How It Works


The CHEETAH NICOM and Starling™ SV provide continuous, accurate, non-invasive hemodynamic monitoring and empower volume management in virtually any clinical setting.

They are based on Bioreactance®, a technology that was created by Cheetah Medical's scientists over years of research and development, followed by extensive testing and validation. The basis behind this technology is the use of time delay, or phase shifts, which occur when an alternating electrical current (AC) is passed through the thorax. 

The unique, patented Bioreactance® technology takes measurements continuously and with extreme precision. Additionally, it requires only 4 sensors that are easily placed on the thorax. The sensors can be placed anywhere on the chest or back as long as two are positioned above and two are positioned below the heart.

It's important to note Bioreactance technology should not be confused with bioimpedance, an older technology that has certain limitations when used for assessing fluid responsiveness.





Detailed Explanation

Download the bioreactance technology paper.

To learn more about the phase shift, click here.


Bioreactance technology begins by placing 4 dual sensors on the patient. The Cheetah Medical monitor puts in a signal at a frequency of 75 kHz into the thorax via the outer portion of the sensors.  The known frequency is then received via the inner portion of the sensors from which the monitor compares to the original signal. It will then observe to what extent a time delay, or phase shift, has occurred helping to determine patient fluid responsiveness.

An advantage of Bioreactance technology is the signal is only affected by pulsatile flow. The signal is reflected from the base of the aorta back to the sensors. 

Pressure, volumetric flow, resistance, capacitance, compliance, velocity, and viscosity are some of the things that contribute to flow.  Ultimately there is a relationship to “time” with all of these factors.  In short, these factors of pulsatile flow cause a shift in the signal called “phase shift”, but is better understood as a “time delay”



The CHEETAH NICOM and Starling SV received signal is compared to what was put into the thorax.  It determines how much blood had to have been coming out of the left ventricle and into the base of the aorta to cause that specific time delay; this becomes the stroke volume.  Because there are ECG leads built into the unique Cheetah Medical sensors, heart rate can be detected.  This allows one to obtain Cardiac Output, or HR X SV = CO.