely strong analgesic and sedative effects, even in very small doses. Fentanyl can drastically lower heart and respiratory rates, affecting the measurements of the polygraph sensors and leading to results that do not represent the normal emotional or cognitive responses to questions.
5.4 Stimulant Drugs (such as cocaine and amphetamines): These substances increase alertness, accelerate heart rate, and can cause hyperactivity. During a polygraph examination, this results in an increase in sympathetic nervous system activity, which can lead to artifacts in measurements such as elevated heart rates and irregular breathing. These physiological changes can be misinterpreted as reactions to the questions asked, affecting the accuracy of the polygraph results.
5.5 Speed (Amphetamines): As a stimulant, speed increases alertness, attention, and energy, and can cause euphoria. It also raises heart rate and blood pressure, which can result in altered measurements on the polygraph. This increased physiological activity can be incorrectly interpreted as signs of deception or nervousness.

5.6 Crack (a form of smoked cocaine): Crack is a highly addictive form of cocaine that produces an intense but short-lived high. This stimulant causes a rapid and powerful increase in sympathetic nervous system activity, which can lead to an increase in breathing rate and heartbeats, complicating the interpretation of polygraph charts.
5.7 MDMA (Ecstasy): Commonly used in festive environments, MDMA can cause intense feelings of well-being, hyperactivity, and a distortion in sensory and temporal perception. These effects can significantly alter emotional and physiological responses during a polygraph, as the subject may exhibit increased reactivity to sensory and emotional stimuli, potentially confusing the test results.
5.8 Cannabis: THC, the main psychoactive component of cannabis, can have sedative effects or, in some cases, cause paranoia. The response of an individual under the effects of cannabis can be unpredictable; some users experience a decrease in anxiety, while others may exhibit an increase. These variables affect the stability of the polygraph measurements, complicating the interpretation of the results.
5.9 Opiates (such as heroin and morphine): Opiates have a significantly depressant effect on the central nervous system, decreasing heart rate and blood pressure, and slowing breathing. These changes can mask the physiological fluctuations that the polygraph seeks to measure in response to psychological stress and dishonesty, resulting in a high rate of false negatives.

6. Identification of Substances in the Body Through Urine Testing
To ensure the integrity and accuracy of a polygraph test, it is crucial to determine if a subject has consumed substances that could alter their physiological responses. An effective way to do this is through the use of urine tests, which can detect the presence of drugs and alcohol in the body. Here’s a detailed explanation of how these tests work and their application in the context of a polygraph examination:

6.1 Detection Method
Urine tests are widely used to detect drugs and their metabolites in the body. These tests can identify a variety of substances, including illicit drugs, alcohol, prescription medications, and designer drugs. The procedure is relatively straightforward and non-invasive, allowing it to be conducted quickly before a polygraph test.

6.2 Detectable Substances
6.2.1 Alcohol: Although alcohol is metabolized quickly, its metabolites can be detected in urine for an extended period.
6.2.2 Cannabinoids (marijuana, hashish): Can be detected up to several weeks after use, depending on usage frequency.
6.2.3 Cocaine: Its metabolites can be detected several days after use.
6.2.4 Opiates (heroin, morphine, fentanyl): Generally detectable from 1 to 3 days after consumption.
6.2.5 Amphetamines and methamphetamines: Detectable in urine for up to 48 hours after use.
6.2.6 MDMA (ecstasy): Detectable up to 2-4 days after consumption.
6.2.7 Designer Drugs: Different tests can detect various designer drugs; the detection window varies depending on the specific substance.

