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Impedance cardiography: Pulsatile blood flow and the biophysical and electrodynamic basis for the stroke volume equations

Donald P. Bernstein
Donald P. Bernstein
   | Dec 03, 2009
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Article Category: Reviews
Published Online: Dec 03, 2009
Page range: 2 - 17
Received: Nov 25, 2009
DOI: https://doi.org/10.5617/jeb.51
Keywords
© 2010 Donald P. Bernstein, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Fig. 1

ECG, aortic pressure, aortic blood flow Q, aortic rate of change of pressure dP/dt, and rate of change of flow, which is acceleration dQ/dt. From a canine model In: Li J-K. The arterial circulation: physical principles and clinical applications. Totowa, NJ: Humana Press; 2000, p. 78.
ECG, aortic pressure, aortic blood flow Q, aortic rate of change of pressure dP/dt, and rate of change of flow, which is acceleration dQ/dt. From a canine model In: Li J-K. The arterial circulation: physical principles and clinical applications. Totowa, NJ: Humana Press; 2000, p. 78.

Fig. 2

Schematic of a multi-compartmental parallel conduction model of the thorax. The transthoracic electrical impedance Z(t) to an applied AC field represents the parallel connection of a quasi-static base impedance Z0 and a time-dependent component of the blood impedance, ΔZb(t). Z0 represents the parallel connection of all static tissue impedances, Zt, and the static component of the blood resistance, Zb. Ze represents the quasi-static EVLW compartment. A voltmeter (U) and AC generator (~) are shown. From reference 37.
Schematic of a multi-compartmental parallel conduction model of the thorax. The transthoracic electrical impedance Z(t) to an applied AC field represents the parallel connection of a quasi-static base impedance Z0 and a time-dependent component of the blood impedance, ΔZb(t). Z0 represents the parallel connection of all static tissue impedances, Zt, and the static component of the blood resistance, Zb. Ze represents the quasi-static EVLW compartment. A voltmeter (U) and AC generator (~) are shown. From reference 37.

Fig. 3

Behavior of AC as applied to pulsatile blood flow. → = AC flow. v = red cell velocity; Δρb(t) = changing specific resistance of flowing blood.; Qin = flow into aortic segment; Qout = simultaneous flow out of aortic segment; dA(t) = time-dependent change in aortic CSA. From reference 13.
Behavior of AC as applied to pulsatile blood flow. → = AC flow. v = red cell velocity; Δρb(t) = changing specific resistance of flowing blood.; Qin = flow into aortic segment; Qout = simultaneous flow out of aortic segment; dA(t) = time-dependent change in aortic CSA. From reference 13.

Fig. 4

Absolute spatial average velocity (i.e. reduced average velocity <v>/R, s–1) vs. conductivity change in an in vitro pulsatile ejection model over one cardiac cycle. Note that, upon red cell acceleration in early ejection, the peak rate of change of the reduced average velocity parallels the peak rate of change of conductivity (r = 0.99). From reference 23.
Absolute spatial average velocity (i.e. reduced average velocity <v>/R, s–1) vs. conductivity change in an in vitro pulsatile ejection model over one cardiac cycle. Note that, upon red cell acceleration in early ejection, the peak rate of change of the reduced average velocity parallels the peak rate of change of conductivity (r = 0.99). From reference 23.

Fig. 5

ECG, ΔZ(t) and dZ/dt waveforms from a human subject. For ΔZ(t) note Nyboer’s maximum down-slope backward extrapolation to find ΔZmax. Also note Kubicek’s maximal systolic up-slope forward extrapolation of ΔZ(t). For dZ/dt, point B = aortic valve opening; point X = aortic valve closure; Y = pulmonic valve closure; O = rapid ventricular filling wave; Q–B interval = pre-ejection period (s); B–C interval = time-to-peak (TTP, s) of dZ/dtmax; B–X interval; left ventricular ejection time (TLVE, s). dZ/dt waveform to right shows the square wave integration (shaded area), dZ/dtmax remaining constant over the ejection interval, which represents outflow compensation. Modified from reference 13.
ECG, ΔZ(t) and dZ/dt waveforms from a human subject. For ΔZ(t) note Nyboer’s maximum down-slope backward extrapolation to find ΔZmax. Also note Kubicek’s maximal systolic up-slope forward extrapolation of ΔZ(t). For dZ/dt, point B = aortic valve opening; point X = aortic valve closure; Y = pulmonic valve closure; O = rapid ventricular filling wave; Q–B interval = pre-ejection period (s); B–C interval = time-to-peak (TTP, s) of dZ/dtmax; B–X interval; left ventricular ejection time (TLVE, s). dZ/dt waveform to right shows the square wave integration (shaded area), dZ/dtmax remaining constant over the ejection interval, which represents outflow compensation. Modified from reference 13.

Fig. 6

Relationship between esophageal ECG (A), aortic pressure (B), aortic expansion (C), aortic blood flow (D), pulmonic expansion (E), ΔZ(t) (F), and dZ/dt (G). Note that dZ/dtmax precedes peak aortic blood flow (Qmax) during the period of peak flow acceleration in early systole. Modified from reference 13.
Relationship between esophageal ECG (A), aortic pressure (B), aortic expansion (C), aortic blood flow (D), pulmonic expansion (E), ΔZ(t) (F), and dZ/dt (G). Note that dZ/dtmax precedes peak aortic blood flow (Qmax) during the period of peak flow acceleration in early systole. Modified from reference 13.

Fig. 7

Ascending aortic dP/dt, ascending aortic pressure P, and dZ/dt from a human. Note that dZ/dtmax peaks precisely with ascending aortic dP/dtmax. Note computer artifact. Courtesy of Kirk L. Peterson, M.D.; From the cardiac catheterization laboratory at the University of California School of Medicine, San Diego.
Ascending aortic dP/dt, ascending aortic pressure P, and dZ/dt from a human. Note that dZ/dtmax peaks precisely with ascending aortic dP/dtmax. Note computer artifact. Courtesy of Kirk L. Peterson, M.D.; From the cardiac catheterization laboratory at the University of California School of Medicine, San Diego.

Fig. 8

ECG, ultra-low frequency ballistocardiogram (BCg), dZ/dt, and ΔZ(t) from a human. Note that the “I” wave of the HJ interval peaks precisely with dZ/dtmax. The unlabeled noisy signal above ECG is a phonocardiogram. From reference 49.
ECG, ultra-low frequency ballistocardiogram (BCg), dZ/dt, and ΔZ(t) from a human. Note that the “I” wave of the HJ interval peaks precisely with dZ/dtmax. The unlabeled noisy signal above ECG is a phonocardiogram. From reference 49.

Fig. 9

Square root acceleration step-down transformation. On the y-axis, the ohmic equivalent of peak aortic reduced average blood acceleration (PARABA), which is dZ/dtmax/Z0., and the linear extrapolation of the square root transformation, ohmic mean velocity on the x-axis (x = √y and y = x2). From reference 13.
Square root acceleration step-down transformation. On the y-axis, the ohmic equivalent of peak aortic reduced average blood acceleration (PARABA), which is dZ/dtmax/Z0., and the linear extrapolation of the square root transformation, ohmic mean velocity on the x-axis (x = √y and y = x2). From reference 13.

Fig. 10

Box plots showing that, as oleic acid-induced pulmonary edema worsened, as reflected by decreasing Z0, the systematic underestimation of flow-probe CO by ICG-derived CO increased. From reference 74.
Box plots showing that, as oleic acid-induced pulmonary edema worsened, as reflected by decreasing Z0, the systematic underestimation of flow-probe CO by ICG-derived CO increased. From reference 74.
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