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Biomedical subjects

D B Olsen

Publications and source records attributed to D B Olsen.

At least 73 records · Page 4Linked to original sources
PubMed1991

Control systems for the electric heart.

Methods to predict and control cardiac output (CO) accurately in total artificial heart (TAH) recipients have varied significantly in the last few decades. Early models exhibited minimal control mechanisms and involved fixed pumping parameters. Elaborate electromechanical systems that have recently evolved require intricate communication between the circulating blood volume and the electric pump to maintain blood flow to critical organs. Attempts to quantitate specific end-organ blood flow, metabolic alterations, and oxygen delivery and, finally, to link these functions to the control of the TAH have not succeeded. Current devices seek to predict the needed CO by monitoring preload, afterload, or a combination of both. No consensus has developed concerning the appropriate physiologic parameters that should be surveyed in vivo and then used to regulate the output of the TAH.

Electric Power Supplies↗
PubMed1991

Calves chronically implanted with a total artificial heart as a pharmacological model.

Pharmacological therapy for congestive heart failure includes drugs that have both inotropic and vasoactive effects, although it is sometimes difficult to differentiate between the two effects. An animal with an implanted total artificial heart (TAH) allows the investigation of the vascular effect of these drugs in the absence of the effect on the myocardium. An advantage of the TAH model is its sensitivity to changes in right and left ventricular preload and afterload. Four instrumented TAH calves were given vasoactive drugs and the response was compared to control. Epinephrine, dopamine, isoproterenol, and nitroprusside were selected because of the predictability of their responses. Epinephrine caused a significant increase in systemic vascular resistance (SVR), and dopamine caused a significant increase in Pulmonary vascular resistance (PVR) and Isoproterenol caused a significant decrease in PVR. TAH implanted calves can thus serve as a pharmacological model to study the vascular response, which may be useful in investigation of new agents with inotropic and vascular effects.

Animals↗
PubMed1991

Structure-function relationship of hammerhead ribozymes as probed by 2'-modifications.

Hammerhead ribozymes containing 2'-fluoro- or 2'-aminonucleotides were prepared by automated chemical synthesis. Incorporation of 2'-fluorouridines, 2'-fluorocytidines or 2'-aminouridines did not appreciably decrease catalytic activity. The presence of 2'-aminocytidines, however, reduced the activity about 20-fold. No catalytic activity could be measured for ribozymes in which all adenosines were replaced by the 2'-fluoro analogue in presence of MgCl2. No single position could be found responsible for this loss of activity. In an attempt to construct ribozymes to hydrolyse HIV-RNA in the 5'-LTR region several constructs were tested on synthetic substrate as well as on run-off transcripts of about 1000 nucleotides length.

Antiviral Agents↗
PubMed1991

Right-left ventricular output balance in the totally implantable artificial heart.

Pneumatically powered artificial hearts readily accommodated the higher net stroke volumes by the right ventricle than from the left ventricle. We published that this discrepancy was approximately 8% of the left ventricular cardiac output. A variety of methods have been used to achieve balance between the right and left atrial pressures. Relatively large volume-displacement chambers (VDC) present potential problems, but do provide balance. The VDC in volumetrically coupled right-left stroke volumes was eliminated by using a small-diameter interatrial shunt (IAS). Preliminary studies demonstrated excellent balance in contracted and expanded blood volume (preload) and by hypotension and hypertension created with vasoactive drugs (afterload). At a mean aortic pressure of 120 mmHg, heart rate of 120 BPM, cardiac output of 8 L/minute and right atrial pressure of 13 mmHg, the peak IAS flow was 3.2 ml/beat in a right to left direction and 8.0 ml/beat in a left to right direction. The net left to right flow was 4.8 ml/beat. Over a wide range of preload (2 to 20 mmHg) and afterload (45 to 180 mmHg), the left atrial pressure was routinely 5 mm Hg more than the right atrial pressure. Elimination of the VDC reduces the number of components, volume, and weight of the totally implantable artificial heart. The IAS offers a simple solution to a very complex problem and provides a device that is simpler to implant and is possible to explant.

Animals↗
PubMed1990

Investigation of the inhibitory role of phosphorothioate internucleotidic linkages on the catalytic activity of the restriction endonuclease EcoRV.

