IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 44, NO. 1, JANUARY 1997 I 1

Development of a Microcontroller-B ased Automatic Control System for the Electrohydraulic

Total Artificial Heart Hee Chan Kim, Member, IEEE, Pratap S. Khanwilkar,” Student Member, IEEE,

Gill B. Bearnson, Student Member, IEEE, and Don B. Olsen

Abstruct- An automatic physiological control system for the actively filled, alternately pumped ventricles of the volumetrically coupled, electrohydraulic total artificial heart (EHTAH) was developed for long-term use. The automatic control system must ensure that the device: 1) maintains a physiological response of cardiac output, 2) compensates for any nonphysiological condi- tion, and 3) is stable, reliable, and operates at a high power efficiency. The developed automatic control system met these requirements both in vitro, in week-long continuous mock cir- culation tests, and in vivo, in acute open-chested animals (calves). Satisfactory results were also obtained in a series of chronic animal experiments, including 21 days of continuous operation of the fully automatic control mode, and 138 days of operation in a manual mode, in a 159-day calf implant.

Zndex Terms- Artificial biological organs, biological control systems, blood pumps, implantable biomedical devices, micro- processor applications.

I. INTRODUCTION HE goal of this study was to develop an automatic T physiological control system for a totally implantable

electrohydraulic total artificial heart (EHTAH) and to d strate its physiological performance both in vitro and in vivo.

Pneumatically driven total artificial hearts (TAH’s) and ven- tricular assist devices (VAD’s) based on manual control have been successfully used in clinical applications. Electrically powered systems with automatic control are being pursued for long-term mechanical circulatory support [ 11-[3] to reliably operate for up to five years in humans. Such electrical systems are expected to overcome the pneumatic system’s problems of infection and of limited patient mobility due to large diameter drivelines connected to a relatively immobile driving unit. The Artificial Heart Research Laboratory at the University of

Manuscript received October 24, 1994; revised April 25, 1996. This work was supported by the National Institutes of Health under a grant from the National Heart, Lung, and Blood Institute’s Contract N01-HV-88106, and by the State of Utah, and by the University of Utah. The work of H. C. Kim was supported by the Korea Science and Engineering Foundation under a 1994 post-doctoral research fund. Asterisk indicates corresponding author.

H. C. Kim is with the Artificial Heart Research Laboratory, Seoul National University, Seoul, Korea.

*P. S. Khanwilkar is with MedQuest Products Inc. and the Artificial Heart Research Laboratory, University of Utah, 803 North, 300 West, Salt Lake City, UT 84103 USA. (e-mail: pratap.k@m.cc.utah.edu).

G. B. Bearnson, and D. B. Olsen are with the Artificial Heart Research Laboratory, University of Utah, Salt Lake City, UT 84103 USA.

Publisher Item Identifier S 0018-9294(97)00643-5.

Fig. 1. Proposed configuration of the EHTAH system implanted in a man. The present paper describes mock circulation and animal (calf) studies using the blood pump and its physiological control system.

Utah is developing an electrically powered artificial heart for long-term use, the EHTAH.

A. EHTAH System Description

Fig. 1 is an artist’s conception of the proposed EHTAH system implanted in a human. It consists of four major subsystems: 1) a blood pump with sensors and an electrical- to-mechanical energy converter, 2) an implantable control unit with internal batteries, 3) an external monitoring and control unit with external batteries, and 4) a set of external and implanted coils for transcutaneous energy transmission (TET) and separate coils or optical transceiver unit for information telemetry.

