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Biomedical subjects

E N Lightfoot

Publications and source records attributed to E N Lightfoot.

8 recordsLinked to original sources
PubMed1979

A Monte Carlo simulation of convective dispersion in the large airways.

A numerical model describing the local interactions between convection and diffusion in the first 11 generations (0 to 10) of the human bronchial tree is presented. The model, based on a Monte Carlo procedure, is used to investigate the effects of four velocity profiles: (i) parabolic, (ii) asymmetrical, (iii) asymmetrical with swirling and (iv) flat. Behavior was investigated for three diffusivities: (i) 0.75 cm2/s (He/air), (ii) 0.25 cm2/s (N2/O2) and (iii) 0.1 cm2/s (SF6/air) on the convection-diffusion interaction. The results of these simulations showed that 'Taylor dispersion' is an important effect, with respect to tracer segregation, and that it is of major significance only in the largest airways. By generation 10, molecular diffusion begins to dominate over Taylor dispersion. It was also found that use of a parabolic velocity profile, or application of the Gill-Sburamanian dispersion theory seriously overestimates axial dispersion. On the other hand, the use of a flat velocity profile underestimates dispersion.

Bronchi↗
PubMed1979

Inert gas transport in the microcirculation: risk of isobaric supersaturation.

This paper is concerned with the theretical background and implications of isobaric supersaturation and bubble formation in the microcirculation following an abrupt shift from one inspired inert gas to another. The use of more than one inert gas, simultaneously or sequentially, has become common in diving and presents risks as well as potential benefits. A review of microcirculatory model useds, theoretical approaches to decompression, and order of magnitude calculations indicates that present empiricisms are inadequate for predicting such supersaturation phenomena. This is true whether based on the familiar assumption of perfusion-limited behavior or its diffusion-limited counterpart. The "chromatographic" model used here, which considers both perfusion and axial diffusion in tissue cylinders, shows that these combined effects can produce unexpectedly high local supersaturation. The implications include new possibilities for the experimental evaluation of gas transport models as well as practical risks of inert gas shifts in diving and certain diagnostic procedures.

Brain↗
PubMed1978

The effect of shear, specific surface, and air interface on the development of blood emboli and hemolysis.

Heparinized dog blood was exposed to shear and foreign surfaces in conicylindrical test cells. The cells were injection molded from polycarbonate and were filled using a technique that avoided contact of the blood with air. Particulate-matter formation was measured and was found to be dominated by the surface-to-blood-volume ratio and to be independent of shear rate. Hemolysis was also measured and was found to vary linearly with shear rate and to increase with increasing surface-to-blood volume ratio. Thus, at low shear rates and high specific surface conditions, the degree of hemolysis was found to be minimal while particulate-matter formation was high. The results suggest that the safety of extracoporeal perfusion procedures cannot be inferred from hemolysis measurements alone. In one series of tests, a gas-blood interface was generated at a rate equivalent to the rate of surface renewal in conventional disc oxygenators. The gas-blood interface failed to contribute significantly to the damage indices, which suggests that the apparent superiority of membrane oxygenators may be a result of factors other than the absence of a blood-gas interface.

Biomechanical Phenomena↗
PubMed1976

Asparaginase entrapped in red blood cells: action and survival.

As a strategy to avoid serious allergic reactions to the antitumor agent asparaginase, this enzyme was entrapped in autologous red blood cells before intravenous injection into monkeys. Additional advantages of this approach are prolonged enzyme half-life and targeting of this agent into the reticuloendothelial system.

Animals↗
PubMed1975

Nitrogen elimination in man during decompression.

The effect of ambient pressure on inert gas elimination during decompression was investigated using human subjects breathing air in a dry hyperbaric chamber. This was done by measuring nitrogen recovery during three different decompression schedules following identical simulated dives. Five subjects were used, each with normal pulmonary function. In each case the simulated dives consisted of exposure for 40 min to air at 4 ATA corresponding to a depth of about 100 fsw and 28 degrees C. Following these exposures each subject was decompressed in different experiments to 50 fsw (2.515 ATA) and to 10 fsw (1.303 ATA) while breathing a mixture of 80:20 helium-oxygen. In addition, two of these subjects were denitrogenated isobarically, at 100 fsw, breathing 80:20 helium-oxygen. Significant differences in nitrogen-elimination rate were observed, with nitrogen removed most effectively at 50 fsw and least at 100 fsw. To explained these unexpected results it is tentatively suggested asymptomatic bubble formation occurred at both 10 and 50 fsw.

Decompression↗
PubMedDate not supplied

An anionic galactomannan polysaccharide gum from a newly-isolated lactose-utilizing bacterium. I. Strain description and gum characterization.

As part of an effort to obtain microorganisms able to produce polysaccharide gums from whey and whey permeate, soil samples from farm fields regularly treated with whey were screened for bacteria able to produce gums from lactose. The most promising organism isolated (ATCC 55046) is a facultative anaerobe, tentatively identified as a new Erwinia species on the basis of biochemical and morphological tests. The organism produces a polysaccharide gum from lactose and other sugars (herein named lactan gum) composed of mannose, galactose, and galacturonic acid with an approximate molar ratio of 5:3:2 and containing no organic acid modifying groups. The weight average molecular weight of the gum is approximately 7 x 10(6). Aqueous solutions of lactan gum exhibit shear-thinning and elastic flow behavior with an estimated power law model flow index of 0.26 at 1% (w/w) gum. The viscosity of aqueous 1% (w/w) lactan gum solutions is stable over a pH range of 2-11, being particularly stable in alkaline environments. Aqueous 1% (w/w) gum solutions at pH 5-11 show excellent thermostability, retaining at least 80% of the original viscosity after being heated to 121 degrees C for 15 min. These flow properties indicate potential industrial applications in food and nonfood products requiring a moderate degree of thickening, wet-end additives and coating agents for paper products, ceramics, detergents, and binders for building materials.

Bacteria, Anaerobic↗