Respiratory Suppression in Polygraph Testing: Guide

What Respiratory Suppression Actually Means

Respiratory suppression refers to a measurable reduction in breathing activity that occurs when a person responds to specific questions during a polygraph examination. This reduction can manifest as shallower breaths (decreased amplitude), a slower breathing rate (reduced cycling), or a temporary cessation of breathing altogether (apnea). The changes are captured by pneumograph sensors positioned around the examinee's chest and abdomen, and they appear as visible alterations in the respiratory tracing on the polygraph chart [1]Verified APA Standards of Practice
Confirms APA requirement for two pneumograph components recording thoracic and abdominal patterns separately, and standards for continuous physiological recordings.

In the context of polygraph testing, respiratory suppression is considered a physiological marker of arousal associated with the autonomic nervous system's response to psychologically significant stimuli. When an examinee encounters a question that carries emotional weight or triggers a deception-related response, the body's natural breathing rhythm can be disrupted [2]Verified PDD Terminology Reference for the Science of Psychophysiological Detection of Deception
Confirms apnea as ultimate manifestation of respiratory suppression, countermeasure indicators in breathing, and that breathing is one of the first areas examiners check for countermeasures. According to the APA's PDD Terminology Reference, apnea is considered the ultimate manifestation of respiratory suppression, and true involuntary apneas almost always occur near the bottom of the exhalation cycle [2]Verified PDD Terminology Reference for the Science of Psychophysiological Detection of Deception
Confirms apnea as ultimate manifestation of respiratory suppression, countermeasure indicators in breathing, and that breathing is one of the first areas examiners check for countermeasures. This disruption is precisely what examiners look for when evaluating the respiratory channel. Learn more about how the autonomic nervous system drives polygraph responses in our psychological and physiological foundations guide.

Respiratory suppression is not a binary indicator of truthfulness or deception. Rather, it is one component of a multi-channel physiological assessment. The presence of respiratory suppression at specific points during the test, particularly during relevant questions, may suggest heightened physiological arousal that could be associated with deception. However, it must always be evaluated in context with the other measured channels and the overall testing conditions. This is why the numerical scoring system integrates data across all channels before any determination is made. For more on how this scoring works, see our guide to evaluating polygraph data with automated scoring.

Where Respiratory Suppression Fits in Polygraph Science

The polygraph instrument measures three primary physiological systems: respiration, electrodermal activity (EDA), and cardiovascular activity [3]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Benussi's 1914 experiments, Arther's dual pneumograph innovation discovering differences approximately 33% of the time, and the development timeline of polygraph technology. Respiratory suppression belongs to the first of these domains and is recorded by the pneumograph component of the instrument. For a deeper understanding of how the cardiovascular channel works alongside respiration, see our guide to diagnostic vs. screening polygraphs.

Historically, respiration was among the earliest physiological measures studied in the context of deception detection. In 1914, Italian psychologist Vittorio Benussi published "Die Atmungssymptome der Lüge" (The Respiratory Symptoms of Lying) in the journal Archiv für die gesamte Psychologie (Vol. 31, pp. 244–273) [4]Verified Vittorio Benussi, the Gustav Mahler of Psychology
Confirms Benussi published 'Die Atmungssymptome der Lüge' in Archiv für die gesamte Psychologie, Vol. 31, pp. 244–273 (1914), and details his quotient laws methodology. Using a pneumograph, Benussi discovered a method for calculating the quotient of inhalation to exhalation time as a means of detecting deception [3]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Benussi's 1914 experiments, Arther's dual pneumograph innovation discovering differences approximately 33% of the time, and the development timeline of polygraph technology. He conducted experiments and concluded that lying caused emotional changes resulting in detectable respiratory alterations [4]Verified Vittorio Benussi, the Gustav Mahler of Psychology
Confirms Benussi published 'Die Atmungssymptome der Lüge' in Archiv für die gesamte Psychologie, Vol. 31, pp. 244–273 (1914), and details his quotient laws methodology. His research provided early empirical support for the principle that deception produces distinctive physiological signatures and laid the groundwork for respiratory analysis in polygraph science.

Modern polygraph science treats respiratory data as an essential part of the diagnostic picture. The American Polygraph Association (APA) Standards of Practice require that all polygraph examinations record respiration patterns using pneumograph components, with thoracic and abdominal patterns recorded separately using two pneumograph components [1]Verified APA Standards of Practice
Confirms APA requirement for two pneumograph components recording thoracic and abdominal patterns separately, and standards for continuous physiological recordings. Without respiratory analysis, a polygraph examination cannot be considered complete or standards-compliant. The 2011 APA meta-analysis, which examined 38 studies involving 3,723 examinations by 295 scorers, found that validated polygraph techniques produced an overall decision accuracy of 87% (confidence interval: 80–94%) [5]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms 87% overall decision accuracy (CI: 80-94%), 89% for event-specific diagnostic tests, from analysis of 38 studies and 3,723 examinations with 295 scorers. For event-specific diagnostic tests, accuracy reached 89% [5]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms 87% overall decision accuracy (CI: 80-94%), 89% for event-specific diagnostic tests, from analysis of 38 studies and 3,723 examinations with 295 scorers. For a comprehensive view of polygraph development, see our history of the APA.

