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Biomedical subjects

H C Kim

Publications and source records attributed to H C Kim.

356 records · Page 20Linked to original sources
PubMedDate not supplied

Chronic peritoneal inflammation by cyanate in rats.

OBJECTIVE: During peritoneal dialysis, the peritoneum is exposed to waste products, including urea. Urea forms cyanate spontaneously at body temperature and pH, and cyanate carbamylates amino acids, peptides, and proteins. Cyanate may contribute to peritoneal injury with morphological changes in the peritoneum. To test this hypothesis, we injected cyanate into rats. METHODS: Experiments were performed in two groups of 7 rats each. In the cyanate group, each rat received 1 mL of 1.5 micromol/L potassium cyanate dissolved in 40 mmol/L sodium bicarbonate solution intraperitoneally each experiment day. In the control group, each rat received 1 mL of 1.5 micromol/L potassium bicarbonate instead of potassium cyanate. The rats in both groups were anesthetized and killed at the 85th day after the first injection. After formalin fixation, tissue samples from abdominal walls and livers were sliced, embedded in a standard manner, and stained with hematoxylin and eosin. RESULTS: Parietal peritoneum from rats in the cyanate group showed a mild increase in the number of fibroblasts, with collagen deposits, infiltration by mononuclear cells, vascular congestion, round-shaped transformation of mesothelial cells, widening of submesothelial spaces, and abundant denudation of mesothelial cells. The visceral peritoneum from rats in the cyanate group showed collagen deposits with fibroblastic proliferation. CONCLUSIONS: Cyanate can induce chronic inflammation in the peritoneum, and exposure of the peritoneum to cyanate may contribute to peritoneal injury in patients being treated with peritoneal dialysis.

Animals↗
PubMedDate not supplied

Cardiac output regulation in the moving actuator total artificial heart without a compliance chamber.

A new cardiac output regulation method for the moving actuator total artificial heart (TAH) has been developed without using an extra compliance chamber or any transducer. The left and right ventricular sacs are alternately pumped by the pendulous moving actuator, with the left sac attached to the actuator and a free right ventricle. Preload sensitive cardiac output response is achieved by adjusting heart rate just below the level needed to generate atrial collapse, while maintaining full-fill and full-ejection conditions. The motor current waveform analysis detects mild atrial suction related to the amount of venous return. In addition, the structural characteristic of the pendulous moving actuator allows for manipulation of the left and right ventricular output difference by adjusting the asymmetry of stroke angle to either the left or right. In mock circulatory system tests, cardiac output increased from 5 to 9 L/min, with left atrial pressure (LAP) maintained at approximately 5 mmHg higher than right atrial pressure (RAP) over a physiologic range of preload (0-12 mmHg of RAP) and afterload [80-120 mmHg of aortic pressure (AoP)].

Algorithms↗
PubMedDate not supplied

Development of an automatic control algorithm for the electrohydraulic total artificial heart without transducers.

To achieve a reliable and simple implantable total artificial heart, the number of implanted transducers providing the physiologic information required for automatic control should be minimized. To address this need, a new automatic control algorithm, based on a transducerless electrohydraulic total artificial heart (EHTAH) system, is proposed. The current EHTAH physiologic control algorithm relies on two implanted pressure transducers. Without these transducers, the information required for automatic control must be extracted from the running motor's parameters. These parameters correlated with the differential pressure across the axial flow pump used to actuate the EHTAH. Changes in this differential were chosen as a cue for cardiac output control. This algorithm can be viewed as depending upon systemic vascular resistance determined by subtracting mean right atrial pressure (RAP) from mean aortic pressure (AoP) and dividing the result by total cardiac output (CO). The difference between mean AoP and mean RAP was confirmed to correlate with the differential hydraulic pressure across the energy converter during the left systolic phase. As an interim configuration, a single differential pressure transducer measuring the differential hydraulic pressure across the energy converter was tested on a Donovan mock circulation system. The resultant CO response shows good sensitivity according to changes in both preload and afterload.

Algorithms↗
PubMedDate not supplied

A tether-free, moving actuator total artificial heart.

