The basic principle of multi-parameter monitor
2022-10-13 10:09:43
| The functions of the monitors are different, and their specific working principles are different, but generally the sensors sense various physiological changes, and then the amplifier will strengthen the information and then convert it into electrical information. At this time, the data analysis software will calculate the data. Analysis and editing, finally display the various function modules in the display, or record as needed, print down, when the monitored data exceeds the set indicators, it will activate the alarm system and send a signal to the attention of the medical staff.  Hardware composition  Measurement server (including physiological sensors (ie sensors), signal amplifiers, data simulation processing, data analysis processing, data output interfaces, etc.)  Data analysis and recording and alarm system  1 Basic structure of the monitor  1.1 Physical structure of the monitor  The monitor is made up of physical modules of various sensors and a built-in computer system. Various physiological signals are converted into electrical signals by sensors, and are sent to a computer for pre-amplification processing to display, store and manage the results. According to its physical structure, it can be roughly divided into three types.  1.1.1 Single-parameter monitors: such as blood pressure monitors, blood oxygen saturation monitors, ECG monitors, etc.  1.1.2 Multi-function, multi-parameter integrated monitor: It can simultaneously monitor parameters such as ECG, respiration, body temperature, blood pressure and blood oxygen.  1.1.3 Plug-in combination monitor: It consists of a separate and detachable physiological parameter module and a monitor host. Users can purchase different plug-in modules according to their own requirements to form a monitor suitable for their special requirements. .  1.2 Display technology in the monitor  Including: digital tube, mainly used for single parameter monitoring; CRT display; LCD display; EL display; true color TFT display; currently the main function of the multi-function monitor is TFT plasma display, the display mode is generally VGA mode, the resolution is 640 × 480 pixels.  2 multi-parameter monitor  2.1 ECG (ECG) monitoring  The electrochemical activity of excitable cells in the myocardium causes electrical stimulation of the myocardium, which in turn causes mechanical contraction of the heart. The closing action current generated by this exciting process of the heart flows in the body volume conductor and propagates to various parts of the body, thereby causing a potential difference change in different surface parts of the human body. The electrocardiogram (ECG) records the potential difference of the body surface in real time.  The concept of a lead refers to a waveform diagram in which a potential difference between two or more body parts of a human body changes with a cardiac cycle.  At present, the standard electrocardiograph used in clinical practice measures the ECG, the limb electrodes are placed on the wrist and the ankle, and the electrode in the ECG monitoring is equivalently placed in the chest and abdomen region of the patient. Although the placement positions are different, they are equivalent and their definitions are the same. Therefore, the ECG leads in the monitor correspond to the leads in the electrocardiograph, which have the same polarity and waveform.  The monitor can generally monitor 3 or 6 leads, can display the waveform of one or two leads at the same time, and can directly display the heart rate. The powerful monitor can monitor the 12-lead ECG; the waveform can be further analyzed. , extract ST segment waveforms and arrhythmia events.  The monitor ECG does not completely replace the standard ECG machine, because the current ECG waveform of multi-parameter monitoring generally cannot provide a more detailed waveform of the ECG waveform, and the microstructural diagnosis capability is not very strong, mainly because the purpose of the two is different. The purpose of monitoring is to monitor the patient's heart rate for a long time and in real time, and the result of the electrocardiograph is a short-term result under certain conditions. The measurement conditions of the former are very bad, while the latter have better conditions when measuring. Therefore, the passband of the amplifier in the measurement circuit of the two instruments is different. The electrocardiograph requires at least 0.05 Hz to 80 Hz, and the monitor is generally at 1 Hz to 25 Hz.  The ECG signal is a very weak electrical signal that is easily subject to outside interference. The manufacturer of the monitor fully considered and adopted some anti-interference measures during product design, but some interference is still insurmountable.  2.1.1 Myoelectric interference. When the muscles affixed under the core electrode are contracted, the myoelectric signal produces interference with the ECG signal because such interference has the same spectral bandwidth as the ECG signal.  2.1.2 Motion interference. The patient's activity will cause changes in the ECG signal, depending on the magnitude and frequency of the activity, such as within the bandwidth of the ECG amplifier, the instrument is difficult to overcome.  