How Normal Breathing Works

To understand respiratory suppression, it helps to first understand how normal breathing functions. Respiration is controlled by the brainstem's respiratory center, specifically a dense network of neurons located in the ventrolateral area of the lower medulla oblongata known as the pre-Bötzinger complex [6]Verified Pre-Bötzinger Complex: A Brainstem Region That May Generate Respiratory Rhythm in Mammals
Confirms the pre-Bötzinger complex as a functionally and anatomically specialized site in the ventrolateral medulla oblongata essential for generating inspiratory breathing rhythm. This complex, first identified in 1991 by Smith and colleagues, is essential for generating the inspiratory breathing rhythm in mammals [6]Verified Pre-Bötzinger Complex: A Brainstem Region That May Generate Respiratory Rhythm in Mammals
Confirms the pre-Bötzinger complex as a functionally and anatomically specialized site in the ventrolateral medulla oblongata essential for generating inspiratory breathing rhythm. Under normal resting conditions, a healthy adult breathes approximately 12 to 20 times per minute [7]Verified Understanding Vital Signs: The Importance of Your Respiratory Rate
Confirms normal adult respiratory rate of 12-20 breaths per minute and that breathing is uniquely controllable among vital signs as it can be overridden by voluntary control, with each breath following a rhythmic cycle of inhalation and exhalation. The diaphragm contracts during inhalation, expanding the thoracic cavity and drawing air into the lungs, while exhalation occurs passively as the diaphragm relaxes.

What makes breathing unique among the three polygraph channels is its dual control mechanism. Breathing is regulated both automatically by the autonomic nervous system and voluntarily by the cerebral cortex [8]Verified The Polygraph and Lie Detection
Confirms NRC 2003 report findings on respiration being easily brought under voluntary control, the respiratory centers in the medulla and pons, and that polygraph research needs further theoretical development. You can consciously hold your breath, breathe faster, or slow your breathing — a fact the American Lung Association notes is unique among vital signs [9]Verified Understanding Vital Signs: The Importance of Your Respiratory Rate
Confirms respiratory rate is a unique vital sign because while controlled by the autonomic nervous system, you can also override it. As the NRC's 2003 report confirmed, "respiration is easily brought under voluntary control" and variations in respiration can produce changes in heart rate and electrodermal activity [8]Verified The Polygraph and Lie Detection
Confirms NRC 2003 report findings on respiration being easily brought under voluntary control, the respiratory centers in the medulla and pons, and that polygraph research needs further theoretical development. This dual control is both a strength and a challenge for polygraph testing: it allows genuine autonomic responses to appear on the chart, but it also creates the possibility that examinees might attempt to deliberately manipulate their breathing patterns. Our guide to myths about beating lie detectors explores this topic in detail.

The Sympathetic Nervous System and Stress Response

When a person experiences psychological stress, fear, or anxiety, the sympathetic branch of the autonomic nervous system activates what is commonly known as the fight-or-flight response. This activation produces a cascade of physiological changes including increased heart rate, elevated blood pressure, enhanced sweat gland activity, and alterations in breathing patterns. Psychological stress can result in respiratory patterns that differ significantly from those produced by normal metabolic needs [10]Verified Physiology, Respiratory Rate
Confirms normal adult respiratory rate of 12-20 breaths per minute, pre-Bötzinger complex role, and that psychological stress can result in respiratory patterns differing from metabolic needs.

The respiratory effects of sympathetic activation can include decreased breathing amplitude (breaths become shallower as chest wall muscles tighten), reduced breathing rate (the cycle between breaths slows or becomes irregular), baseline shift (the overall tracing may move upward or downward on the chart), apnea episodes (temporary cessation of breathing for one or more cycles), and irregular rhythm (the normally steady pattern becomes erratic or unpredictable) [11]Verified Nelson & Handler: Pneumograph Signal Processing and Feature Extraction
Describes pneumograph data processing techniques, respiratory excursion measurements, and the development of the OSS-3 scoring algorithm by Raymond Nelson.

These autonomic changes are what polygraph examiners classify as respiratory suppression. The key principle is that these changes are involuntary at their origin, even though an examinee may attempt to overlay voluntary control. The trained examiner's task is to identify and differentiate between genuine autonomic responses and voluntary or artifactual disturbances. For more on how the autonomic nervous system plays a central role in polygraph testing, see our detailed guide to the psychophysiological basis of the CQT.

