2 Principles. Mindray DPM 4
Mindray DPM 4 is a multi-parameter patient monitor intended for use by medical professionals in health care institutions. It provides comprehensive monitoring of vital signs, including ECG, SpO2, NIBP, RESP, and temperature. The DPM 4 is designed to be user-friendly and easy to operate, with a large, high-resolution display and intuitive menu navigation. It also features advanced alarm management capabilities and networking options for remote monitoring. Whether you are in the hospital, clinic, or home healthcare setting, Mindray DPM 4 can help you provide the best possible care for your patients.
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2
Principles
2.1 General
The intended use of the DPM4 patient monitor is to monitor a fixed set of parameters including
ECG, RESP, SpO2, NIBP, TEMP, IBP, and CO2 (IBP and CO2 are optional). It consists of the following functional parts:
Parameter measurement;
Main control part;
Man-machine interface;
Power supply;
Other auxiliary functions;
These functional units are respectively detailed below.
Figure 2-1 Structure of the DPM4
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2.1.1 Parameter Measurement
The parameter measurement and monitoring are the core functions of the patient monitor. The parameter measurement part of the DPM4 patient monitor consists of the measurement probe, parameter input socket assembly, NIBP assembly and the main control board.
This part converts the physiological signals to electrical signals, processes those signals and conducts the calculation by the preset program or command delivered from the main control board, and then sends the values, waveforms and alarm information (which will be displayed by using the man-machine interface) to the main control board.
2.1.2 Main Control Part
In the DPM4 patient monitor, the main control part refers to the main control part of the main control board. It drives the man-machine interface, manages the parameter measurement and provides users with other special functions, such as storage, recall of waveforms and data. (See
Figure 2-1)
2.1.3 Man-Machine Interface
The man-machine interface of the DPM4 patient monitor includes the TFT display, recorder, speaker, indicator, buttons and control knob.
The TFT display is the main output interface. It, with the high resolution, provides users with abundant real-time and history data and waveforms as well as various information and alarm information.
The recorder is a subsidiary of the display, which is used for the user to print data.
The speaker provides the auditory alarm function.
The indicator provides additional information about the power supply, batteries, alarms and so on.
The buttons and control knob are the input interface, which are used for the user to input the information and commands to the patient monitor.
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2.1.4 Power Supply
The power supply part is an important part of the patient monitor. It includes the main power
PCB, backlight board, batteries and fan.
The main power PCB converts the external AC current to the 5V DC current, which are supplied for the whole system. For the TFT display, there is a special requirement on the power supply, so a backlight board is used. The batteries supply power for the system for a short time when there is no external AC current. The fan is used for the heat sink of the system.
2.1.5 Other Auxiliary Functions
The DPM4 patient monitor also provides the network upgrade function for the service engineers to upgrade the system software without disassembling the enclosure.
2.2 Hardware Description
The structure of the DPM4 patient monitor is shown in the following figure.
Figure 2-2 Functional structure of the DPM4
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The DPM4 PCB connection is shown in the following figure.
Figure 2-3 PCB connection
Basic functions and working principles of modules are described in the following sections.
2.2.1 Main Board
2.2.1.1 General
The main board is the heart of the patient monitor. It implements a series of tasks, including the system control, system scheduling, system management, data processing, file management, display processing, printing management, data storage, system diagnosis and alarm.
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2.2.1.2 Principle diagram
Figure 2-4 Working principle of the main board
2.2.1.3 Principle
The main board is connected with external ports, including the power input port, multi-way serial port, TFT display interface, analog VGA interface, network port and analog output port. Besides, on the main board is also a BDM interface reserved for the software debugging and software downloading.
CPU System
RTC
CPU is the core part of the main board. It, connected with other peripheral modules through the bus and I/O cable, implements the data communication, data processing, logical control and other functions.
RTC provides the calendar information (such as second, minute, hour, day, month and year).
CPU can read and modify the calendar information from RTC.
Ethernet Controller
Ethernet Controller supports the IEEE802.3/IEEE802.3u LAN standard, and supports two data transmission rate: 10Mbps and 100Mbps. CPU exchanges data with the Ethernet through the
Ethernet Controller.
