Patient monitoring systems continuously measure important physiological parameters of critically ill patients. There are several categories of patients who may need monitoring, including those recovering from surgery or serious illness in intensive care units. Patient monitoring systems organize and display information, correlate parameters, process data to detect abnormalities, provide therapy information, and ensure better care with fewer staff. Key parameters monitored include ECG, heart rate, blood pressure, temperature, and respiratory rate. Cardioscopes specifically monitor heart rate and ECG morphology to detect arrhythmias or changes indicative of serious conditions. They have slower sweep speeds and long persistence screens to enable observation of waveforms.

1. PATIENT MONITORING
SYSTEMS
Construction-working
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2. The objective of patient monitoring is to have a quantitative
assessment of the important physiological variables of the
patients during critical periods of their biological functions.
Patient monitoring systems are used for measuring continuously
or at regular intervals, automatically, the values of the patient’s
important physiological parameters.
There are several categories of patients who may need
continuous monitoring or intensive care.
Critically ill patients recovering from surgery, heart attack or
serious illness, are often placed in special units, generally
known as intensive care units, where their vital signs can be
watched constantly by the use of electronic instruments
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3. Organizing and displaying
• Organizing and displaying information in a form
meaningful for improved patient care,
Correlating
• Correlating multiple parameters for clear
demonstration of clinical problems,
Processing
• Processing the data to set alarms on the development
of abnormal conditions,
Providing
• Providing information, based on automated data,
regarding therapy and
Ensuring
• Ensuring better care with fewer staff members.
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4. Electrocardiogram (ECG),
Heart rate (instantaneous or average),
Pulse rate
Blood pressure (indirect arterial blood pressure, direct arterial blood pressure or venous blood pressure),
Body temperature and respiratory rate.
In addition to these primary parameters, electroencephalogram (EEG), oxygen tension (pO2) and respiratory
volume also become part of monitoring in special cases.
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7. ▪ The most important physiological parameters monitored in the intensive care
unit are the heart rate and the morphology or shape of the electrical waveform
produced by the heart.
▪ This is done to observe the presence of arrhythmias or to detect changes in
the heart rate that might be indicative of a serious condition, also called
‘Cardioscopes’
▪ The cardioscope has the usual circuit blocks like vertical and horizontal
amplifiers, the time base and the EHT (extra high tension) for the cathode ray
tube.
▪ However, they differ in two important aspects as compared to the conventional
instrument.
▪ These are slower sweep speeds and a long persistence screen.
▪ The slow sweep is an outcome of the low frequency character of the ECG
signal.
▪ The slow sweep speed necessitates the use of a long persistence screen to
enable a convenient observation of the waveform.
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8. Disposable type pregelled
electrodes to pick up the ECG
signal.
Amplifier and a cathode ray
tube (CRT) for the amplification
and display the ECG which
enable direct observation of the
ECG waveform.
A heart rate meter to indicate
average heart rate with audible
beep or flashing light or both
with each beat.
An alarm system to produce
signal in the event of
abnormalities occurring in the
heart rate
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10. ▪ The system carries out high-speed real-time sampling of an incoming analog waveform, followed by the
digital measurement of each successive sample and the subsequent storage of the stream of data.
▪ Once the data is stored in the digital form, it can be recalled for conversion back to analog form or for other
processing operations.
▪ This ‘replay’ process can be continuous, and its speed can be chosen to provide a non-fading, flicker-free
trace on the CRT, irrespective of the speed of the original recording, or to provide a low-speed output to
drive a conventional chart recorder.
▪ Any digital method of waveform recording will have an analog–digital converter, which feeds data
corresponding to the input signal into a digital store in a controlled ‘write’ cycle.
▪ The data is retrieved via a similar controlled ‘read’ cycle and is reformed via a digital/analog converter for
display.
▪ As the regenerated signal is based on a finite number of measurements of the input signal, it is inevitably
degraded as compared to the original.
▪ Two important factors governing the final resolution are the sample rate and word length.
▪ The former must be high enough to provide enough resolution on the time axis, while the latter depends on
the number of bits provided by the analog/digital converter or store which determines the number of levels
between zero and full scale on the vertical axis (Y-axis).
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11. ▪ In actual operation, the selected trigger signal initiates a scan and
writes in sequence into each address of the 1024 word length store.
▪ The writing sequence depends upon the instructions from the 10-
stage write address counter, which is controlled by the time base
speed control.
▪ The write-cycle control logic is designed to update or refresh the
store whenever a trigger pulse is received and hence the display
follows changes in the input waveform as they occur.
▪ A separate read address counter continuously scans all addresses at a
fixed rate and drives the Y-deflection system of the CRT via a
digital/analog converter.
▪ At the same time, the time base ramp generator is initiated, with the
required speed, by the address counter at the start of the scan.
▪ The address input to the store is alternated, if necessary, by a data
selector between the write and read address counters.
▪ Read out generally takes place on alternate clock pulses which are
otherwise unused for writing; but with a fast sweep rate, where all
clock pulses are required while writing, read out takes place between
successive writing scans.
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12. ▪ Two basic types of storage devices are used to
store digital information in memory monitors:
shift registers and random-access memories.
▪ The other important component of memory
monitors is the analog-to-digital converter.
▪ Out of the methods available for A to D
conversion, the counter or dual ramp methods
are very effective for slow conversion rates.
▪ For higher conversion rates, the successive
approximation, tracking, parallel or flash
techniques are preferred.
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13. ▪ This sequential device loads the data present on its inputs
and then moves or “shifts” it to its output once every clock
cycle, hence the name Shift Register.
▪ A shift register basically consists of several single bit “D-
Type Data Latches”, one for each data bit, either a logic “0”
or a “1”, connected together in a serial type daisy-chain
arrangement so that the output from one data latch becomes
the input of the next latch and so on.
▪ Data bits may be fed in or out of a shift register serially, that
is one after the other from either the left or the right
direction, or all together at the same time in a parallel
configuration.
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Sampling Rate:
• Signals with high bandwidth require
sampling to be carried out at a high
rate to obtain all its features. A high
sampling rate, however, necessitates
a large memory to store all the data.
• A sampling rate, which is three times
the highest frequency component to
be displayed, has been found to be
generally adequate. For monitoring
purposes the bandwidth is usually
limited to 50 Hz.Therefore, a
sampling rate of 150 or above will be
satisfactory
Word Length:
• The ECG signals, before they are
coded in the digital form, are
amplified in a preamplifier and
brought to a level of 0–1 V.
• The accuracy of conversion of analog
signals depends on the number of
bits used in the conversion.
• The greater the number of bits per
word, the greater will be the
resolution, as a greater number of
levels will be available to accurately
define the value of the sampled
signal.
Memory Capacity:
• The contents of each channel
memory are displayed with each
sweep across the CRT screen.
• Therefore, the stored signal must roll
on the screen with a time interval,
which must be convenient for
viewing
• Increasing either the sampling rate
or the display time interval will
increase the memory size
proportionately

