How does impedance cardiography work

By injecting a high frequency, low amplitude, constant current signal into the chest, the signal will naturally take the path of least resistance through the blood. As the heart beats, the volume of blood in the aorta changes, as does the measured impedance to the constant current signal. As blood volume increases, impedance decreases, and vice-versa. ICG requires 4 electrodes — 2 outside electrodes which supply the constant current source CCS and 2 inside electrodes which sense the changes in impedance SNS.

Check out this video for more information on how to apply spot electrodes for ICG, or refer to our Electrode Placement poster. I am not going to attempt to tackle the debate of spot vs.

It is important to note that the measured impedance with bands will be higher than what is obtained with spot electrodes. For this blog post, all example data sets have been collected using spot electrodes. We will use Z o for consistency moving forward, but it is good to be aware of the various ways the signal is referenced.

Since it is a measure of electrical resistance, Z o is measured in Ohms. Below is an example Z o over several cardiac cycles:. For those that need a refresher — this is the notation for the first derivative of Z, or the change in impedance relative to time.

Below are two examples of how the filter works on "difficult" dZ signals. In these two cases the signal is totally stable and reproducible after application of the HD-Z filter.

It is immediately evident that a heart failure patient and an athlete present very different waveforms and that these waveforms contain the necessary information to compute SV.

In relation to its poor reception, FM radio contains cracks and distortion. No other device has been successfully used in such difficult conditions and provides clinically useful information in such a dynamic fashion. What is impedance cardiography? How does ICG Work?

What are the limitations of standard ICG? This technology, originally used by NASA in the 's, has benefited from the advent of the microprocessor and the better understanding of the cardiac cycle, thanks to technology such as echocardiography and magnetic resonance imaging. Today, noninvasive methods of measuring of cardiac output are coming into clinical use on a larger scale than ever before and are compared with other methods such as thermodilution and the direct and indirect Fick methods.

SVR is representative of the force that the left heart must pump against in order to deliver the stroke volume into the periphery. SVR is directly proportional to blood pressure and indirectly proportional to blood flow CO. These two indices are both BioZ specific parameters. VI is the maximum rate of impedance change, and is representative of aortic blood velocity. ACI is the maximum rate of change of blood velocity and representative of aortic blood acceleration.