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    Hi everyone.

    I refer to an introductory talk in the website created by Lorenzo Theremino, and start a discussion on the reading of HRV data.
    The acronym is composed of the initials of the words Heart Network Variability, and it consists in measuring the time that elapses between two successive cardiac contractions.
    The argument is quite extensive, and it lends itself to observations and experiments within the reach of hobbyists and electronics enthusiasts, I think leaving space for new research not yet addressed by experienced officers.
    I would first like to clarify that of course, these are medical data, the interpretation which may be made by the researchers do not have a specific medical preparation, It is to be considered a personal opinion, and may not be valid in the scientific community.
    However, this clarification does not preclude the possibility that some types of measurements designed by non-professionals may in the future express relevant data, which they will be reported to competent staff for later evaluation in the scientific field.
    Until that moment, the use of data obtained by the change of life style or therapies, or for the diagnosis, shall be deemed not lawful, and each researcher will be directly responsible for non-professional person before use of the data.

    After the due warning, we go to the interesting part.
    You may find a lot of information on the Internet, both in English and Italian, about the HRV.
    At first, This measure had stimulated the attention of the industry because it was believed he could predict cardiovascular risks, but the latest tests seem smentirne reliability in this regard.
    The practical application is currently best known is the evaluation of overtraining in competitive athletes.
    The Lorenzo user, in his first speech in the site Theremino, also he cites a new line of research, which would enable measurements to be made on the functioning of the autonomic nervous system, and in particular it seems possible to measure the extent of the pain.

    At the moment, the HRV measurements are performed in the time domain and frequency.
    In the first case, is taken into account the time that elapses between two successive beats. This measurement can be subsequently analyzed by the calculations over several adjacent measurements, For example quadratic root or percentage of intervals of adjacent intervals differences exceeding a set limit.
    In the second case, instead, measuring the frequency of the different durations of changes.
    This information can be detailed here
    ENG – Heart Rate Variability PARTE II (Definition and main analyzes)
    and also in other sites, doing some’ with google search.

    Another topic to be explored is the method used to read the contractions of the heart muscle.
    Also here, the options are currently two:
    – optical reading of blood flow through the skin (fotoplestimografia)
    – classical reading with skin electrodes
    If I understand correctly, Lorenzo said that the first option does not work well for reading HRV.

    This is my first speech deliberately introductory, hoping to soon see other contributions, and be able to go into that.


    Making the Fourier analysis is fairly easy, many of our applications they use and then have ready and well-tested functions.


    Welcome back all of you who follow this new item on the measurement of heart rate variability.
    I find the issue is particularly challenging because the parameter ENG It can be correlated with the effects of the sympathetic and parasympathetic activity on our cardiac system. Many are induced effects SNA (Autonomic Nervous System) our cardiovascular activities; some examples? the induction of vasodilation and vasoconstriction, the stimulation of cutaneous sweating caused by eccrine glands, dilation or the pupillary constriction as a result of suitable light stimuli or sensory and many others among which precisely the variability of the time that elapses between a beat and the next. Most effects induced by the SNA are not measurable with complex technologies, ma … I'd say … to everyone because systems like Theremino make <simple> any application.
    The ENG measured over short time intervals (gives 1 a 5 minutes) It is now considered a parameter indicative of the training state or “youth” of the heart muscle. All this is known in the literature and are already in the systems business that pemettono to monitor cardiac activity with the wrist systems or smartphones.
    What can be new and original? the measure of pain.
    Exact. You got it right. To date we do not have a scale that measures pain in a way <objective>, what is available are some tables in which pain is measured as a component <subjective>. These tables are seen on the wall in all hospitals. American researchers are trying to measure pain objectively by dilating or narrowing the pupil. The system of this Pain O Meter it would be very simple: a dark cylinder prevents ambient light from reaching the eye and therefore interfering with the pupillary diameter (photomotor reflex), a controlled emission light source (crown of white LEDs) It illuminates the inside of the cylinder front surface of the eye and the pupil tightens up to a fixed and stable level over time, at this point any painful perception is able to change the pupil diameter through the activation of SNA, a camera of a smartphone through a specific app is able to quantify the intensity of pain by measuring precisely the variations in the pupil diameter raportandole to a quantitative scale. It is not science fiction, some images are already available on the WEB.
    The system Emotion Meter realized with the Theremino is similar to professional systems for the measurement of GSR (Galvanic Skin Response) and it is capable of recording painful events (I tried, just a pinch on the arm! try it for yourself!!!) and are reasonably confident that the measurement of the heart rate variability (ENG) can be as eloquent.
    What you need? a detector of heartbeats in kit, un Theremino (modulo master) and a program like Theremino suitably modified to process ECG (with Fourier transform) ECG data collected in selectable intervals between 1 e 5 minutes.
    A system so might actually be an alternative to the measurement of changes in pupil diameter for a QUANTITATIVE estimate of pain. Logical that must be validated in a clinical setting before it can be considered a reliable tool … Say no more. Let's see if … I curiously at our electric friends.

