Microcontroller

An 8-bit microcontroller was chosen to process the output signal produced by the amplification stage. The Microchip PIC16F877A was selected due to its additional output and processing power, and also its onboard 10-bit analogue to digital converter and in-circuit debugging features. Using this highly integrated microcontroller allowed for a simpler design and trouble shooting debugging process. Due to the use of a microcontroller to calculate the beats per minute (BPM), it was decided that a liquid crystal display (LCD) module would be the most flexible way of displaying this numerical output. It was originally planned that several seven segment displays could be used, but again it was deemed worthwhile to integrate the display unit together and limit the number of components required. In addition, the information which the LCD could convey was greater. Below is a block diagram of the microcontroller and LCD process:

 

Regarding the actual BPM calculation (assuming that it was possible to translate each R part (the blip/spike peak) into singular events occurring in a timely fashion of course) it was originally going to be done by measuring the total number of spikes within a certain amount of time and then multiplying this count by a factor (as it is done when using a clock and your hand). With the use of the microcontroller however more precise measurements were able to be made resulting in an output of greater accuracy and speed.

Electrode Theory

        An interface is necessary between the body and the electronic measuring device when recording potentials and currents in the body.  Biopotential electrodes produce small voltages directly related to the changing electric field produced by a beating heart..  The Ag/AgCl electrode is a practical electrode that approaches the characteristics of a perfectly nonpolarizable electrode.  Perfectly nonpolarizable refers to the freedom of ions to pass through the electrode-electrolyte interface to be transduced into an electrical current.  The electrode converts the ionic current produced by the body into a voltage, and the ECG amplifies this voltage.  

The electrode-electrolyte interface is the junction where the ionic transfer occurs.  A temporary current is induced in the electrode from the changing electric field of the beating heart.  This current causes electrons and anions to move across the electrode-electrolyte interface in the direction opposite to the flow of the current, and for cations to migrate across this interface in the direction of the current.  This temporary separation of charge produces a temporary potential.  This potential is created from a current induced from the heart and is thus directly related to the changing electric field produced by a beating heart.  The ECG circuit hugely amplifies the potential, and the output gives the electric characteristics of a beating heart. 

Another sensor that was considered was the piezoelectric sensor.  Piezoelectric materials generate an electric potential when mechanically strained.  During a heart beat, the pressure in the blood vessels is higher than when the heart is in its resting stage.  This higher blood pressure causes a physical deformation in the skin, and thus a piezoelectric sensor can produce an electic potential during every heartbeat.  The principal reason why the piezeoelectric sensor is less than ideal is that it is pressure sensitive.  In order to pick up a signal the nurse or doctor would have to press the sensor hard against the patient which could cause a permanent deformation of the piezoelectric material  This information, combined with the fact that hospitals across the nation use Silver/Silver Chloride sensors,  made it obvious that the silver-silver chloride sensors were the best to use for this project.  :)

ECG Instrumentation


In order to record the ECG, we need a transducer capable of converting the ionic potentials
generated within the body into electronic potentials which can be measured by conventional
electronic instrumentation. Such a transducer consists of a pair of electrodes, which measure
the ionic potential difference between their respective points of application on the body
surface. Electrodes may be classified either as polarisable, in which case they behave as
capacitors, or non−polarisable, in which case they behave as resistors. Common electrodes
have characteristics that lie between these extremes; the silver−silver chloride electrode
discussed below approximates more closely to a non−polarisable electrode.


Electrode placement
The most obvious way to record the ECG is between the Right Arm (RA) and the Left Arm
(LA) although another two combinations using the Left Leg (LL) are also used clinically
(RA−LL and LA−LL).

Another electrode is also used to connect the patient to the common ground of the
instrumentation. Usually, this ground electrode is attached to the right leg.



Silver−silver chloride electrode
Electrodes for recording biopotentials are composed of a metal (usually silver for ECG
measurement), and a salt of the metal (usually silver chloride). In addition, some form of
electrode paste or jelly is applied between the electrode (normally a flat silver disc) and the
skin. The combination of the ionic electrode paste and the silver metal of the electrode forms
a local solution of the metal in the paste at the electrode−skin interface (also referred to as
the electrode−tissue or electrode−electrolyte interface). Hence, some of the silver dissolves
into solution producing Ag+ ion


problem???


