1, input section
2, the amplification part
3. Control circuit
4. Display part
5. Recording part
6. Power supply part
7. Classification
Important parameter
1, input resistance: the input resistance of the preamplifier. The larger the input resistance, the smaller the waveform distortion caused by different contact resistances of electrodes, and the higher the * * * mode rejection ratio. Generally, it is required to be greater than 2mΩ, and internationally it is greater than 50MΩ.
2.* * Mode rejection ratio: ECG machines generally use differential amplification circuits, which can suppress in-phase (also known as * * mode signals, such as interference signals generated by surrounding electromagnetic fields) and amplify out-of-phase signals (also known as differential mode signals, that is, ECG signals to be collected). * * * Mode rejection ratio (CMRR) refers to the ratio of the differential mode signal (ECG signal) amplification factor Ad to the * * * mode signal (interference and noise) amplification factor Ac of the electrocardiograph, indicating the anti-interference ability. The requirement is greater than 80dB, which is greater than 100dB internationally.
3. Reverse polarization voltage: Due to polarization, a polarization voltage will be generated between the skin and the surface electrode. This is mainly due to the voltage holding phenomenon formed after the cardiac current flows, and the polarization voltage has a great influence on ECG measurement, which will produce baseline drift and other phenomena. The highest polarization voltage can reach tens or even hundreds of millivolts. If the polarization voltage is not handled well, the interference will be serious.
Although the electrodes used in ECG machine have adopted special materials, due to the changes of temperature and the influence of electric field and magnetic field, the electrodes will still produce polarization voltage, which is generally 200 ~ 300 mV, which requires ECG machine to have an amplifier and recording device that can withstand polarization voltage. More than 300mV is required, and more than 500mV is required internationally.
4. Sensitivity: the amplitude of recorded waveform when the standard voltage 1mV is input. It is usually expressed in mm/mV, which reflects the magnification of the whole amplifier. The standard sensitivity of electrocardiograph is 10mm/mV. The purpose of specifying the standard sensitivity is to facilitate the comparison of various electrocardiograms.
5. Internal noise: refers to the noise generated by the electronic thermal movement when the internal components of the ECG machine work, rather than the noise generated by improper use of external interference. This kind of noise makes the ECG machine still have tiny chaotic waves without input signals. If this noise is too large, it will not only affect the beauty of the graph, but also affect the normality of ECG waveform. Therefore, the noise is required to be as small as possible, and the noise waveform cannot be seen in the tracing curve. Noise can be calculated by the input amplitude, which is generally lower than the effect of adding a few microvolts to dozens of microvolts at the input end. The international regulation is10 ≤ μ v.
6. Time constant: When DC is input, the signal amplitude recorded by ECG will gradually decrease with the increase of time, and the time required for the output amplitude to decrease from 100% to about 37%. Generally, it is required to be greater than 3.2s If the amplitude is too small, it will drop too fast, and even the input square wave signal will become a sharp wave signal, which cannot reflect the real situation of ECG waveform.
7. Frequency response: The ECG waveform of human body is not single frequency, but can be decomposed into sine wave components with different frequencies and proportions, which means that the ECG signal is rich in higher harmonics. If the electrocardiograph has the same gain for signals with different frequencies, the recorded waveform will not be distorted. However, the amplifier's amplification ability to different frequency signals is not necessarily the same. When the electrocardiograph inputs signals with the same amplitude and different frequencies, the relationship between the amplitude and frequency of its output signal is called frequency response characteristic. The frequency response characteristics of electrocardiograph mainly depend on the frequency response characteristics of amplifier and recorder. The wider the frequency response, the better. The general ECG amplifier can easily meet the requirements, and the recorder is the main factor to determine the frequency response. The general requirement is 0.05~ 150Hz(-3dB).
8. Insulation: In order to ensure the safety of medical staff and patients, the electrocardiograph should have good insulation. Insulation is usually expressed by the resistance of power supply to bushing, and sometimes by the leakage current of bushing. Generally, it is required that the insulation resistance of the power supply to the shell should not be less than 20MΩ, or the leakage current should be less than 100μA a ... Therefore, ECG usually adopts "floating technology".
9. Safety: ECG machine is an electronic device directly connected with human body, so we must pay great attention to its safety to human body. In terms of safety, electrocardiographs can be divided into three types: B type, BF type and CF type (see GB 10793-89 for details). According to the International Electrotechnical Commission (IEC), the direct connection between medical electrical equipment and patients is called application part. In order to further ensure the safety of patients, isolation measures, photoelectric coupling and electromagnetic wave coupling are often added to the application part of medical electrical equipment according to the isolation degree of the application part.
According to the isolation degree of the application part, medical electrical equipment is divided into B type, BF type and CF type.
Type b: the application part is not isolated.
Type BF: Partial floating isolation can be used in vitro and in vivo, but not directly in the heart.
CF type: floating isolation, strong electric shock protection, can be directly used in the heart.
