Impedance Cardiography (ICG) is a noninvasive technology for measuring total electrical conductivity of the human body and its changes over time to process continuously a number of hemodynamic parameters such as Stroke Volume (SV), Heart Rate (HR), Cardiac Output (CO), Body water, Total peripheral Resistance (TPR) and Cardiac Power (CP).
Two basic technologies are currently in use for impedance cardiography:
- The Thoracic ICG, were the sensors are placed on the root of the neck and the lower part of the chest.
- The Whole-body or Regional ICG, were four pairs of sensors are used, one pair on each limb or only two pairs of sensors are used, performing best when placed on one wrist and on the contralateral ankle.
The most significant advantage of the Whole-body Impedance Cardiography – ICG in comparison to the Thoracic ICG is the use of the peripheral impedance signal for the calculation of the Stroke Volume. About 75% of the peripheral impedance waveform is borne by the systolic blood volume pulsation of the arterial vasculature of the upper and lower limbs, and the remaining 25% arrive from the trunk (thorax).
While the Whole-body Impedance Cardiography -ICG peripheral volumetric signal is borne throughout the length of the arterial tree, the Thoracic ICG waveform is generated by multiple sources including the aorta, lungs, vena cava, and artifacts due to heart movement.
As a result, the peripheral systolic impedance changes are more reliable then the thoracic impedance changes for calculating the cardiac stroke volume.
In addition, due to the use of peripheral signals, the responses to vasodilation therapy is better depicted by the Whole-body ICG (that is utilized by NICaS) when compared with a Thoracic Impedance Cardiography -ICG.