6.3 Advantages of Urine Tests:
6.3.1 Speed and Efficiency: Results can be available within minutes or hours.
6.3.2 Cost-Effectiveness: They are more economical compared to other methods like blood or hair analysis.
6.3.3 Broad Detection Range: Capable of identifying multiple types of substances in a single sample.
6.4 Application of Urine Tests in Polygraph Examinations:
Before proceeding with a polygraph, conducting a urine test can help ensure that the results will not be influenced by drugs or alcohol. If the test indicates the presence of psychoactive substances, the polygraph examination should be postponed or canceled, depending on the administering body’s policy. This ensures that the physiological responses measured during the polygraph reflect true emotional and cognitive reactions to the questions asked, free from chemical distortions.
The use of urine tests for detecting psychoactive substances is a vital tool for maintaining the accuracy and reliability of polygraph tests. By identifying and excluding subjects who have consumed potentially altering substances, test administrators can have greater confidence in the validity of their results and make informed decisions based on reliable data.
This strategy forms a crucial part of the evaluation process prior to conducting a polygraph test, ensuring that high standards of precision and ethics are maintained in the administration of these tests.

7. Informed Consent for Conducting Polygraph Tests
7.1 Individuals who do not provide written consent cannot undergo a polygraph test. Informed consent is a fundamental pillar in the administration of polygraph tests, ensuring that all participants are fully informed about the nature, procedures, potential risks, and consequences of the test before it is conducted.

7.2 Elements of Informed Consent:
7.2.1 Comprehensive Information about the Test: Before the test, individuals must be provided with a detailed explanation of how the polygraph works, what types of questions will be asked, and how the results will be interpreted and used. This includes a description of the devices that will be used and the measurements that will be recorded.
7.2.2 Voluntariness: Consent to undergo the test must be completely voluntary, without any pressure or coercion. Individuals must have the freedom to withdraw their consent and discontinue the test at any time if they wish.
7.2.3 Confidentiality and Use of Information: It must be clearly explained how the confidentiality of the test results will be handled and to whom they may be disclosed. Additionally, the subject must be informed about how the results will be used, whether for employment, legal, or other purposes.
7.2.4 Potential Risks and Benefits: Although the polygraph test is generally safe, individuals should be informed about any potential emotional or physical discomfort they may experience during the test. They should also be aware of the potential benefits and limitations of the polygraph results.
7.2.5 Right to Consultation: Individuals should be offered the opportunity to ask questions and discuss any concerns with the test administrator before giving their consent.

7.3 Documentation of Informed Consent
Consent must be documented in writing. The informed consent document must be signed by the subject before proceeding with the test, ensuring that they have understood all the information and agree to participate voluntarily under those terms.
Including informed consent as an exclusion criterion is essential to maintaining the ethical integrity of polygraph practice. It ensures that the rights and well-being of the participants are protected, and that the tests are conducted fairly and transparently. This not only reinforces the legal and ethical validity of the test but also promotes the trust and cooperation of the participants, key elements for obtaining reliable results.

This document thoroughly details the exclusion criteria for conducting polygraph tests, identifying specific conditions and situations under which individuals are not suitable for these assessments. Aspects related to physical and mental health, age, as well as the influence of psychoactive substances, have been considered, highlighting how these factors can affect the integrity of the polygraph results.
Physical health conditions, including severe cardiovascular diseases, respiratory and neurological problems, can compromise the individual’s safety during the test and distort the physiological measurements that the polygraph attempts to capture. On the other hand, mental health conditions, especially psychotic disorders, affect the subject’s ability to process and respond coherently to questions, which can lead to misinterpretations of the data.
The influence of psychoactive substances is particularly problematic, as they alter the basic physiological responses that are fundamental to the operation of the polygraph. Implementing drug and alcohol screening tests before the examination is essential to ensure that the results truly reflect the individual’s emotional and cognitive responses to the questions posed, free from chemical interferences.
In summary, the rigorous application of these exclusion criteria is crucial to protect the integrity of the polygraph test and ensure the safety and well-being of the participants. By adhering to these guidelines, test administrators can conduct more accurate and reliable assessments, thereby enhancing the effectiveness of the polygraph test as a tool in various contexts, including legal investigations and employment selection processes. This approach ensures that only suitable subjects are evaluated, maintaining high standards of accuracy and professional ethics.