Impedance cardiography (ICG) is a noninvasive technology measuring total electrical conductivity of the thorax and its changes in time to process continuously a number of cardiodynamic parameters, such as Stroke Volume (SV), Heart Rate (HR), Cardiac Output (CO), Ventricular Ejection Time (VET), Pre-ejection Period and used to detect the impedance changes caused by a high-frequency, low magnitude current flowing through the thorax between additional two pairs of electrodes located outside of the measured segment. The sensing electrodes also detect the ECG signal, which is used as a timing clock of the system

How it works?

  • Four pairs of electrodes are placed at the neck and the diaphragm level, delineating the thorax
  • High frequency, low magnitude current is transmitted through the chest in a direction parallel with the spine from the set of outside pairs
  • Current seeks path of least resistance: the blood filled aorta (the systolic phase signal) and both vena cava superior and inferior (the diastolic phase signal, mostly related to respiration)
  • The inside pairs, placed at the anatomic landmarks delineating thorax, sense the impedance signals and the ECG signal
  • ICG measures the baseline impedance (resistance) to this current
  • With each heartbeat, blood volume and velocity in the aorta change ICG measures the corresponding change in impedance and its timing
  • ICG attributes the changes in impedance to (a) the volumetric expansion of the aorta (this is the main difference between ICG and Electrical Cardiometry) and (b) to the blood velocity-caused alignment of erythrocytes as a function of blood velocity
  • ICG uses the baseline and changes in impedance to measure and calculate hemodynamic parameters

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