Blog EMG & ECG News Technology

What is ECG (electrocardiography) and how does it work?

waiting room

ECG (electrocardiography) is a technique of accumulating electrical alerts generated by the guts. This enables us to know the extent of physiological arousal that somebody is experiencing, nevertheless it can be used to raised perceive somebody’s psychological state.

Under we’ll undergo the significance of physiological arousal in feelings, the physiology of the guts, how the exercise may be measured, and what parameters are of curiosity.

Emotional Arousal

When individuals are requested to determine the reason for a rise in physiological arousal, they typically misattribute the supply. We’d assume we perceive every thing that’s happening with our physique, however research present that that is typically not the case.

An influential research by Schacter and Singer in 1962 [1] confirmed how this happens. Individuals have been advised that their imaginative and prescient can be examined after they got nutritional vitamins. They have been as an alternative both given epinephrine (also referred to as adrenaline), or a placebo drug.

They have been then informed that the the consequences of the drug have been the identical as epinephrine, or that they could really feel some discomfort, or they have been advised nothing in any respect.

Epinephrine is understood to activate the central nervous system, bringing about such modifications as elevated coronary heart price and pupil dilation. The individuals have been then positioned in a ready room with a accomplice (an actor employed by the researchers) of the research who both pretended to be indignant, or comfortable.

The indignant or glad circumstances have been a collection of standardised steps (step fifteen of the comfortable situation: “Stooge replaces the hula hoop and sits down together with his ft on the desk. Shortly thereafter the experimenter returns to the room.”) that have been meant to affect the emotional state of the participant.

The participant then needed to full a questionnaire about how they have been feeling. They discovered that not solely was the emotional state of the participant influenced by the obvious emotion of the accomplice (and extra so within the epinephrine situation), however that the individuals additionally attributed that emotion to occasions solely unrelated to the state of affairs they have been at present in.

This instructed that individuals (and other people extra usually) are much less conscious of the malleability of their emotional states, misattributing how they’re influenced.

Why can we deliver that up? Let’s clarify: physiological arousal is said to emotional arousal, but the explanations for our emotional state could be troublesome to know.

With this in thoughts, monitoring arousal utilizing biosensors presents an goal various to the in any other case subjective inferences that individuals inevitably make. Coronary heart exercise is intently linked to physiological and psychological arousal, making it excellent for understanding our psychological states in larger element.

How can the beat of your coronary heart be recorded and made out there for evaluation and interpretation? What’s ECG precisely? Let’s determine this out.


Physiology and performance of the guts

Earlier than we dig deeper into the basics of ECG, let’s undergo the fundamentals of coronary heart physiology and performance:

  • The guts has 4 chambers. The higher two chambers (left/proper atria) are entry-points into the guts, whereas the decrease two chambers (left/proper ventricles) are contraction chambers that ship blood out to the physique. The circulation is cut up right into a “loop” via the lungs (pulmonary) and one other “loop” by means of the physique (systemic).
  • The cardiac cycle refers to a whole heartbeat from its era to the start of the subsequent beat, comprising a number of levels of filling and emptying of the chambers. The frequency of the cardiac cycle is mirrored as coronary heart price (beats per minute, or bpm).
  • The guts operates routinely – it’s self-exciting (this can be a distinctive function in comparison with different muscle mass within the physique that require nervous stimuli for excitation). The rhythmic contractions of the guts happen spontaneously, however are delicate to nervous or hormonal influences, notably to sympathetic (arousing) and parasympathetic (decelerating) exercise.

anatomy of the heart

Easy methods to measure coronary heart exercise?

Coronary heart exercise may be recorded in two methods:

1. Electrocardiography (ECG, EKG)

ECG data the electrical exercise generated by coronary heart muscle depolarizations, which propagate in pulsating electrical waves in the direction of the pores and skin. Though the electrical energy quantity is in truth very small, it may be picked up reliably with ECG electrodes hooked up to the pores and skin (in microvolts, or uV).

The complete ECG setup includes at the very least 4 electrodes that are positioned on the chest or on the 4 extremities in accordance with commonplace nomenclature (RA = proper arm; LA = left arm; RL = proper leg; LL = left leg). In fact, variations of this setup exist so as to permit extra versatile and fewer intrusive recordings, for instance, by attaching the electrodes to the forearms and legs. ECG electrodes are sometimes moist sensors, requiring using a conductive gel to extend conductivity between pores and skin and electrodes.
ecg placement ecg2.  Photograph-Plethysmography (PPG).