0018-9294/97$10.00 0 1997 IEEE

experiments described in this paper

own in Fig. 2. Although they are TAH system, the TET and ncluded in this study. The

aturized using hybrid circuits lanted ‘for the experiments de- devices used in this study, all

external control1

edyne, Carlsbad, CA, and ESMF company, Lansdale, PA). The motor requires a power input of 35 (45) W to pump 5(10) LMin on the mock circulation. The interatrial shunt (IAS), the EHTAH’s balancing mechanism, is formed by a small orifice, 4.3 mm in diameter, between

n in the center of Fig. 3. The EHTAH , and its precursor, the EHTAH20 serie bench and animal

ch natural ventricle is replaced by its artificia ich consists of a blood compartment and a hydraulic fluid compartment separated by a flexible diaphragm. Smootlh, seamless polyurethane blood-

Fig. 3. energy converter subsyste

Photograph of the ass

schematically shows the

KIM et al.: MICROCONTROLLER-BASED AUTOMATIC CONTROL SYSTEM FOR THE ELECTROHYDRAULIC TOTAL ARTIFICIAL HEART 19

END DIASTOLE BLOOD FLOW

?!-!T BLOOD

pressure transducer

END SYSTOLE H-- BLOOD

pressure transducer

Fig. 4. An EHTAH ventricle at: (a) end-diastole and (b) end-systole.

conditions: 1) end-diastole (the end of the filling stage) and 2) end-systole (the end of the ejection stage).

C. Requirements for a TAH Control System

For long-term use, a control algorithm embedded in the implanted control unit must stabilize the operation of the blood pump and meet changes in physiological demand un- der varying hemodynamic conditions. Three functions must be performed automatically without any manual intervention during long-term implantation. The TAN control scheme must be: 1) sensitive to and respond to the body’s need for varying cardiac output, 2) able to compensate or attenuate any device- originated nonphysiological conditions, and 3) stable, reliable, and operate the TAH efficiently. Each functional requirement is explained below.

First, the cardiac output of the device must respond to phys- iological changes. Typically, greater exercise by the EHTAH recipient will require the device to provide a greater cardiac output. The device must also not respond to sudden changes in physiological conditions, such as the transiently elevated pressure caused by the Valsalva maneuver or a cough.

Second, with a volumetrically coupled TAH, an inherent imbalance in fluid volume between the systemic and the pulmonary circulation will occur. The major contributing

factors to this phenomenon are the bronchial blood flow as a left-to-left shunt, and higher valvular regurgitation on the left side [4]. The pathological consequence is excessively high left atrial pressure (LAP) with extremely low right atrial pressure (RAP). This causes pulmonary edema, a fatal lung condition, in a fairly short period of time.

Third, for stable and reliable operation, the automatic con- trol system must have various safety functions to handle abnormal situations and alarm functions to give warning of the occurrence of possible hazardous conditions. Efficient opera- tion is also necessary in view of energy, thermal management, weight, and recharging consideration. Reduced total power consumption reduces the impact of thermal and mechanical effects on surrounding tissue. Also, it reduces the required power level and weight of the TET and internal/external battery systems.

11. METHODS

A. EHTAH Control System Hardware

The control scheme utilizes a variable rate system with full stroke volume. Cardiac output response is preload sensi- tive and relatively afterload insensitive, while balanced atrial pressures are maintained by an IAS. The IAS is artificially created between the right and left atrial cuffs, and is simple to fabricate and implant [5]. Also, adaptive trigger level control, and several safety and alarm functions provide efficient and stable long-term operation.

In the final EHTAH design shown in Figs. 1 and 2, an external and an internal controller comprise the electronic subsystem. The internal controller consists of a physiological controller and a motor commutator. Information is transmitted bidirectionally between the external controller and the internal physiological controller.

1) Znternal Controller: To physiologically regulate the arti- ficial heart’s output, a feedback loop is required. The automatic control system for the EHTAH is implemented with a mi- crocontroller and two pressure transducers. The physiological controller and the commutator of the internal controller, shown in Fig. 2, are each based on a microcontroller [MC68HCll, 8-b complementary metal-oxide semiconductor (CMOS) mi- crocontroller, Motorola Inc., Phoenix, AZ]. The integrated circuit pressure transducers (Kulite, Leonia, NJ), located in the base of each ventricle, monitor the pressure in the hydraulic fluid. Functionally, the physiological controller, whose block diagram is shown in Fig. 5, can be represented as a system to generate motor speed and direction commands to the commu- tator based on the left and right pressure transducer waveforms or the data sent from the external controller according to the operator-defined operating mode. The commutator drives a three-phase brushless dc motor in the energy converter with a commutation scheme which uses the motor’s back emf waveform to sense rotor speed and direction. Communication between the physiological controller and the commutator is performed by a synchronous serial peripheral interface device embedded in the microcontroller chip.