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▪ The ECG signal is sensed differentially by the RA (right arm) and LA (left arm) electrodes and is amplified
by an isolation ECG amplifier.
▪ The patient circuit is isolated by using a transformer and by modulating the 102 kHz carrier signal with
amplified and filtered ECG.
▪ The modulated carrier is demodulated, amplified and applied to an analog-to-digital converter.
▪ The converter samples the waveform at a rate of 250 samples/s, converts each sample to an 8-bit parallel
word, and enters the word into the recirculating memory where it replaces the oldest word stored.
▪ The recirculating memory, usually employed, consists of eight 1024-stage shift registers operating at a
clock rate of 250 kHz.
▪ The output of each shift register is fed back to its input, so that the contents of the shift registers
recirculate continuously.
▪ Hence, a waveform acquired at a rate of 250 samples/s is available at a rate of 250,000 samples/s.
▪ The samples are reconverted into an analog signal for presentation on the CRT display. The sweep time is
so arranged that it matches the time to read out 1024 samples.
▪ The most recent four seconds of the original ECG waveform are traced in four milliseconds.
▪ The relatively fast repetition rate of the stored information causes the displayed waveform to appear
bright with no fading.

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▪ At any time, the freeze control can be activated to obtain a fixed display on the CRT screen.
▪ In this position, feeding of new signals into the memory is discontinued and all values in the memory
then return to the same positions after each recirculation through the memory.
▪ The display in the frozen position helps to observe a particular event more conveniently.
▪ For the display of heart rate on the CRT screen, the original ECG waveform is shaped and supplied to
the tachometer circuit to compute and display the heart rate.
▪ Adjustable heart rate alarm limits are indicated visually and in the audible form. Operation of these
limits is carried out by using two comparators to sense when the heart rate goes beyond set limits.