An electromechanical moving-actuator TAH was developed and implanted for 5 days in a calf experiment. The efficiency and durability were further improved using pendulous motion of the actuator. This new pendulum pump has a circular motion produced by gear mechanisms connected to the motor. It has a height (from valves to housing bottom) of 7 cm and centrally directed inlets and outlets for good fittability. Active filling (-10 mmHg) inside inner blood sacs was produced by the suction effects of the outer sacs attached to a moving actuator. Two acute animal experiments were performed using the pendulum pump with a Coridale sheep (50 kg weight), and a male calf (70 kg weight). A test was made of 30 minutes of tether-free operation of the implanted pendulum pump inside the small chest of the calf. The pump shows the engineering feasibility of the implantable electrical TAH inside a human chest cavity.

Animals↗
PubMedDate not supplied

Right-left ventricular balance in implanted electrically powered artificial hearts.

An electrohydraulic total artificial heart (EHTAH), using an interatrial shunt (IAS) for right-left heart balance, was evaluated in acute, in vivo, open-chested calves. The EHTAH system demonstrated physiologic autoregulation with Starling-like responsiveness to preload. Output varied from 4 to 9 L/min, as right atrial pressure increased from 3 to 15 mmHg. Device output was minimally influenced by afterload. The efficacy of an IAS to balance the EHTAH was demonstrated over a wide range of preload and afterload conditions. Interatrial shunt flow rates, reflective of the degree of right-left imbalance, varied from 2% to 14% (IAS flow from left to right) of cardiac output. Left atrial pressures typically did not exceed right atrial pressures by more than 6-8 mmHg using an instrumented vascular graft such as the IAS. The simplicity and distinct anatomic, surgical, and engineering advantages of the IAS approach to right-left balance of implanted electrically powered artificial hearts justify further development toward a reliable long-term design.

Animals↗
PubMedDate not supplied

Serotonin induced platelet aggregation in systemic sclerosis.

We studied in vitro platelet aggregation response to serotonin in 19 patients with systemic sclerosis and 18 matched controls. Individuals with early systemic sclerosis had increased % platelet aggregation at 3 minutes over a wide range of serotonin concentrations when compared to individuals with late systemic sclerosis. Patients with generalized disease did not differ from those with limited disease. No significant differences in initial slope of platelet aggregation were detected in any patient subgroup. These data support previous studies suggesting platelet activation in systemic sclerosis and further suggest that future studies of platelet abnormalities in systemic sclerosis should consider the effects of disease duration.

Adult↗
PubMedDate not supplied

Adaptive full-ejection point detection for automatic control of the electrohydraulic total artificial heart.

An adaptive algorithm to detect full ejection points was developed for the automatic control of the electrohydraulic total artificial heart (EHTAH). To automatically control the EHTAH, systole in each ventricle is completed when a hyper-pressurization spike is detected on the oil side of that ventricle. A problem associated with the method of determining ventricular full ejection under variable afterload pressure is that a fixed level comparison method could fail to provide a normal full ejection condition. To increase system stability, safety, and efficiency, there is a definite need to vary the full ejection trigger level with changes in afterload. In this study, the full ejection trigger level for the current beat was changed based on the estimated afterload derived from the previous beat's pressure waveform. To increase this estimate's accuracy, an adaptive averaging window was used to determine which part of the previous pressure waveform would be used for the afterload estimation. With this enhanced control scheme, mock circulation tests with the EHTAH device demonstrated that estimated afterload tracked actual afterload. This scheme was also used successfully to control the EHTAH device implanted in three chronic calves.

Animals↗
PubMedDate not supplied

In vivo performance evaluation of a transcutaneous energy and information transmission system for the total artificial heart.