80 IEEE TRANSACTIONS ON BIOMEDICAL E

Physiological Controller

for pressure waveform digitizahon was implemented in firmware.

with variable heart

likelihood of t h o

ch the operator’s manual adjust- motor speed and heart rate;

r. The four main ler are as follows:

and afterload. 1) Full-Stroke Opera

To maintain full stroke conditions must be satis may cause a hgher the simultaneous occ full-eject in the other.

the internal physiological -232 serial communication link

ing hydraulic oil pressure waveforms;

atic control for the EHTAH is own as the Starling’s

hydraulic oil volume at t that one ventricle is fully However, an undesirable EH full-eject could be creat

To prevent such a res condition of full-eject the other was establishe 5 cc larger than the op phase is made to chang at the full-eject point of in the other. To obtain t point occws, the driv rnm Hg), from systole, is digiti

determine whether to r If a fixed value for

and it is either too low

KIM ef al. ' MICROCONTROLLER-BASED AUTOMATIC CONTROL SYSTEM FOR THE ELECTROHYDRAULIC TOTAL ARTIFICIAL HEART 81

Fig. 7. Left- and right-ventricular hydraulic oil pressure waveform analysis to calculate parameters used in the automatic control routine. Motor's rotational direction changes at the full-ejection point where the systolic pressure rises over the trigger level F ( n ) which is given by: F ( n ) = estimated afterload (n ) +d , estimated afterload (n ) = {estimated afterload ( n - 1) + P(n)} /2 , where d is a predetermined constant, 30 and 60 mm Hg for the right and left side, respectively, and P(n) is the average systolic pressure. Two averaging windows to calculate P(n) and the ADFP are illustrated on the left-ventricular waveform.

range of the systolic arterial pressure, the TAH will be unstable [7] . The TAH's operation will result in either a very high heart rate condition (low trigger level case) or excessive tension on the blood pump membrane (high trigger level case). An adaptive method of changing the reference trigger level is, therefore, necessary for reliable long-term operation. To accomplish this function, the average systolic driving oil pressure was estimated, as shown in Fig. 7. All calculations and control signals regarding the pressure waveform, including those for preload estimation described below, are also graph- ically depicted in Fig. 7. An averaging window was used to calculate an arithmetic average of systolic driving oil pressure. In this window-averaging method, the center point location and the width of the window are critical to get a correct estimation for the arterial pressure. These two parameters were updated at every beat based on the duration of the previous beat's systole. Fig. 7 shows that the window's center point was located at the mid-point of the previous systolic period, and its width was a quarter of the previous systolic period.

For beat-to-beat stability, a restriction was imposed on the variability of the beat length. If the difference in systolic period between two adjacent beats was more than 96 msec, the most recent estimation result was discarded. To the esti- mated systolic driving oil pressure value, operator-selectable offsets-typically of 60 mm Hg for the left ventricle and 30 mm Hg for the right-were added to obtain the desired beat-to-beat full-eject trigger levels for each ventricle [SI.

2) Response to Both Preload and Afterload Changes: The object of the automatic control system is to regulate the cardiac output at a level desirable for the given preload regardless of afterload. If the stroke volume is fixed, heart rate is the only parameter which will change cardiac output. Heart rate is determined by the stroke time which can be adjusted by motor speed in each direction. As shown in Fig. 8(a), a generic form of the automatic control system with motor speed as a control input and heart rate or cardiac output as a control

output can be developed. Instead of handling hemodynamic variables directly, by introducing an average diastolic filling pressure (ADFP) in the hydraulic oil side as a controlled variable, a relatively simple control system was established as shown in Fig. 8(b). The ADFP was calculated from the diastolic portion of the hydraulic oil pressure waveform. The object of the control system of Fig. 8(b) is to keep the ADFP constant as referenced by desired average diastolic oil pressure (DADP). The following equations show how the full-fill time of each ventricle and the resultant heart rate are determined by the atrial pressure (preload) only under the condition of constant ADFP:

