The primary vital signs are clinical measurements that are displayed and recorded
across the biomedical field; predominantly on patient monitors. Patient simulation
provides accurate mimicking of physiological vital signs to calibrate and test these
devices, ensuring patient safety. There are five crucial vital signs that are
regularly simulated:

  • Blood pressure
  • Oxygen saturation
  • Heart rhythm
  • Respiratory rate
  • Temperature
    Patient simulation is a fundamental part of service tests for patient monitors,
    which are required at regular service intervals. Service testing consists of a
    wide range of checks for each function or parameter.
    The first tests are usually visual and electrical safety tests. This is followed
    by performance testing and includes:
  • Integrity testing (Leak checks, over pressure testing)
  • Performance accuracy (Patient simulation)
  • Printer checks (Speed, amplitude
  • Alarm checks (Pitch, frequency, volume)
  • Physiological simulations (Patient simulation)

Why perform patient simulations?
Vital signs are crucial in communicating a patient’s condition and severity of a
disease to health care clinicians. Patient monitors observe these vital signs
continuously and provide warnings in the case of a serious event.

Patient simulation is a key part of performance test procedures, ensuring that
patient monitoring devices are measuring correctly and accurately, by conforming to
the manufacturer’s specifications and international standards.
Why do we test each parameter? What’s its significance?
NIBP (Blood pressure measurement)

  • To determine transducer linearity and static pressure is within
    specification.
  • Leaks can occur within the cuff or pressure system so leakage
    tests required.
  • An overpressure test to ensure the pop off valve safeguards against a build-
    up of pressure.

IBP (Blood pressure measurement)

  • To test pressure transducer performance for its linearity
  • Dynamic pressure testing for blood pressure
    variations (hypotension/hypertension)
    SpO2 (Oxygen saturation measurement)
  • Testing for faulty probes. i.e LED degradation, contaminated
    lenses or damage to wiring
  • Ensuring accurate calibration of SpO2 monitor
  • Verifying the audible alarms

ECG (Heart rate measurement)

  • Linearity test for heart rate amplitude and frequency
  • Determining correct arrhythmia recognition
  • Gain change sensitivity test
    Temperature
  • Linearity testing of temperature measurement
  • Ensuring the correct temperature sensor is selected (YSI400/YSI700)
    Respiration
  • Accurate detection of sleep apnoea and verifying alarms
  • Linearity testing of respiration rates

How we perform patient simulations?

Patient simulation is implemented by following performance verification

procedures from medical device manufacturer service manuals. Ideally, a multi-
parameter patient simulator is used to test a device in one test sequence, which

provides a practical approach to the biomedical technicians. Each parameter has a
different method for performance testing.
NIBP measurement principles primarily rely on the oscillometric method. It
determines systolic, diastolic and mean arterial values by detecting the vibrations in
the arterial wall at various pressure points by means of an inflated cuff. Testing the
monitor accuracy involves both static and dynamic pressure simulations at specific
values. System leak and over pressure tests are also part of the procedure, executed
through the use of a manometer and a built-in pump, to ensure patient safety.
IBP is an invasive form of blood pressure measurement and uses a liquid filled
catheter, which is placed in an artery. The arterial pressure is converted by a

pressure transducer into an electrical signal. This is typically 5μV/mmHg. Testing
the monitor for its linear sensitivity is essential in determining its accuracy. Patient
simulation is performed by outputting defined DCV values.
SpO2 estimates the amount of oxygen in the blood by analyzing the absorption
of light by hemoglobin across two different wavelength LEDs (RED/IR). If more
red than infrared light is being absorbed there are less oxygenated blood cells.
SpO2 simulation is often implemented using optical simulation “fingers”. These
devices provide variable attenuation to light in the red and IR wavelengths.
ECG measures tiny electrical signals from the heart using ECG leads placed
on various parts of the body. These signals are amplified, measured and
displayed on a patient monitor. ECG simulations are electrically generated
cardiac arrhythmias or performance waveforms with pre-set amplitudes and
frequencies.

Respiration utilizes the ECG leads to measure transthoracic impedance. As
the thoracic cavity expands during inspiration, the impedance of the chest
increases. During expiration the impedance of the chest decreases.
Simulating respiration involves set baseline impedances with
delta impedances providing respiration rates.