2.1.3 Electrode contact interference. Any interference from the human body to the path of the ECG amplifier will cause strong noise, which may obscure the ECG waveform, mainly due to poor contact between the electrode and the patient's skin. The instrument should be well grounded to protect against patient and operator safety.  2.1.4 Interference from high frequency electric knives. When a high-frequency electrosurgical knife or electrocoagulation is used in the operation, the electrical signal generated by the electric energy applied to the patient's body is much larger than the electrocardiographic signal, and the frequency component is very rich, so that the electrocardiographic amplifier reaches saturation and cannot observe normal. ECG waveform. In the anti-high-frequency electric knife interference part of the monitor standard, it is required that the monitor returns to the normal state within 5 s after the high-frequency electric knife is removed.  2.2 Non-invasive blood pressure (NIBP) monitoring  The monitor is usually measured manually and automatically when measuring blood pressure, and can be set as needed. Blood pressure refers to the pressure of blood on the blood vessel wall. During each contraction and relaxation of the heart, the blood flow to the blood vessel also changes, and the pressure in the arteries and veins is different. The blood pressure in different parts is different. . Clinically, the human blood pressure is characterized by the pressure values ​​of the systolic and diastolic phases in the arteries of the upper arm and the heart at the same height, which are called systolic blood pressure (high pressure) and diastolic blood pressure (low pressure). The arterial blood pressure of the human body is a physiological parameter that is easy to change, and has a great relationship with the mental state, emotional state, posture and posture of the person.  The vibration method is a method of measuring blood pressure. Its principle is to fully compress the arterial blood vessels and block the arterial blood flow when the cuff is inflated to a certain pressure, and then as the cuff pressure decreases, the arterial blood vessels will appear: complete blocking - involute - full release . Throughout the procedure, the pulsation of the arterial wall will create a gas oscillation in the gas within the cuff, which has a definite correspondence with arterial systolic pressure, diastolic blood pressure and mean pressure. Therefore, the systolic, mean and diastolic pressures of the site to be tested can be obtained by measuring, recording and analyzing the pressure vibration waves in the cuff during deflation.  The vibration method eliminates the human factor, and the measurement is more objective and reversible. If the measurement conditions are guaranteed, there is also a high consistency.  The premise of the oscillation method is to find regular arterial pressure pulsations. If the conditions of the measurement make this detection method difficult, the measured value may become unreliable, and the measurement time may increase or may not be measured. For example, in the measurement, the instrument will not be able to detect regular arterial fluctuations due to the patient's movement or external disturbances affecting the pressure change in the cuff, which may result in measurement failure.  Nowadays, some monitors have adopted anti-interference measures. For example, the ladder deflation method is used to automatically judge the interference and normal arterial pulsation waves, so that it has anti-interference ability to a certain extent, but if the interference is too serious or lasts. Too long, this anti-jamming measure can't do anything.  Therefore, in the non-invasive blood pressure monitoring process, should try to ensure good conditions, while paying attention to the choice of cuff size, the location of the placement and the tightness of the bundle.  2.3 Arterial Oxygen Saturation (Sp02) Monitoring  Oxygen is the first living condition for human survival. The effective oxygen molecules in the blood are transported to tissues throughout the body by binding to hemoglobin (Hb) to form oxyhemoglobin (Hb02).  The value used to characterize the proportion of oxyhemoglobin in the blood is called oxygen saturation. The definition is: HbO2/(HbO2+Hb).  The oxygen saturation probe is similar to the one shown on the right, and the probe is clamped to the finger when in use. The measurement is based on the difference in light absorption characteristics of hemoglobin and oxyhemoglobin in the blood, and the red light (660 nm) and the infrared light (940 nm) of the two different wavelengths are respectively transmitted through the tissue and then converted into an electrical signal by the photoreceiver. Two light-emitting diodes (LEDs) placed side by side are fixed on the upper wall, emitting red light with a wavelength of 660 nm and infrared light of 940 nm. The lower wall has a photodetector that converts the red and infrared light transmitted through the finger artery into an electrical signal. The weaker the photoelectric signal detected, the tissue, bone, where the light signal penetrates the probe. The more you absorb it with blood. The absorption coefficients of the two kinds of light, such as skin, muscle, fat, venous blood, pigments and bones, are constant, so they only affect the magnitude of the DC component in the photoelectric signal. However, the concentration of HbO2 and Hb in the blood changes periodically with the pulse action of the blood, so their absorption of light also pulsates, thereby eliciting the signal intensity output from the photodetector to pulsate with the concentration ratio of HbO2 and Hb in the blood. Change the ground to get the SPO2 value.  