Electrocardiogram machine can be cardiac activity of myocardial excitation generated by bioelectric signals (ECG signals) automatically recorded for clinical diagnosis and scientific research of the commonly used medical electronic instruments. Domestic generally according to the recorder output channel is divided into: single channel, three channel, six channel and twelve channel electrocardiograph and so on.
Components
1, input section
2, amplifier section
3, control circuit
4, display section
5, recording section
6, power supply section
7, classification
Important Parameters
1, input resistance: the input resistance of the pre-amplifier. The input resistance of the amplifier. The larger the input resistance, the smaller the waveform distortion caused by different electrode contact resistance, and the higher the ****mode rejection ratio. The general requirement is greater than 2MΩ, the international greater than 50MΩ.
2, *** mode rejection ratio: ECG machine is generally used differential amplifier circuit, this circuit for the same phase (also known as *** mode signals, such as the surrounding electromagnetic field generated by the interference signal) has a suppression effect on the heterodyne signals (also known as the differential mode signals, need to be captured by the ECG is the differential mode signals) has an amplification effect. *** mode rejection ratio (CMRR), refers to the ECG machine's differential mode signal (ECG signal) amplification Ad and *** mode signal (interference and noise) amplification Ac ratio, indicating the size of the anti-interference ability. Requirements are greater than 80dB, international greater than 100dB.
3, anti-polarization voltage: between the skin and surface electrodes will be polarized due to polarization and polarization voltage. This is mainly due to the formation of voltage retention phenomenon after the flow of cardiac current, polarization voltage has a great impact on the ECG measurement, will produce baseline drift and other phenomena. Polarization voltage can reach tens of millivolts or even hundreds of millivolts at the highest. Poorly handled polarization voltage, the resulting interference will be very serious.
Although the electrodes used in electrocardiographs have been made of special materials, due to temperature changes and the influence of electric and magnetic fields, the electrodes still produce polarization voltage, generally 200-300mV, which requires the electrocardiographs to have an amplifier and recording device that is resistant to polarization voltage. Requirements greater than 300mV, international greater than 500mV.
4, sensitivity: is the input 1mV standard voltage, the amplitude of the recorded waveform. Usually expressed in mm/mV, which reflects the size of the amplifier amplification. ECG standard sensitivity of 10mm/mV. the purpose of the standard sensitivity is to facilitate the comparison of various ECG.
5, internal noise: refers to the internal components of the electrocardiogram machine work, due to the electronic thermal movement of the noise, rather than due to improper use of the noise formed by external interference, this noise so that the electrocardiogram machine does not have the input signal there is still a small noise wave output, this noise if too large, not only affect the graphic aesthetics, but also affects the normality of the heart wave, so the smaller the better, the smaller the better, in the tracing curve should not see the noise, the noise is the same, and the noise is the same. The noise waveform should not be visible in the tracing curve. The size of the noise can be calculated by folding to the input side of the role of the size of the general requirement is lower than the input side to join a few microvolts to tens of microvolts below the role of the signal. International regulations 10 ≤ μV.
6, time constant: in the DC input, the ECG machine tracing the signal amplitude will gradually decrease with the increase of time, the output amplitude from 100% down to about 37% of the time required. The general requirement is greater than 3.2s, if it is too small, the amplitude decreases too quickly, or even make the input square wave signal into a sharp signal, which does not reflect the true situation of the ECG waveform.
7, frequency response: human ECG waveform is not a single frequency, but can be decomposed into different frequencies, different proportions of the sine wave components, that is to say, the ECG signal contains a wealth of high harmonics. If the ECG machine has the same gain for signals of different frequencies, the traced waveform will not be distorted. However, the amplifier's ability to amplify signals of different frequencies is not necessarily the same. When an ECG machine is fed with signals of the same amplitude and different frequencies, the relationship between the amplitude of the output signal and the change in frequency is called the frequency response characteristic. The frequency response characteristics of an ECG machine depend mainly on the frequency response characteristics of the amplifier and recorder. The wider the frequency response, the better, the general ECG machine amplifier is easier to meet the requirements, while the recorder is the main factor in determining the frequency response. The general requirement is 0.05~150Hz (-3dB).
8, insulation: in order to ensure the safety of medical personnel and patients, ECG machine should have good insulation. Insulation is often used to indicate the resistance of the power supply to the chassis, and sometimes with the chassis of the leakage current. The general requirement of the power supply to the chassis insulation resistance of not less than 20MΩ, or leakage current should be less than 100μA. For this reason, electrocardiographs are usually used "floating ground technology".