(1)

(2)

MVP-ADFl' SV - - - R, Tf

60 HR =

Tfl + Tfr where

MVP mean venous pressure (mean LAP or RAP); R, equivalent inflow resistance of the blood pump; Tf full-fill time in seconds (Tfl for the left and Tfr

for the right ventricle); SV stroke volume; HR heart rate in bpm (beats per minute). Since MVP (preload) is independent of the arterial pressure

(afterload), by keeping the ADFP constant, preload sensi- tive, and afterload insensitive, cardiac output response was achieved. The EHTAH's axial flow pump has a unique feature that permits a variety of differential pressures to be achieved at the selected hydraulic flow rate by varying motor speed [9]. This property of an axial flow pump was utilized to keep ADFP constant under various preload, afterload, and flow rate conditions. Based on this relationship, the established control law can be expressed as follows: The automatic heart rate control algorithm controls motor speed to keep the ADFP constant and slightly negative as referenced to the DADP. By

82 IEEE TRANSACTIONS ON BIOMEDI

control system (a) a generic form of a closed-loop control system to oad and (b) the proposed control system for the same performance rage diastolic oil pressure, respectively

the given preload re tolic filling pressure

, the full-fill time of each ventricle is determined

ad and preload are reflected handled by the automatic

where

MVP mean venou

ADFP is greater (less) than the DADP, the motor speed

resulting expression

MAP as preload and aft

differential pressure and d by a family of lines as

between eith

is much more The automatic

e differential pressure across

KIM et al.: MICROCONTROLLER-BASED AUTOMATIC CONTROL SYSTEM FOR THE ELECTROHYDRAULIC TOTAL ARTIFICIAL HEART

~

83

3 Phase ? Right Systole (RS) f Left Systoie(LS) U Send LS speed register

to communtator

8 point window averaging of LS low gain waveform (LSP)

& 64 point window

averaging of RD high gain waveform (RDP)

afterioad estimation from LSP buffer, and

left Full-ejection trigger

Window averaging for right ADFP from

RDP buffer

8 point window averaging of RS low gain waveform (RSP)

64 point window averaging of LD high gain waveform (LDP)

no

Window averaging for afterioad estimation from

RSP buffer, and right Full-ejection trigger level

adlustment

for left ADFP from

Increase LS speed Decrease Ls speed increase RS speed register by 200 RPM register by 200 RPM register by 200 RPM register by 200 RPM

4 > + A + I f

Change Direction

Jump to other no

Fig. 9. Flowchart of the automatic control algorithm.

and then averaged. The A D P estimation routine consists of two averaging sections depicted in Fig. 7. The first section calculates and stores a temporary average value for every 64 samples. Based on the 1-kHz sampling rate, this routine provides a temporary average value every 64 ms and stores it in an average buffer. When the diastolic period ends and the systolic phase starts, the second averaging section fetches the temporary average values from the average buffer and

then calculates the final average value. In this second section, the data from the first half of diastole is excluded from final averaging to delete the effect of any transients on the leading part of the diastolic waveform.

1 ) In Vitro Tests: The developed automatic control system for EHTAH was tested on a Donovan-type mock circula- tion system (MCS). This system consists of four chambers which simulate systemic arterial, pulmonary arterial, systemic

84 IEEE TR

0 5 10 15 RAP [mmHg]

(a)

RAP [mmHg] @)

Fig. 10. Results of the MC tests showing: (a) cardiac output (CO) and (b) LAP changes according to the RAP vanation withm a physiological range of AoP

venous, and pulmo y venous circulations. Each chamber is a lumped-parameter model of the corresponding part of the circulatory system. This system has been extensively used for in vitro performance tests of the artificial heart. This MCS permits not only a simulation of a broad range of preload conditions by varying pressure in the systemic venous chamber, but also, a range of afterload variations

systemic and pulmonary arterial resistance. flow rate was achieved and adjusted by

gh compliant and collapsible

ANSACTIONS ON BIOMEDI

KIM et al.. MICROCONTROLLER-BASED AUTOMATIC CONTROL SYSTEM FOR THE ELECTROHYDRAULIC TOTAL ARTIFICIAL HEART 85

connected to the MCS, the blood pump was immersed in a 37-”C water bath to simulate the in vivo environment.

