The Index of Motor Current Amplitude Has Feasibility in Control for Continuous Flow Pumps and Evaluation of Left Ventricular Function

Abstract

The index of motor current amplitude (ICA) has feasibility in continuous-flow ventricular assist device control. It can demonstrate the safe range of pump speed, which exists between the starting point of total assistance (t-point) and the starting point of sucking (s-point). The objective of this study was to investigate how the ICA characteristic curve changes with each condition of contractility, preload, and afterload changes. We changed preload, afterload, and contractility of closed-mock circulation and plotted the change of the ICA value against pump speed. Then the shift of ICA characteristic curve against the change of each condition was considered. When preload increased, ICA characteristic curves showed the expansion of a safe range. When afterload increased, ICA characteristic curves were shifted to the high rotation side, slightly narrowing a safe range. When contractility increased, ICA characteristic curves showed the shift of a convex above to narrowing of a safe range. As these shift patterns were observed even when the driving conditions of a circuit changed, reproducibility was checked. Understanding the feature of a shift pattern of ICA characteristic curves correctly, a possibility that change of the heart function could be predicted by change of ICA value and a possibility for a flexible control method based on ICA, according to hemodynamic state, were suggested.

Classification of Physiologically Significant Pumping States in an Implantable Rotary Blood Pump: Effects of Cardiac Rhythm Disturbances

“…While a WDI exceeding a calculated threshold indicated either suction or regurgitation, establishing which of these two states was actually occurring was done visually (with reference to a graph of WDI against speed) rather than as an automated process. Endo et al (6,7) from Miyazaki Medical College investigated the index of current amplitude, taken as the difference in maximum and minimum value of the pump current waveform, divided by its simultaneous mean value. They were able to detect the transition between partial and total assist of the native heart (the t-point) as well as the transition between total assist and suction (the spoint).…”

“…Experimentation in the transition of pumping states has previously been investigated by a number of groups (4)(5)(6)(7)(8)(9)(10)(11)(12). Various groups (9) employ invasive sensors to aid in this process (e.g., to measure the pump flow signal).…”

“…However, it is desirable to avoid their use due to a considerable reduction in system reliability and increased cost. Research efforts have thus predominantly involved waveform analysis of the noninvasive pump motor feedback signals (current or speed), from which a number of useful indices have been derived by various authors (5)(6)(7)(8)(10)(11)(12) as indicators of either over-or underpumping of the heart. For example, Yuhki et al (5) considered a waveform deformation index (WDI) based on a spectral analysis of the speed signal; Endo et al (6,7) investigated the symmetry in the current amplitude; and Voigt et al (12) used the amplified, differentiated current signal as a suction indicator.…”

“…Research efforts have thus predominantly involved waveform analysis of the noninvasive pump motor feedback signals (current or speed), from which a number of useful indices have been derived by various authors (5)(6)(7)(8)(10)(11)(12) as indicators of either over-or underpumping of the heart. For example, Yuhki et al (5) considered a waveform deformation index (WDI) based on a spectral analysis of the speed signal; Endo et al (6,7) investigated the symmetry in the current amplitude; and Voigt et al (12) used the amplified, differentiated current signal as a suction indicator. Most groups, however, fall short of developing algorithms to automate the detection of these abnormal pumping states, and thus do not provide a statistical assessment of the success of their methods (5)(6)(7)(8).…”

“…For example, Yuhki et al (5) considered a waveform deformation index (WDI) based on a spectral analysis of the speed signal; Endo et al (6,7) investigated the symmetry in the current amplitude; and Voigt et al (12) used the amplified, differentiated current signal as a suction indicator. Most groups, however, fall short of developing algorithms to automate the detection of these abnormal pumping states, and thus do not provide a statistical assessment of the success of their methods (5)(6)(7)(8). The studies that have presented numerical results (4,11,12), however, provide a valuable platform against which a comparison with the current study can be made.…”