Movement artefact
If the electrode is moved with respect to the elctrolyte, this mechanically disturbs the
distribution of charge at the interface and results in a momentary change of the half−cell
potential until equilibrium can be re−established. If a pair of electrodes are in contact with
an electrolyte and one moves while the other remains stationary, a potential difference
appears between the two during this motion. This potential is referred to as moverment
artefact and can be a serious cause of interference in the measurement of ECG (or any other
biopotential).

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Objective :

• to detect heart beat using sensor(electrode)
• to apply the sensor that can read the beat when heart pumping the blood
• to detect any abnormal beat calculation 
• that can be related to any illness/disease 
• to study the symptom of any disease that related to heart beat
• to use Arduino and PIC as a controller
• to use LCD and seven segment as a display
• to apply warning beeper with LED flash
• to apply at critical monitoring and daily monitoring
• to store data retrieve

pulse!!!!

Heart beat measurement indicates the soundness of the human cardiovascular system. This project demonstrates a technique to measure the heart beat by sensing the change in blood volume in a finger artery while the heart is pumping the blood. 

*for this project this concept explain how the measurement should be done. this is an early idea to make the HB monitoring .

ECG types


source from http://thehealthgurus.info/

• The electrodes carry information of the heart top, bottom and lateral side of the heart
• Eithoven Triangle:
• First lead: 1 2 3
• The heart is an organ tridimencionall
• ECG quick painless and noninvasive tool
• A shunt is formed by two electrodes

HEART LEADS

2 types: Standard and precordial

THE 12-lead ECG standard is explained as follows:

1. Limb leads (classical) total 6,

3 bipolar (I II III) and

the pole. (AVR AVF and AVL)

2. Or precordial chest leads (V1-V2-V3-V4-V5-V6)

STANDARD LEADS

These only evaluate the frontal plane of the heart

To the extent that action potentials in the heart come to a positive electrode give positive vibes. As will move in the opposite direction negative waves.

BIPOLAR: D1, D2, D3

Eithoven leave the triangle (above)

They have two poles + and -

UNIPOLAR

Emmanuel Goldberg introduced the augmented leads of the extremities. Bone the unipolar

The low voltage unipolar Captan then came to the voltage increase

Referrals are also known as unipolar or expanded

AVR voltage amplitude = right arm

AVF = ampllitud voltage standing arm

AVL = voltage amplitude right arm

HEX SHAFT AXIAL

This axis is the sum of all the voltages of the standard leads, sum that will give us the direction that target the summation of action potentials that pass through the heart (vector in the direction of force)

The heart is the center of the standard leads

• All vectors that hexa graphing the axial axis between -30 and 110 is normal.
• All that plot between – 30 and -90 will have an orientation to the left and will be negative
• All that is between 110 and (+ -) 180 is positive, being in the right quadrant or right orientation will have
• All that is between -90 and (+ -) 180 on the dial will be indeterminate

Precordial

They are so called because they are in the precordium, on the heart

The precordial leads are V1, V2 V3 V4 V5 V6

• V1 and V2-voltage measure right heart
• V3 and V4-measure voltage or septum septum
• V5 and V6-voltage measured left heart

In this picture we see the 12-lead:

Use of ECG for Diagnostic Purposes



diagnostic information can be obtained from the ECG waveform, by analysis of the amplitude and relative timing of the various segments. In general, cardiac muscle damage, or infarcts, are correlated with loss of amplitude. Abnormal heart rates (arrhythmias) can be observed and treated; for examples slow rhythms (bradycardia) can be treated with stimulants or a pacemaker whilst in the case of fast (tachycardia) depressants can be prescribed. Ectopic beats are beats which originate from a region of the heart other than the SA node. An ectopic beat in the ventricle causes an extra R−wave, indicative of a premature ventricular contraction (PVC).

These abnormal conditions are usually identified by one of two means:

• Ambulatory monitoring for up to 24 hours of patients who have been identified as being at risk of heart attacks. Data compression techniques (eg beat−to−beat interval histograms) are often used although advances in memory technology is reducing the need for these.