2) Acute In Vivo Tests: After in vitro MCS evaluation of the developed EHTAH system and the automatic controller, acute in vivo experiments in open-chested calves were undertaken. In these acute studies, cardiac output was measured using an implanted ultrasonic flow probe. RAP was manipulated to simulate preload change by increasing and decreasing blood volume through a heart-lung bypass machine. Aortic pressure (AoP) was varied by pharmacological agents. A total of six acute in vivo experiments were conducted during the duration of the device’s development.

3) Chronic In Vivo Tests: A total of eight and four calves were chronically implanted with the EHTAH20 series and EHTAH30 series systems, respectively. The EHTAH30 series of systems had a redesigned blood pump which provided better anatomic fit and greater cardiac output capability than the EHTAH20 series system. Surgical implantation and pre- and post-operative management procedures were the same as those previously established in the authors’ laboratory for pneumatically driven TAH animals [lo]. During weaning from bypass and stabilization of the animal in the operating room, the controller functioned in the manual mode and was adjusted by an operator. Typically, automatic control was initiated only after the implanted animal’s chest had been closed, its physiological condition had stabilized, it had been transported to the post-operative care facilities, and it had been given ample recuperation time. The dynamic efficacy of the automatic control was tested by subjecting the calf to treadmill exercise and determining the controller’s response as well as the resulting pressures.

111. RESULTS

A. Mock Circulation and Acute Animal Experiments

Fig. 10 shows a typical result of mock circulation tests with the EHTAH 20 series of systems. The test was performed by varying preload and afterload to obtain the control system’s re- sponse. The developed automatic control system demonstrated very satisfactory performance. As Fig. 10(a) shows, with a rise in RAP from 0 to 12 mm Hg, the cardiac output increased from 4 to approximately 9 L/min. No noticeable difference in cardiac output was seen for the three different AoP conditions (80-120 mm Hg). MCS tests have also shown the IAS to be effective in establishing ventricular balance over a wide range of preload and afterload condition [ l l ] . Fig. 10(b) shows the LAP and the RAP remained in acceptable proximity of each other. The maximum difference between LAP and RAP was 7 mm Hg. Fig. 10(b) also shows that the LAP remained below 20 mm Hg as RAP (and cardiac output) increased.

In acute animal experiments with open-chested calves, the automatic control system demonstrated physiological autoregulation as shown in Fig. 11. Fig. ll(a) shows that the EHTAH20 series’ heart rate responded to changes in preload. When RAP was low (3-5 mm Hg), measured cardiac output was typically 4 L/min. As RAP increased to 12-15 mm Hg, output progressively rose to a maximum of 8-9 L/min. Slightly lower cardiac output in the acute experiments than

on the MCS was achieved at low RAP. This lower output is probably due to the limited availability of blood volume for filling the TAH in the animal as compared to that available in the MCS. Fig. 1l(b) shows that the IAS performed its balancing function: LAP and RAP track each other, with the LAP being slightly higher than the RAP. Fig. ll(c) shows that the EHTAH’s cardiac output and heart rate are relatively insensitive to changes in afterload.

B. Chronic Animal Experiments Twelve chronic animal implants with the EHTAH20 and

EHTAH30 series of systems were performed in calves. In six out of eight chronic experiments with the EHTAH20

series [12], the steady-state operation of the automatic control mode was tested. There existed no significant difference in performance of the automatic control system between in vitro and in vivo studies. Since the main purpose of the chronic implants with the EHTAH20 series was the verification of IAS performance in terms of balanced atrial pressures and long-term patency, no effort to manipulate preload and afterload change through exercise or pharmacological method was attempted. Measurement of cardiac output by dye dilution was used to confirm the estimated cardiac output which was calculated by the control system based on a fixed stroke volume and the measured heart rate (CO = HR x SV). While operating in automatic mode, the estimated cardiac output was within f10% of the measured values.

