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Biomedical subjects

A P MacKenzie

Publications and source records attributed to A P MacKenzie.

At least 19 recordsLinked to original sources
PubMed1990

Mechanisms for reduced total lung capacity at birth and during hyaline membrane disease in premature newborn monkeys.

To determine whether the cause of reduced total lung capacity (TLC) in hyaline membrane disease (HMD) is due to alveolar collapse, alveolar edema, or both, TLC was measured by N2-washout in premature Macaca nemestrina monkeys during the first 3 h of life. The TLC of animals with HMD was only one-third that of healthy premature monkeys over the first 3 h of life (p less than 0.01). At 3.5 h, lung tissue was rapidly frozen in situ during lung inflation to TLC. Samples of frozen lung tissue were freeze dried, embedded, sectioned, and examined by point counting. Animals with HMD had alveolar saccules filled with the residue of proteinaceous fluid, but little alveolar collapse was noted. The proportion of points falling on empty alveolar spaces was 74% in the healthy animals but only 18% in animals with HMD (p less than 0.01); there was a 70-fold increase in the residue present in alveoli of animals with HMD (p less than 0.05). In a separate experiment, rapid serial measurements of TLC by N2-washout showed that healthy premature monkeys, but not those with HMD, have a steady increase in TLC during the first few minutes of life, presumably due to clearance of lung liquid. Although the initial cause of reduced TLC in HMD appears to be inadequate clearance of fetal lung liquid, by 3 h of age proteinaceous alveolar edema is primarily responsible.

Animals↗
PubMed1978

Instrumentation for direct observation of frozen hydrated specimens in the electron microscope.

Instrumentation and techniques are described for the transfer and observation of frozen hydrated specimens in the transmission electron microscope. The transfer is accomplished without the complexity of a vacuum transfer device but also without significant sublimation of specimen ice or frosting. Examples are given of the transfer and observation of thin sections of rapidly frozen muscle and of rapidly frozen thin film preparations of isolated cells.

Animals↗
PubMed1977

Non-equilibrium freezing behaviour of aqueous systems.

The tendencies to non-equilibrium freezing behaviour commonly noted in representative aqueous systems derive from bulk and surface properties according to the circumstances. Supercooling and supersaturation are limited by heterogeneous nucleation in the presence of solid impurities. Homogeneous nucleation has been observed in aqueous systems freed from interfering solids. Once initiated, crystal growth is ofter slowed and, very frequently, terminated with increasing viscosity. Nor does ice first formed always succeed in assuming its most stable crystalline form. Many of the more significant measurements on a given systeatter permitting the simultaneous representation of thermodynamic and non-equilibrium properties. The diagram incorporated equilibrium melting points, heterogeneous nucleation temperatures, homogeneous nucleation temperatures, glass transition and devitrification temperatures, recrystallization temperatures, and, where appropriate, solute solubilities and eutectic temperatures. Taken together, the findings on modle systems aid the identification of the kinetic and thermodynamic factors responsible for the freezing-thawing survival of living cells.

Ammonia↗
PubMed1976

On the adequacy of the draw-sealing of gas-filled glass ampoules.

It is recommended that a very clear distinction be made between draw-sealed and tip-sealed glass ampoules. We would, that is, defend the draw-seal for its proven value and its demonstrated freedom from microscopic channels. Where tip-sealing is still employed, we would suggest its reevaluation. Little more can be said in the absence of an immediate reason for the differences in the behavior of the glass in the course of the two procedures. Others may be able to explain the persistence of the capillary in the tip-seal in physico-chemical terms. As to balloon-seals, the third "variety" in common use, it would seem that their characteristics must derive from the way they are made. Ballooned tip-seals appear to have been shown by Greiff et al. (1975) to suffer the same shortcomings as the simple tip-seal. Where a draw-sealed ampoule is heated at the tip after the completion of the seal, a ballooned end would seem to have to retain the true seal effected in the draw process. It is perhaps sufficient to let the subject rest with a reassurance as to the adequacy of the common draw-seal.

Argon↗
PubMed1976

The physico-chemical basis for the freeze-drying process.

To the extent that the final form and quality of a freeze-dried product depends on the way the freeze-drying is conducted, an understanding of the many factors involved is most important. The numerous effects of the design and mode of operation of the freeze-drying equipment on the course of the process need to be known, as do the properties intrinsic to the material to be freeze-dried. Much can be learned and predicted from the study of the "supplemented phase diagram", a series of experimental plots describing the equilibrium and the non-equilibrium phase behavior of the system in question. Such diagrams map and distinguish eutectic and amorphous phase behavior. Further information is available from gravimetric studies allowing the construction of "desorption isotherms", the plots describing the loss of sorbed water accompanying the sublimation of ice, frequently termed "secondary drying". These plots relate the water retained by the product to the "water activity", or relative humidity at different temperatures. Observations in the freeze-drying microscope contribute additional information, in that they reveal the actual course of the process at the microscopic level. These and other laboratory findings facilitate the analysis and comparison of pilot-plant and commercical scale processing experiences. Where scientific and engineering factors appear to interrelate, the nature and extent of the interdependence can often be determined.

Crystallization↗
PubMed1972

Scanning electron microscopy of spore germination in Dictyostelium discoideum.

The ellipsoidal dormant spores of Dictyostelium dicoideum prepared by freeze-drying had a uniform, compact appearance with fine wrinkles or ridges on the surface. Swollen spores were uneven in appearance, without fine wrinkles but with a seemingly expanded surface covering. The surfaces of the postgermination spore husks appeared unaltered except for a single straight exit slit along the longitudinal plane.

Cell Wall↗