As part of an electromechanical total artificial heart (TAH) program, an integrated transcutaneous energy and information transmission (TEIT) system has been developed. In vivo performance of the developed system was evaluated through a simplified animal model without implant of a TAH. The design features include the small size of the implanted part, and dual coil structure of the external part. In the transcutaneous energy transmission (TET) system based on magnetic induction, the external primary and implanted secondary coils have the shape of a truncated cone, 7.0 and 3.8 cm in diameter, and 23 and 12 turns of Litz wire, respectively. The external coil is driven by a 350 to 410 kHz tuned class E amplifier that has a minimum switching loss of power transistor. In vitro test results using 1 cm thick dog's skin showed a flat total efficiency (DC to DC) of 75% for 20 to 30 W of delivered mean power. In order to achieve bidirectional communication between implanted and external components, a small circuit board containing four light emitting diodes and a photodiode was incorporated in each TET coil facing each other across the skin. Unmodulated optical pulse transmitted digital data (9600 baud, RS-232 protocol) in error free condition through an up to 15 mm thick dog's skin patch accommodated 18 degrees of misalignment. Three subacute in vivo studies were conducted in dogs to evaluate performance of the developed system. The secondary set was implanted in the mild flank region of the dog, and the output was percutaneously connected to the control system to drive the external TAH on the mock circulatory system.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Intravenous ketorolac and subarachnoid opioid analgesia in the management of acute postoperative pain.

BACKGROUND AND OBJECTIVES: Ketorolac is a parenteral nonsteroidal anti-inflammatory drug that provides analgesia through a peripheral mechanism. The purpose of this study was to evaluate whether the scheduled administration of intravenous ketorolac improves the analgesia provided by subarachnoid opioids after surgery. METHODS: Patients undergoing major urologic surgery were enrolled in a randomized, placebo-controlled, double-blinded study and received one of two analgesic regimens. All patients were given subarachnoid opioid analgesia consisting of morphine (range, 0.55-0.8 mg) plus fentanyl (25 micrograms) at the completion of surgery just prior to awakening. In addition to subarachnoid opioids, patients received four doses of either intravenous placebo (group 1, n = 21) or ketorolac (group 2, n = 17) administered 30 minutes before the anticipated completion of surgery and at 6, 12, and 18 hours after surgery. Patients in group 2 who were 65 years old or older received 30 mg ketorolac initially, with subsequent doses of 15 mg. Those younger than 65 years of age received 60 mg ketorolac initially, with subsequent doses of 30 mg. Pain scores were assessed by a blinded observer using a 10-cm visual analog scale (VAS) at 1, 8, and 24 hours after the operation. Intravenous morphine requirements while in the postanesthesia care unit (PACU) and during the following 24 hours, as well as the incidence of pruritus, nausea, naloxone usage, and bleeding were also recorded. Results were analyzed using the Wilcoxon rank-sum, Fischer's exact, chi-square, and Student's t tests. RESULTS: Patients receiving intravenous ketorolac (group 2) in addition to subarachnoid opioids had significantly lower pain scores 1 hour after surgery, and required less supplementary intravenous morphine within the first 24 postoperative hours (P < .05). The percentage of patients requiring no analgesic intervention while in the PACU was significantly higher for those receiving ketorolac (P = .01). The incidence of opioid-related side effects was similar between groups, and no perioperative bleeding was observed. CONCLUSIONS: When used in conjunction with subarachnoid opioids, the scheduled administration of intravenous ketorolac during the first 24 hours after major urologic surgery significantly enhances analgesia and reduces the need for supplemental intravenous opioids without affecting the incidence of side effects. Intravenous ketorolac is a safe and useful adjuvant to subarachnoid opioids in the management of acute postoperative pain.

Acute Disease↗
PubMedDate not supplied

Development of a prototype magnetically suspended rotor ventricular assist device.

A continuous flow centrifugal blood pump with magnetically suspended impeller has been designed, constructed, and tested. The system can be functionally divided into three subsystem designs: 1) centrifugal pump and flow paths, 2) magnetic bearings, and 3) brushless DC motor. The centrifugal pump is a Francis vane type design with a designed operating point of 6 L/min flow and 100 mmHg pressure rise at 2,300 RPM. Peak hydraulic efficiency is over 50%. The magnetic bearing system is an all active design with five axes of control. Rotor position sensors were developed as part of the system to provide feedback to a proportional-integral-derivative controller. The motor is a sensorless brushless DC motor. Back electromotive force voltage generated by the motor is used to provide commutation for the motor. No slots are employed in the motor design in order to reduce the radial force that the bearings must generate. Tests pumping blood in vitro were very encouraging; an index of hemolysis of 0.0086 +/- 0.0012 was measured. Further design refinement is needed to reduce power dissipation and size of the device. The concept of using magnetic bearings in a blood pump shows promise in a long-term implantable blood pump.

Blood Volume↗