Apnea

What Is Apnea in Polygraph Testing?

Apnea in polygraph testing refers to a temporary cessation of breathing observed in the respiratory tracings recorded by the pneumograph sensors. During apnea, the examinee stops breathing for a period — typically a few seconds to several seconds — creating a visible flat line or near-flat segment in the respiratory channel data.

Apnea is distinguished from blocking by its location in the breathing cycle. Apnea typically occurs near the end of the expiratory segment (after the examinee has exhaled), whereas blocking occurs near the inspiratory peak (when the examinee holds their breath at the top of an inhalation). This distinction is diagnostically significant because the two patterns may have different underlying causes and implications.

Causes of Apnea During Polygraph Examinations

Apnea observed during a polygraph test can result from several different causes, and the examiner must carefully evaluate which explanation is most likely:

Stress-Related Apnea

Genuine psychophysiological stress caused by a deceptive response to a relevant question can trigger involuntary respiratory changes, including temporary breathing cessation. This type of apnea is diagnostically significant and forms part of the respiratory suppression patterns scored in polygraph analysis.

Deliberate Countermeasure Apnea

Examinees attempting to manipulate their polygraph results may deliberately hold their breath during specific questions as a countermeasure technique. Deliberate apnea during comparison questions can artificially inflate the respiratory change at those questions, potentially masking deception on relevant questions.

Medical Apnea

Some examinees may experience breathing pauses related to medical conditions such as sleep apnea, chronic obstructive pulmonary disease (COPD), anxiety disorders, or medication side effects. Medical apnea is typically noted during the suitability screening portion of the pre-test interview.

Apnea as a Scored Feature

Apnea is one of the respiratory features included in the Defensible Dozen — the approximately twelve validated physiological features used in polygraph chart interpretation. When apnea occurs consistently following relevant questions but not comparison questions (or vice versa), it contributes to the differential scoring that determines the test outcome.

In automated scoring systems like OSS-3 and ESS, respiratory changes including apnea are captured through the Respiration Line Length (RLL) measurement — a mathematical calculation of the total path length of the respiratory tracing over a defined time window. Apnea reduces the line length, producing a lower RLL value that the algorithm incorporates into its classification model.

Distinguishing Apnea from Blocking

Proper differentiation between apnea and blocking is important for accurate chart analysis:

• Apnea — Breathing cessation at or near the bottom of the breath (end of exhalation). May be involuntary stress response or deliberate suppression
• Blocking — Breathing cessation at or near the top of the breath (peak of inhalation). More frequently associated with deliberate countermeasure attempts

Both patterns are flagged by trained examiners during chart analysis and may be correlated with activity sensor data to determine whether physical movement accompanied the respiratory change.

For more information on respiratory measurement in polygraph testing, visit the Polygraph Examiner Hub or learn how a polygraph works.