Download Microcontroller based PACEMAKER device with ECG feedback

MICROCONTROLLER BASED CARDIAC MONITORING SYSYTEM
WITH SMS SERVICE
Abstract
The project aims at developing a patient monitoring system. The system
contains an ECG simulator to generate ECG waveform. The ECG simulator
has control to vary heart rate as well as to generate different types of
arrhythmias. The monitoring system keeps track of the heart rate activity.
If there is any abnormality, it will send a SMS to a remote station to get
the medical assistance.
The ECG simulator is designed using an oscillator and pulse shaping circuit.
The monitoring system contains an 8-bit ADC, 8-bit microcontroller and a
GSM modem. The GSM modem is serially interfaced with the
microcontroller. Standard AT command set is used to control GSM modem.
Block Diagram
A typical ECG Circuit:
A ECG Simulator module will be developed which will provide the ECG
waveform in its natural shape at the output.
The feedback from ECG module will pass through a missing pulse detector.
The output of the missing pulse detector is high when the ECG continues.
Any break in ECG will trigger the missing pulse detector to go high
consequently triggering the microcontroller to generate a trigger for the
emergency.
Block Diagram:
LCD display
ECG
Simulator
Missing
pulse
detection
Circuit
Level
Converter
Microcontroller
AT89C51
GSM
MODEM
Dialer
Circuit
Major Components:
AT89C51
Microcontroller
GSM Modem (Serial Interface)
IC555
Timer IC
CD4521
CD4017
LM741
OPAMP
IC7805
Voltage regulators
IC 7815
Voltage regulator
16x2 Lampex LCD
Rotary Switches
BC547, BC557
NPN, PNP Transistors
1N4007
Diodes
W10
Rectifier
Resistance, Capacitors etc.
ECG Background
William Einthoven developed the first electrocardiogram in 1903 using a
crude galvanometer. Technology has advanced ECG measurement, but the
principle remains the same. The electrocardiogram is the wave
representation of the potential difference caused by heart activity. A grasp
of the electrocardiogram has to be gained for two reasons: 1. An
understanding of the wave forms the basis for the design of the electronic
circuit to measure it; and 2. An understanding allows the concept of what
an ECG is, and how its deviation enables analysis of health. The potential
difference is created by the flux of ions in cells, a typical cell with Sodium
and Potassium ions as shown in figure.
When the heart pumps, the cell wall offers greater permeability and an
excess of sodium is able to flow inside the cell. When the sodium flows into
the cell there is no longer a negative potential with respect to the outside.
This is known as depolarisation. Eventually after the excitation passes, the
cell repolarises, returning the potential to a negative one.
The standard for diagnostic ECG is twelve leads, however in the case of
more portable, easy to use ECG one lead (usually Lead II) can be used.
Lead II can diagnose the more common diseases like arrhythmias. Cells
are originally polarised such that the potential inside each cell is negative
with respect to the outside. Depolarisation occurs first, making the outside
of the cell negative with respect to the inside. This imbalance causes an
ionic current to flow, and the Left Arm to register a positive with respect to
the right arm. This is known as the Pwave. The depolarisation then passes
to the atrioventricular node. It is still relatively negative to the left ventricle
causing a current and positive voltage from the left to right arms. This is
the R-wave. The T wave is a representation of the repolarisation of the
depolarised cells. Physicians can diagnose a person’s health by reading
these waves. From a signal processing perspective, the potential difference
between left and right arms is typically 1-3mV and the frequency of the
ECG signal lies between .02 and 150Hz. The quality of an ECG sensor could
be categorised by its bandwidth. Usually sensors designed for the end of
the market that this device was designed for only measure frequencies of
up to 30Hz. If specifications for ECG emergency care were to be met, the
frequency measured should extend to 1kHz. The problem with larger
spectrums is that a proportional amount of noise must be battled with the
frequencies that are measured.
Glossary
ARRHYTHMIA: an abnormal rhythm of the heart beat.
ASYSTOLE: a failure of the heart to beat or contract at a time when
it should have.
ATRIA: the top or collecting chambers of the heart. There are two of
these, the right atrium and the left atrium.
AV NODE: or atrioventricular node is a special conduction centre in
the heart. It is located between the two lower chambers (ventricles)
of the heart and receives the electrical impulse from the upper
chambers (atria) of the heart and passes it downward into the lower
chambers (ventricles).
BLOOD PRESSURE: the pressure of the blood against the walls of the
blood vessels. The term usually refers to arterial blood pressure. It is
determined by the force of the heart beat, the resistance to the flow
of blood in the arteries, the elasticity of the vessel walls, and the
blood’s thickness. The blood pressure is expressed as one number
over another, i.e., 120/80. The first number represents the systolic
pressure and the second, the diastolic pressure. Both are recorded in
millimetres of mercury. Strenuous physical activity, excitement,
nervous tension, or fright raise the systolic pressure.
BRADYCARDIA: a slow heart rate, generally under 50 beats per
minute.
BUNDLE BRANCH BLOCK: a blockage of one of the specialised
conducting pathways within the lower chambers of the heart.
BUNDLE OF HIS: also called common bundle or AV bundle. A bundle
of specialised muscle fibres which conducts impulses from the AV
node to the lower chambers of the heart. Named after Wilhelm His, a
German medical scientist.
CAPTURE: when a pacemaker impulse or discharge succeeds in
causing the ventricles of the heart to beat or contract.
CARDIAC OUTPUT: the amount of blood pumped by the heart per
minute.
CATHETERIZATION: in cardiology, the process of examining the
heart by means of introducing a thin tube (catheter) into a vein or
artery and passing it into the heart. The pacemaker lead inserted
through the vein for pacing is a type of catheter.