The results of four chronic animal experiments with the EHTAH30 series systems are summarized in Table I [13]. The first two experiments were of short duration (0-5 days). In the two animal experiments of longer duration with the EHTAH30 series systems, the automatic control system was operated. The control mode was switched from manual to automatic mode on the 18th post operative day in the 32-day survivor. Abrupt reduction of not only heart rate by 10 bpm, but the LAP and the RAP by 5 mm Hg were achieved, which indicates the appropriateness of the automatic control mode over manual control under the given hemodynamic condition. In the longest survivor, the automatic control system operated for the first 21 post-operative days, which was later changed to manual mode because of pressure-transducer connector failure. The animal’s body weight continually increased from 8 1 kg, preoperatively, to 135 kg. The heart rate varied between 115-144 bpm during automatic control operation, and the cardiac output measured by dye dilution method ranged from 9.3 to 10.5 L/min. The mean AoP, mean PAP, mean LAP, and mean RAP ranged between 85-105 mm Hg, 25-55 mm Hg, 8-22 mm Hg, and 4-20 mm Hg, respectively.

To investigate the response of the automatic control system to changes in physiological condition, the longest surviving animal was subjected to a treadmill exercise test. The exercise was started on the 15th post-operative day after the animal had recovered fully from surgical intervention. Hemodynamic change was induced with 30 min of exercise at a speed of 1.7 kmk and the exercise was performed three times under both manual and automatic control modes for comparison purpose. The heart rate during exercise varied between 128-135 bpm under automatic mode and was fixed at 125 bpm under manual

IEEE TRANSACTIONS ON BIOMED

TABLE I

Respiratory failure; pulmonary embolism

systems include: 1) aortic pressure as change [14], 2) cardi

to its pre-exercise level after exercise. cant difference between

under manual mode from and 4, ra

Hg for LAP and RAP, cardiac output the b

was successfully demons

KIM et al.’ MICROCONTROLLER-BASED AUTOMATIC CONTROL SYSTEM FOR THE ELECTROHYDRAULIC TOTAL ARTIFICIAL HEART

25

s 20

E E 15

I

v

5

~ Manual Control Mode I

........................

I I

0 10 20 30 40

Time (min)

20 ...................................................................................................................................................................................................................................................

n 1 ~ ) 15 r E

“E 10 v LL

6 5

0

I A Manual Control Mode

....................................................................................

Exercise I

0 10 20 30 40

Time (min) (b)

Fig. 13. (a) LAP and (b) RAP during exercise of 159 days surviving animal. Results in manual and automatic mode are represented by open marks connected by dotted lines and solid marks with solid lines, respectively. The exercise was performed three times under each mode.

The EHTAH’s balancing method, the IAS, has several advantages over balancing methods used by other groups. The most commonly used mechanism to compensate the effective pump output difference is a volume displacement chamber (VDC) [ 181. By absorbing and releasing appropriate volume of gadfluid from and to the interventricular space, the VDC handles the instantaneous volume change inside the pump housing relatively easily. Problems in using the VDC are an increased number of separate implanted components, loss of compliance volume by gadfluid diffusion through the flexible polymer membrane (which forces a provision for an infusion port subcutaneously implanted for periodic external filling of the chamber), and loss of flexibility of the VDC’s membrane by fibrous ingrowth. Other balancing methods use a two- phased fluid volume compensation chamber using freon as a working fluid [19], a small compliance chamber attached to a cuff in the left atrium into which part of the working hydraulic fluid for the right ventricle is bypassed [20], and the compliance of the air trapped inside the pump housing [21].