Test Equipment

We use a handheld and battery-operated vital signs simulator capable of undertaking
six synchronized vital signs parameters. This enables medical device engineers to
quickly, easily and accurately perform NiBP, SpO2, ECG, temperature, IBP and
respiration functionality tests simultaneously, using a single portable instrument

Technical Specifications
Non-Invasive Blood Pressure Simulation
Waveform Oscillometric
Pulse Volume High, Medium, Low, Paediatric
Heart Rate 20 – 300BPM
Integrated Pump 0 to 350mmHg user configurable
Leak Test User configurable between 0-350mmHg
Chronometer Configurable up to 999 secs
Digital Manometer 0 – 410mmHg
Pressure Accuracy +/- 0.5% FS
Pressure Units mmHg, inHg, kg/cm2, cmH2O, mBar,

PSI, in H2O and kPa
Oxygen Saturation Simulation (PULS-R)
Range 30 to 100%
Repeatability ± 5%** of reading between 30-59% SPO2
± 3% of reading between 60-89% SPO2
± 1% of reading between 90-100% SPO2

Accuracy of simulation when used with the corresponding R-
curves *Based on using the same probe and monitor setup

Note that some monitor types might not be able to display low range sats Heart Rate 30-300BPM*
Accuracy ± 1BPM
Compatibility Beijing Choice, Criticare, GE Tuffsat,
Masimo, Mindray, Nellcor, Nellcor
Oximax, Nihon Kohden, Nonin,
Novametrix, Philips / HP

***Subject to monitor capability
ECG Arrhythmia Simulator
Simulation 5 lead simulation including high level output
on Normal Sinus Rhythm (NSR), ST
Elevation, ST Depression, Myocardial
Infarction, Tall T
Heart Rate 20 – 300 BPM
Accuracy ±1 BPM
Amplitudes Lead II : 0.5 – 5 mV (in steps of 0.5 mV).
Other leads are proportional to Lead II
by the following percentages:
Lead I : 60 %
Lead II : 100 %
Lead III : 40 %
V1 : 63 % [ Reference LA ]
V2 : 71 % [ Reference LA ]
V3 : 68 % [ Reference LA ]
V4 : 80 % [ Reference LA ]
V5 : 55 % [ Reference LA ]
V6 : 49 % [ Reference LA ]

Accuracy ±2%
Connection high-level ECG 3.5mm jack plug
ST Elevation / Depression
Heart Rate 20 – 300BPM
Elevation % 7%, 13%, 20%
Elevation Slope Positive, Negative, Flat
Myocardial Infarction
Type Ischemia, Injury, Infarction, Inferior Infarction
Heart rate 20 – 300 BPM
Tall T
Heart Rate 80 bpm
T wave Amplitude 0 – 1.2mV (steps of 0.1mV)

Arrhythmia Waveforms (Atrial)
Simulation 5 lead simulation
Amplitudes 0.5 / 1 / 1.5 / 2 / 2.5 / 3 / 3.5 / 4 / 4.5 / 5 mV.
Heart rate (where applicable) 20 – 300 BPM
Atrial
Sinus Arrhythmia (SA), Missing beat, Atrial Flutter (AFLT),
Atrial Fibrillation (AFB), Paroxysmal Atrial Tachycardia (PAT),
Junctional Premature Contraction
Atrial Conduction
First Degree AV Block, Second Degree AV Block – Mobitz I,
Second Degree AV Block – Mobitz II, Third Degree AV Block,
Right Bundle Branch Block (RBB), Left Bundle Branch Block
(LBB), Left Anterior Hemiblock
Ventricular
Premature Ventricular Contraction – Intermittent Premature Ventricular
Contraction – Continuous, Bigeminy, Trigeminy, Ventricular Flutter
(VFLT), Ventricular Fibrillation Fine (VFBF), Ventricular Fibrillation
Coarse (VFBC),Monomorphic Ventricular Tachycardia (MVT),
Polymorphic Ventricular Tachycardia (PVT) Right Focal (PVC).
Performance Waveforms
Shape Sine, Square, Triangle
Rate 0.1 to 0.9Hz (in steps of 0.1Hz)
1 to 100Hz (in steps of 1Hz)
Amplitude Lead II : 0.5 – 5 mV (in steps of 0.5 mV).

Other leads as above.

