Development of counterpulsation algorithm for a moving-actuator type pulsatile LVAD.

A pulsatile left ventricular assist device (LVAD) was used to support the aortic blood pumping function of an injured left ventricle, and as a result helped its recovery. It is important to observe a left ventricle's pumping status and to adjust the operating status of a LVAD to reduce the left ventricle's pumping load and thus to enhance its recovery. To observe the left ventricle's pumping status, an electrocardiogram (ECG) signal is generally used because it is a result of the natural heart's blood pumping function. In this paper, we describe the development of an ECG based counterpulsation control algorithm that prevents simultaneous aortic blood co-pumping by a left ventricle and a moving-actuator type pulsatile LVAD and as a result, reduces the natural heart's pumping load. In addition, to verify the algorithm's applicability for LVAD control we designed three ECG based automatic pump control algorithms that use a developed counterpulsation control algorithm. These algorithms control the operating status of a LVAD automatically and, at the same time, maintain a counterpulsing status. The results of in vitro experiments show that the counterpulsing effect between a left ventricle and a LVAD was successfully produced and that the newly designed automatic pump control algorithms met their own control purposes with a counterpulsing effect.

Robust motor speed control under time varying loads in moving actuator type artificial heart (AnyHeart).

The Moving Actuator type artificial heart(AnyHeart) as well as many other artificial hearts uses a motor as its power source. For controllability of control parameters such as pump rate, pump output, blood pressure profile and flow form, the precise motor speed control is important. However, because the implantable device has limited carrying capacity of hardware components in size and number, applying diverse motor control methods are not possible. In addition, the existing PI (Proportional-Integral) motor controller does not show satisfactory performance. A new controller that is sufficiently robust for the changes of load and physical system parameters has been designed and tested. The robust speed controller is based on the sliding mode control method that is applicable to a system of which the ranges of uncertainty in physical parameters are known. In a mock circulation system test, the actual speed showed good tracking characteristics in respect to the reference speed. Fast follow-up characteristics were also observed under high afterload and speed conditions. The speed error, current and power consumption were reduced by about 40%. The proposed control technique overcomes the limitations of the PI controller, and makes important improvements in both performance and stability.

Estimation of coupled assist flows in a moving-actuator bi-ventricular assist device using interventricular pressure.

An assist flow estimation scheme for a moving-actuator biventricular assist device (MA-BVAD) using interventricular pressure (IVP) has been developed. The scheme uses a waveform feature parameter of IVP, peak IVP time (PIT), for estimation of the filling volumes of both left and right blood sacs simultaneously. In a regression analysis on data from an in vivo test in an 85 Kg male calf for 20 days, the PIT was found to have high correlation with the blood sac filling volume (R=0.883: left filling volume, R=0.967: right filling volume). A conceptual equation hypothesizing this correlation between PIT and filling volume was established based on the observation and the unknown parameters were identified using least squares parameter optimization. The estimation equation identified proved highly accurate (R=0.916 for left flow, R=0.970 for right flow). The accuracy of the estimation scheme promises very good practical applicability.

Analysis of the interventricular pressure waveform in the moving-actuator total artificial heart.

Right and left filling pressures are important parameters in the automatic control of a total artificial heart (TAH) within normal physiologic ranges. Our TAH is composed of a moving actuator, right and left ventricles, and an interventricular space (IVS) enclosed by a semirigid housing. During operation of the TAH, the IVS volume is changed dynamically by the difference between the ejection volume of one ventricle and the inflow volume of the other. We measured the interventricular pressure (IVP) waveform by using a pressure sensor and analyzed the relationship between the IVP and the preload condition. From in vitro and in vivo experiments, we found that the measured filling pressures were linearly related to the negative peak value of the IVP. Additionally, we found that we could use the time interval from actuator start to the positive peak value of the IVP (outflow valve opening) as a useful parameter to estimate the blood filling volume of the diastole ventricle.

Implantable control, telemetry, and solar energy system in the moving actuator type total artificial heart.