Research in neuroscience has demonstrated that deception activates specific brain regions — the frontal lobe works to suppress the truth, the limbic system activates due to anxiety, and the temporal lobe responds to memory retrieval and fabrication [12]Verified How do lie detectors work?
Confirms three brain areas activated during deception (frontal lobe, limbic system, temporal lobe) and that Benussi published findings on respiratory symptoms of a lie in 1914. These neural processes produce the downstream physiological effects that pneumograph sensors are designed to capture. Notably, a 2001 study by Kurohara and colleagues specifically found that respiratory responses to deception showed inhibitory breathing characterized by decreased expiratory volume and minute ventilation, which contrasted sharply with the hyperventilation pattern observed during general stress tasks [13]Verified Respiratory changes during detection of deception
Found that deception produced inhibitory breathing characterized by decreased expiratory volume and minute ventilation, contrasting with hyperventilation during general stress.

Thoracic and Abdominal Pneumograph Components

A standard APA-compliant polygraph instrument uses two pneumograph sensors to record respiratory activity [1]Verified APA Standards of Practice
Confirms APA requirement for two pneumograph components recording thoracic and abdominal patterns separately, and standards for continuous physiological recordings. These are typically corrugated rubber tubes, strain gauge transducers, or piezoelectric sensors that encircle the examinee's body at two locations [14]Verified Cardiovascular and Respiratory Factors Affecting Polygraph Recordings
Describes two pneumograph sensors measuring respiration rate, amplitude, and synchronicity, and that respiratory suppression occurs due to cortical modulation of medullary respiratory centers.

The upper thoracic pneumograph is positioned around the upper chest to measure rib cage expansion during breathing. The abdominal pneumograph is positioned around the abdomen to measure diaphragmatic breathing activity [1]Verified APA Standards of Practice
Confirms APA requirement for two pneumograph components recording thoracic and abdominal patterns separately, and standards for continuous physiological recordings. Using dual sensors serves several critical purposes. First, it provides a more complete picture of respiratory activity, since thoracic and abdominal breathing can operate somewhat independently. Some people are predominantly chest breathers while others rely more heavily on diaphragmatic breathing.

Richard O. Arther was a pioneering polygraphist who experimented with recording thoracic and abdominal breathing patterns simultaneously in the 1950s, discovering differences between the two patterns approximately 33% of the time [3]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Benussi's 1914 experiments, Arther's dual pneumograph innovation discovering differences approximately 33% of the time, and the development timeline of polygraph technology. Second, dual sensors make it significantly more difficult for an examinee to manipulate their breathing without detection, because altering one breathing pattern while maintaining the other is extremely challenging. A 2012 study by Ogawa, Matsuda, Hirota, and Takasawa specifically assessed different respiratory transducers for polygraph testing, evaluating their effectiveness in capturing accurate respiration data [15]Verified Assessment of Respiratory Transducers for Polygraph Testing
Assessed different respiratory transducer types for polygraph testing to evaluate effectiveness in capturing accurate respiration data.

What the Pneumograph Tracing Looks Like

On a polygraph chart, the pneumograph channels appear as continuous wave-like tracings. Each peak represents an inhalation and each trough represents an exhalation. A normal, relaxed breathing pattern produces a smooth, rhythmic waveform with consistent amplitude (the height of each wave) and a steady cycling rate (the frequency of waves over time).

When respiratory suppression occurs, the examiner will observe changes in these tracings that deviate from the established baseline pattern. The suppressed breathing may appear as flattened waves (reduced amplitude), wider spacing between peaks (reduced rate), or in extreme cases, a nearly flat line indicating apnea [11]Verified Nelson & Handler: Pneumograph Signal Processing and Feature Extraction
Describes pneumograph data processing techniques, respiratory excursion measurements, and the development of the OSS-3 scoring algorithm by Raymond Nelson. As described in the APA's PDD Terminology Reference, true involuntary apneas almost always occur near the bottom of the exhalation cycle [2]Verified PDD Terminology Reference for the Science of Psychophysiological Detection of Deception
Confirms apnea as ultimate manifestation of respiratory suppression, countermeasure indicators in breathing, and that breathing is one of the first areas examiners check for countermeasures. These changes become particularly significant when they correlate with the presentation of specific test questions.

