Stroke volume equation for impedance cardiography

Abstract

The study's goal was to determine if cardiac output (CO), obtained by impedance cardiography (ICG), would be improved by a new equation N, implementing a square root transformation for dZ/dtmax/Z0, and a variable magnitude, mass-based volume conductor Vc. Pulmonary artery catheterisation was performed on 106 cardiac surgery patients pre-operatively. Post-operatively, thermodilution cardiac output (TDCO) was simultaneously compared with ICG CO. dZ/dtmax/Z0 and Z0 were obtained from a proprietary bioimpedance device. The impedance variables, in addition to left ventricular ejection time TLVE and patient height and weight, were input using four stroke volume (SV) equations: Kubicek (K), Sramek (S), Sramek-Bernstein (SB), and a new equation N. CO was calculated as SV x heart rate. Data are presented as mean +/- SD. One way repeated measures of ANOVA followed by the Tukey test were used for inter-group comparisons. Bland-Altman methods were used to assess bias, precision and limits of agreement. P< 0.05 was considered statistically significant. CO implementing N (6.06 +/- 1.48 l min(-1)) was not different from TDCO (5.97 +/- 1.41 l min(-1)). By contrast, CO calculated using K (3.70 +/- 1.53 l min(-1)), S (4.16 +/- 1.83 l min(-1)) and SB (4.37 +/- 1.82 l min(-1)) was significantly less than TDCO. Bland-Altman analysis showed poor agreement between TDCO and K, S and SB, but not between TDCO and N. Compared with TDCO, equation N, using a square-root transformation for dZ/dtmax/Z0, and a mass-based Vc, was superior to existing transthoracic impedance techniques for SV and CO determination.

Cardiovascular Reserve and Risk Profile of Postmenopausal Women After Chemoendocrine Therapy for Hormone Receptor–Positive Operable Breast Cancer

“…A phonocardiogram (Hewlett Packard, model 21050A; Hewlett Packard, Palo Alto, CA) was integrated with the impedance cardiograph to identify the first and second heart sounds in order to landmark respective B and X points of dZ/dt waveforms for determination of left ventricular ejection time. Impedance cardiography was used to calculate stroke volume during 7-second sampling periods at the end of each minute using Bernstein's equation [30]. Blood pressure (cuff sphygmomanometer), heart rate, stroke volume, cardiac output, and cardiac power output (cardiac output ϫ mean arterial pressure) were obtained at the end of each exercise stage.…”

Pulse Wave Velocity and Cardiac Output vs. Heart Rate in Patients with an Implanted Pacemaker Based on Electric Impedance Method Measurement

“…50 kHz and 52 kHz) [6]. For the estimation of stroke volume (SV), the Sramek-Bernstein equation was applied [2], [7]. The left ventricular ejection time (LVET) was calculated from energy of the PCG by filtering and subsequent detection of the heart sounds, see Figure 2.…”

Physiological quality assessment of stored whole blood by means of electrical measurements

“…Bioimpedance of stored blood should also be taken into account when impedance cardiography is postoperatively used to determine cardiac output in patients with blood transfusion, since the ion balance will be disturbed [5].…”

“…Diagnostic methods such as impedance plethysmography, impedance cardiography and impedance pneumography are based on monitoring the volume changes by electrical impedance changes of tissues [5,29].…”