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Analog Output
The D/A converter converts the digital ECG/IBP signals sent from CPU to the analog signals, which are provided for the external after low-pass filtered by the filter and amplified by the amplifier.
FPGA and VRAM
VRAM stores the displayed data. CPU stores the displayed data to VRAM through FPGA. FPGA gets data from VRAM, processes them, and then sends them to the relevant graphic display device.
In addition, FPGA also extends multiple serial ports, which communicate with peripheral modules. FPGA transfers the received data to CPU through the bus; CPU delivers data to FPGA through the bus, and then the FPGA transfers those data to the peripheral modules.
Watchdog
When powered on, watchdog provides reset signals for CPU, FPGA and Ethernet Controller.
The patient monitor provides the watchdog timer output and voltage detection functions.
2.2.2 ECG/RESP/TEMP Module
2.2.2.1 General
This module provides the function of measuring three parameters: electrocardiograph (ECG), respiration (RESP) and temperature (TEMP).
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2.2.2.2 Principle diagram
Figure 2-5 Working principle of the ECG/RESP/TEMP module
2.2.2.3 Principle
This module collects the ECG, RESP and TEMP signals through the transducer, processes the signals, and sends the data to the main board through the serial port.
ECG Signal Input Circuit
The input protection and filtering circuits receive the ECG signal from the transducer, and filter the high-frequency interference signal to protect the circuit against the damage by defibrillator high-voltage and ESD.
The right-leg drive circuit gets the 50/60Hz power common-mode signal from the lead cable, and sends the negative feedback signal to the human body to reject the common-mode interference signal on the lead cable, which helps the detection of the ECG signal.
The lead-off detecting circuit checks whether the ECG lead is off, and sends the information to
CPU.
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ECG Signal Process Circuit
The difference amplifying circuit conducts the primary amplification of the ECG signal and rejects the common-mode interference signal.
The low-pas filtering circuit filters the high-frequency interference signal beyond the frequency band of the ECG signal.
The PACE signal refers to the ECG pace signal. It has significant interference to the ECG signal detection. The PACE rejection circuit can rejects the PACE signal, which helps the ECG signal detection.
The main amplifying/filtering circuit conducts the secondary amplification of the ECG signal, filters the signal, and then sends the ECG signal to the A/D conversion part.
Pace Detect
This part detects the PACE signal from the ECG signal and sends it to CPU.
Temperature Detect Circuit
This circuit receives the signal from the temperature transducer, amplifies and filters it, and then sends it to the A/D conversion part.
Carrier Generate Circuit
The RESP measurement is based on the impedance method. While a man is breathing, the action of the breast leads to changes of the thoracic impedance, which modulates the amplitude of the high-frequency carrier signal. Finally, the modulated signal is sent to the measurement circuit.
The purpose of this module is generating the high-frequency carrier.
RESP Signal Input Circuit
This circuit couples the RESP signal to the detecting circuit.
RESP Signal Process Circuit
The pre-amplifying circuit conducts the primary amplification of the RESP signal and filters it.
The detecting circuit detects the RESP wave that has been modulated on the actuating signal.
The level shifting circuit removes the DC component from the RESP signal.
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A/D
The main amplifying/filtering circuit conducts the secondary amplification of the RESP signal, filters the signal, and then sends it to the A/D conversion part.
The A/D conversion part converts the analog signal to the digital signal, and sends the signal to
CPU for further processing.
CPU System
Implementing the logical control of all parameter parts and A/D conversion parts;
Implementing the data processing for all parameters;
Implementing the communication with the main board.
Power & Signal isolate Circuit
Isolating the external circuits to ensure the safety of human body;
Supplying power for all circuits;
Implementing the isolation communication between the CPU System and the main board.
2.2.3 IBP Module
2.2.3.1 General
This module provides the function of measuring Invasive Blood Pressure (IBP).
2.2.3.2 Principle diagram
Figure 2-6 Working principle of the IBP module
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2.2.3.3 Principle
This module collects the IBP signal through the transducers, processes it and sends it to the main board throgh the serial port.