•  Exercise stress ECGs in which the patient is taken close to maximum heart rate by exercising, for example on a tread mill. Changes in the ECG waveform during this process give the cardiologist indications as to the efficiency and capacity of the heart’s pumping action. PVCs may only occur when the body is under physical stress, as this makes demands for higher cardiac output. Exercise testing can also be used to assess the effectiveness of therapeutic and surgical treatments.

A more specialised application of ECG analysis is the detection of foetal distress prior to and during labour. An additional problem here is the separation of the maternal and foetal ECGs (adaptive filtering techniques are usually required in addition to careful positioning of the ecletrodes).

All the above applications involve the analysis of the ECG waveform and the extraction of

various features of the waveform. In each case, the heart rate provides information of value

and needs to be calculated. There are two types of heart rate meters (also known as

cardiotachometers):

• the averaging heart rate meter which calculates the average heart rate from a count or estimate of the number of beats over a period of time.

• the beat−to−beat heart rate meter which computes the reciprocal of the time interval between two consecutive heart beats and updates the information with each heart beat.( this method will be use in this project )

ECG

The heart is one of the most vital organs within the human body. It acts as a pump that circulates oxygen and nutrient carrying blood around the body in order to keep it functioning. The circulated blood also removes waste products generated from the body to the kidneys. When the body is exerted the rate at which the heart beats will vary proportional to the amount of effort being exerted. By detecting the voltage created by the beating of the heart, its rate can be easily observed and used for a number of health purposes.An electrocardiogram (ECG) is a graphical trace of the voltage produced by the heart. A sample trace of a typical ECG output for a single beat is shown below. There are 5 identifiable features in an ECG trace which corresponds to different polarization stages that makes up a heartbeat. These deflections are denoted by the letters P, Q, R, S and T.

ECG history ^_^ -part 2 (•‿•)

The etymology of the word is derived from the Greek electro, because it is related to electrical activity, kardio, Greek for heart, and graph, a Greek root meaning "to write".

Alexander Muirhead is reported to have attached wires to a feverish patient's wrist to obtain a record of the patient's heartbeat while studying for his Doctor of Science (in electricity) in 1872 at St Bartholomew's Hospital This activity was directly recorded and visualized using a Lippmann capillary electrometer by the British physiologist John Burdon Sanderson. The first to systematically approach the heart from an electrical point-of-view was Augustus Waller, working in St Mary's Hospital in Paddington, London. His electrocardiograph machine consisted of a Lippmann capillary electrometer fixed to a projector. The trace from the heartbeat was projected onto a photographic plate which was itself fixed to a toy train. This allowed a heartbeat to be recorded in real time. In 1911 he still saw little clinical application for his work.

1911 ECG machine ಠ▃ಠ

An initial breakthrough came when Willem Einthoven, working in Leiden, the Netherlands, used the string galvanometer he invented in 1901. This device was much more sensitive than both the capillary electrometer Waller used and the string galvanometer that had been invented separately in 1897 by the French engineer Clément Ader.^[9] Rather than using today's self-adhesive electrodes Einthoven's subjects would immerse each of their limbs into containers of salt solutions from which the EKG was recorded.

Einthoven assigned the letters P, Q, R, S and T to the various deflections, and described the electrocardiographic features of a number of cardiovascular disorders. In 1924, he was awarded the Nobel Prize in Medicine for his discovery.

Though the basic principles of that era are still in use today, many advances in electrocardiography have been made over the years. The instrumentation, for example, has evolved from a cumbersome laboratory apparatus to compact electronic systems that often include computerized interpretation of the electrocardiogram.

ECG-heartbeat history ^_^  -part 1

ECG is used to measure the rate and regularity of heartbeats, as well as the size and position of the chambers, the presence of any damage to the heart, and the effects of drugs or devices used to regulate the heart, such as a pacemaker.

Most ECGs are performed for diagnostic or research purposes on human hearts, but may also be performed on animals, usually for diagnosis of heart abnormalities or research.

ECG placement

* this how to place electrode to patient body.