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Biomedical subjects

L O Reynolds

Publications and source records attributed to L O Reynolds.

12 recordsLinked to original sources
PubMed1993

A model for thromboembolization on biomaterials.

A model was developed to describe the kinetics of protein and platelet deposition and embolization on biomaterials. The model assumes that proteins can be adequately represented by fibrinogen, albumin, and Factor XII, that protein adsorption is Langmuir-type, that surfaces are homogeneous, and that all adsorption and deposition steps are first order. Eleven model parameters were determined from literature experimental data from ex vivo experiments utilizing canine and baboon blood on Silastic, one parameter came from adsorption of Factor XII on glass, and three parameters were obtained by minimizing differences between experimental and predicted fibrinogen adsorption, and platelet deposition and embolization behavior. The model well predicted observed behavior for fibrinogen adsorption, platelet deposition, and platelet embolization on Silastic, and platelet embolization from both polyacrylamide and HEMA-MAAC.

Animals↗
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↗
PubMed1982

Ventilation and perfusion alterations following homologous blood transfusion.

A previous study in this laboratory examined the effect of micropore ultrafiltration of blood products on pulmonary gas exchange and subsequent pulmonary dysfunction--related morbidity and death. Morbidity and death from pulmonary failure was not affected; however, gas exchange was improved following ultrafiltration with 40 micrometers filters, as reflected by lower Bohr dead-space fractions. This difference might be explained by reduction of the microaggregate load seen in the pulmonary microvasculature. The purpose of this study was to examine in more detail these gas exchange alterations, paying particular attention to the correlation of changing Bohr dead-space ventilation detected with multiple inert gas analysis with direct determinations of microaggregate size and number. Fourteen patients with isolated cutaneous thermal injury scheduled for major early burn would excision were selected for study. Following transfusion with homologous blood products, the ventilation/perfusion ratio (Va/Q) distributions determined by inert gas analysis remained essentially unchanged except for subtle changes in both high VA/Q and dead-space compartments, resulting in significantly increased Bohr dead-space fractions (P less than 0.05). This combination of gas exchange alteration is consistent with vasoactive and occlusive changes in the pulmonary microvasculature following microaggregate infusion. The correlation of changing dead-space ventilation with the total microaggregate load was poor (r = 0.15) but was significant when compared with counts of microaggregates greater than 90 micrometers in diameter (r - 0.85). These findings suggest that gas exchange alterations following blood transfusion are primarily reflected by increased dead-space ventilation secondary to vasoconstriction and occlusion of the pulmonary microvasculature with microaggregates greater than 90 micrometers in diameter.

Adolescent↗
PubMed1981

Multi-lead spinal cord stimulation for control of motor disorders.

This report presents observations in 160 patients undergoing chronic spinal cord stimulation for various disorders of the motor system and compares the results obtained using older conventional two-electrode bipolar stimulation with a newly developed four-electrode multiple level system. Improvement was noted in 84% of the 75 patients with cerebral palsy, 67% of the 42 patients with dystonia, 62% of the 21 patients with torticollis and 73% of the 22 patients with post-traumatic neurologic loss. Significant improvements were noted when comparing the two-electrode system with the new multiple level electrode. Marked to moderately improved patients increased from 57 to 84% in cerebral palsy, from 44 to 82% in dystonia, from 53 to 75% in torticollis and from 53 to 80% in dystonia, from 53 to 75% in torticollis and from 53 to 80% in posttraumatic neurologic conditions. There was a corresponding marked drop in unimproved patients in each condition.

Adolescent↗
PubMed1976

Transport calculations for light scattering in blood.

In vivo measurement of the oxygen saturation levels in blood may be obtained from relative amounts of backscattered monochromatic light at two different wavelengths, as measured with a fiber-optic catheter oximeter. Because of the short mean free path length of light in blood, the backscattering can be well approximated by a previously-derived, one-wavelength transport theory solution for the half-space searchlight problem. This solution, unlike simple diffusion approximations has the advantage that the boundary condition describing illumination of a localized area of blood by a monodirectional light beam can be rigorously satisfied. Sample calculations using the solution are compared with experimental values of the reflectance of blood.

Animals↗
PubMedDate not supplied

Size distribution measurements of microaggregates in stored blood.

Microaggregates in various blood preparations were studied, before and after filtration, using an optical scattering (laser) technique which measures number density and size of aggregates in flowing blood. These measurements were comparable to screen filtration pressures. In all blood units, storage increased aggregates in the 20 to 170-microns range. Whole blood and red blood cells were comparable, while removal of leukocytes and platelets by an inverted spin technique essentially prevented formation of aggregates in all size ranges. Platelet-depleted units of whole blood also reduced aggregates. Removal of cryoprecipitate did not significantly affect aggregate size distribution; however, blood modified by both platelet and cryoprecipitate removal reduced aggregates. Commercially available microfilters reduced aggregates initially, but some increase ("shedding") occurred with continued use. The optical scattering technique did not require the dilution or red blood cell lysis needed in other techniques. Therefore, this method has potential for aggregate detection in in vivo flowing blood.

Blood Platelets↗
PubMedDate not supplied

Characterization of blood microemboli associated with ex vivo left ventricular assist devices in a bovine model.

