The non-invasive cardiac output is through the cardiac impedance technique, and the human tissue can be equivalent to a conductor, which will produce impedance when the human body passes through high-frequen cy alternating current, so the chest of the human body is equivalent to a cylindrical conductor, in which the electrical conductivity of the blood is better. when the heart is in systole or diastole, the blood flow, velocity and volume in the aorta will change accordingly. At this time, the electrical impedance of the blood also changes with the change of blood volume, and the impedance cardiogram can be drawn according to the change of imped ance.
The MICG module of the system chooses the four-electrode method as the method to detect the cardiac imped ance signal based on the consideration of stability and portability. as shown in the figure, An and D electrodes are used as the excitation signal source for cardiac impedance signal acquisition, that is, the input high frequency current is loaded into the chest of the human body through this electrode, B and C are used as measuring electrodes, and the cardiac impedance signal is detected through these two electrodes, where the D electrode is placed at the xiphoid process. And the distance between B and C is regarded as chest distance L, which can be used in the later calculation of other hemodynamic parameters. The distance between A, B and C, D is generally about 3cm.
| Parameter identification | Parameter definition | Formula | Normal value range |
| CO | Cardiac output: the total amount
of blood pumped by the left
ventricle per minute. | CO SV HR | 4.0-8.0 L/Min |
| SV | Stroke output: the total amount
of blood pumped by the left
ventricle per heartbeat. | 60-130ML | |
| CI | Cardiac output index: cardiac
output after standardized
treatment of body surface area. | CI=CO/BSA | 2.5-4.5 liters / min / m 2 body
surface area |
| SI | Stroke output index: stroke
volume after body surface area
standardization | SI=SV/BSA | 35-65ML/m2body surface area |
| HR | Heart rate: number of heartbeats
per minute | HR=60/RR | 60–100 hops per minute |
| PEP | Pre-ejection period: the time taken from left ventricular depolarization to aortic opening | Depends on the heart rate
preload and the contractility
of the heart | |
| LVET | Left ventricular ejection time: the interval between aortic valve opening and aortic valve closure (exercise systole) | Depends on the preload of
the heart rate and the
contractility of the heart | |
| TFC | Chest fluid content: intrapleural
electrical conductivity obtained
mainly by detecting intravascular,
intraalveolar and intrapleural
interstitial fluid. | TFC=1000/Z0 | Male：30—50 / 1000 EU
Female：21—37 / 1000 EU |
| STR | Systolic time ratio: the ratio of
myocardial electrical excitation to
mechanical contraction | STR=PEP/LVET | |
| EF | Ejection fraction | EF=0.84-064*STR | |
| SQI | Signal quality index | 0-100 SQI range
101-201 SQI range
in Artefact mode
254 No signal |
ICG waveform mainly includes ECG waveform, cardi ac impedance differential waveform and cardiac impedance waveform. There are 22 parameters, such as cardiac output (CO), stroke volume (SV), pre-ejec tion period (PEP), left ventricular ejection time (LVET), systolic time ratio (STR), cardiac index (CI), body surface area (BSA), ejection fraction (EF), myocardial contractility index (IC), heart rate (HR) and so on.
A new generation of non-invasive cardiac output monitors provides an alternative to using conventional invasive methods such as thermodi lution. our ICG and thermodilution cardiac output measurements were taken from many patients undergo ing right heart catheterisation. Linear regression analysis showed good correlation between thermodilution and our ICG about the line y = 1.0054x-0.1367 (r = 0.94).
> It can be used as a routine diagnosis to evaluate cardiac function.
> Monitor the effect of drugs on cardiac function, guide treatment, and choose the best treatment.
> Real-time monitoring during operation and recovery, timely detection of life-threatening hemodynamic conditions and rescue.
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