    I respond to Maurizio asking me if the photoplethysmography (PPG) is a better system, or worse than the electrocardiographic detection (ECG) for the measurement of time (in msec) between a heartbeat and the other. I believe that PPG has significantly more decisive variables than an ECG (vasodilation induced by temperature variations in the room, emotional states, limb position to an extent that if you raised can be affected by a different “flooding” the vascular bed than when it is lowered, Valsalva maneuver, interference with the acts of breath …). The ECG is much less influenced by all these variables and therefore would say more reliable allowing “triggerare” better the measure of time. In the market are expensive software that allow to carry out measures of HRV by a PPG path (Consensys PRO) or systems that are based on exploiting specific plug Mathlab (Kardia v2.6 oppure HRVAS 1.0.0 …). Systems are not for everyone, requiring licenses … and in any case they are not validated by any Ministry of Health.
    Then? I think a Pain O Meter based on Theremino ECG is truly a gem !!!
    (because of this your space that welcomes everyone with sympathy and enthusiasm —> experienced and inexperienced)

    • This reply was modified 2 years, 4 months ago by lorenzo58sat.
    • This reply was modified 2 years, 4 months ago by lorenzo58sat.
    • This reply was modified 2 years, 4 months ago by Amilcare.

    Hello Lorenzo.

    Given your expertise, I think your contribution to the field of biometrics Theremino will be very useful.

    After reading your advice on using ECG instead of PPG, I went to see me the Theremino sensors, in particular the AD8232, which it is very interesting.
    If you are not sure, given the cost paltry, I ordered one, to cite some evidence, although I do not know when ... The work takes me more energy and time.
    Meantime, given your experience about, I ask an opinion: the positioning of the electrodes is recommended in Theremino on the chest, while the suggestion of dell'AD8232 manufacturer is on the limbs.
    Certainly the positioning on the chest reduces noise, but it requires the use of disposable electrodes, in the long run they are expensive, not to mention that when you need are finished and to reorder.
    I saw for sale in ebay two alternatives: tongs to put on wrists and ankles, and suction electrodes.
    What do you think about it? The first is practical but I imagine they are noisier, the latter can also be used on the chest, but I do not know how long they attacked.
    obviously, adhesives disposable electrodes are more hygienic, but if the use is always done by the same person, I would say this is not a problem.
    The cost is more or less equal for both solutions.


    Let's see if they are able to respond.
    The application of ECG electrodes on the human body follows the logic conceived in 1901 by physiologist Einthoven: apply AT THE ENDS’ (Poso sn, Right Wrist and Ankle sn) 3 electrodes connected to an operational amplifier by instrumentation which ensures a strong rejection of the common mode. The logic is to put your heart at the center of a TRIANGLE EQUILATERAL ideal and measure the intensity of the electric vector generated by the heart activity. The Einthoven derivations are 3 (Dl, D2 e D3) and measure the electrical activity of different projections (angles of 60 °). In D1 junction electrodes as I have said 3 and in particular a positive (on the wrist sn) and one negative (on right wrist), the third is the reference (ankle sn). In D2 and D3 the electrodes have a different “orientation” for which they may give a picture of cardiac activity according to observation angles rotated by 60 ° with respect to the previous configuration. These insights and choices were enough to Einthoven to deserve the Nobel in 1924. The cardiac electrical activity could be observed with 3 viewing angles (0°, 60° e 120°).
    In subsequent years Goldberger came to mind to connect the negative electrode with the ground reference (the ankle sn) and to apply the electrode of positive measure on the left wrist (aVL derivation), then the right (Apr) and finally on the leg sn (aVF). Logically the other two electrodes (the negative and the reference) They had to be moved on the other two limbs. So it took was a simple diverter 3 vie e 3 positions to have twice as much information on cardiac activity. Let's say that in lead aVL, aVR aVF and the viewing angle becomes -30 °, +90° e -150°.
    Era “easy” at this point imagine how wanting to short-circuit the three ends (wrist sn, dx wrist and leg sn) could be applied to the electrode of positive measure directly on the heart to have much more intense signals and observation angles. This idea came to Dr.. Wilson spotted 6 points on the chest directly over the heart (V1 – V6) for more specific and detailed images. In this case it then all three ends connected to the reference electrode and the negative electrode while the positive is the measuring electrode. How to do? with a diverter 3 vie e 6 positions.
    OK why I say this? to make it clear that the AD8232 system is a task that has instrumentation amplifier 2 measuring electrodes (positive, negative) and a reference that must be placed correctly on the human body: should ALWAYS put the positive on the pulse sn, the negative dx on the wrist and the reference somewhere at the bottom. Always a triangle. Always the widest possible. I CAN CERTAINLY BE CLOSE 3 ELECTRODES, we will always have the measures but logic is this: try to look at the heart from different angles to achieve significant and standardized results. The heart has to be in the middle of an ideal triangle.
    And the right leg?
    Here is the key fact!! the right leg (with a wire) It must be connected to MASS OF THE INSTRUMENT. The mass of the instrument IS NOT’ the reference electrode of our operational amplifier (AD8232 specifically) but its metal container that has to be connected to an efficient earth leakage. If you are linking the reference to the mass of the electrode would certainly unmanageable auto-oscillations of the entire system. The mass is also connected to each screen braiding the 3 electrodes.

