GE Cardiocap 5 Service Manual

							
Measurement Parameters 
Before each stimulation, the sequence offset, noise, and threshold for response detection is 
measured. Offset is a baseline of the noise measurement. Noise is calculated by the same algorithm 
as the response signal itself. The response detection threshold is calculated based on the noise. If the 
response is not greater than the threshold, it is interpreted as no response. 
The EMG response is measured as integrated muscle activity. The EMG measurement starts 3 ms after 
the stimulation and lasts 15 ms. The 3-ms delay helps prevent the effect of stimulation artifact. 
When using a MechanoSensor, response is measured as movement of the thumb, which is the area of 
positive signal. 
Regional block 
A regional block cable can be used as a nerve locator in local anesthesia. A maximum current of  
5.0 mA is given every second, every other second, or every third second. The response measurement 
is ocular. 
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6.4 Components for NESTPR hemodynamic parameters 
6.4.1 Serial communication 
NESTPR 
 
Figure 6-11. Serial communication and opto isolation 
Serial communication between the NESTPR unit and the CPU is done by a RS485-type bus whose 
buffers get their supply voltage (+5 VDC) from the DC/DC board. In the isolation section, their supply 
voltage (+5 V) is obtained from the isolated power supply. The data transmission rate is 500 kbps. 
The serial communication buffers are also controlled by the Reset signal so that when the Reset is 
active, the buffer does not transfer data. Reset is also an RS485. Additionally, an auxiliary logic power 
reset keeps the reset active for about 500 ms despite the state of reset in the module bus. Time 
constant determines the power-up reset time. Components prevent the unit from sending data during 
reset. 
ECG board communication with the module bus is made through RXD and TXD pins.  
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Measurement Parameters 
6.4.2 NIBP board 
Address Bus
 
Figure 6-12. NIBP board functional block diagram 
Pressure transducers 
The NIBP board contains two piezo-resistive pressure transducers (B1 and B2). Transducer B1 
measures the pressure of the blood pressure cuff and the pressure fluctuations caused by arterial wall 
movement. Transducer B2 detects the cuff hose type as well as Cuff loose and Cuff occlusion 
conditions. The transducers are temperature-compensated internally. They are supplied by a constant 
voltage and their output voltage changes up to 40 mV maximum (50 kPa, 375 mmHg). 
Signal processing 
The NIBP board is controlled with 80C51FA microprocessor at 16 MHz oscillator frequency. The 
microprocessor system is equipped with its own power-up reset in addition to the external RS485 
reset line. 
Two signals from the pressure transducers are amplified and sent to the A/D converter. After the 
converter, digitized signals are sent to the microprocessor for data processing. Before the converter, 
one signal adjusts the offset to the pressure safety level. 
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Software control 
Software controls the valves and pump. In addition to ON/OFF signals for each component, a common 
power switch for the valves and the pump is used at pump/valve failures. 
Memory 
NIBP program memory (EPROM) size is 128k × 8. The RAM (32k × 8 bit) stores variable NIBP 
measurement values. The EEPROM (64 × 16 bit) stores the calibration values for the pressure 
transducers, the pulse valve constants gained during measurements, the PC board identification, and 
the module serial number. 
Watchdog timer 
The NIBP board is equipped with a software-independent safety circuit to disconnect supply voltages 
from the pump and the valves if the cuff has been pressurized longer than preset time. The pressure 
limit is specified to a maximum of 15 mmHg (2.0 kPa). As soon as the cuff pressure rises over  
15 mmHg (2.0 kPa), a timer starts counting. The timer is adjusted to stop the pump and open the 
valves in 2 minutes 10 seconds in adult/child mode and in 1 minute 5 seconds in infant mode. 
Valves 
Exhaust valves 1 and 2 empty the cuff and the joining chamber after the measurement. Exhaust valve 
1 is used as a safety valve in infant mode; it opens at 165 mmHg (22.0 kPa). Exhaust valve 2 is used 
as a safety valve in adult mode; it opens at 320 mmHg (42.7 kPa). 
The bleed valve empties the cuff during measurement.  
The zero valve connects pressure transducer B1 to open air. 
Power supply section 
All connections are established via a 25-pin connector (D-type, female). The unit needs a +5 V, ± 15 
V, and +15 VD (dirty) power supply to operate. The pump and the valves use a separate +15 VD power 
line. Supply voltages are generated in the DC/DC board. The reference voltages ± 5 Vref and +10 Vref 
are generated on the NIBP board. 
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Measurement Parameters 
6.4.3 ECG board 
Patient signals are connected to overload protection circuits (resistors and gas-filled surge arresters) 
and analog switches to instrumentation amplifiers. The signals are amplified by 480 and limited by 
slew rate. Then they are A/D-converted, analyzed, and transferred to the module bus in digital form. 
 