The classification of heart by electrocardiograph is the power device of human blood circulation. It is precisely because the heart automatically and continuously carries out rhythmic contraction and relaxation activities that blood keeps flowing in the closed circulatory system and life can be maintained. Before and after the heart beats, the myocardium is excited. In the process of excitement, a weak bioelectric current will be generated. In this way, every cardiac cycle of the heart is accompanied by bioelectricity changes. This bioelectric change can be transmitted to all parts of the body surface. Because the tissues in different parts of the human body are different and the distance from the heart is different, the potentials of ECG signals in different parts of the human body are also different. For a normal heart, the direction, frequency and intensity of this bioelectricity change are regular. If the electrical signals of different parts of the body surface are detected by electrodes, then amplified by an amplifier and recorded by a recorder, the electrocardiogram can be obtained. Doctors can diagnose heart diseases according to the shape, amplitude and relative time relationship of recorded ECG waveforms, and then compare them with normal ECG. Such as arrhythmia, myocardial infarction, premature beat, hypertension, cardiac ectopic beat, etc.
Electrocardiograph is an instrument used to record physiological electrical signals produced by heart activity. Because of its mature and reliable diagnostic technology, simple operation, moderate price and no harm to patients, ECG has become one of the most popular medical electronic instruments in hospitals at all levels.
A, the classification of electrocardiogram machine
Electrocardiograph has different classification methods. For example:
(1) Classification by machine function
According to the function of the machine, ECG machine can be divided into graphic ordinary ECG machine (analog ECG machine) and graphic analysis and diagnosis ECG machine (digital intelligent ECG machine).
(2) According to the classification of recorders
Recorder is the tracer element of electrocardiograph. For analog electrocardiograph, most of the recorders used in the early days were moving coil recorders with disc spring as the zero-return torque, and most of them were position feedback recorders after 1990s. For a digital electrocardiograph, the recorder is a thermal printer or a dot matrix printer.
1. Moving coil recorder: The structural principle of the moving coil recorder is a fixed magnetic circuit composed of magnetic steel and rotatable coils. The output signal of the power amplifier of the electrocardiograph is applied to the coil of the recorder, and the recording pen is fixed on the coil. When ECG signal is output, the power amplifier outputs current to the coil, and the coil rotates. When the deflection angle of the coil is the same as the zeroing torque of the belleville spring, the deflection is stopped. In this way, the recording pen driven by the coil can draw the ECG waveform on the recording paper.
2. Position feedback recorder: The position feedback recorder is a recorder without mechanical return spring, and the special electronic circuit can play the role of return spring. When the machine is powered off, the stylus of the position feedback recorder can move at will.
3. Dot-matrix thermal recorder: The thermal recorder uses the heating point of the semiconductor sintered on the ceramic substrate to burn the graphics and characters on the thermal paper, and the thermal paper will develop color when heated.
(3) Classification by power supply mode
According to the power supply mode, it can be divided into DC, AC and AC /DC electrocardiographs. Among them, AC and DC are the most commonly used. The type of DC power supply is mainly powered by rechargeable batteries. The AC power supply type adopts AC -DC conversion circuit, which first converts AC into DC, and then supplies it to ECG after being stabilized by high stability voltage stabilizing circuit.
(4) Display the derivative of the recordable signal.
According to the first derivative of recordable signal, ECG can be divided into single lead and multi-lead (such as three lead, six lead and twelve lead). There is only one channel for ECG signal amplification of single-lead ECG machine, and the ECG waveform of each lead should be recorded one by one. That is, it cannot reflect the changes of ECG at the same time. Multichannel ECG has multiple amplification channels. For example, a six-channel ECG has six amplifiers, which can reflect the simultaneous changes of ECG signals of six leads at a certain time.
(v) Instructions for use 1. Turn the power switch to "On".
2. Turn the power switch to "AC", "line", "TBST", "PAPER SPEED (25mm/s)", "sensitivity (L)" and "STOP", and the crystal lamp will glow.
3. Adjusting the baseline control button should change the position of the tracing pen and make it stop near the center of the recording paper.
4. Press the "Check" key, the "Stop" light goes out and the "Check" light comes on.
5. Press the calibration key "lmV" to make the stylus swing correspondingly with the press of the calibration key.
6. Press "Start". At this time, the "check" light is off, the "start" light is on, and the recording paper moves at a speed of 25mm/s..
7. Continue to press the calibration key, and you can see a clear calibration square wave on the walking record paper, and its amplitude should be10 mm. ..
8. Press the "Lead Selector" key to switch from "Test" to "I" and "II".
9. After clearly recording on ECG paper, you can continue to press the "Lead Selector" key to switch it from "I" lead to "II" lead, and so on, and repeat the above operations to complete the ECG recording of 12 lead.
10. After the instrument is used, cut off the power supply and do a good job of cleaning. And make the instrument use registration.