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Biomedical subjects

J F Chen

Publications and source records attributed to J F Chen.

At least 91 records · Page 5Linked to original sources
PubMed1985

Improved light sources for induction of sister chromatid differentiation.

Various light sources, including ultraviolet light, mercury, germicidal, fluorescent, and incandescent lamps, were studied for their ability to induce sister chromatid differentiation (SCD) in rat bone marrow cells. The light sources were used along with Hoechst 33258 and Giemsa stains for SCD induction. When those lamps which emit significant amounts of heat were used, 60 degrees C incubation in 2X SSC was found to be unnecessary for SCD induction. A high wattage lamp, a high ambient temperature, a short distance between the lamp and the slides, or a light with 360 nm wavelength, minimized the required exposure time to the light. The pH value of the mounting buffer was also a significant factor. Fluorescent black light and incandescent lamps were found to be ideal light sources for SCD induction.

Animals↗
PubMed1981

Large scale isolation of human erythrocyte membranes by high volume molecular filtration.

A molecular filtration procedure for preparing large quantities of human erythrocyte ghost membranes is presented. Hemolysate ghost membranes are rapidly cycled in the retentate channel of the filtration apparatus, while hemoglobin is removed as it passes through Pellicon filters into the filtrate channel. Several-liter quantities of washed packed erythrocytes can be processed in a few hours with this system, and the filtration procedure does not appear to alter intact erythrocyte or ghost membranes. Intact erythrocytes in isotonic solution can be circulated through the retentate channel for 16 h with only 3% hemolysis and with preservation of their original morphology in scanning electron microscopy. Ghost membranes isolated by the procedure are virtually identical in morphology, polypeptide composition and acetylcholinesterase content to membranes isolated by conventional centrifugation techniques.

Cell Fractionation↗
PubMed1979

Cloning of genes for bacterial glycosyltransferases. II. Selection of a hybrid plasmid carrying the rfah gene.

A hybrid ColE1 plasmid containing DNA from Escherichia coli K12 were identified which was capable of correcting the defect in UDP-galactose:lipopolysaccharide alpha1,3-galactosyltransferase in an rfaH mutant of Salmonella typhimurium. Expression of the gene for this enzyme was also demonstrated in several strains of E. coli by direct assay. The E. coli and S. typhimurium enzymes are similar in catalytic properties and immunologic specificity. The finding of the galactosyltransferase activity in E. coli extracts is surprising since the alpha1,3-galactosylglucose disaccharide which is the product of the enzyme-catalyzed reaction does not appear to be present in the E. coli lipopolysaccharide.

DNA, Recombinant↗
PubMedDate not supplied

A simple and compact total artificial heart for temporary use.

Thromboembolism and anatomic fit are the major issues to be addressed in the design of a heart replacement device for total circulatory support. In an attempt to overcome these problems, a simple 70 mm3 displacement pusher plate, low pressure, pneumatically driven TAH was developed for temporary use. For optimal anatomic fit, easy implantation, and better flow patterns, the 5.7 X 10.7 cm total artificial heart (1) TAH was made of two essentially flat pumps integrated into a single unit. This single package approach avoids the dead space that occurs between the two pieces of conventional TAH and thus minimizes overall volume. It was designed to be positioned in the pericardial sac in a fashion similar to the natural ventricles and, based upon previous anatomic studies, fit in the average sized adult patient. In contrast to conventional free diaphragm pumps, the diaphragms of this TAH are supported by pusher plates that have a unique guide mechanism at the center to ensure a linear-controlled diaphragm motion and consequent uniform blood flow distribution. The guide of each pusher plate nests into the other, resulting in minimal thickness of the package. By using a simple displacement transducer, reliable output monitoring, with the possibility of selection of various pumping modes and adjustment of stroke volume, is possible. The authors anticipate this efficient and practical TAH to be a suitable temporary heart replacement device.

Heart Failure↗
PubMedDate not supplied

A biolized implantable ventricular assist device compatible with IABP console.

A low pressure pneumatic pusher plate blood pump was developed for temporary right, left, or biventricular assist. Important features of this pump are its 1) driveability by the standard, easily available intraaortic balloon pump (IABP) console; 2) gelatin coated internal surface for blood compatibility; 3) essentially flat disc shape, 3 cm thick and 11 cm in diameter, for optimal anatomic fit; and 4) unique pusher plate guide mechanism to ensure linear motion without deflections of the diaphragm, and consequent uniform flow distribution into the pump. The guide telescopes into itself to avoid a housing protrusion for easy implantability; this controlled movement also provides a number of performance, control, and diagnostic benefits. The pump's 60 ml displacement gives up to 4.7 L/min at 80 bpm and 6.7 L/min at 120 bpm outputs in a mock loop. This VAD has been implanted in two calves for 43 to 84 days, continuously driven by a Datascope IABP console. An average 5 L/min pump output has been observed in both synchronous and fixed rate modes. No anticoagulation was required. We expect extensive clinical use of this VAD, based on its reliability, low cost, and simplicity.

Animals↗
PubMedDate not supplied

Muscle powered circulatory assist device for diastolic counterpulsator.

