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Biomedical subjects

T P Stewart

Publications and source records attributed to T P Stewart.

9 recordsLinked to original sources
PubMed1990

Pressure relief characteristics of an alternating pressure system.

The pressure relieving characteristics of an alternating pressure mattress are compared to the characteristics of a traditional hospital mattress. The trochanteric pressures of 20 healthy volunteers had a mean of 95 (SD = 49) on a hospital mattress while the trochanteric pressures on the alternating pressure mattress had a mean of 67 (SD = 9) for the inflated cells and a mean of 23 (SD = 7) for the deflated cells. Statistical analysis revealed significantly lower interface pressure for the alternating pressure mattress.

Adult↗
PubMed1988

Kinetic measurements of fusion of phosphatidylserine-containing vesicles by electron microscopy and fluorometry.

Large unilamellar vesicles (REV) containing phosphatidylserine and phosphatidylethanolamine at a ratio of 1:3 were induced to fuse by adding calcium (4 mM). The kinetics of fusion was monitored by fluorometry using terbium or dipicolinic acid-containing vesicles. The morphology and the states of vesicle aggregation and fusion were examined at approx. 2, 30, 60, 150 and 900 s after calcium addition, by rapid quenching and freeze-fracture electron microscopy. The size and the state of aggregation of vesicles are quantitated from 4000 randomly selected vesicles. The aggregation and fusion kinetics as assayed by fluorescence volume mixing is very well simulated and predicted by the mass action model. The model essentially predicts the time course of the distribution of the aggregates and the increase in size of fused particles as measured by electron microscopy, although in some cases the predicted fusion rate exceeds that by morphometric measurement. No morphological features can be defined as fusion intermediates, although bead-like and rim-like materials may be attributed to the remnants of broken diaphragms between fusion partners.

Calcium↗
PubMed1979

Interactions of La3+ with phosphatidylserine vesicles. Binding, phase transition, leakage and fusion.

The interaction of La3+ with phosphatidylserine vesicles is elucidated by binding studies, differential scanning calorimetry, X-ray diffraction, freeze fracture electron microscopy, and release of vesicle contents. La3+ effectively competes with Ca2+ for phosphatidylserine binding sites. The saturation level is close to a La/lipid ratio of 1:3. A concentration of 0.1 mM of La3+ is sufficient to induce fusion between sonicated vesicles.

Calorimetry, Differential Scanning↗
PubMed1979

Selective decoration of hydrophilic moieties of membrane molecules in freeze fracture.

Selective decoration of the hydrophilic moieties of phospholipid molecules on freeze fractured bilayer faces was made using residue water vapor in an oil-free vacuum unit. The preferential decoration technique was applied to label structural faults of bilayers, such as domain boundaries and other regions of molecular dislocation which are not visible by conventional morphological observations.

Freeze Fracturing↗
PubMed1979

Correlative statistical analysis and computer modelling of intramembraneous particle distributions in human erythrocyte membranes.

The planar distribution of intramembranous particles on the P faces of freeze-fractured human erythrocyte membranes is characterized by radial distribution, angular distribution and differential density distribution analysis. Various degrees of intramembranous particle aggregation induced by spectrin removal and low pH are differentiated through computation. Random hard disk models with various disk diameters are built for comparison studies. In all samples, the 80 +/- 10 A particles are found to have a preferred neighboring distance of 100 +/- 10 A, but no preferred angular relation is found between neighboring particles. A pattern recognition process using both radial and density distribution analyses reveals that none of the particle distributions observed may be regarded as random. The fact that the particle distributions observed are neither even nor random suggests that factors other than long range electrostatic force alone are involved in determining the particle distribution.

Computers↗
PubMed1979

Complex phase mixing of phosphatidylcholine and phosphatidylserine in multilamellar membrane vesicles.

The phase mixing in dipalmitoyl phosphatidylcholine and bovine brain phosphatidylserine mixtures suspended in aqueous salt solutions was studied by differential scanning calorimetry, freeze-fracture electron microscopy and X-ray and electron diffraction. The pure dipalmitoyl phosphatidylcholine has two well-defined solidus phases P beta' and L beta' and a liquidus phase L alpha while the pure phosphatidylserine has a broad transition from L beta to L alpha. The mixture exhibits some dipalmitoyl phosphatidylcholine characteristics up to 30% phosphatidylserine when pure P beta' phase no longer exists. Phase mixing is observed at all compositions. An addition of 3% phosphatidylserine is found to be sufficient to destroy the sharp L beta'--P beta' transition observed in pure dipalmitoyl phosphatidylcholine. The transition between L beta' and P beta' in these mixtures is displaced to lower temperatures and becomes gradual as depicted by all three techniques, but freeze-fracture gives more definite information of the continuous transition. The most striking observation on the morphology of the mixed membranes (3--30% phosphatidylserine in dipalmitoyl phosphatidylcholine) is the presence of banded patterns (P beta') at temperatures well below the main transition peak as detected by differential scanning calorimetry.

Calorimetry, Differential Scanning↗