Modern computerized polygraph systems like the Lafayette LX6 — a 10-channel system with LXSoftware bundled with the Objective Scoring System (OSS-3) scoring algorithm [16]Verified LXSoftware with OSS-3 Scoring Algorithm
Confirms LX6 as a 10-channel polygraph system with LXSoftware bundled with OSS-3 algorithm and RLE respiratory measurement tool — or the Stoelting CPS Elite, the fourth-generation Computerized Polygraph System with 32-bit processing and a sampling rate of 360 samples per second per channel [17]Verified CPS Elite Polygraph Systems
Confirms Stoelting CPS Elite as fourth-generation Computerized Polygraph System with 360 samples per second per channel and piezo respiration sensor options, display these tracings digitally and allow examiners to zoom in on specific chart segments, measure amplitude changes precisely, and apply algorithmic analysis to the respiratory data. The LXSoftware also includes an RLE (Respiration Line Length) tool that measures the ratio of the relevant response divided by the comparison response and produces a suggested pneumograph score [16]Verified LXSoftware with OSS-3 Scoring Algorithm
Confirms LX6 as a 10-channel polygraph system with LXSoftware bundled with OSS-3 algorithm and RLE respiratory measurement tool. For more on how these algorithms compare, see our guide to evaluating polygraph data and automated scoring. However, fundamental visual pattern recognition skills remain essential for competent chart evaluation.

The Five Primary Respiratory Response Patterns

Polygraph examiners are trained to recognize several distinct types of respiratory changes that may occur during an examination. Understanding these patterns is essential for accurate chart interpretation and proper scoring.

Amplitude suppression is the most common form of respiratory suppression. Breathing becomes noticeably shallower during or immediately following a relevant question. The pneumograph tracing shows reduced wave height compared to the baseline or comparison question responses. This pattern suggests the examinee's respiratory muscles are tensing due to sympathetic nervous system activation [11]Verified Nelson & Handler: Pneumograph Signal Processing and Feature Extraction
Describes pneumograph data processing techniques, respiratory excursion measurements, and the development of the OSS-3 scoring algorithm by Raymond Nelson.

Rate suppression (bradypnea) occurs when the breathing cycle slows measurably. Instead of the established baseline rhythm, the examinee takes fewer breaths per minute. On the chart, this appears as increased spacing between respiratory peaks. Rate changes are particularly significant when they consistently occur at the same questions across multiple chart runs.

Apnea is a temporary cessation of breathing, sometimes lasting several seconds. The pneumograph tracing goes essentially flat during the apneic episode. According to the APA's PDD Terminology Reference, when apneas are specifically associated with certain questions during a polygraph examination, they are considered significant physiological reactions and strongly diagnostic of deception [2]Verified PDD Terminology Reference for the Science of Psychophysiological Detection of Deception
Confirms apnea as ultimate manifestation of respiratory suppression, countermeasure indicators in breathing, and that breathing is one of the first areas examiners check for countermeasures. While dramatic when observed, apnea must be carefully evaluated to determine whether it is an autonomic response or a deliberate countermeasure attempt.

Baseline change occurs when the overall positioning of the respiratory tracing shifts upward or downward on the chart. This indicates a sustained change in resting lung volume — the examinee may be unconsciously holding a partial inhalation or maintaining a higher level of muscle tension in the thorax. Baseline shifts often accompany amplitude suppression.

Irregularity occurs when the normally rhythmic breathing pattern becomes erratic. Breaths vary in depth and timing without the consistent rhythm seen during baseline. While some irregularity is normal, a marked increase in breathing irregularity during relevant questions may be considered a form of respiratory disturbance worthy of scoring. Research has shown that an improved method for calculating respiratory line length significantly increased discrimination performance in the concealed information test [18]Verified Improved method for calculating the respiratory line length in the concealed information test
The weighted average method successfully removed systematic bias in respiration line length calculations and significantly increased discrimination performance in CIT data, while the weighted average method for analyzing respiratory movements showed higher detection efficiency than simple averaging [19]Verified Effectivity of the weighted average method for analysis of respiratory movements in the concealed information test
Confirmed weighted average method showed higher detection efficiency than simple averaging, with respiration speed and rate discriminating groups across 20 seconds.

Deception-Related Causes

The primary theoretical basis for using respiratory suppression as a deception indicator rests on the psychophysiology of deception. When a person attempts to deceive, particularly in a structured testing environment where the consequences of detection are meaningful, several cognitive and emotional processes activate simultaneously.

Cognitive load increase plays a significant role — formulating and maintaining a deceptive response requires more mental processing than telling the truth, which can disrupt the automatic regulation of breathing. Three main areas of the brain are stimulated during deception: the frontal lobe works to suppress the truth, the limbic system activates due to the anxiety that comes from lying, and the temporal lobe activates in response to retrieving memories and creating mental imagery [12]Verified How do lie detectors work?
Confirms three brain areas activated during deception (frontal lobe, limbic system, temporal lobe) and that Benussi published findings on respiratory symptoms of a lie in 1914. Fear of detection triggers the sympathetic nervous system, producing the fight-or-flight cascade that directly affects respiratory patterns. Emotional conflict between the desire to deceive and the awareness of being monitored creates internal tension that manifests physiologically. And attentional focus narrows to the threatening question, temporarily overriding normal automatic breathing regulation.