Accuracy 2%
Shape Pulse
Rate 20 ms pulse duration, 4 second delay
Amplitude Lead II : 1 mV. Other leads as above
Accuracy 2 %
Pacer Waveforms
Available synchronous atrial, asynchronous atrial,
paver only, ventricular pacer, atrial &
ventricular pacer
QRS 1mV
Pacer Pulse Amplitude 0.1 – 2 mV
Pacer pulse Polarity positive, negative
Pacer pulse width 0.1 – 2ms
R Wave Detection
Heart Rate 70 bpm
R wave width 10 – 120 ms (steps of 10ms)
Temperature Simulation
Simulation YSI 400 / 700 Static
Range preset at 25, 33, 37and 41°C
Accuracy ±0.1 °C
Default setting YSI 400 37°C
Respiration Simulation
Rates 5, 10, 15, 30, 60, 120, 180 Breaths per Minute
Base resistances 250, 500, 750, 1000 ohms
Accuracy ±5%
Resistance Variations 0.1, 0.5, 1.0, 1.5 ohms
Accuracy ±10%
Default Settings 15bpm / 250Ω / 0.1Ω
Apnoea Simulation 0 – 60 seconds duration 0 – 300 seconds

interval.
Invasive Blood Pressure Simulation Accuracy ± 1mmHg
Channels 2 channels (Channel 2 set at 50% of Channel 1) Excitation Voltage 2–16V
Static 0 to 300mmHg Impedance 350Ω
Dynamic 0-300mmHg for Systolic & Diastolic Nominal Simulated 5μV / V / mmHg

Instrument Sensitivity whe
n used with the Corresponding R Curves
Resolution Range Repeatability
1% steps 30-59% ±5%
1% steps 60-89% ±3%
1% steps 90-100% ±1%

ECG (Heart rate measurement)
The heart, central in the respiratory system, converts bioelectric pulses to a biomechanical
operation (blood flow). The function of the heart is monitored by measuring the electrical
activity (millivolt signals) generated in the heartand isreferred to as electrocardiography.
The most common ECG tracing of a cardiac cycle (heartbeat) is represented below and
consists of a P wave, the QRS complex and aT wave. The typical duration of the electrical
activity is usually around 400-600 ms. The ECGtrace represents the change in voltage across
different parts of the body (limbs) because
of depolarisation (contracting or systole) and repolarisation (relaxing or diastole) in the heart
muscles. The baseline voltage of the ECG is referred to asthe isoelectric line.
1) The P wave is generated during the atrialdepolarisation.
2) Following this, the right and left ventriclesare depolarised, generating the QRS
complex.
3) During the T wave, the ventriclesrepolarise.
4) During the latter part of the T wave, the human heart is most vulnerable against
disturbance or fibrillation.

Unipolar vs bipolar leads
ECG leads are split between unipolar and bipolar leads. The limb leads (I, II and III) are
bipolar, having both a positive and negative pole. The augmented leads(aVL, aVF and aVR)
and precordial leads (V1-6) are considered unipolar, having only a true positive pole. The
negative pole consists of signals from other poles.

Colour coding
ECG leads are marked with both abbreviations and colour coding according to the
corresponding placement on the body. There are two common markings available on the
market today. These are shown in the table below.


The ECG Machine
To observe an ECG, the difference between two electrical signals at different points on the
body must be amplified. Then the electrical potentials can be displayed on the screen.
ECG Machines may typically use 3 lead, 5 leader 12 lead configurations. Placement of
the ECG leads is standardized so that the interpretation of the ECG is consistent.
Cardiac conditions that can be diagnosed using ECG’s include abnormally fastheart
rate (tachycardia), abnormally slow rate (bradycardia), heart block, acute myocardial
infraction (a blood clot in the heart), ischemia (a restriction in the blood supply to a
part of the heart) and numerous other conditions.
These conditions come under the generic termof heart arrhythmias.

Testing ECG monitor
Due to the important analysing role of the ECG monitor, it is crucial to ensure that the
input circuits of the ECG monitor are able to measure the small ECG signals accurately.
That the software is able to interpret these signals to the corresponding conditions and
that alarms are visible and audible according to the manufacturer’s specifications.
Therefore, the following simulations and performance tests are often part of the regular
maintenance:
∙ Linearity of heart rate measurement
∙ QRS beep
∙ Alarms (high and low)
∙ Alarms for disconnected electrodes
∙ Arrhythmias recognition (asystolic)
∙ Sensibility test
∙ Zero offset
∙ Frequency response
∙ Printer calibration (amplitude, timing)