An automatic physiological control system of the actively filled, altemately pumped, volumetrically coupled, EHTAH was developed, tested on the mock circulation and chronically implanted in calves. The performance of the developed control system was confirmed through in vitro MCS tests as well as in vivo chronic studies. The resultant cardiac output

response curves, as shown in Figs. 10 and 11, are very similar to that of the natural heart except that the EHTAH provides considerable output around zero RAP. This is one of the features of an actively filled device that is favorable in terms of delivering as much cardiac output as possible. Overall performance was adequate for animal survival for up to 159 days without major complications related to the control system. Furthermore, adequacy of the developed automatic control response to changes in physiological condition was demonstrated through animal exercise tests.

The demonstrated features of the developed automatic control system include: 1) a unique and relatively simple automatic control algorithm incorporating the IAS concept which enhances the system’s simplicity, 2) separate physi- ological controller and commutator which provide easy and independent maintainability and upgradability, 3) a single chip microcontroller-based and potentiometer-absent analog circuitry system which simplifies hardware architecture and miniaturization, 4) an EEPROM-based internal controller reprogrammable from outside the patient using RS-232 communication, 5) a flexible and modular structured software system, 6) interrupt driven U0 functions in software which enables concurrent system performance and were proven for the worst-case timing latency, 7) the potential for totally automatic operation, which eliminates any need of manual

88 IEEE TI?

intervention under the variation of odynamic condition, and 8) intelligent emergency g and alardalert functions included in software.

The related work done for the development of a totally im- plantable control system includes: 1) transducer elimination to enhance the system simplicity and reliability by utilizing motor current waveform to estimate pressures [22] and 2) electronic miniaturization and packaging for implantation, including the use of hybrid circuit and surface mount technology [23].

In vivo test results with the EHTAH20 system senes showed the importan refining device-specific anatomic fit, implantation, and PO erative control. Using these lessons based on the results of extehsive failure analysis and corrective action taken after every animal experiment, we designed the EHTAH30 system series of blood pump. The EHTAH30 blood

1 departure from the EHTAH20. As a result, eriments with the EHTAH30 were of short roper placement and malpositioning of the

EHTAH resulting in distortion of the vena cava, and improper blood flow patterns caused by the inflowloutflow blood conduit orientations. The 32-day EHTAH30 animal died from a combination of a la dministration of anti-coagulation regimen during the early post-operative period, and of a ventricle who ular orientation and design of its housing and conduits may have caused undesirable flow characteristics inside it, accelerating the effect of the lack of anti-coagulants. The EHTAH30’s blood pump design has since been refined to minimize such occurrences. The 159-day animal died from two possible causes of the energy converter’s mechanical failure, both of which were related to the fact that specifications set by us were not met by the supplier of the motorhearing assembly. As a result, we simplified the design of the energy converter as well as tightened our supplier

to be done to complete and plantable EHTAH. Areas of

and 4) integrate and system as shown in

RE CES

[l] R T V Kung, L. S Yu, B Ochs, S Pamis, and 0 H Frazier, “An atrial hydraulic shunt in a total artificial heart-A balance mechanism

,” Amer Soc Artf Intern Organs J., vol. 39,

Ford,R A Nazarian,D. Prophet, J S Sapirstein, testing of a completely

” Amer. Soc. Art$ Intern Organs.

VSACTIONS ON BIOMEDICAL

131

~ 4 1

151

[61

[91

T. C. Rntoul, K. C. But1

Kmoshta, H. C. IQm, in implanted electrical

D. B. Olsen, R. K Whi

for the actively filled electr 2, pp. 152-162, 1988

heart and for cardiac Surgery, D H. Slatter

K. R. Crump, P. S Kh 1985, pp 1141-1147.

M425-M430, 1992. E. Tatsumi, P. S. Khanwi W. Long, A C Hansen,

Intern. Organs J., vol. A J. Snyder, G. Rosen “Introductory lecture on CO

C S. Kwan-Gett, M. J. July 3, 1984, pp 167-19

Trans Amer. So H. C a m and

a totally implantable J , vol. 38, no 3, pp.

electrohydraulic total

KIM et al.’ MICROCONTROLLER-BASED AUTOMATIC CONTROL SYSTEM FOR THE ELECTROHYDRAULIC TOTAL ARTIFICIAL HEART 89

Hee Chan Kim (M’95) received the Ph.D. degree in control and instrumentation engineering from Seoul National University, Seoul, Korea, in 1989.