The inhibitory effect of phosphorothioate residues, located within one strand of double-stranded DNA, on the hydrolytic activity of the restriction endonuclease EcoRV was investigated. Specific incorporation of a phosphorothioate group at the site of cleavage yielded the sequence 5'-GATsATC-3'. This modified sequence was cleaved at a relative rate of 0.1 compared to the unmodified substrate. Substrates 5'-GATsAsTC-3' and 5'-GsATsATC-3', both containing one additional phosphorothioate substitution, were linearized at a rate of 0.04 relative to unmodified DNA. However, under the same conditions, fully dAMPS-substituted DNA was found to be virtually resistant to the hydrolytic activity of EcoRV. Further experiments showed that double-stranded DNA fragments generated by PCR containing phosphorothioate groups within both strands are potent inhibitors of EcoRV catalysis. The inhibition was independent of whether the inhibitor fragment contained an EcoRV recognition site. We concluded that substitution of the phosphate group at the site of cleavage by a phosphorothioate residue decreases the rate of EcoRV-catalyzed hydrolysis most significantly. Substitution of other phosphate groups within the recognition sequence plays a limited role in enzyme inhibition. The presence of multiple dNMPS residues at regions of the DNA removed from the EcoRV recognition site may decrease the amount of enzyme available for catalysis by nonspecific binding to EcoRV.

Base Sequence↗
PubMed1990

Inhibition of the restriction endonuclease BanII using modified DNA substrates. Determination of phosphate residues critical for the formation of an active enzyme-DNA complex.

The restriction endonuclease BanII catalyzes the cleavage of double-stranded DNA and recognizes the degenerate sequence 5'-GPuGCPyC-3'. The poly-linker of M13mp18 contains one such sequence, 5'-GAGCTC-3'. The three other possible sites recognized by the enzyme were prepared by site-directed muta-genesis. The substitution of phosphate groups by phosphorothioate residues at some positions within the various recognition sites had relatively little effect on the rate of cleavage of the DNA. However, when the DNA contained a phosphorothioate group at the site of cleavage the rate of linearization of the DNA was decreased by a factor of 9. Interestingly, DNA which contained an additional phosphorothioate internucleotidic linkage immediately 3'-outside the recognition site could not be linearized by the enzyme. The results indicate that an important contact between enzyme and substrate is perturbed by the presence of the sulfur atom at this position.

Base Sequence↗
PubMed1990

Blood compatibility of PEO grafted polyurethane and HEMA/styrene block copolymer surfaces.

HEMA/styrene (HEMA/STY) block copolymers and poly(ethylene oxide) 4,000 M.W. (PEO4K) grafted Biomer (B-PEO4K) surfaces have been synthesized, characterized, and evaluated as blood-contacting materials. These surfaces have demonstrated improved blood compatibility, compared to Biomer, in in vitro and ex vivo experiments. Biomer vascular grafts (6 mm I.D. 7 cm in length) were fabricated by a dip coating process. The luminal surface was modified either with PEO grafting, HEMA/STY coating, or Biomer coating (control). These surface-modified grafts were implanted in the abdominal aortas of dogs and evaluated for graft patency and protein adsorption. Surface protein layer thickness was measured by transmission electron microscopy (TEM). B-PEO4K and Biomer showed thick multilayers of adsorbed proteins (1000-2000 A) after 3 weeks to 1 month implantation. In contrast, HEMA/STY only showed a monolayer protein thickness (less than 200 A), even after 3 months. Visualization of adsorbed plasma proteins (albumin, IgG, and fibrinogen) was performed with scanning electron microscopy (SEM)/TEM using an immunogold double antibody technique. The pattern of protein distribution showed high concentrations of fibrinogen and IgG, and less albumin adsorbed onto Biomer and B-PEO4K. In contrast, HEMA/STY showed a patchy protein distribution pattern with high concentrations of albumin and IgG, and relatively less fibrinogen. Adsorbed monolayer patterns showed improved compatibility over multilayered proteins. The Biomer and B-PEO4K grafts occluded within 1 month, while HEMA/STY grafts were patent for over 3 months. The thin and stable adsorbed protein layer on HEMA/STY surfaces may be associated with the microdomain structures of the surface, and will play an important role in long-term in vivo blood compatibility. This manuscript will evaluate the long-term in vivo performance of these polymers, analyze the extent of protein adsorption onto the surfaces, and correlate protein layer thickness to the thrombogenicity of the polymer surfaces.

Adsorption↗
PubMed1990

High-efficiency oligonucleotide-directed plasmid mutagenesis.

A number of single- and double-base substitutions have been introduced into either the polylinker region or the lacZ gene in the plasmid vector pUC19. The efficiencies of these changes upon transfection of TG-1 bacterial cells were generally 70-80%. A strategy has been devised by which the wild-type DNA can be selectively destroyed. It is primarily based on the resistance of phosphorothioate internucleotide linkages to some restriction enzymes. A mismatch oligonucleotide is introduced into a gapped region and the gap is filled using three deoxynucleoside 5'-triphosphates and one deoxynucleoside 5'-[alpha-thio]triphosphate. Reaction with a restriction enzyme that is unable to hydrolyze phosphorothioates ensures that the DNA containing the mismatch oligonucleotide is only nicked. Concomitantly, the DNA that does not contain the desired mutation is linearized. Subsequent reactions with an exonuclease and DNA polymerase I yield mutant homoduplex DNA for transfection.