These deception-related causes typically produce respiratory suppression that is time-locked to relevant questions, meaning the suppression begins at or shortly after the question is asked and gradually resolves as the examiner moves to subsequent questions. This temporal correlation within the polygraph reaction window is a key factor in determining whether observed respiratory changes are diagnostically significant. A 2001 Japanese study specifically found that deception produced inhibitory breathing characterized by decreased expiratory volume and minute ventilation — a qualitatively different pattern from the hyperventilation observed during general stress [13]Verified Respiratory changes during detection of deception
Found that deception produced inhibitory breathing characterized by decreased expiratory volume and minute ventilation, contrasting with hyperventilation during general stress.

Non-Deception Causes of Respiratory Changes

Not all respiratory suppression indicates deception. Examiners must be aware of numerous non-deception-related factors that can produce similar breathing changes. General test anxiety is common — many examinees, even truthful ones, experience anxiety about the testing process itself, particularly if they fear a false positive result. Understanding false negatives in polygraph testing helps examiners distinguish between anxiety-driven and deception-driven responses.

Question sensitivity can arise when a question touches on a personally distressing topic that produces emotional arousal without deception being present. Surprise or confusion from an unexpected or confusing question can momentarily disrupt breathing rhythm. Physical discomfort from sitting in the polygraph chair for extended periods, sensor pressure, or room temperature can also affect breathing.

Medical conditions such as asthma, COPD, and sleep apnea can produce respiratory irregularities that complicate chart interpretation. Mental health conditions including anxiety disorders and PTSD can produce respiratory irregularities unrelated to deception. Medications affecting respiratory function and autonomic nervous system activity can also produce changes. Additionally, research has demonstrated that intentional memory suppression strategies can alter physiological responses, as participants who suppressed crime-related memory retrieval showed significantly decreased memory-related ERP effects [20]Verified Intentional retrieval suppression can conceal guilty knowledge in ERP memory detection tests
Demonstrated that motivated participants could suppress crime retrieval, significantly decreasing memory-related ERP effects and potentially evading detection.

This is precisely why polygraph examiners spend considerable time during the pre-test phase establishing rapport, reviewing questions, and identifying any medical or psychological conditions that might affect respiratory readings. Proper in-test instructions and admonitions also play a critical role in minimizing non-deception artifacts.

Numerical Scoring of Respiratory Responses

Modern polygraph scoring uses standardized numerical systems where examiners assign values to each physiological channel based on the observed responses at relevant versus comparison questions. Respiratory data is scored alongside EDA and cardiovascular data to produce a total score that determines the examination outcome.

The examiner evaluates respiratory responses by comparing the breathing patterns observed during relevant questions against those observed during comparison questions within the same chart run. If the respiratory suppression is more pronounced at relevant questions, the examiner assigns a negative score to the respiratory channel. If the suppression is more pronounced at comparison questions, a positive score is assigned. If the responses are equivalent, a zero score is recorded.

Multiple chart runs — typically three or more — are conducted to establish consistency and reliability. The respiratory scores from each chart run are combined with the EDA and cardiovascular scores to produce a cumulative total. This total is then compared against established cut scores to determine whether the result is deceptive, non-deceptive, or inconclusive.

The Objective Scoring System version 3 (OSS-3), developed by Raymond Nelson and bundled with Lafayette's LXSoftware [16]Verified LXSoftware with OSS-3 Scoring Algorithm
Confirms LX6 as a 10-channel polygraph system with LXSoftware bundled with OSS-3 algorithm and RLE respiratory measurement tool, and Stoelting's CPS Fusion software represent the current generation of automated scoring tools that can assist examiners in evaluating respiratory data. However, examiner judgment remains essential, particularly in identifying artifacts and contextual factors that automated systems may not account for.

Multi-Channel Integration

Respiratory data is never evaluated in isolation. The APA Standards of Practice require multi-channel analysis combining respiration with electrodermal activity and cardiovascular measures [1]Verified APA Standards of Practice
Confirms APA requirement for two pneumograph components recording thoracic and abdominal patterns separately, and standards for continuous physiological recordings. This multi-channel approach significantly enhances overall diagnostic accuracy.

The rationale for multi-channel integration is that different individuals may show their primary physiological response to deception in different channels. Some examinees demonstrate pronounced respiratory suppression with minimal EDA changes, while others show strong EDA responses with relatively stable breathing patterns. By evaluating all three channels simultaneously, the examiner captures a more complete picture of the examinee's physiological state.

The 2021 comprehensive meta-analysis of the Comparison Question Test by Honts and colleagues, which analyzed 138 datasets, found significant effects and confirmed that the CQT can be accurate, with motivation level having a positive linear relationship with outcome measures [21]Verified A comprehensive meta-analysis of the Comparison Question Polygraph Test
Meta-analysis of 138 datasets confirming CQT can be accurate, with motivation level showing positive linear relationship with outcome measures. This underscores the importance of proper test administration alongside multi-channel analysis for achieving optimal results.