IBP Signal Process Network
The IBP signal is the differential signal. After the common-mode filtering, the difference signal is amplified by the difference amplifying circuit which changes the dual-end signal to the single-end signal. After the low-pass filtering, the IBP signal is sent to the CPU System for processing.
CPU System
Converting the analog signal obtained by the circuit to the digital signal;
Implementing the logical control of all parameter parts;
Implementing the data processing for the two parameters;
Implementing the communication with the CPU board.
Power & Signal isolate Circuit
Isolating the external circuits to ensure the safety of human body;
Supplying power for all circuits;
Implementing the isolation communication between the CPU System and the main board.
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2.2.4 SpO
2
Module
2.2.4.1 General
This module provides the function of measuring the Pulse Oxygen Saturation (SPO
2
).
2.2.4.2 Principle diagram
Figure2-7 Working principle of the SpO2 module
2.2.4.3 Principle
The SpO2 measurement principle
1. Collecting the light signal of the red light and infrared transmitting through the finger or toe which is pulsing;
2. Processing the collected signal to get the measured result.
The drive circuit of the LED and the gain of the amplifying circuit should be controlled according to the different perfusions and transmittances of the tested object.
Led Drive Circuit
This circuit supplies the LED with the drive current, which can be regulated.
SPO2 Signal Process Network
The pre-amplifying circuit converts the photoelectric signal to the voltage signal and conducts the primary amplification.
The gain adjusting and amplifying circuit conducts the secondary signal amplification and adjusts the gain.
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A/D
The biasing circuit adjusts the dynamic range of the signal, and sends it to the A/D conversion part.
The A/D conversion part converts the analog signal to the digital signal, and then sends it to CPU
D/A
for further processing.
The D/A conversion part converts the digital signal received from CPU to the analog signal, and provides the control signal for the Led Drive Circuit and SPO2 Signal Process Network.
CPU System
Implementing the logical control of all the circuits;
Implementing the data processing for the SpO
2
parameter;
Implementing the communication with the CPU board.
Power & Signal isolate Circuit
Isolating the external circuits to ensure the safety of human body;
Supplying power for all circuits;
Implementing the isolation communication between the CPU System and the CPU board.
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2.2.5 NIBP Module
2.2.5.1 General
This module provides the function of measuring the Non-Invasive Blood Pressure (NIBP) parameter.
2.2.5.2 Principle diagram
Figure 2-8 Working principle of the NIBP module
2.2.5.3 Principle
The NIBP is measured based on the pulse vibration principle. Inflate the cuff which is on the forearm till the cuff pressure blocks the arterial blood, and then deflate the cuff according to a specified algorithm. While the cuff pressure is decreasing, the arterial blood has pulses, which are sensed by the pressure transducer in the cuff. Consequently, the pressure transducer, connected with the windpipe of the cuff, generates a pulsation signal, which is then processed by the NIBP module to get the NIBP value.
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Valve Drive Circuit
This circuit controls the status (ON/OFF) of valves. It, together with the Motor Drive Circuit, implements the inflation and deflation of the cuff.
Motor Drive Circuit
This circuit controls the action of the air pump. It, together with the Valve Drive Circuit, implements the inflation and deflation of the cuff. Besides, it provides the status signal of the motor for the A/D conversion part.
NIBP Signal Process Network
The NIBP signal is the differential input signal. The difference amplifying circuit amplifies the dual-end difference signal and converts it to the single-end signal; meanwhile, this circuit sends a channel of signal to the A/D conversion part, and the other to the DC isolating and amplifying circuit.
The DC isolating and amplifying circuit removes DC components from the signal, amplifies the
A/D
signal, and then sends it to the A/D conversion part.
The A/D conversion part converts the analog signal to the digital signal, and sends it to the CPU
System for further processing.
Over Pressure Detect
The circuit detects the NIBP pressure signal. Once the pressure value exceeds the protected pressure value, it will send a message to the CPU System, which asks the Valve Drive Circuit to open the valve to deflate the cuff.