The moving actuator type total artificial heart (TAH) developed in the Seoul National University has numerous design improvements based upon the digital signal processor (DSP). These improvements include the implantability of all electronics, an automatic control algorithm, and extension of the battery run-time in connection with an amorphous silicon solar system (SS). The implantable electronics consist of the motor drive, main processor, intelligent Li ion battery management (LIBM) based upon the DSP, telemetry system, and transcutaneous energy transmission (TET) system. Major changes in the implantable electronics include decreasing the temperature rise by over 21 degrees C on the motor drive, volume reduction (40 x 55 x 33 mm, 7 cell assembly) of the battery pack using a Li ion (3.6 V/cell, 900 mA.h), and improvement of the battery run-time (over 40 min) while providing the cardiac output (CO) of 5 L/min at 100 mm Hg afterload when the external battery for testing is connected with the SS (2.5 W, 192.192, 1 kg) for the external battery recharge or the partial TAH drive. The phase locked loop (PLL) based telemetry system was implemented to improve stability and the error correction DSP algorithm programmed to achieve high accuracy. A field focused light emitting diode (LED) was used to obtain low light scattering along the propagation path, similar to the optical property of the laser and miniature sized, mounted on the pancake type TET coils. The TET operating resonance frequency was self tuned in a range of 360 to 410 kHz to provide enough power even at high afterloads. An automatic cardiac output regulation algorithm was developed based on interventricular pressure analysis and carried out in several animal experiments successfully. All electronics have been evaluated in vitro and in vivo and prepared for implantation of the TAH. Substantial progress has been made in designing a completely implantable TAH at the preclinical stage.

Intelligent Li ion battery management based on a digital signal processor for a moving actuator total artificial heart.

An intelligent Li Ion battery management (ILBM) system was developed based on a digital signal processor (DSP). Instead of using relatively complicated hardware charging control, a DSP algorithm was used, and favorable characteristics in volume, mass, and temperature increase of the implantable battery were achieved. In vitro tests were performed to evaluate the DSP based algorithm for Li Ion charging control (24 V dc motor input power 16 W, 5 L/min, 100 mmHg afterload). In this article, the first improvement was volume reduction using a Li Ion battery (3.6 V/Cell, 900 mA, seven cells: 25.2 V, 22.7 W). Its volume and mass were decreased by 40% and 50% respectively (40*55*75 mm, 189 g), compared to previously reported results, with total energy capacity increased by 110% (more than 60 min vs 25 min run time in the other battery). The second improvement includes the ILBM, which can control the performance detection for each unit cell and has a low temperature rise. The ILBM's unit cell energy detection was important because the low performance of one cell dropped to 50% of the total performance along with a 20% increase in surface temperature. All electronics for a transcutaneous energy transmission (TET), battery, and telemetry were finalized for hybridization and used for total artificial heat (TAH) implantation.

A solar cell system for extension of battery run time in a moving actuator total artificial heart.

An implantable total artificial heart (TAH) system has strong dependence upon the external battery performance for operation. Even under sophisticated battery management control, the usable external battery performance continues to decrease, which limits TAH performance. One of the ways to overcome this energy problem is to use a solar system (SS). An SS can provide electrical power for the partial TAH drive or battery recharge. This article presents a new concept for use of the solar cell for obtaining double external battery performance. To achieve it, numeric simulations were carried out to obtain the proper magnitude of solar parameters. In the TAH used, the battery power for a cardiac output of 4-6 L/min is approximately 17 W/20 min. From simulated results, the optimal power and voltage of the SS were found to be 7 W, Voc = 27 V in the case of the 24 V motor. Each solar cell includes Voc = 0.5 V, Isc = 37 mA/cm2, FF (fill factor) = 0.77, and efficiency = 10%. Based on the simulation, the effect of solar power capacity on battery run time was studied. With use of 6.5 W SS (W 304 x H 245 x D 16 mm, 1.1 kg), battery performance decreased in vitro from 100% (fully charged) to > 55% vs 0% in the conventional battery system after 20 min operation. However, it dropped to below 20% when using W SS (W 192 x H 192 x D 16 cm, 0.6 kg). The results showed doubled battery run time could be obtained compared with a system without the SS. It was concluded that the proposed SS can be put to practical use as a future energy source for a TAH.