Biomedical subjects

W W Choi

Publications and source records attributed to W W Choi.

42 records · Page 3Linked to original sources

PubMed1984

Comparison of four opioid analgesics as supplements to nitrous oxide anesthesia.

The hemodynamic changes, plasma norepinephrine levels, pupil size, and rapidity of postoperative mental recovery were measured and compared in 72 patients randomly assigned in a double-blind manner to receive either morphine, meperidine, fentanyl, or sufentanil as supplements to nitrous oxide anesthesia. Meperidine, unlike the other opioids, which did not change heart rate, consistently increased it. Hemodynamic responses to laryngoscopy and intubation were suppressed by fentanyl and sufentanil, but not by morphine or meperidine. The sufentanil group was the only group in which median norepinephrine levels remained consistently below preinduction values. The frequency with which opioids had to be administered (doses/hr) was significantly less with sufentanil than with morphine and meperidine. Meperidine produced less constriction of the pupils than the other opioids and the duration of miosis was shorter. Fentanyl and sufentanil were associated with a more rapid return of mental function than morphine and meperidine. Meperidine caused deleterious effects on objective tests of psychomotor and cognitive skills that were not reflected by subjective evaluation of rate of recovery from anesthesia. The authors conclude that moderate doses of fentanyl and sufentanil are better supplements to nitrous oxide anesthesia than morphine or meperidine and that fentanyl and sufentanil are equally satisfactory. Subjective effects of the opioids correlated well with changes in pupil diameter.

Adjuvants, Anesthesia↗

PubMedDate not supplied

Development of an electrohydraulic total artificial heart at the National Cardiovascular Center, Osaka, Japan.

The authors have been developing an electrohydraulic total artificial heart with a basic concept placing the blood pumps and an electrohydraulic energy converter separately, in the thorax and the abdominal region, respectively, to minimize anatomic constraints. Major problems of the system were a high energy consumption of 56 W at 6 L/min output and an insufficient maximum output of 6.7 L/min. The energy converter was redesigned to overcome these problems. A three phase, 4 pole brushless DC motor, which has maximum efficiency of 79% at a motor rotation of 2500 rpm with a load of 0.1 Nm, was developed for the new energy converter. Flow-channel design of the regenerative oil pump was optimized, which resulted in increasing the maximum flow rate at one directional motor rotation from 18 to 29 L/min. In vitro performance of the electrohydraulic total artificial heart was evaluated in a mock circulation with physiologic pressure conditions. Maximum output was increased to 10.7 L/min at a pump rate of 120 bpm and energy consumption of the motor at 6 L/min output was reduced to 18 W. Based upon these favorable results, the system is now being assembled for chronic animal implantation.

Animals↗

PubMedDate not supplied

Development of a precise controller for an electrohydraulic total artificial heart. Improvement of the motor's dynamic response.

In an electrohydraulic total artificial heart developed at the National Cardiovascular Center (Osaka, Japan), two blood pumps are pushed alternatively by means of the bidirectional motion of a brushless DC motor for pump systole and diastole. Improvement in the dynamic response of the motor is very important to obtain better pump performance; this was accomplished by using power electronic simulation. For the motor to have the desired dynamic response, it must be commutated properly and the damping ratio (zeta), which represents transient characteristics of the motor, must lie between 0.4 and 0.8. Consequently, all satisfactory specifications with respect to power consumption must be obtained. Based on the simulated results, the design criteria were determined and the precise controller designed to reduce torque ripple and motor vibration, and determine motor stop time at every direction change. In in vitro tests, evaluation of the controller and dynamic response of the motor was justified in terms of zeta, power consumption, and motor stop time. The results indicated that the power consumption of the controller and the input power of the motor were decreased by 1.2 and 2.5 W at zeta = 0.6, respectively, compared to the previous system. An acceptable dynamic response of the motor, necessary for the reduction of torque ripple and motor vibration, was obtained between zeta = 0.5 and zeta = 0.7, with an increase in system efficiency from 10% to 12%. The motor stop time required for stable motor reoperation was determined to be over 10 msec, for a savings in power consumption of approximately 1.5 W. Therefore, the improved dynamic response of the motor can contribute to the stability and reliability of the pump.

Biomedical Engineering↗

PubMedDate not supplied

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.

Animals↗

PubMedDate not supplied

Conscious sedation for procedures under local or topical anesthesia.

For many surgical procedures in otolaryngology general anesthesia is not required, but it is difficult to block completely all noxious sensations with local or topical anesthesia. Intravenously administered antianxiety and analgesic drugs can make the procedure more tolerable for the patient. A technique of conscious sedation based upon titrating diazepam to specific eye signs and fentanyl to specific end points is described. Safety is maintained by ensuring that the patient is always in verbal contact with the surgeon. The rationale for administering the sedative before the narcotic is presented along with the treatment of side effects and untoward responses to the drugs.

Administration, Topical↗

PubMedDate not supplied

Development of a totally implantable total artificial heart controller.

Using a one chip microcontroller, 87C196 (One chip EPROM), and an erasable and programmable logic device (EPLD), an implantable control system to drive a pendulum type electromechanical total artificial heart was developed. This control system consists of four parts: a main management system, a motor driver with power regulator, a state monitoring system, and a communication portion. The main system has a speed detector, proportional and integral (PI) control, pulse width modulation (PWM) generation, serial communication, and an analog data processor. Two kinds of power system are used, separated by eight photocoupler arrays to improve system stability. When the performance of each compartment was compared with that of the previously used Z80 microprocessor based control system, good correspondence was shown. Logic power consumption was reduced to one third that of the previous controller. Using mock circulation tests, the overall performance of the control system was evaluated.

Blood Flow Velocity↗