Figure 6-13. ECG board block diagram 
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Analog ECG section 
The ECG cable is connected to connector pins E1 to E6 on the input board, which contains an overload 
protection circuit. 
Analog switches connect leads to amplifiers. The state of the switches depends on the cable type. 
Lead-off, noise, and pacemaker are detected by a slew rate detector. 
Lower frequency is determined by a high-pass (HP) filter 0.5 Hz (monitor bandwidth) or 0.05 Hz 
(diagnostic or ST bandwidth). 
ECG filtering 
The Cardiocap/5 monitor has three ECG filtering modes: 
MONITORING 0.5 to 30 Hz (with 50 Hz reject filter) 
0.5 to 40 Hz (with 60 Hz reject filter) 
DIAGNOSTIC 0.05 to 100 Hz 
ST FILTER 0.05 to 30 Hz (with 50 Hz reject filter) 
0.05 to 40 Hz (with 60 Hz reject filter) 
Filtering reduces high-frequency noise and low-frequency (for example, respiratory) movement 
artifacts. 
The monitoring filter is used in normal monitoring. The diagnostic filter is used if more accurate 
diagnostic information is needed. The ST filter gives more accurate information of ST segment, but 
reduces high-frequency noise. 
The high-pass filters 0.5 Hz and 0.05 Hz are done with hardware. The monitor sends a command to the 
NESTPR unit determining which corner frequency (0.5 Hz or 0.05 Hz) is to be used. 
The 50 Hz and 60 Hz reject filters are low-pass filters with zero at 50 Hz or 60 Hz correspondingly and 
they are done with software. They are for the mains supply filtering. When these filters are used, 3 dB 
value for low-pass filter is 30 Hz or 40 Hz. 
Software filters are not used in diagnostic mode. Then, the upper frequency is limited by hardware and 
the –3 dB frequency is 100 Hz. 
Respiration section 
Analog switches control the current supply source of the impedance respiration measurement. The 
lead selection for the 3-lead cable can be seen from the following table: 
Selected lead Current source between Signal measured from 
I R - L F 
II R - F L 
III L - F R 
   
Position on body surface IEC Standard coding AAMI standard coding 
right arm R = red RA = white 
left arm L = yellow LA = black 
left leg F = green LL = red 
   
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Measurement Parameters 
When the 5-lead cable is used, the current source is between L-F and the signal is measured from the 
N, independently on the lead selection. 
The respiration amplifier consists of the operational amplifiers and the components around them. An 
analog switch controls the gain of the first stage of the preamplifier. 
The synchronous rectifier consists of the analog switches, which detect the respiration signal from 31 
kHz amplitude modulated raw signal. 
The amplifier stage consists of the differential amplifier and the last amplifier. The differential amplifier 
consists of the operational amplifiers and the components around them. This stage is AC-coupled on 
both sides for minimizing the offset voltages. 
The last amplifier amplifies the signal derived from the differential amplifier stage. 
The respiration signal is zeroed at the beginning of the measurement. Zeroing is also used for fast 
recovery of the measurement after the motion artifact. This is done in the amplifier section. 
NOTE: The respiration measurement is switched OFF for 20 seconds when defibrillation is detected at 
the defibrillation detector. 
Microprocessor section 
The microprocessor contains RAM and EPROM. The processor uses external EEPROM memory. The 
microprocessors internal 8-channel A/D converter converts the ECG signals to digital form. 
Isolated section 
See STP board later in this chapter. 
The patient isolation of ECG is 5 kV. 
WARNING: Do not touch battery-operated monitor during defibrillation procedure. 
Power supply section 
See STP board later in this chapter. 
There is a test connector (X20) on the board for voltages +5 VREF, +5V, +12V, GND and –12V. 
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6.4.4 STP board 
 
To NIBP Board  
Figure 6-14. STP board block diagram 
Microprocessor unit 
The STP board uses an Intel 80C196KC-16 processor with three A/D converters, external memories, 
an 8-bit data bus, a 16 MHz oscillator, an open collector reset, and a watchdog timer. The processors 
internal UART communicates with the CPU board. High speed I/O obtains the pulse control sequence 
for pulse oximetry measurement. The oscillator provides its timing clock. 
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Measurement Parameters 
Isolation section 
The outputs of the two opto isolators are analog signals in the isolated section, however, the signal is 
processed on logical high-low level. Reset line is an open collector type with a pull-up resistor, 
allowing the processor to use its internal watchdog function. 
Power supply section 
Isolated supply voltages of the boards are developed from +15 Vdirty voltage from the DC/DC board. 
The power supply is a switched mode circuit, where the FET transistor switch is controlled by an 
oscillator using a bipolar timer. The frequency of the oscillator is about 30 kHz and the pulse ratio is 
50%. Control of the FET switch is slowed to suppress spurious interference. 
A special pulse transformer is used in the circuit. In the secondary circuit, normal linear regulators are 
used except for +5 V (low drop type linear regulator). 
6.4.5 STP board—Pulse oximetry measurement section 
 
Figure 6-15. Pulse oximetry measurement block diagram 
LED control signals 
The processor sends pulse-width modulated signals, IRED intensity and RED intensity, that are 
converted to DC voltage and filtered. Switches send either RED or IRED intensity forward to the 
amplifier in the LED driving circuit. 
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LED driving circuit 
The differential amplifier circuit measures the voltage difference that corresponds to the LED current. 
Its output is sent back to the processor in 0 to 5 V level. There are feedback circuits from LED current 
measurement and LED intensity control. 
Background light is measured by picking up a sample from the signal. The sample is modified to 0 to 5 
V level and sent to the processor. 
Measured signal preamplification 
The preamplifier is a current-to-voltage converter with gain selection. The higher gain is used for 
measuring thin tissue. 
Digitally controlled amplifier 
The D/A converter is a digitally-controlled amplifier after which there is another constant amplifier. 
Red and infrared channel separation 
Switches separate red and infrared channels. The operational amplifier functions as a buffer and after 
this, an infrared DC signal is sent to the processor. A capacitor separates out the AC signal, which is 
sent to the processor after amplification. There is a switch to choose the amplification constant. 
6.4.6 STP board—Temperature measurement section 
The value of NTC resistor in the probe depends on the patients temperature, which is measured with 
the following principle. 
The temperature signal is produced by voltage dividers, part of which is the temperature probe used 
on the patient. The output is amplified by the calibrated amplifier whose offset voltage makes its 
output spread on both sides of zero. A wider output range (measurement range) means better 
resolution. 
 
Figure 6-16. Temperature measurement principle 
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