All through the cardiac cycle, blood strain all through the physique will increase and reduces – even within the outer layers and small vessels of the pores and skin. Peripheral blood stream might be measured utilizing optical sensors hooked up to the fingertip, the ear lobe or different capillary tissue.

The gadget has an LED that sends mild into the tissue and data how a lot mild is both absorbed or mirrored to the photodiode (a light-sensitive sensor). PPG clips use dry sensors and might be hooked up a lot faster in comparison with ECG setups, making the system comparatively straightforward to make use of, and fewer bothersome for members.

Cardiac parameters of curiosity

Recording coronary heart price knowledge provides you entry to the next parameters that may be interpreted with respect to a participant’s arousal:

Coronary heart Fee (HR). HR displays the frequency of an entire heartbeat from its era to the start of the subsequent beat inside a selected time window. It’s sometimes expressed as bpm. HR may be extracted utilizing ECG and PPG sensors.

Inter-Beat Interval (IBI). The IBI is the time interval between particular person beats of the guts, usually measured in models of milliseconds (ms). Sometimes, the RR-interval is used for the evaluation.

Coronary heart Fee Variability (HRV). HRV expresses the pure variation of IBI values from beat to beat. HRV is intently associated to emotional arousal: HRV has been discovered to lower underneath circumstances of acute time strain and emotional stress (which means that the heartbeat is extra constant).

HRV has additionally been discovered to be considerably lowered in people reporting a larger frequency and period of every day fear [2]in addition to in sufferers affected by post-traumatic stress dysfunction (PTSD) [3]. For IBI and HRV evaluation, ECG sensors are advisable as they’re extra delicate to sure sign traits which PPG sensors can’t decide up.

QRS complex

Why mix ECG with different sensors?

In fact, knowledge based mostly on coronary heart fee alone gives beneficial insights into nonconscious arousal in response to emotionally loaded stimulus materials. Nevertheless, knowledge solely based mostly on ECG or PPG knowledge can‘t inform us whether or not the arousal was as a consequence of constructive or unfavorable stimulus content material.

Why? The change in coronary heart fee is in truth similar. Each constructive and destructive stimuli may end up in a rise in arousal triggering modifications in coronary heart fee.

In different phrases: Whereas ECG/PPG are splendid measures to trace emotional arousal, they don’t seem to be capable of reveal emotional valence, the path of an emotion. The true energy of ECG/PPG methods unfolds as these sensors are mixed with different knowledge sources reminiscent of facial features evaluation, EEG, and eye monitoring.


[1] Schacter, S., & Singer, J. (1962). Cognitive, social and physiological determinants of emotional state. Minneapolis: Psychological Evaluation.

[2] Brosschot, J. F., Dijk, E. V., & Thayer, J. F. (2007). Every day fear is said to low coronary heart fee variability throughout waking and the next nocturnal sleep interval. Worldwide Journal of Psychophysiology, 63(1), 39-47. doi:10.1016/j.ijpsycho.2006.07.016

[3] Tan, G., Dao, T. Okay., Farmer, L., Sutherland, R. J., & Gevirtz, R. (2010). Coronary heart Fee Variability (HRV) and Posttraumatic Stress Dysfunction (PTSD): A Pilot Research. Utilized Psychophysiology and Biofeedback, 36(1), 27-35. doi:10.1007/s10484-Zero10-9141-y

Additional Studying

Curious to dig deeper into ECG? Take a look at our listing of must-reads to study extra about cardiac knowledge recordings and evaluation.

  • Dutton & Aron (1974). Some proof for heightened sexual attraction beneath circumstances of excessive nervousness. Journal of Character and Social Psychology 30: 510–517. (hyperlink)
  • Nickel & Nachreiner (2003). Sensitivity and Diagnostics of the Zero.1-Hz Element of Coronary heart Price Variability as an Indicator of Psychological Workload. Human Elements 45 (four): 575–590. (hyperlink)
  • Jönsson (2007). Respiratory sinus arrhythmia as a perform of state nervousness in wholesome people. Worldwide Journal of Psycho-physiology 63 (1): 48–54. (hyperlink)
  • Brosschot, Van Dijk, & Thayer (2007). Every day fear is said to low coronary heart fee variability throughout waking and the next nocturnal sleep interval. Worldwide Journal of Psychophysiology 63 (1): 39–47. (hyperlink)
  • Hagit et al. (1998). Evaluation of coronary heart fee variability in posttraumatic stress dysfunction sufferers in response to a trauma-related reminder. Organic Psychiatry 44.

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