CPU System
Implementing the logical control of all the circuits;
Implementing the data processing for the NIBP parameter;
Implementing the communication with the CPU board.
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2.2.6 Recorder Module
2.2.6.1 General
This module is used to drive the heat-sensitive printer.
2.2.6.2 Principle diagram
Figure 2-9 Working principle of the recorder module
2.2.6.3 Principle
This module receives the to-be-printed data from the main board, converts them to the dot matrix data, sends them to the heat-sensitive printer, and drives the printer.
Step Motor Drive Circuit
There is a step motor on the heat-sensitive printer. The step motor drives the paper. This circuit is used to drive the step motor.
Printer Status Detect Circuit
This circuit detects the status of the heat-sensitive printer, and sends the status information to the
CPU system. The status information includes the position of the paper roller, status of the heat-sensitive recorder paper and the temperature of the heat-sensitive head.
CPU System
Processing the data to be printed;
Controlling the heat-sensitive printer and step motor;
Collecting data about the status of the heat-sensitive printer, and controlling the printer;
Implementing the communication with the CPU board.
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2.2.7 Button Panel
2.2.7.1 General
This module provides a man-machine interactive interface.
2.2.7.2 Principle diagram
Figure 2-10 Working principle of the button panel
2.2.7.3 Principle
This module detects the input signals of the button panel and control knob, converts the detected input signals to codes and then sends to the main board. The main board sends commands to the button panel, which, according to the commands, controls the status of the LED and the audio process circuit to give auditory/visual alarms.
CPU
Detecting the input signal of the button panel and control knob;
Controlling the status of LED;
Controlling the audio process circuit;
Regularly resetting the Watchdog timer;
Communicating with the CPU board.
Audio Process Circuit
This circuit generates audio signals and drives the speaker.
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Watchdog
When powered on, the Watchdog provides the reset signal for CPU.
The patient monitor provides the watchdog timer output and voltage detection functions.
2.2.8 Power PCB
2.2.8.1 General
This module provides DC working current for other boards.
2.2.8.2 Principle diagram
Figure 2-11 Working principle of the power PCB
2.2.8.3 Principle
This module can convert 220V AC/12V DC or the battery voltage to 5V DC and 12V DC voltages, which are supplied for other boards. When the AC voltage and batteries coexist, the AC voltage is supplied for the system and used to charge the batteries.
AC/DC
This part converts the AC voltage to the low DC voltage for the subsequent circuits; besides, it supplies the power for charging the batteries.
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Battery Control Circuit
When the AC voltage and batteries coexist, this circuit controls the process of charging the batteries with the DC voltage converted by the AC/DC part. When the AC voltage is unavailable, this circuit controls the batteries to supply power for the subsequent circuits.
5V DC/DC
This part converts the DC voltage to the stable 5V DC voltage and supplies it for the external boards.
12V DC/DC
This part converts the DC voltage to the stable 12V DC voltage and supplies it for the external boards.
Power Switch Circuit
This circuit controls the status of the 5V DC/DC part and the 12V DC/DC part, thus to control the switch of the patient monitor.
Voltage Detect Circuit
This circuit detects the output voltages of the circuits, converts the analog signal to the digital signal, and sends the digital signal to the main board for processing.
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2.3 Software Description
2.3.1 General
Figure 2-12 System function
As shown in Figure 2-12, in the red frame is the software system, on the left to the red frame are the inputs of the software system, and on the right to the red frame are the outputs. The parameter measurement module exchanges data with the software through the serial port, while the user interacts with the system through the button panel. Among the output devices, the recorder and alarm device receive data through the serial ports, the analog output component is an MBUS component, and the LCD and network controller are controlled directly by CPU.
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2.3.2 System Task
NO Task
1 System initialization
Function
Initializing the system
Period
In case of a startup
1 second 2 Data processing
3
Display of timer information
12
13
14
Record output
NIBP processing
WATCHDOG task
Analyzing and saving the data
Implementing the timed refreshing
Outputting records
Implementing NIBP-related processing
Managing the system watchdog
1 second
5
Switchover of modules and screens
Switching over between waveforms and parameters on the screen
6
Processing of user commands and screens
Processing the user inputs by buttons and displaying them on the screen.
