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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.

Tumor necrosis factor alpha (TNF) is a mediator of injury in the critically ill. Its small molecular size (17 kd) should allow its clearance during continuous hemodiafiltration (CHD). The authors studied TNF extraction in 12 critically ill patients (APACHE II score 26.3 mean; range, 19-34) receiving CHD. Tumor necrosis factor levels were measured in prefiltered and filtered blood and ultradiafiltrate at 0.4 and 24 hours of therapy. Before CHD, mean plasma TNF levels were 261 pg/ml (95% confidence interval [CI]: 184-578) and 291 pg/ml (95% CI: 0-589) after 24 hours. There were no statistically significant differences between prefilter and postfilter TNF levels. Most ultradiafiltrate samples (74%) contained demonstrable TNF (mean, 314 pg/ml; 95% CI: 67-561). Daily TNF excretion was a mean of 15.9 micrograms (+5.6 standard error [SE]), with a mean daily clearance of 27.5 L (95% CI: 2.5-52.5). The authors conclude that significant amounts of TNF are excreted in the ultradiafiltrate during CHD. This observation may provide a rationale for use of similar therapies in critically ill patients in the absence of conventional indications for dialytic support.

The relative resistance of S. epidermidis implant-associated infections to antibiotic therapy has been ascribed to a protective function of the gluelike biofilm matrix produced by strains of S. epidermidis in contact with artificial surfaces. Using a standardized S. epidermidis biofilm assay we determined the periods of exposure required by various antibiotics to produce cessation of biofilm metabolic activity. Rifampin has the superior rate of action, producing substantial disruption of biofilm activity by 7 hr of exposure, but leading to replacement of the susceptible bacterial cells by rifampin-resistant mutant survivors. Other antibiotics required longer periods of exposure, in excess of 48 hr, but produced a bactericidal outcome. Combinations of antibiotics with rifampin produced strikingly divergent results. Cefazolin and vancomycin (cell wall active antibiotics) produced a bactericidal outcome at 16 hr of exposure, whereas gentamicin (aminoglycoside) neutralized the rapid action of rifampin with metabolic activity maintained at 48 hr. We confirmed the selectively protective function of the S. epidermidis biofilm with regard to antibiotic action. In vitro biofilm assays may be of value in guiding antibiotic therapy in S. epidermidis implant-associated infection.

A univalved artificial heart (AH) powered electromagnetically in the frequency range of 1-30 Hz was developed to obtain a totally implantable AH. This small sized AH consisted of a vibrating tube, coils, magnets, and a jellyfish valve as an outlet AH valve. The fluid mechanical, hemodynamic, and hematologic properties were evaluated in a mock circulation and 10 animal experiments using adult goats. This vibrating electromagnetic AH could generate more than 10 L/min as an output volume, with 10 Hz vibration using 20 volts supplied voltage. It could also provide two kinds of flow and pressure patterns, in constant-peak and periodic-peak patterns. The values of free hemoglobin remained within acceptable limits. The authors concluded that this new type of pump was useful as a totally implantable AH, ventricular assist, or organ assist system.

Multiple factors have been implicated in the hematologic response to erythropoietin (EPO). The authors studied 54 hemodialysis patients; 44 received 1.5 g of iron intravenously, 16 received oral iron for 12 weeks, and 24 were treated with EPO. Some patients received these treatments in sequence. The factors evaluated were serum albumin, protein catabolic rate, serologic evidence of hepatitis B or C, parathormone (PTH), and aluminum levels. Red cell production was expressed as milliliters of red blood cell increase per day per kilogram of body weight. For patients receiving EPO, hematologic response was normalized to 50 U/kg/dialysis. Of the patients on oral iron, 31% had a good response (hematocrit greater than or equal to 30%). Of the patients who received iron intravenously, 50% had a good response (hematocrit greater than or equal to 30%). All patients treated with EPO responded well, except for one patient who did not respond to doses of EPO up to 200 U/kg/dialysis. The response to intravenous iron dextran was more rapid than the response to oral iron or EPO. Nutritional factors (serum albumin and protein catabolic rate), serologic evidence of hepatitis, elevated PTH levels, or elevated aluminum levels did not significantly affect the response to iron supplementation or EPO treatment.