CIRCUITRY: the electrical portion of your pacemaker designed to
pace the heart at a pre-established rate, and with a demand
pacemaker, to sense your own underlying rhythm.
CORONARY ARTERIES: the arteries that supply blood to the heart
muscle itself.
CARDIAC INSUFFICIENCY: inability of the heart to pump adequately.
Causes shortness of breath, fluid retention, etc.
DEMAND: a type of pacemaker that fires only when necessary; i.e.,
when the heart’s own intrinsic rate becomes slower than the rate at
which the pacemaker is programmed to operate.
DEPOLARIZATION: electrical activity spreading through the heart,
causing it to contract or beat.
DIASTOLE: relaxation of the heart between contractions.
ECTOPIC: electrical stimulation of cardiac contractions beginning at a
point other than the sinoatrial (SA) node.
ELECTROCARDIOGRAM: often called EKG or ECG. It is a graphic
record of the electric currents produced by the heart.
ELECTRODE: the wire connecting the pacemaker (pulse generator) to
the heart. It is responsible for carrying the electrical discharge to the
heart and the sensed electrical activity of the heart back to the
pacemaker.
ENDOCARDIAL: refers to the inside layer of the heart. An endocardial
electrode is one that is inserted via a vein, and the tip contacts the
internal surface of the heart.
EPICARDIAL: the outer layer of the heart. An epicardial electrode is
one that is attached directly to the heart’s outer surface.
FIBRILLATION: rapid uncoordinated contractions of the heart muscle
occurring when the individual muscle fibres take up independent
irregular contractions.
FIBROSIS: scarring of the heart or other organs of the body. Within
the electrical portion of the heart this scarring may cause heart block
or other rhythm disturbances.
HEART BLOCK: a condition where the transmission of electrical
discharges from the upper chambers of the heart to the lower
chambers are partially or completely blocked, resulting in the
chambers NOT working in a synchronised way.
HYPERTENSION: an unstable or persistent elevation of blood
pressure above the normal range. May eventually lead to an
enlarged heart and kidney damage.
HERMETIC SEAL: a process where the battery and circuitry of the
pulse generator are sealed within a metal container that cannot be
penetrated by body fluids.
INTRINSIC RATE: patient’s own natural heart rate.
MYOCARDIAL INFARCTION: the damage or death of areas of the
heart muscle (myocardium) resulting from a reduction in the blood
supply reaching that area.
NITROGLYCERIN: a medication used to relax the muscles in the
blood vessels. Often used to relieve attacks of angina pectoris and
spasm of coronary arteries. It is vasodilator.
PACE: a condition in which a heart beat is initiated by a pacemaker.
PAC: premature atrial contraction, a heart beat which has originated
early in the upper chambers of the heart (atria). It is considered
ectopic since it is not in the usual conduction pathway.
PROGRAMMABLE PACEMAKER: a type of pacemaker which can be
adjusted from the outside of the body using a specific instrument
(programmer). The programmer can be used to vary the rate of
pacing as well as the electrical output of the pacemaker. This does
NOT require surgery.
PULSE: a rhythm in the arteries caused by the contractions of the
heart.
PULSE GENERATOR: referring to the entire pacemaker; that is the
circuitry and batteries together, which produce the periodic electrical
impulse to the heart.
PURKINJE FIBRES: specialised muscular fibres forming a network in
the walls of the heart’s lower chambers. Believed to be involved in
conducting electrical impulses to the muscular walls of the ventricles.
These impulses are responsible for the contractions of the ventricles.
PVC: premature ventricular contraction. Similar to PAC but occurring
within the lower chambers of the heart.
RATE RESPONSE: a function that allows the pacemaker to increase
the heart rate during exercise.
REED SWITCH: a component of the circuitry of a demand pacemaker
that is activated by placing a magnet over the unit. This causes a
demand pacemaker to become a fixed-rate unit by bypassing the
sensing circuitry.
RHYTHM: a regular and repetitive recurrence of a beat.
SA NODE: sinoatrial node, the special nerve centre in the upper right
chamber of the heart that in most instances initiates each beat.
SENSE: the ability of a pacemaker to recognise the electrical impulse
of a heart beat.
SEPTUM: a thick muscular wall dividing the heart into right and left.
SINUS RHYTHM: a normal type of rhythm initiated from the upper
chambers of the heart with the electrical impulse passing normally
into the lower chambers.
STIMULUS: an electrical discharge by the pacemaker to the heart.
STOKES / ADAMS ATTACKS: fainting spells associated with a
temporary lack of perfusion of the blood to the brain generally
associated with complete heart block.
SYSTOLE: the contraction of the heart which forces blood through
the arteries.
SYNCOPE: fainting.
TACHYCARDIA: a rapid heart rate usually over 120 beats per minute.
THRESHOLD: the lowest amount of electrical energy from a
pacemaker stimulus necessary to cause the heart to contract.
TITANIUM: a type of metal used to make the outer case of the
pacemaker.
TRANSVENOUS: a type of electrode which is generally endocardial. It
is inserted through a vein and passed to the heart, with the tip of the
electrode placed in the endocardiumin.
TRANSTHORACIC SURGERY: when an opening is made between the
ribs so that epicardial electrodes can be sewn directly to the outer
wall of the left ventricle.
VENTRICLES: the lower chambers of the heart. There are two, the
right and left ventricles. The right ventricle pumps blood to the lungs
and the left ventricle pumps blood throughout the body.
Conclusion:
The proposed project is a real demonstration of the working of a
demand type pacemaker, which can take action in real time in the
absence of feedback from heart. The pacemaker device is completely
programmable which can provide varying output controllable by
user.
The project is proposed to be developed by using low cost
components and thus it is economical and compact.