Identifying Artifacts in Respiratory Data

One of the most critical skills for a polygraph examiner is distinguishing between genuine respiratory suppression caused by autonomic arousal and artifacts — breathing disturbances caused by non-physiological or non-relevant factors. Common artifacts include coughing or throat clearing, sighing or deep breaths, body movement or repositioning, talking (answering questions always creates a brief respiratory disturbance), swallowing, and external noise or distraction.

Trained examiners annotate the polygraph chart in real-time, marking any observed artifacts so they can be excluded from scoring. The APA Standards of Practice emphasize that physiological recordings should be continuous and of sufficient amplitude to be easily readable by both the examining and any reviewing examiner [1]Verified APA Standards of Practice
Confirms APA requirement for two pneumograph components recording thoracic and abdominal patterns separately, and standards for continuous physiological recordings. This ensures that artifact identification and exclusion are transparent and reproducible.

Since breathing is more readily controlled than other activity recorded with the polygraph, it is one of the first areas examiners look for indications of countermeasures [2]Verified PDD Terminology Reference for the Science of Psychophysiological Detection of Deception
Confirms apnea as ultimate manifestation of respiratory suppression, countermeasure indicators in breathing, and that breathing is one of the first areas examiners check for countermeasures. Indicators include paced breathing, breath holding, very slow breathing, irregularly shaped waveforms, hyperventilation, and tactical use of deep breaths [2]Verified PDD Terminology Reference for the Science of Psychophysiological Detection of Deception
Confirms apnea as ultimate manifestation of respiratory suppression, countermeasure indicators in breathing, and that breathing is one of the first areas examiners check for countermeasures.

Examiner Approach and Its Impact

The manner in which an examiner conducts the test can significantly influence the quality of respiratory data obtained. Research has demonstrated that an overly interrogative examiner approach can compromise polygraph validity and lead to elevated false positive rates. A professional, neutral examiner approach helps establish a comfortable testing environment where genuine physiological responses can emerge without being obscured by excessive anxiety or defensive reactions.

Proper pre-test procedures, including thorough question review and rapport building, help minimize situational anxiety that could produce respiratory artifacts. The examiner should also provide clear in-test instructions and admonitions about normal breathing and sitting still during the chart collection phase. For understanding how symptomatic questions help identify outside-issue concerns that might affect respiration, see our dedicated guide.

Common Breathing Countermeasure Attempts

Some examinees attempt to manipulate their breathing patterns to defeat the polygraph. Common countermeasure strategies include deliberately slowing breathing during comparison questions (to create artificially large responses at those questions), holding breath during relevant questions, performing subtle hyperventilation to alter baseline readings, and attempting to maintain artificially regular breathing throughout the test.

These deliberate breathing control attempts create characteristic patterns that experienced examiners can identify. For instance, voluntarily controlled breathing typically appears more regular and mechanical than natural breathing, lacks the subtle variability seen in genuine respiration, and may show inconsistencies between thoracic and abdominal channels (since it is extremely difficult to simultaneously control both). The dual pneumograph requirement specifically makes respiratory countermeasures more difficult to execute without detection.

However, a significant 2010 study by Honts and Crawford specifically examined whether polygraph examiners could reliably detect countermeasures from respiratory patterns [22]Verified Polygraph countermeasures cannot be detected from respiratory signatures
Found that polygraph examiners could not reliably detect countermeasures from respiratory patterns, raising important questions about countermeasure detection policy. The findings raised important questions about the detectability of respiratory countermeasures, highlighting both the challenge and the importance of continued research in this area. The study found that countermeasure detection claims may create significant false positive risks for innocent examinees who display normal stress-related breathing variations [22]Verified Polygraph countermeasures cannot be detected from respiratory signatures
Found that polygraph examiners could not reliably detect countermeasures from respiratory patterns, raising important questions about countermeasure detection policy. For more on why common countermeasure methods fail, see our article on 10 myths about beating a lie detector test debunked.

Health Factors Examiners Must Consider

Several medical conditions can affect respiratory patterns during polygraph testing. Examiners must be aware of these conditions and factor them into their analysis. Asthma and COPD can produce irregular breathing patterns, reduced amplitude, and episodes of respiratory distress unrelated to deception. People with COPD often have a respiratory rate higher than normal, closer to 20-30 breaths per minute [7]Verified Understanding Vital Signs: The Importance of Your Respiratory Rate
Confirms normal adult respiratory rate of 12-20 breaths per minute and that breathing is uniquely controllable among vital signs as it can be overridden by voluntary control. Sleep apnea sufferers may have altered baseline respiratory patterns. Cardiovascular conditions can affect the relationship between breathing and heart rate (respiratory sinus arrhythmia). Anxiety disorders may produce chronic hyperventilation or irregular breathing patterns.