The pulsation law of the photoelectric signal is consistent with the beat of the heart, so the repetition period of the signal is detected, and the pulse rate can also be determined.  The method can measure blood oxygen saturation in arterial blood, and the necessary condition for measurement is to have pulsating arterial blood flow, clinically adopting sensors with arterial blood flow and thin tissue thickness, such as fingers, toes, earlobe, etc. Part.  The reason for the limited measurement in the measurement: if the measured part is strenuously moving, it will affect the extraction of the regular pulsation signal, and the measurement cannot be performed. When the patient's peripheral circulation is severely poor, it will lead to the arterial blood flow in the measured part. If it is reduced, the measurement will be inaccurate or impossible to measure; in patients with severe blood loss, when the body temperature of the measurement site is low, external strong light will strike the probe, which may cause the photoelectric receiver to deviate from the normal range, resulting in inaccurate measurement. Avoid illuminating the probe with strong light.  2.4 Respiratory (Resp) monitoring  Most of the respiratory measurements in multi-parameter monitors use the thoracic impedance method. The thoracic movement of a person during breathing causes a change in the body resistance of the human body, and the amount of change is about 0.1 Ω to 3 Ω, which is called respiratory impedance. The monitor generally uses a two-electrode lead of the ECG lead to inject a safe current of 0.5 mA to 5 mA into the human body with a constant current of a carrier frequency of 10 kHz to 100 kHz, thereby picking up an electrical signal of a change in respiratory impedance on the same electrode. The change in respiratory impedance describes the dynamic waveform of the breath and extracts the respiratory frequency parameters. The movement of the thorax and the non-respiratory movement of the body cause changes in the body's electrical resistance. When the frequency of change is the same as the frequency band of the amplifier of the breathing channel, it is difficult for the monitor to determine which is the normal respiratory signal and which is the interference signal. When the patient has severe physical activity, the measurement of respiratory rate will be inaccurate.  2.5 body temperature (Temp) monitoring  The measurement of the body temperature of the multi-parameter monitor generally uses a thermistor with a negative temperature coefficient as a temperature sensor, which is obtained according to the characteristic that the resistance value of the thermistor changes with temperature. The monitor generally provides a single body temperature, and the high-end monitor provides dual-channel temperature. The body temperature probe has two kinds of body surface probes and intracavity probes.  When the body temperature is measured for the patient, there is a thermal balance between the measured site and the probe. At the beginning of the installation, since the sensor has not fully reached the thermal equilibrium with the human body temperature, the temperature displayed at this time is not accurate, and it is necessary to reach the thermal equilibrium after a period of time (3 min to 5 min) to truly reflect the actual temperature.  When performing body surface temperature measurement, be careful to keep the sensor in good contact with the patient's body surface. If there is no sticking or patient movement, there is a gap between the sensor and the skin, which may result in a low measurement value.  2.6 End-tidal carbon dioxide (PetC02) monitoring  End-tidal carbon dioxide is an important monitoring indicator for anesthetized patients and patients with respiratory and metabolic diseases. The main measurement method of C02 is infrared absorption method, which is mainly based on the absorption procedure of specific infrared light according to different concentrations of CO 2 . There are two main types of C02 monitoring: main-stream and side-stream. The mainstream type is to directly place the gas probe in the patient's respiratory airway catheter, directly convert the concentration of CO2 in the breathing gas, and then send the electrical signal to the monitor for analysis and processing to obtain the PetC02 parameter. The bypass flow optical sensor is placed in the monitoring instrument, and the gas sampling tube is used to extract the patient's breathing gas into the monitor for concentration analysis.  DC C02 monitoring, should pay attention to the problem: Because the C02 sensor is an optical device, care should be taken to avoid serious contamination of the sensor by patient secretions.  The bypass C02 monitor generally has a gas-water separator that removes moisture from the breathing gas. Be sure to check that the gas water separator is working effectively, otherwise the moisture in the gas will affect the accuracy of the measurement.  |
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