Linearity of heart rate measurement
The purpose of this test is to verify the capability of the monitor to measure and display
heart rate accurately. It is recommended to simulate several values in range spanning
30-300 beats per minute (bpm).
Compare the readings with the simulated values and check whether this is within
manufacturer specifications(normally +/- 1bpm or +/- 1% of reading).
QRS beep
To aid the monitoring process, it is a requirement to fit the ECG monitor with an
audible QRS beep. This provides a clear beep each time the QRS wave passes. Frequency
and pitch variations can provide a clear indication of the heart rate without having to
have line of sight to the ECG recorder.
Alarms (high and low)
IEC 60601-1-8 provides the requirements for alarms on medical devices. Alarms can vary
in frequency, pitch, volume and melody. In general, the greater the urgency, the higher
the pitch, volume and pulse frequency (or melody).

During the performance test of the ECG recorder, alarms can be tested by simulating

different heart rates and arrhythmias using a patient simulator. At the end of the test,
the final alarm condition can be tested by disconnecting the leads one by one. The
monitor should go into alarm condition when this happens.
Record whether the alarm on the monitor occurs at the set value(s) and whether the
alarm(s) is at the correct pitch and frequency(refer to the instruction manual).
Arrhythmias recognition (asystolic)
ECG monitors, which are able to interpret the ECG recording, are required to provide an
alarm when they detect a seizure in blood circulation (or lack of pulse). This is the case
during ventricular fibrillation and asystole (flat line) when no electrical nor mechanical
activity is present in the heart. Ventricular
fibrillation is a condition whereby the ventricles contract erratically with the net result of
poor to no blood circulation from the ventricles to the body. During coarse VFIB, the
waveform amplitudes are significantly larger than during fine VFIB. The latter is close to an
asystole.
All cases of VFIB lead to rapid loss of consciousness in the patient and must be treated
immediately with the use of a defibrillator
Sensitivity test (gain)
To ensure the input circuits of the ECG recorder are sensitive enough to measure the
ECG mV signals, the input amplifier settings are tested by supplying a normal sinus
rhythm (NSR) at (e.g.) 60 bpm and with a 1mV amplitude.
When the NSR is displayed on the screen, change the gain of the monitor and check if
the changes in amplitude are relative to the gain change i.e. a doubling in gain would
result in a doubling of amplitude. The heart rate should not be affected. Some ECG
recorders are supplied with a printer and can allow for gain and amplitude settings to be
easily cross referenced.
Zero offset
The zero offset test demonstrates the aligning of the isoelectric line of the ECG wave form
with the zero line of the ECG recorder. This is achieved by checking whether the ECG line
(flat line on the recorder) is at zero mV when no leads are connected. When the recorder is
fitted with a printer, the printed line shall be at zero m Volt.

Frequency response
To limit the sensitivity of the ECG recorder from external signals i.e. mains frequency and
other artefacts, the input circuits are fitted with filters. So called high pass filters – HPFs
(allowing signals of greater frequency to pass through) and low pass filters – LPFs (allowing
frequencies of lower frequencies to pass through) provide a bandwidth of allowable
frequencies.
Typical values are 0.5Hz / 1 Hz for HPFs and 40Hz for LPFs in monitor mode and 0.05 Hz
for HPF and 40 / 100 / 150 Hz for LPF’s in diagnostic mode.
These filter settings can be selected based upon the application. To test the settings of the
filters, performance wave forms such as a sinus of triangular waveform can be simulated to
the ECG recorder. By varying the frequency in and outside the bandwidth, the
performance can be verified.
Printer calibration (amplitude, timing)
ECG recorders with build-in printer facility are required to be tested for linearity of the
printer speed. Printer rolls typically move at 25 mm / seconds. To test printer speed and
linearity,
a fixed frequency sinusoidal wave can be simulated. This should result in a consistent
wavelength width across the print out and must correspond to the print speed.
ECG recording paper consists of a matrix of squares each 1mm x 1mm. At a speed of
25mm/s and a sensitivity of 10mm/mV each square represents 0.04s and 0.1mV
respectively.
A signal with an amplitude of 1 mV and frequency of 1 Hz should have an amplitude of10
mm and wavelength of 25 mm
Instrument Sensitivity
Resolution Range Repeatability
1% steps 30-59% ±5%
1% steps 60-89% ±3%
1% steps 90-100% ±1%