Base Sequence↗
PubMed1990

A moving-actuator type electromechanical total artificial heart--Part I: Linear type and mock circulation experiments.

A new type of motor-driven total artificial heart system with a moving-actuator mechanism has been developed. The prototype system consists of a brushless dc motor inside of a rolling-cylinder, two arc-shaped pusher-plates and two polyurethane sacs. The moving-actuator type electromechanical pump has structural advantages of small size and light weight, as compared to other reported motor-driven pumps with fixed-actuator mechanisms. The results of the mock circulation tests are reported in this paper with a cardiac output of 9 L/min at an aortic pressure of 120 mmHg and a heart rate of 120 bpm. The fulfillment of the basic control requirements of the artificial heart was also confirmed, i.e., preload sensitive and afterload insensitive cardiac output response and balanced right and left ventricular outputs.

Algorithms↗
PubMed1990

A moving-actuator type electromechanical total artificial heart--Part II: Circular type and animal experiment.

A new type of electromechanical total artificial heart (TAH) based on circular rolling-cylinder mechanism was developed to overcome critical problems in motor-driven artificial hearts such as large size and difficulties in fitting the heart to atrial remnants and arterial vessels. Its performance and reliability were evaluated in mock circulation and in an animal implant experiment. The total weight and volume of the pump is 650 g and 600 mL, respectively. This new pump was implanted in a calf for total heart replacement and 96 h of survival was achieved. The whole system, including pump, controller, and control algorithm performed well enough to improve the prospect of eventual clinical application of our TAH system.

Animals↗
PubMed1990

Loss of anticoagulant effect of heparin during circulation of human blood in vitro.

Device-induced thrombogenesis was studied in an in vitro model using human blood circulated through an artificial ventricle. A new constant pressure filtration technique was used to detect circulating microemboli, the activated partial thromboplastin time (APTT) test was used to monitor the blood for the presence of anticoagulant activity of heparin, and hemolysis was quantified by measuring the plasma free hemoglobin level. Circulation of blood through a 20-ml stroke volume pneumatically driven ventricle for 6-9 h resulted in a significant reduction of APTT, indicating the loss of the anticoagulant effect of heparin. Microemboli concentration was minimal until the APTT decreased below 125 s, at which time the microemboli concentration increased rapidly. This was presumed to be due to the formation of thrombi following a decrease in heparin activity. A significant increase in hemolysis was also noted when blood was pumped. None of these changes was noted in the nonpumped control blood. Spontaneous loss of heparin activity in blood circulated by a pneumatically driven pump may have clinical implications and may help understanding of the problems associated with device-induced thrombogenesis.

Adult↗
PubMed1990

Quantification of perivalvular thrombus formation in blood pumps by polar coordinate mapping.

A polar coordinate mapping technique (PCMT) to quantitatively describe perivalvular thrombus formation was applied in the examination of prosthetic valves from paracorporeal assist devices. The method begins by photographing the upstream and downstream views of the freshly retrieved valves using transparency film. The valve images are then projected onto 10 x planforms of the valves, and the boundaries of the observable thrombi are traced. The radial thrombus length is then measured at 5 degrees increments and plotted on Cartesian coordinates as a function of polar coordinate. Mean radial thrombus length and incidence of thrombus are calculated. Statistical analysis can then be used to test for differences in the length, incidence, and pattern of thrombus formation between test groups. The effect of valve selection, anti-coagulant regime, and other factors that influence thrombus formation can be quantitatively compared with the PCMT. Consequently, the PCMT could be a valuable assessment tool for efforts being made to reduce thrombosis in prosthetic blood pumps.

Animals↗
PubMed1990

Detection of microemboli by constant-pressure filtration during in vitro circulation of bovine and human blood.

The constant-pressure filtration (CPF) method has been developed to assess blood microemboli (BME) in terms of their ability to occlude microvascular flow. Previous reports suggest that the method is sensitive to the effects of platelet stimulation and to blood-pumping conditions. BME production and heparin activity were studied in bovine and human blood pumped by a Pellethane ventricle with Pellethane molded valves connected via smooth quick-connects to a Pellethane horseshoe-shaped reservoir. In each experiment, blood was collected into heparin by cardiac puncture from a stunned animal or by venepuncture from a human donor. The blood from each donor was filled into three ventricle-reservoir systems (50 cc ventricle and 1,500 cc reservoir for the bovine blood, and 20 cc ventricle and 150 cc reservoir for the human blood). One of the systems received aspirin (ASA; 25 mg/dl) shortly after the onset of pumping, whereas the other two served as pumping and non-pumping controls. The blood was pumped in a full-fill/full-eject mode for up to 10 h. BME concentration was measured by the CPF method in which the blood was filtered through 20-microns pore filters at 20 mm Hg for 10 s, and the flowrate curves were evaluated from occlusion model. Heparin activity was measured by the activated partial thromboplastin time (APTT) test. In the early period after the onset of pumping, the BME concentration increased, whereas the APTT decreased from an initial value of greater than 250 s, with the relative rate of change for both the BME and the APTT being the following: pumping control greater than pumping ASA blood greater than quiescent control.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Volume homeostasis in calves with artificial atria and ventricles.