Interleukin-1 (IL-1) was measured in the plasma and in mononuclear cell (MC) lysates from patients on maintenance hemodialysis (HD) using either cuprophan (CU) or polysulfone (PS) membranes. Basal plasma levels of IL-1 in HD patients were significantly higher than those of uremic patients on conservative treatment or of healthy subjects. In 10 patients on conservative treatment, plasma levels of IL-1 increased significantly after 3 and 6 months of HD. During a single HD session, plasma IL-1 fell to 21% (CU) and 22% (PS) of pre-HD levels. Hemodialysis patients had a significantly higher intracellular IL-1 content than normal controls. During HD, a further increase was seen regardless of the membrane employed. A parallel in vitro study showed that IL-1 produced during HD requires at least 24 hours to be released, and that both CU and PS are able to bind and clear IL-1.

Surface pitting of certain mechanical heart valve (MHV) explants has prompted investigation into possible causes of cavitation during MHV operation. Leaflets of a 29 mm MHV were glued shut with B-datum (BD) gaps fixed at 0.0089, 0.0174, and 0.0219 cm. Each BD gap setting was tested in a steady flow chamber, with leakage flow established at transvalvular pressures (delta P) of 20 to 200 mmHg. Laser Doppler velocimeter (LDV) velocity measurements were recorded 220 microns distal to the BD, along with leakage flowrates. Maximum LDV velocities were compared with those calculated using the mass conservation equation. At identical P, the LDV flow velocities for the three BD settings were found to be approximately equal. This indicates a geometric independence of the leakage flow velocity. At atmospheric pressure, the local velocity necessary to cavitate blood as a liquid is approximately 13 m/sec. These results demonstrate that the leakage velocity is insufficient to cause cavitation. A simplified theoretical model is proposed to illustrate the necessary delta P to produce Venturi related cavitation.

A 64 ml (effective stroke volume) in vitro electrohydraulic ventricular assist device (VAD) prototype has been built. The energy converter is an axial flow pump driven by a brushless direct current (DC) motor. Systole begins as silicone oil is pumped from the volume displacement chamber (VDC) into the ventricle, displacing the flexing diaphragm separating the oil and the blood. In diastole, the motor reverses, providing active filling by pumping oil from the ventricle into the VDC. The surface mount electronic internal controller provides motor commutator, energy management, telemetry, and physiologic control functions. Energy is supplied externally by either a 12 V DC power supply or a 12 V DC rechargeable battery and is transmitted through the skin by a transcutaneous energy transformer (TET). Energy can also be supplied by a 12 V DC rechargeable internal battery. Bidirectional infrared telemetry is used to transmit information between the internal and external controllers.

A study was undertaken to evaluate hemolysis and subsequent renal damage in 14 patients undergoing cardiopulmonary bypass (CPB) surgery. In all patients, free haptoglobin disappeared completely 30 to 90 minutes into CPB, while free hemoglobin (Hb) levels increased progressively. The NAG index and alpha 1M index also increased progressively, indicating renal tubular injury due to hemolysis (Study 1). An additional 20 patients were monitored intraoperatively for plasma free Hb levels by a newly developed colorimetric method using a haptoglobin coated strip. Free Hb levels during CPB exceeded 30 mg/dl in 14 patients, who were immediately given haptoglobin. This treatment eliminated plasma free Hb within 30 minutes, and effectively prevented hemoglobinuria. Haptoglobin treatment brought significant decreases in the NAG index and alpha 1M index, suggesting a protective effect on renal function (Study 2).

Erythropoietin (EPO) has been used widely for correcting anemia in hemodialyzed (HD) patients. Enhancement of phagocytic function during EPO treatment of HD patients has been studied, but no data have been available on the effect of EPO on neutrophil chemiluminescence (CL) after challenge with phorbol myristate acetate (PMA). CL was measured in prehemodialysis whole blood samples from 15 stabilized patients and 15 normal healthy control subjects (C) after challenge with PMA. Before EPO treatment, CL was noted to be significantly higher in HD patients than in C, which changed significantly after 5 weeks of treatment (Rx) and continued for 13 weeks of Rx. There was a significant increase in hematocrit in these HD patients after 5 weeks that persisted until the 13th week. It was concluded that there is a significant decrease in whole blood CL in response to challenge with PMA during correction of anemia in HD patients treated with EPO. This study demonstrated that EPO could decrease enhanced PMA-activated reactive oxygen metabolite production and suggested that this decrease may protect against tissue damage, including red blood cell hemolysis in the uremic milieu.