7 System monitoring
System monitoring, voltage monitoring and battery management
8 Network connection Implementing the network connection
9 Network data sending Sending the network data
10 Network data receiving Receiving the network data (viewbed)
11 ECG analysis
Analyzing ECG signal, calculating ECG values
(HR, ARR and ST), and saving the analysis results.
In case of a screen change event
In case of a button event
1 second
1 second
1 second
1 second
1 second
In case of a record event
1 second
1 second
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2.3.3 System Function
The system tasks can be classified as follows.
Figure 2-13 System task
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2.4 System Parameter
2.4.1 General
For the DPM4 patient monitor, signals are collected by modules, and the results are transferred to the main board through the adapter board, thus to process and display the data and waveforms.
Commands from the main board, as well as the status information of modules, are transferred through the adapter board. In addition, the adapter board adapts and changes the power supply.
The structure of the whole system is shown in the following figure.
Figure 2-14 System Structure
As shown in Figure 2-14, the five modules and measurement cables monitor and measure NIBP,
SpO
2
, ECG/RESP/TEMP, IBP and CO
2
in real time, and send the results to the main board for processing and displaying. If necessary, the results are sent to the recorder for printing.
The parameter monitoring functions are described respectively in the following sections.
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2.4.2 ECG/RESP
ECG
The DPM4 patient monitor has the following ECG functions:
1. Lead type: 3-lead, 5-lead, 12-lead
2. Lead way:
3-lead (1 channel):
5-lead (2 channels):
12-lead (8 channels):
3. Floating input
4. Right-foot drive
5. Lead-off detection
I, II, III
I, II, III, aVR, aVL, aVF, V
I, II, III, aVR, aVL, aVF, V1-V6, CAL
6 2-channel ECG waveform amplification; processing ECG signals of any two leads
The ECG circuit processes the ECG signals. It consists of the following parts:
1. Input circuit: The input circuit protects the ECG input level, and filters the ECG signals and external interference. The ECG electrode is connected to the input circuit through the cable.
2. Buffer amplifying circuit: This circuit ensures extremely high input impedance and low output resistance for ECG.
3. Right-foot drive circuit: The output midpoint of the buffer amplifying circuit is fed to the RL end of the 5-lead after the inverse amplification, so as to ensure that the human body is in the equipotential state, decrease the interference, and increase the common-mode rejection ratio of the circuit.
4. Lead-off detection: The lead-off causes changes in the output level of the buffer amplifying circuit. Therefore, the lead-off can be detected with a comparator, and the state of lead-off can be converted TTL level for the Micro Controller Unit (MCU) to detect it.
5. Lead circuit: Under the control of MCU, the lead electrodes should be connected to the main amplification circuit.
6. Main amplification circuit: The measurement amplifier is composed of 3 standard operation amplifiers.
7. Subsequent processing circuit: This circuit couples the ECG signals, remotely controls the gains, filters the waves, shifts the level, amplifies the signal to the specified amplitude, and sends the signal to the A/D converter.
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RESP
The DPM4 patient monitor measures the RESP based on the impedance principle. While a man is breathing, the action of the breast leads to impedance changes between RL and LL. Change the high-frequency signal passing the RL and LL to amplitude-modulation high-frequency signal
(AM high-frequency signal), which is converted to the electric signal after being detected and amplified and then sent to the A/D converter. The RESP module consists of the RESP circuit board and coupling transformer. The circuit has several functions: vibration, coupling, wave-detection, primary amplification and high-gain amplification.