An ex vivo left ventricular assist device (LVAD) model was used in calves to study the production of blood microemboli (BME) and to evaluate possible correlations between constant-pressure filtration (CPF) measurements of flow-resistant BME, light-scattering microemboli detection (LSMD), observable thrombus accumulation, and hematologic markers. Aortic LVAD cannulae were implanted through the chest wall in two calves, and each calf received a series of LVADs, each operating 1-4 days. Blood samples from the LVADs underwent CPF through 20 mu pore filters at 20 mm Hg to produce estimates of occlusive BME concentration. Laser (He-Ne) light was directed through the outflow cannula, and the differentially-scattered light was detected for computer estimation of microemboli size, volume, and frequency. Blood chemistry and coagulation parameters were also analyzed. Removed LVADs were examined with polar coordinate mapping of accumulated perivalvular thrombi. One ventricle produced significantly greater CPF results, LSMD results, and Factor XII levels. During the use of that ventricle, the CPF results increased slowly with time after LVAD connection, while the LSMD results and Factor XII levels increased immediately after connection, followed by a later decrease. This contrast is explainable in terms of the dynamic development of BME strength. The calf model appears useful for the study of thrombogenesis, and the CPF and LSMD methods of BME analysis complement each other, and other measurements.

Animals↗
PubMedDate not supplied

Markers of thromboembolization in a bovine ex vivo left ventricular assist device model.

The production of blood microemboli (BME) was studied using an ex vivo exteriorized left ventricular assist device (LVAD) model in calves. Each of eight calves received a series of three LVADs, each operating for 24 hr. Blood microemboli were measured directly by a laser (624 nm and 828 nm) light scattering microemboli detection (LSMD) system through the LVAD outflow cannula and by constant pressure filtration (CPF) of blood samples from the LVAD outflow cannula. Hematologic parameters were also measured. After LVAD removal, perivalvular thrombi were evaluated using polar coordinate mapping. The average LSMD and CPF results correlated. For example, in one series of three calves, one ventricle exhibited significantly greater thrombogenesis than did the other ventricles, as indicated by both the LSMD and CPF results. In a series of five calves, one calf developed an abnormally high activated thromboplastin time (APTT), even in the absence of heparin. For two of the three ventricles tested in that calf, microemboli concentration (CPF), Factor XII activity, level of fibrin degradation products (FDP), and accumulated thrombus were significantly lower than for the other calves. The whole blood viscosity (WBV, at 230 s-1) in this calf also decreased to lower values than were seen with the other calves.

Animals↗
PubMedDate not supplied

Differential light scattering cuvettes for the measurement of thromboemboli in high shear blood flow systems.

Newly developed optical scattering cuvettes were constructed as a modification of our existing 1.0 mm and 3.0 mm internal diameter (ID) cuvettes to facilitate the measurement of platelet microemboli ranging from 20 microns to 1,000 microns diameter in whole blood in 0.9 mm ID flows ranging from 250 to 4,000 ml/min. A perturbation solution to the one-speed radiative transport equation was used in the design and calibration of these cuvettes. A series of tests were performed with these cuvettes in an extracorporeal left ventricular assist device bovine model, and in a recirculating closed-loop flow system containing anticoagulated whole baboon blood, to determine to what extent they affect platelet and erythrocyte function ex vivo and in vitro. Serial hemolysis tests, thromboxane radioimmunoassay measurements, platelet counts, and activated partial thromboplastin times were measured. All of these tests with cuvettes in the extracorporeal and in vitro circuits were statistically indistinguishable from baseline measurements, suggesting the usefulness of this system for the measurement of microemboli in blood-contacting materials of extracorporeal circuits and cardiac assist devices.

Animals↗
PubMedDate not supplied

Light scattering detection of microemboli in an extracorporeal LVAD bovine model.

Thromboembolization studies were performed on two calves supported by extracorporeal left ventricular assist devices (LVAD) using a light scattering (He Ne Laser) microemboli detector (LSMD). The LSMD system was placed on the outflow cannula of the LVAD in the extracorporeal loop of each animal. The measurements included the size, number, and rate of production of circulating microemboli in the range 20 microns less than microemboli diameter less than 1,000 microns. These data were compared to independently and concurrently obtained measurements of emboli shear rate (CPF), platelet count, red blood count (RBC), leukocyte count (WBC), plasma free hemoglobin, factors XIII, X, and V, and sorbitol dehydrogenase. Embolic number and volume were seen to be most dynamic in the very early phases of acute thromboembolization (0-40 minutes) with a peak embolic response within the first 30 minutes. The dynamics of reduced emboli volume, rather than number, may be implicated in the later stages of the thromboembolic passivation of these ventricles. The LSMD results generally showed an inverse correlation of microemboli volume rate with CPF measurements for each ventricle. LSMD, CPF, and leukocyte and platelet counts, showed a direct correlation with reduced counts for each additional ventricle for both calves. Factor XII was seen to have a more direct correlation in time with LSMD measurements for each ventricle than other parameters under investigation. This study represents the first time laser scattering and filtration methods have been applied simultaneously with hematologic assays in order to study the dynamics of device associated thrombogenesis.

Animals↗