We examined whether replacement of cardiac atria and ventricles with total artificial hearts (TAH), a procedure that removes cardiac nerves and all sources of atrial natriuretic factor (ANF), would cause alterations in volume homeostasis in awake calves. Preoperatively, extracted plasma immunoreactive (ir)ANF levels were 13.3 +/- 0.6 and remained postoperatively at 10.5 +/- 0.4 pg/ml (P less than 0.01). TAH implantation caused systemic and pulmonary hypertension (P less than 0.01), salt retention, edema, and significant elevations of plasma renin, aldosterone, and arginine vasopressin. In intact calves rapid infusion of 6 liters of normal saline raised irANF levels to 73.7 +/- 6.5 pg/ml (P less than 0.01) and elicited a large natriuresis and diuresis. No such response to 6 liters of normal saline was obtained after calves had recovered from TAH implantation. Reduction of cardiac output (CO) by 50% caused further salt retention and no change in irANF levels. Elevation of CO back to and 33% above base line produced only a diuresis, whereas salt retention persisted and irANF levels remained unchanged. The same maneuvers elicited in surgical control calves (artificial ventricles only, largely intact atria) a significant increase in irANF levels and a diuresis and natriuresis. In conclusion, alterations in volume homeostasis observed after TAH implantation seem to be the consequence of at least two pathophysiological mechanisms: 1) functional ANF "deficiency," characterized by apparently unregulated ANF secretion from noncardiac sites, and 2) cardiac denervation.

Animals↗
PubMed1990

Ventilatory control during exercise in calves with artificial hearts.

To determine the role of cardiac reflexes in mediating exercise hyperpnea, we investigated ventilatory responses to treadmill exercise in seven calves with artificial hearts and seven controls. In both groups, the ventilatory responses were adequate for the metabolic demands of the exercise; this resulted in regulation of arterial PCO2 and pH despite the absence of cardiac output increase in the implanted group. In this group, there was a small but significant reduction of arterial PO2 by 4 +/- 3 Torr and a rise of blood lactate by 1.1 +/- 1 mmol/l. When cardiac output was experimentally increased in the implanted calves to a level commensurate with that spontaneously occurring in the control calves, ventilation was not affected. However, experimental reductions of cardiac output led to an immediate augmentation of exercise hyperpnea by 4.56 +/- 4.3 l/min and a further significant lactate increase of 1.2 +/- 1.22 mmol/l that was associated with a significant decrease in the exercise O2 consumption (0.32 +/- 0.13 l/min). These observations indicate that neither cardiac nor hemodynamic effects of increased cardiac output constitute an obligatory cause of exercise hyperpnea in the calf.

Animals↗
PubMed1990

Developing an artificial fallopian tube: successful in vitro trials in mice.

This report describes the design and testing of an artificial fallopian tube for the treatment of tubal infertility. Within the device, mouse eggs incubated with sperm were fertilized and a microinfusion pump was used to transport the fertilized ova through the tube. Normal offspring resulted from transfer of the developing embryos into pseudopregnant recipients. These results provide encouraging evidence that an artificial fallopian tube warrants further investigation as a potential alternative to in vitro fertilization.

Animals↗
PubMed1989

Incomplete primer extension during in vitro DNA amplification catalyzed by Taq polymerase; exploitation for DNA sequencing.

Polyacrylamide gel electrophoresis of DNA fragments obtained by the polymerase chain reaction using Taq polymerase revealed the presence of multiple fragments shorter than the expected product. These abortive extension products were observed even when analysis by agarose gel electrophoresis showed only a single band. The production of prematurely terminated fragments can be exploited for the sequencing of PCR products if phosphorothioate groups are incorporated base specifically during the reaction in the presence of two oligonucleotide primers, one of which is 5'-32P-labeled. The addition of snake venom phosphodiesterase to the reaction mixture after completion of the amplification cycles digests each fragment from the 3'-end to a phosphorothioate group so that the sequence can be read by polyacrylamide gel electrophoresis.

Base Sequence↗