18. FREQUENCY
RESPONSE OF
CARDIOSCOPES:
▪ Some monitors have two selectable frequency
response modes, namely Monitor and
Diagnostic.
▪ In the ‘Monitor’ mode or ‘Filter-in’ mode, both the
low and high frequency components of an
electrocardiogram are attenuated.
▪ It is used to reduce baseline wander and high
frequency noise.
▪ The Monitor mode bandwidth is generally 0.4 to 50
Hz (3 dB points).
▪ In the ‘Diagnostic’ mode, the instrument offers
expanded bandwidth capability of 0.05 to 100
Hz.
▪ Some instruments include a 50 Hz notch filter to
improve the common mode rejection ratio and
this factor should be kept in mind while
checking the frequency response of the
instrument.
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19. ▪ lnput Circuit:
There are three prominent circuit
blocks:
(i) low-pass filter circuit, to
suppress RF interference,
(ii) high voltage protection circuit,
like electrocardiographs, to
provide voltage clamp in the
presence of defibrillator
pulses, and
(iii) over voltage protection circuit.
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20. ▪ Electrosurgery Interference:
▪ RF interference occurs due to any one of two possible modes.
▪ The first and usually the most severe is due to conduction, i.e. the RF
energy is actually carried via the patient into the monitor.
▪ The second is radiation, by which the RF energy is transmitted through
the air and is induced into the circuits of the monitoring instrument, its
leads and cables.
Leads Off Detector:
▪ The “leads off’ detector circuit usually works on the principle that loss
of body contact of either the RA or LA electrode causes a rather high
impedance change at the electrode/ body contact surface,
consequently causing a loss of bias at the appropriate amplifier input.
▪ This sudden change makes the amplifier to saturate, producing
maximum amplitude waveform.
▪ This waveform is rectified and applied to a comparator that switches
on an alarm circuit (leads off) when the waveform exceeds a certain
amplitude
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22. BEDSIDE
MONITORS
▪ The system is designed to display an electrocardiogram, heart rate with
high and low alarms, pulse rate, dynamic pressure or other waveforms
received from external preamplifiers.
▪ It also gives immediate and historical data on the patient for trend
information on heart rate, temperature, and systolic and diastolic blood
pressures for periods up to eight hours.
▪ The system basically consists of three circuit blocks: Preamplifier section,
Logic boards and Display part.
▪ The preamplifiers incorporate patient isolation circuits based on optical
couplers.
▪ The ECG waveform has facilities for lead-off detection,‘pacer’ detection
and quick recovery circuit for overload signals.
▪ Various amplified signals are carried to a multiplexer and then to an
analog-to-digital converter, included in the logic board.
▪ The central processing unit along with memory gives X and Y output for the
CRT display.
▪ The character generator output is mixed with theY output for numeric
display on the CRT.
▪ The alarm settings, selection switches for different parameters and the
defibrillator synchronization system communicate with the CPU.
▪ The alarm signals are also initiated under its control.
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Heart rate is derived by the amplification of the ECG signal and by
measuring either the average or instantaneous time intervals between
two successive R peaks.Techniques used to calculate heart rate include:
Average calculation This is the oldest and most popular technique. An
average rate (beats/ min) is calculated by counting the number of pulses
in a given time.The average method of calculation does not show changes
in the time between beats and thus does not represent the true picture of
the heart’s response to exercise, stress and environment.
Beat-to-beat calculation This is done by measuring the time (T), in
seconds, between two consecutive pulses, and converting this time into
beats/min., using the formula beats/ min. = 60/T.This technique
accurately represents the true picture of the heart rate.
Combination of beat-to-beat calculation with averaging This is based on a
four or six beats average.The advantage of this technique over the
averaging techniques is its similarity with the beat-to-beat monitoring
system

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Instantaneous heart rate facilitates detection of arrhythmias and permits the timely observation of incipient cardiac
emergencies.
Calculation of heart rate from a patient’s ECG is based upon the reliable detection of the QRS complex.
Most of the instruments are, however, quite sensitive to the muscle noise (artefact) generated by patient movement.This
noise often causes a false high rate that may exceed the high rate alarm.
A method to reduce false alarm is by using a QRS matched filter.This filter is a fifteen-sample finite impulse- response-
filter whose impulse response shape approximates the shape of a normal QRS complex.
The filter, therefore, would have maximum absolute output when similarly shaped waveforms are input.
The output from other parts of the ECG waveform, like a T wave, will produce reduced output.
The ECG is sampled every 2 ms. Fast transition and high amplitude components are attenuated by a slew rate limiter
which reduces the amplitude of pacemaker artefacts and the probability of counting these artefacts as beats.

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Two adjacent 2 ms samples are averaged and the result is a train of 4 ms samples.
In order to remove unnecessary high frequency components of the signal, a 30 Hz, infinite-impulse-
response, Butterworth filter is employed.
This produces 8 ms samples in the process.
Any dc offset with the signal is removed by a 1.25 Hz high-pass filter.The clamped and filtered ECG
waveform is finally passed through a QRS matched filter
The beat detector recognizes QRS complexes in the processed ECG waveform value that has occurred
since the last heartbeat.
If this value exceeds a threshold value, a heartbeat is counted.
The beat interval averaged over several beats is used to calculate the heart rate for display, alarm limit
comparison, trending and recorder annotation.

28. The threshold in this
arrangement gets
automatically adjusted
depending upon the
value of the QRS wave
amplitude and the
interval between the
QRS complexes.
01
Following each beat, an
inhibitory period of 200
ms is introduced during
which no heartbeat is
detected.
02
This reduces the
possibility of the T wave
from getting counted.
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The inhibitory period is
also kept varied as an
inverse function of the
high rate limit, with
lower high rate limits
giving longer inhibitory
periods.
04
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