A diastolic counterpulsator that uses either skeletal muscle or pneumatic actuation was developed. The unit is positioned between the latissimus dorsi and the chest wall, without interference with collateral blood supply, and is connected in series with the descending aorta. The system was able to generate stroke volumes between 52 and 16 ccs against pressures of 60 and 140 mmHg, respectively. Stroke work at 200 msec stimulation averaged 2.8 X 10(6) ergs. Power output at an afterload of 100 mmHg, and at a rate of 60 bpm, was 0.51 W. Back-up pneumatic actuation provided by an intraaortic balloon pump resulted in a 46% increase in the endocardial viability ratio (EVR).

Animals↗
PubMedDate not supplied

Compliance effect on patency of small diameter vascular grafts.

The compliance mismatch hypothesis as a cause of failure of small diameter grafts was investigated using 4 mm internal diameter, 5 cm long Biolized polyurethane grafts. The luminal surface of 0.5 mm thick Biomer sponge grafts was covered with 100 microns of crosslinked gelatin. Compliance matched, and noncompliant grafts had in vivo compliance values of 13.5 +/- 2.89 and 1.0 +/- 0.7 X 10(-2%) per mmHg, respectively. In vivo compliance defined as 2 X dD/dP X 1/Do was measured in situ using the ultrasonic Hokanson probe. Compliance values of compliant grafts equaled that of the canine carotid artery at 100 mmHg mean arterial pressure. Grafts were implanted using an end-to-end anastomosis in 14 dogs for 6 wk. Patency rates for compliant vs. noncompliant grafts were 64% (9/14) and 50% (7/14). Compliance values for compliant grafts decreased to a mean of 7.14 X 10(-2%) per mmHg. Anastomotic intimal hyperplasia at the proximal and distal ends of compliant and noncompliant grafts measured 239.9 +/- 128, 197 +/- 129 microns, 338.9 +/- 273.6, and 304.3 +/- 179.3 microns, respectively. There were no significant differences in localized anastomotic intimal hyperplasia at either graft end for either graft type. This study did not show any positive effects of graft compliance.

Anastomosis, Surgical↗
PubMedDate not supplied

New crisscross-shaped port design for universal serial pumps.

The long range goal is the development of a clinically useful, implantable, skeletal muscle powered cardiac assist device (MCAD). To accomplish this goal, two criteria must be met: good anatomic fit, and antithrombogenicity. Because of the relative locations of the latissimus dorsi (LD) muscle and aorta, there are two possible port arrangements: "crisscrossed" (C design), in which the ports are crossed to anastomotic sites, and "prong" shaped (P design), in which no crossover takes place. The purpose of this paper is to determine which of these designs is best from a fluid dynamic perspective, and hence has the best possibility for low thrombogenicity. Flow visualization (FV) techniques were used during two pumping conditions in a mock loop: worst case (MCAD off) and best case (MCAD driven optimally). Results of the MCAD off tests showed that both designs required immediate actuation (for example, an IABP console). However, FV studies under optimal conditions indicated superiority of the C design, most likely due to kinetic energy-induced rotary motion combined with a minimal interport distance. It is concluded that the C design provides ideal flow dynamics, even in valveless pumps, and also has application to valved devices.

Counterpulsation↗
PubMedDate not supplied

Effects of mechanical ventilation and spontaneous respiration on hemodynamics in calves with total artificial hearts.

The effects of respiration on hemodynamics were evaluated in four Holstein calves with total artificial hearts (TAH). The electrohydraulic actuated E4T-TAH has a continuously reciprocating actuator packaged between two alternately ejecting blood pumps that passively fill. The hemodynamic parameters (right atrial pressure [RAP], left atrial pressure [LAP], pulmonary artery pressure [PAP], aortic pressure [AoP]), and right and left pump filling (Rt% fill and Lt% fill) were measured when the animal was intubated and mechanically ventilated. These measurements were repeated with spontaneous respiration after the animal was extubated. With mechanical ventilation, LAP, PAP, and AoP were significantly higher during inspiration than during expiration. However, RAP during inspiration was slightly lower than that during expiration. The Rt% fill during inspiration was significantly lower than during expiration, but Lt% fill during inspiration was significantly higher than during expiration. During spontaneous respiration, these changes were opposite to those observed during mechanical ventilation. That mechanical ventilation generates positive intrathoracic pressure during inspiration, but spontaneous respiration generates negative pressure may explain these results. The change in venous return to the right atrium caused the change in RAP to be opposite in direction to that of the other pressures.

Animals↗
PubMedDate not supplied

Initial in vivo tests of an electrohydraulic actuated total artificial heart.

The authors are involved in developing a total artificial heart (TAH) for permanent human use. This device was designed to fit human anatomy, and it has housings made of carbon fiber-epoxy composite and titanium. Tissue valves and protein coating of blood contacting surfaces minimize the need for anticoagulants. A continuously reciprocating electrohydraulic actuator is packaged between two alternately ejecting and passively filling ventricles. The control system varies the pump rate to maintain average left ventricular filling at 90%. This TAH in vivo successively progressed through 1, 5, 9, and 45 day implants in calves of 84, 94, 82, and 82 kg preoperative body weights. The operating modes include automatic and fixed rate. The chronic and acute effects of varying the right pump displaced stroke volume indicated the need for it to be limited to 85% of that of the left for stable hemodynamics at maximum flow. The pump exhibited afterload insensitive and preload sensitive performance. Pump output ranged from 4.0-9.5 L/min at left atrial pressures of 7-16 mmHg at pump rates of 80-160 beats/min in these four experiments. These data suggest that this device will meet clinical hemodynamic requirements; it has the potential for total implantable cardiac replacement.

Animals↗