Medications that affect the central nervous system, including beta-blockers, anxiolytics, antihistamines, and respiratory medications such as bronchodilators, can alter respiratory patterns. The APA Standards require that examiners make basic inquiries into the medical and psychological condition of the examinee and consider any recent drug use prior to testing [1]Verified APA Standards of Practice
Confirms APA requirement for two pneumograph components recording thoracic and abdominal patterns separately, and standards for continuous physiological recordings.

The pre-test interview serves as the critical opportunity for examiners to identify any medical conditions or medications that might affect respiratory readings. This information is documented and considered when interpreting the chart data. In some cases, medical conditions may render an individual unsuitable for polygraph testing, a determination that responsible examiners make in the interest of both accuracy and the examinee's well-being.

APA Standards of Practice for Respiratory Recording

The American Polygraph Association, established in 1966, is the world's leading association dedicated to evidence-based credibility assessment, with more than 2,700 members [23]Verified American Polygraph Association
Confirms APA was established in 1966 and has 2,700+ members dedicated to evidence-based credibility assessment. The APA Standards of Practice specifically require that polygraph instrumentation record respiration patterns using pneumograph components, with thoracic and abdominal patterns recorded separately using two pneumograph components [1]Verified APA Standards of Practice
Confirms APA requirement for two pneumograph components recording thoracic and abdominal patterns separately, and standards for continuous physiological recordings. This dual-channel requirement ensures comprehensive respiratory data collection and aids in countermeasure detection.

The standards further require that physiological recordings during each test be continuous and of sufficient amplitude to be easily readable by the examiner and any reviewing examiner [1]Verified APA Standards of Practice
Confirms APA requirement for two pneumograph components recording thoracic and abdominal patterns separately, and standards for continuous physiological recordings. Pneumograph and cardiograph tracings between one-half inch and one inch in amplitude at the time of data collection are considered of sufficient size to be easily readable.

ASTM International Standards for Polygraph Practice

ASTM International Committee E52 on Forensic Psychophysiology has developed a series of standards covering all aspects of polygraphy [24]Verified ASTM Forensic Science Standards
Confirms ASTM standards E2062, E2031, E2229, E2439, E1954, and E2035 for polygraph-related practices. Key standards relevant to respiratory recording and polygraph practice include E2062, the Standard Guide for PDD Examination Standards of Practice; E2031, the Standard Practice for Quality Control of PDD Examinations; E2229, the Standard Practices for Interpretation of PDD Data; E2439, covering Instrumentation, Sensors and Operating Software Used in PDD Examinations; and E2035, the Standard Terminology Relating to Forensic Psychophysiology [24]Verified ASTM Forensic Science Standards
Confirms ASTM standards E2062, E2031, E2229, E2439, E1954, and E2035 for polygraph-related practices. These ASTM standards are often cited by professional polygraph organizations and provide an independent framework for ensuring examination quality.

Pioneering Research on Respiratory Deception Detection

The study of respiratory changes during deception has a rich scientific history spanning more than a century. Vittorio Benussi's 1914 publication "Die Atmungssymptome der Lüge" in the Archiv für die gesamte Psychologie (Vol. 31, pp. 244–273) represents the earliest systematic study of respiration and deception [4]Verified Vittorio Benussi, the Gustav Mahler of Psychology
Confirms Benussi published 'Die Atmungssymptome der Lüge' in Archiv für die gesamte Psychologie, Vol. 31, pp. 244–273 (1914), and details his quotient laws methodology. Benussi used a pneumograph to measure breathing patterns and calculated the ratio of inhalation to exhalation duration. He postulated the "quotient laws of lies and sincerity," finding that exhalation slows and lengthens after telling the truth, whereas it becomes faster and shorter after a lie [4]Verified Vittorio Benussi, the Gustav Mahler of Psychology
Confirms Benussi published 'Die Atmungssymptome der Lüge' in Archiv für die gesamte Psychologie, Vol. 31, pp. 244–273 (1914), and details his quotient laws methodology. His experiments reportedly found these ratios in nearly all cases tested.

Harold Burtt in 1918 attempted to replicate Benussi's work but could not fully confirm the inhalation-exhalation ratio findings, though he determined that respiratory changes were indeed indicators of deception. He concluded that blood pressure changes were of greater diagnostic value than respiratory changes alone. Nevertheless, Benussi's foundational concept was likely correct, as evidenced by later work including Howard Timm's 1982 research on respiratory recording line length.

The first polygraph was created in 1921 by John A. Larson, a California police officer and physiologist, who devised an apparatus to simultaneously measure continuous changes in blood pressure, heart rate, and respiration rate [3]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Benussi's 1914 experiments, Arther's dual pneumograph innovation discovering differences approximately 33% of the time, and the development timeline of polygraph technology. This instrument formed the basis for modern polygraphy. Leonarde Keeler refined the device in the 1920s, and by 1938 had added the psychogalvanometer (measuring galvanic skin resistance), signaling the birth of the modern polygraph [3]Verified A Comprehensive History of the Polygraph and Truth Verification Methods
Confirms Benussi's 1914 experiments, Arther's dual pneumograph innovation discovering differences approximately 33% of the time, and the development timeline of polygraph technology.