    The adhesive electrodes are fine … costing only a little’ !!!
    I have been dispersed and wordy ? Excuse me if you.

    • This reply was modified 2 years, 4 months ago by lorenzo58sat.
    • This reply was modified 2 years, 4 months ago by lorenzo58sat.

    Hello Lorenzo.

    You think you have been scattered and wordy?
    Instead you have summarized in a few lines of the important concepts that would have required us, we're not in the industry, many hours or days of study and research.
    But it also stimulated my curiosity, and then I'd like to further investigate the issue of the placement of the electrodes.
    I did a quick google search, but I have yet to find the details you want (time is running out), so I ask you: it is possible to effectively use a selector 3 life 6 positions, to precede all'AD8232, to get Wilson measures?
    This, obviously, would allow us to obtain the information that for most people, I mean without special training, They would be difficult to use.
    But since apparently, if I understand, Theremino with the ability to make these measurements can be reached with little money, who knows that a day does not leave a comparable ECG with a professional, but very cheap, to use as before diagnostic investigation in regions of the world where economic resources are few..
    Instead of returning home topic of this discussion, ie the HRV, how relevant the type of derivation?
    The derivation of Einthoven is enough to get the useful readings for evaluation of HRV? If so, which of the three it is the most suitable?
    I'd like to immediately clarify, before moving on to the software, what type of derivation is most suitable for our purposes, and configure the electronic circuit accordingly.
    The ideal would be an interface between body and Theremino that could be used for purposes, both HVR for other inquiries.

    Finally, a further demand for deepening, still on the choice of electrodes: I understand that those adhesives are fine, so much so that I see which are the most widely used, but those gripper or suction cup have defects such as to affect the measurement, or they can be used?
    Also in this case, I ask the question in view of a possible use in the field in poorer regions, where the electrode pads may not be available, and of course the cost factor.

    Thanks for your help


    So let's good to fit the answers to all your questions without going into details too complex but very practical.
    1) the solution is to switch that I used to before in my experiments. It works perfectly but introduces noise in a crazy system. Remember that the strongest signal in the ECG has a value of 1-2mV (complesso QRS) and that very significant are the values ​​in Q and T wave amplitude whose morphological analysis is essential for a correct interpretation of the track. They are intensity signals 10 times less than 1-2 mV and must be obtained and cleaned without alteration. THE SIMPLE MUSCULAR TREMOR is recorded in the track like a huge disturbance. Do you know how much time was lost in the past to get a clean recording? Ok the switch works and is cheap but enough that some contact reed oxides you the feeling passes after 2 days of frustrating attempts.
    2) for the measuring and reference electrodes the speech must be done in an orderly manner:
    2a) all electrodes to 4 arts have the same surface size. Even today ECGs using pliers practices with color coding as it once was.
    2b) the precordial electrodes today are all adhesives were once while blower (these were a metal cup attached to a rubber bulb that if squeezed vacuum generated beneath him by adhering the skin to the metallic cup). It was a delusion. In the midst of recording there was always some precordial derivation is peeling to lose grip … and ricominciavi all over again!
    2c) Skin contact ALL of the electrodes should be wetted with saline solution to lower the resistivity. Since then the man is a primate … There are also subjects that should hairy shaved before applying the electrodes (it happens often)
    2d) the dimensioning and position of the electrodes are 2 delicate parameters, see why. Imagine an electrode as an antenna. Its ability to pick up a signal depends on its size and the distance of the signal. The electrical signal from the heart travels throughout the body and get to the last phalanx of a hand or a foot, but with the travel the road fades and becomes weaker. Ok clear? On the other hand a measuring electrode placed at 1 meters away from the heart “sees” a heart wider area. So the surface (in cm2) an electrode, its distance from the heart, the intensity of the electrical signal generated and skin conductivity (last element to be crossed before arriving at the electrode metal surface) are all factors that greatly affect system efficiency. Keep in mind the example steradians in an LED emission … this car is similar although it works in reverse.
    2e) the gripper electrodes have no flaws. Those suction cup are becoming casino. Those adhesives are excellent but expensive (these then there are various types, but never mind).
    3) branch D1 Einthoven is perfect. It is one that sees the heart 0 degrees according to a vector that goes from the hand to the right hand sn. You can bring up the measurement electrodes on the chest. Now imagine a perfect equilateral triangle on the chest with a central heart. Put on the left vertex of the electrode positive measure, on the right the electrode Negative measuring and down the reference. This last can also put behind the chest, at the bottom under the lung. It works fine there too (or perhaps even better).
    4) When you exercise your body sweats more in the wrong places and the electrodes come off even if they are of good quality. Appropriate areas choose to minor skin perspiration.
    5) The branch D1 is perfect for detecting HRV likely to be ok D2. I would exclude D3.

    If this continues … I deleted ex officio by the blog. I'm sure.


    Go on, it's interesting. However, to measure the variability only counts the frequency. To which would position the electrodes where the signal is stronger, that is, as in the images we published. I would not use a commutator, that only introduce additional noise. Also, if the signal is strong on the type of electrode used affects less on the results.

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