Since 1982, he has been a Research Member at Department of Biomedical Engineering, Seoul National University, where he started the totally im- plantable artificial heart development project. From 1989 to 1991, he was with the Artificial Heart Research Laboratory, University of Utah, Salt Lake City, UT, where he was a Staff Engineer working on the NIH-funded electrohydraulic total artificial

heart project. He joined the faculty of Department of Biomedical Engineering at Seoul National University in 1991 where he is presently an Assistant Professor. He rejoined the University of Utah group as a Visiting Research Professor from 1993 to 1994. His research interests focus on electrical engineering as related to artificial intemal organs.

Dr. Kim is a member of IEEEEMBS, American Society for Artificial Intemal Organs, and Korea Society of Medical and Biological Engineering.

Pratap S. Khanwilkar (S’83) received the B.Tech. (honors) degree in electrical engineering from the Indian Institute of Technology, Kharagpur, India, in 1984, the M.S. degree in bioengineering in 1987, and the M.B.A. degree in 1992 from the University of Utah, Salt Lake City, UT. He is currently earning the Ph.D. degree in bioengineering at the University of Utah.

He has designed and developed artificial hearts and ventricular assist devices since 1988. He was the Project Manager and Systems Engineer for the

NIH-funded electrohydraulic total artificial heart project from 1989 to 1993. His primary focus was system design and in vivo testing. He is currently the Director of Engineering at the Artificial Heart Research Laboratory, University of Utah. He is also the President of MedQuest Products Inc., a business which commercializes mechanical circulatory support devices and performs contract medical device R&D for clients worldwide. He teaches marketing, business, and technology management to MBA students at area universities. His current research interests include the design of a totally implantable magnetically suspended rotary blood pump for long-term use.

Mr. Khanwilkar is an Amencan Society for Quality Control (ASQC)- certified Quality Engineer (1995) and is also a member of the Association for the Advancement of Medical Instrumentahon (AAMI), Intemational Society for Rotary Blood Pumps (ISRBP), and American Marketing Association (AMA)

Gill B. Bearnson (S’83-M’86-S’87-MSS-S’94) received the B.S. and M.E. degrees in electrical engineering from the University of Utah, Salt Lake City, UT, in 1986 and 1988, respectively. He is presently a candidate for the Ph.D. degree in elec- trical engineering with graduation planned for June 1997.

Since 1989, he has been a Research Engineer at the Artificial Heart Research Laboratory at the University of Utah. His research interests are in the areas of design and control of blood pumps and

related devices, including brushless dc motor design and control and response to changes in physical exertion of the patient.

Don B. Olsen received the B.S. degree from Utah State University, Logan, UT, in 1952, a D.V.M. degree from Colorado State University, Ft. Collins, CO, in 1956, and did post-doctoral work in pathology at the University of Colorado School of Medicine, Denver, CO (1968-1972).

The Director of the Inshtute for Biomedical Engineering since 1986, he is a Professor of Surgery, Research Professor of Pharmaceuhcs, and Research Professor of Bioengineering at the University of Utah. Involved in biomedical research

for more than 30 years-with 23 years in artificial heart research, perfecting surgical techniques to implant the artificial heart in animals and humans-he trained most of the world’s clinical artificial heart implant teams in the 1980’s. More than 250 patients in the world have received the Utah-developed artificial heart for bridging to cardiac transplantation and he presently leads its commercialization.

Dr. Olsen is a founding fellow of AIMBE, Vice Dean of the Intemational Faculty of Artificial Organs, and Past-President of the American Society for Artificial Intemal Organs. He has received numerous honors and awards, while influencing national and international development and use of biomedical technologies. He has authored or co-authored more than 450 publications. His current research interests include the development of a totally implantable magnetically suspended rotary blood pump and its control.