Modern Respiratory Research in Polygraph Science

The Department of Defense Polygraph Institute (DoDPI), established in 1986, served as the primary federal research institution for polygraph science. In 2007 it was renamed the Defense Academy for Credibility Assessment (DACA), and in 2010 became the National Center for Credibility Assessment (NCCA), now a component of the Defense Counterintelligence Security Agency (DCSA) [25]Verified DoD, DIU Announce Polygraph+ Credibility Assessment Modernization Effort
Confirms NCCA's role coordinating research to improve polygraph accuracy and develop new credibility assessment technologies under DCSA. The NCCA has been appointed the role of coordinating research and development efforts to transform and improve polygraph accuracy and develop new credibility assessment technologies [25]Verified DoD, DIU Announce Polygraph+ Credibility Assessment Modernization Effort
Confirms NCCA's role coordinating research to improve polygraph accuracy and develop new credibility assessment technologies under DCSA.

The 2003 National Research Council report "The Polygraph and Lie Detection" provided a comprehensive review of polygraph science [8]Verified The Polygraph and Lie Detection
Confirms NRC 2003 report findings on respiration being easily brought under voluntary control, the respiratory centers in the medulla and pons, and that polygraph research needs further theoretical development. The NRC acknowledged that respiration is one of the primary physiological processes measured by the polygraph and noted that the respiratory centers in the medulla and pons contain neurons that fire spontaneously to initiate inspiration, with respiration also modified by autonomic reflexes [8]Verified The Polygraph and Lie Detection
Confirms NRC 2003 report findings on respiration being easily brought under voluntary control, the respiratory centers in the medulla and pons, and that polygraph research needs further theoretical development. The report highlighted that polygraph research had "not developed and tested theories of the underlying factors that produce the observed responses," recommending further basic science research [8]Verified The Polygraph and Lie Detection
Confirms NRC 2003 report findings on respiration being easily brought under voluntary control, the respiratory centers in the medulla and pons, and that polygraph research needs further theoretical development.

Significant modern research has expanded our understanding of respiratory analysis in polygraph testing. Nelson and Handler published detailed work on pneumograph signal processing and feature extraction, describing techniques for improving the accessibility and clinical utility of respiratory data in polygraph analysis [11]Verified Nelson & Handler: Pneumograph Signal Processing and Feature Extraction
Describes pneumograph data processing techniques, respiratory excursion measurements, and the development of the OSS-3 scoring algorithm by Raymond Nelson. Matsuda and Ogawa developed an improved method for calculating respiratory line length in the concealed information test, with their weighted average method successfully removing systematic bias and significantly increasing discrimination performance [18]Verified Improved method for calculating the respiratory line length in the concealed information test
The weighted average method successfully removed systematic bias in respiration line length calculations and significantly increased discrimination performance in CIT data. Tsuneoka, Matsuda, and Ogawa further confirmed the weighted average method's superiority, finding that respiration speed and rate discriminated groups across 20 seconds with better performance at longer measurement intervals [19]Verified Effectivity of the weighted average method for analysis of respiratory movements in the concealed information test
Confirmed weighted average method showed higher detection efficiency than simple averaging, with respiration speed and rate discriminating groups across 20 seconds.

The comprehensive 2015 textbook "Fundamentals of Polygraph Practice" by Donald Krapohl and Pamela Shaw provides the most authoritative current reference on evidence-based polygraph practices, covering psychophysiology, data collection, respiratory analysis techniques, and testing protocols [26]Verified Fundamentals of Polygraph Practice
Comprehensive textbook by Krapohl and Shaw covering psychophysiology, data collection, respiratory analysis, and evidence-based polygraph practices. Krapohl, who served as APA President in 2006 and authored more than 100 published research papers on credibility assessment, helped develop the terminology reference that remains the standard in the field [26]Verified Fundamentals of Polygraph Practice
Comprehensive textbook by Krapohl and Shaw covering psychophysiology, data collection, respiratory analysis, and evidence-based polygraph practices.

Looking ahead, the DoD's Polygraph+ modernization initiative, coordinated by the NCCA with expertise from Carnegie Mellon University, MIT, the University of Maryland, and Columbia University, aims to develop next-generation credibility assessment technologies that may further enhance the precision of respiratory and other physiological measurements [25]Verified DoD, DIU Announce Polygraph+ Credibility Assessment Modernization Effort
Confirms NCCA's role coordinating research to improve polygraph accuracy and develop new credibility assessment technologies under DCSA. For a broader perspective on emerging technologies, see our guide to neuroscience-based polygraph tests including fMRI, EEG, and NIRS.