9, safety: ECG machine is directly connected to the human body electronic equipment, must pay close attention to its safety on the human body. From the safety point of view, the ECG machine can be divided into three types: B-type, BF-type and CF-type (see the Chinese people's **** and the national standard GB10793-89 ECG machine and the use of safety requirements). According to the International Electrotechnical Commission (IEC) General Regulations: medical electrical equipment and patients directly connected to the part called "application part". In order to further ensure the safety of patients, the application of medical electrical equipment is often added to the part of the isolation measures, optical-electrical coupling, electromagnetic wave coupling and so on. According to the application part of the degree of isolation, the application of medical electrical equipment is often added to the part of the isolation measures, optical-electrical coupling, electromagnetic wave coupling.
According to the degree of isolation of the application part, medical electrical equipment is divided into B, BF, and CF type.
Type B: There is no isolation of the application part.
Type BF: the application part of the floating ground isolation, can be used in vitro and in vivo, but can not be used directly in the heart.
Type CF: Floating ground isolation, high protection against electric shock, can be used directly in the heart.
Categorization of electrocardiographs The heart is the powerhouse of the body's blood circulation. It is the heart's automatic and continuous rhythmic systolic and diastolic activities that keep the blood flowing in the closed circulatory system and enable life to be sustained. Before and after the heart beats, myocardial excitation occurs. During agitation, a weak bioelectric current is generated. In this way, each cardiac cycle of the heart is accompanied by bioelectrical changes. This bioelectric change can be transmitted to various parts of the body surface. Because the various parts of the body are organized differently and at different distances from the heart, the potentials exhibited by the ECG signals vary in different parts of the body. For a normal heart, the direction, frequency, and intensity of such bioelectric changes are regular. If the electrical signals from different parts of the body surface are detected by electrodes, amplified by an amplifier, and traced down by a recorder, an ECG can be obtained. The doctor can diagnose heart diseases based on the shape of the recorded ECG waveforms, their amplitude and the relative time relationship between the waves, and then compare them with a normal ECG. These include cardiac arrhythmias, myocardial infarction, preterm systole, hypertension, and ectopic beats of the heart.
An electrocardiograph is an instrument used to record the physiologic electrical signals generated by the heart's activity. Because of the ECG machine diagnostic technology is mature, reliable, easy to operate, affordable price, no harm to the patient and other advantages, has become one of the most popular hospitals at all levels of medical electronic instruments.
I. Classification of electrocardiograph
There are different ways to classify electrocardiographs. Such as:
(A) according to the machine function classification
Electrocardiogram machine according to the function of the machine can be divided into graphic tracing ordinary electrocardiogram (analog electrocardiogram) and graphic tracing and analysis of diagnostic functions of electrocardiogram (digital intelligent electrocardiogram).
(2) Classification according to the recorder
The recorder is the tracing element of the ECG machine. For analog electrocardiographs, the early recorders used are mostly moving coil recorders with disc springs as the zero return torque, and position feedback recorders are used after the 1990s. For digital electrocardiographs, the recorders are thermal or dot-matrix printers.
1, moving-coil recorders: moving-coil recorders are structured on the principle of a fixed magnetic circuit composed of magnets and rotatable coils. The output signal of the power amplifier of the ECG machine is added to the coil of the recorder, and there is a recording pen fixed on the coil. When there is an ECG signal 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 return-to-zero torque of the disk spring, the upper deflection is stopped. In this way, the recording pen driven by the coil traces the ECG waveform on the recording paper.
2, position feedback recorder: position feedback recorder is a kind of recorders without mechanical return to zero spring, special electronic circuit can play the role of return to zero spring. When the machine is powered off, the recording pen of the position feedback recorder can be dialed at will.
3, dot-matrix thermal recorder: thermal recorder is the use of heat sintered in the ceramic substrate semiconductor heating point, in the heat color thermal paper stamped out graphics and characters.
(C) according to the power supply mode classification
By the power supply mode, can be divided into DC, AC and AC and DC dual-use electrocardiograph. Among them, AC and DC types are mostly used. The DC type is powered by rechargeable batteries. The AC-powered type uses an AC-DC conversion circuit to change AC to DC, which is then stabilized by a highly stable voltage regulator circuit and supplied to the ECG machine.
(4) According to the number of signal leads that can be recorded at one time
According to the number of signal leads that can be recorded at one time, electrocardiogram is divided into single-conductance and multi-conductance (such as three-conductance, six-conductance, twelve-conductance). Single-conductor electrocardiographs have only one amplification channel for the ECG signals, and the ECG waveforms of each lead have to be traced one by one. That is to say, it cannot reflect the changes of ECG of each lead at the same moment. Multi-conductor electrocardiograph amplification channel has more than one way, such as six-conductor electrocardiograph has six amplifiers, can reflect a moment of six leads at the same time changes in the electrocardiographic signal.