Does the Polygraph Measure Breathing? Respire & Find Out

a stone with breathe written on it

Does the Polygraph Measure Breathing?

In my effort to de-mystify the polygraph, the best place to start is to talk about what it actually measures.

The polygraph is a psycho-physiological instrumentation. This means it measures physiological or bodily reactions when we think, feel or react to something that has caught the attention of our brain.

The brain side of what the polygraph measures is deep and complex, so let’s start with the simpler physiology i.e. what all the wires and tubes you’re attached to actually measure and how (and a little of the why).

Firstly, respiration.

What is respiration?

Some definitions to start with.

Thefreedictionary.com define respiration as:

  1. The action or process of inhaling and exhaling; breathing. Also called ventilation.
  2. An act of inhaling and exhaling; a breath.”

Or if you want a more in depth version,, Merriam Webster gives us the Medical Dictionary definition as:

  1. the movement of respiratory gases (as oxygen and carbon dioxide) into and out of the lungs
  2. a single complete act of breathing, 30 respirations per minute.

Pretty straightforward so far.

How Does the Polygraph Measure Breathing?

Pneumograph tubes used by the polygraph

The pneumograph tubes used in the polygraph

A polygraph measures breathing through the use of pneumograph tubes.

A pneumograph is anything that graphically records the respiratory movement of the thorax (Dictionary.com).

These tubes are filled with air and operate at atmospheric pressure.

When a person breathes in and out i.e. respires, the tubes act a little bit like bellows. They stretch as we inhale and our chest/ thorax expands, then come back to normal as we exhale and let all the air out.

The polygraph uses 2 tubes, one is placed on your upper chest and one on your lower chest.

Why do we Have 2 Tubes?

The reason we have 2 tubes is because there are different ‘breathers’. There are belly breathers and chest breathers.

Chest breathers use their chest muscles to pull the ribcage out and expand the lungs, whilst belly breathers pull the diaphragm down.

Apparently belly breathing is better for you because it fills the lungs up fully – we include the health tips for free.

2 methods of breathing, hence a tube to measure each.

Why Do We Measure Breathing

The polygraph measures breathing because as PsychologyToday put it, it is an “unusual bodily function in that it is both involuntary and voluntary.”

Most of the time, you don’t think about your breathing, it just happens; however, at any given point we can step in and take control.

We can control the rate, the depth and the area. Fast and shallow chest breathing, slow and deep belly breathing.

Voluntary Breathing

You may have heard of people who have taken a test, or have done other research on the internet and come across such a thing as countermeasures, or who believe the test can be controlled.

A man meditating

Meditation can help you control your breathing and therefore your mind.

The main way people try and do it is to control their breathing. Why?

In that same PsychologyToday article, the various ways to relax and control stress, anxiety, blood pressure and heart rate are described, all by voluntarily taking over your breathing.

You may know that as part of the polygraph we also measure blood pressure and heart rate.

So if you start controlling your breathing, it’s going to affect everything else.

In the article it talks about controlling your breathing because it activates the para-sympathetic nervous system which is responsible for calming you down.

Breathing and the Nervous System

This is part of the autonomic nervous system which comprises the sympathetic and para-sympathetic nervous system.

The sympathetic gets you ready for action and the para-sympathetic calms you down.


Are you interested in finding out how the nervous system affects your skin during a polygraph test and what happens if you’re sweaty?

Have a read through this blog asking if the polygraph measures sweat?


In a polygraph test, as an examiner we want the person to be as normal as possible, not trying to control anything.

We Need Clear Data

This allows the instrument to pick up the clearest data and gives us the most accurate charts to read.

The whole point of countermeasures are to mess with that, so people control their breathing to try that. If you have nothing to hide, why would you need to anyway?

Inconclusive Tests

One note of warning: it is abundantly clear on the charts when people stray from their normal pattern of breathing.

A good examiner will spot this and give you instructions to breathe normally. If it keeps happening, the examiner will stop the test and call the result inconclusive.

Involuntary Breathing

Even though it may seem like a good idea to try and control your breathing e.g. if you are nervous, even if you do have nothing to hide, try not to.

Just go with it, an examiner should explain everything to you and make you feel as comfortable as possible with the test.


Do you want a more detailed explanation of what a professional polygraph examiner should do? This blog should explain everything for you.


When we don’t control our breathing, research has shown that breathing can be affected by emotions.

Different Emotions and Breathing

An angry cat

When we’re angry it affects our breathing.

One such research paper ‘Respiratory Feedback in the Generation of Emotion’ by Pierre Philipott and Sylvie Emery states there are 4 main patterns of breathing each associated with a group of emotions:

“Fast and deep breathing was associated with excitement, such as in anger, fear, or sometimes even joy. Rapid shallow breathing was typical of tense anticipation, including concentration, fear, and panic. Slow and deep breathing was most often observed in relaxed resting state. Finally, slow and shallow breathing was associated with states of withdrawal and passiveness, such as depression or calm happiness.”

That’s the why.

A man thinking

When we think hard, Aldert Vrij says it produces a cognitive load.

Because when you lie, you are likely to feel some emotion, either because you don’t want to get caught, you’re worried about what people would think if they found out, or you feel remorseful for what might have happened.

In addition, you may also be busy concentrating on keeping the lie buried and getting your story straight.

A researcher called Aldert Vrij at the University of Portsmouth talks about this concentration in terms of something called cognitive load.

Basically telling a lie and keeping a straight story is a lot of effort on a persons brain. This is what causes the reaction.


Do you know anyone who may be interested in learning about the polygraph? Please share this so we can continue to educate people.

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