As necessary for stroke volume calculation, dZ/dt max/Z 0 must undergo square root transformation to yield an ohmic mean flow velocity equivalent. As conceptualized, the normalized value, dZ/dt max/Z 0, is a dimensionless ohmic mean acceleration equivalent (s –2), and more precisely, the electrodynamic equivalent of peak aortic reduced average blood acceleration (PARABA, d/dt max/R, s –2). s –2) and not a mean flow or velocity surrogate as generally assumed.s –2), it is suggested that dZ/dt max is an ohmic mean acceleration analog (Ω.As a consequence of dZ/dt max peaking in the time domain of peak aortic blood acceleration, d v/dt max (cm s –1), and it is the peak rate of change of the blood resistivity variation dρ b(t)/dt max (Ωcm.A recently introduced method assumes the rapid ejection of forward flowing blood in earliest systole causes significant changes in the velocity-induced blood resistivity variation (Δρ b(t), Ωcm Conceptually, commonly implemented methods assume a volumetric origin for the peak systolic upslope of ΔZ(t), (i.e. In its majority, however, ΔZ(t) is known to primarily emanate from the ascending aorta. ΔZ(t) represents a dual-element composite waveform, which comprises both the radially-oriented volumetric expansion of and axially-directed forward blood flow within both great thoracic arteries. Upon ventricular ejection, a characteristic time dependent cardiac-synchronous pulsatile impedance change is obtained, ΔZ(t), which, when placed electrically in parallel with Z 0, constitutes the time-variable total transthoracic impedance Z(t).
Without ventilatory or cardiac activity, Z is known as the transthoracic, static base impedance Z 0. By Ohm’s Law, the voltage difference measured within the current field is proportional to the electrical impedance Z (Ω). As implemented, using the transthoracic approach, the technique involves applying a current field longitudinally across a segment of thorax by means of a constant magnitude, high frequency, low amplitude alternating current (AC). Impedance cardiography (ICG) is a branch of bioimpedance primarily concerned with the determination of left ventricular stroke volume (SV).
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