Impedance plethysmography measured on the thorax is a special diagnostic application and usually called impedance cardiography (ICG). Sometimes it is also named electrical bioimpedance or thoracic electrical bioimpedance (TEB).

In contrast to impedance plethysmography a standardised electrode position on the chest is used.

The ICG signal shows the mechanical activity of the heart (the 6th vital sign). During systole the ICG signal is mostly generated by volume changes taking place in the aorta. During diastole blood volume changes in the large veins and the pulmonary aorta may also contribute to ICG waveforms, especially in case of pathological changes.

Following picture shows a typical impedance wave (yellow) and the first derivation (red) with typical curve points:

A-Wave - B - C - X - Y - O - PEP - LVET -

Contraction of atrium Opening of aortic  valve Max. systolic flow Closing of aortic valve Closing of pulmonal valve Opening of mitral valve Pre-Ejection Period Left Ventricular Ejection Time

The impedance signal is measured continuously. Therefore a beat-to-beat evaluation is possible.
 

Hemodynamic parameters

	Flow
HR	Heart Rate	Heart beats per minute
BP	Blood Pressure	Pressure exerted by the blood on arterial walls
SV SI	Stroke Volume Stroke Index	Amount of blood pumped by the left ventricle with each heart beat
CO CI	Cardiac Output Cardiac Index	Amount of blood pumped by the heart in one minute
	Contractility
VI	Velocity Index	Reflects the peak velocity of blood flow in the aorta during systole
ACI	Acceleration Index	Reflects  the  maximum acceleration of blood flow in the aorta during systole
HI	Heather Index	Contractility indicator
PEP	Pre-Ejection Period	Duration of electrical systole equal to isovolumetric contraction phase
STR	Systolic Time Ratio	Ratio of electrical systole to mechanical systole
	Fluid
TFC      TFCI	Thoracic Fluid Content TFC Index	Indicator of chest fluid status TFC, normalised to body size
	Vascular
PT	Propagation Time	Propagation time of the pulse wave
PWVao	Pulse Wave Velocity	Velocity of the aortic pulse wave
SVR	Systemic Vascular Resistance	The force the ventricle must overcome to eject blood into the aorta, estimate of “afterload”
SVRI	SVR Index	SVR, normalised to body size
TAC	Total Arterial Compliance	Indicator of the degree of peripheral arterial stiffness / compliance
TACI	TAC Index	TAC, normalised to body size