2.4.3 NIBP
The NIBP is measured based on the pulse vibration principle. Inflate the cuff which is on the forearm till the cuff pressure blocks the arterial blood, and then deflate the cuff according to a specified algorithm. While the cuff pressure is decreasing, the arterial blood has pulses, which are sensed by the pressure transducer in the cuff. Consequently, the pressure transducer, connected with the windpipe of the cuff, generates a pulsation signal. Then, the pulsation signal is filtered by a high-pass filter (about 1Hz), amplified, converted to the digital signal by the A/D converter, and finally processed by the MCU. After that, the systolic pressure, diastolic pressure and mean pressure can be obtained. For neonates, pediatric and adults, it is necessary to select the cuffs of a proper size to avoid possible measurement errors. In the NIBP measurement, there is a protection circuit used to protect patient from over-high pressure.
The NIBP measurement modes include:
1. Adult/pediatric/neonate mode: To be selected according to the build, weight and age of the patient;
2. Manual/Auto/Continuous mode: The manual measurement is also called single measurement; in this mode, only one measurement is done after being started. In the auto measurement mode, the measurement can be done once within the selected period, with the interval being 1, 2, 3, 4, 5, 10, 15, 30, 60, 90, 120, 180, 240 or 480 minutes. In the continuous measurement mode, quick continuous measurement will be done within 5 minutes after being started; it detects the changes in blood pressure effectively.
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2.4.4 SpO2
The SpO2 value is obtained through the pulse waves of the finger tips based on specific algorithm and clinical data. The SpO2 probe is the measurement transducer. It has two inbuilt
LEDs and an inbuilt light receiver. The two LEDs include one red-light diode and one infrared diode, which emit light in turns. When the capillaries in the finger tip are iteratively congested with blood pumped by the heart, the light emitted by the LEDs, after absorbed by the capillaries and tissue, casts on the light receiver, which can sense, in the form of electric signal, the light strength changing with the pulsated blood. The DC/AC ratio of the two photoelectric signals corresponds to the content of the oxygen in the blood. Therefore, the correct pulse oxygen saturation can be obtained with specific algorithm. Moreover, the pulse rate can be obtained according to the pulse waveform.
The circuit of the SpO2 module is involved in four parts: SpO2 probe, signal processing unit,
LED-driven sequencing control part and the MCU.
2.4.5 TEMP
Temperature measurement principle:
1. The transducer converts the body temperature to the electric signal;
2. The amplifier amplifies the electric signal;
3. The CPU processes the data.
The circuit is a proportional amplifier consisting of operation amplifiers. When the temperature reaches the heat-sensitive probe, the heat-sensitive probe generates the voltage signal, which is sent to the A/D converter after being amplified. The probe detecting circuit is a voltage comparator consisting of operation amplifiers. When the probe is disconnected, the voltage input is lower than the comparing voltage, so the voltage comparator outputs the low level; when the probe is connected, the voltage input is higher than the comparing voltage, so the voltage comparator outputs the high level.
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2.4.6 IBP
The IBP module can monitor the arterial pressure, central venous pressure and pulmonary arterial pressure.
Measurement principle: Introduce a catheter, of which the external end is connected to the pressure transducer, into the blood vessel under test, inject the physiological saline. Since the liquid can be transferred by pressure, the pressure inside the blood pressure is transferred by liquid to the pressure transducer, and the dynamic waveform of the pressure inside the blood pressure is obtained in real time. Thus, the arterial pressure, central venous pressure and pulmonary arterial pressure are obtained based on specific algorithm.
2.4.7 CO2
The CO2 module works based on the infrared spectrum absorption principle. The sidestream
CO2 module is composed of the circuit board, inbuilt sidestream infrared light transducer, deflation pump and control. When used, this module requires the external water trap, drying pipe and sampling tube. In the sidestream mode, the deflation rate can be set to 100ml/min,
150ml/min or 200ml/min according to the patient situation. When the CO2 measurement is not being conducted, the sidestream deflation pump and the infrared source are expected to be shut down, thus to extend the service life and reduce the power consumption of the module.
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Key features
- Comprehensive monitoring of vital signs, including ECG, SpO2, NIBP, RESP, and temperature
- User-friendly interface with large, high-resolution display and intuitive menu navigation
- Advanced alarm management capabilities
- Networking options for remote monitoring
- Compact and portable design
- Optional modules for additional monitoring capabilities
- Long battery life
- Cost-effective solution for patient monitoring