Biomedical subjects

J B Hubbard

Publications and source records attributed to J B Hubbard.

4 recordsLinked to original sources

PubMed1995

Physical characterization of heparin by light scattering.

Dynamic and electrophoretic light scattering were used to measure the size and charge heterogeneity of a commercial preparation of heparin. For this preparation of porcine mucosal heparin (M(r) = 10-20 kDa), the diffusion coefficient was 1.2 +/- 0.5 x 10(-8) cm2/S and the mobility was 4.4 +/- 0.9 x 10(-4) cm2/Vs for an unfiltered solution at 22 degrees C in distilled water. This diffusion constant is 2 orders of magnitude smaller than expected for a molecule the size of heparin. A fast diffusion component of 5.8 +/- 1.0 x 10(-7) cm2/S, corresponding to the individual molecule, was observed in the presence of 2 M NaCl, where single molecule motion is better observed. This indicates that a portion of the heparin population is in an aggregated state, which produces a higher scattering intensity than individual heparin molecules. The weight percentage of the aggregates was 5-10 as measured by high performance exclusion chromatography. These aggregates were stable up to a temperature of 75 degrees C as measured by light scattering. This suggests that the aggregates are made up of tightly bound heparin molecules. From the diffusion coefficients we estimate the average aggregate to be made up of about 50 heparin monomers, and from the mobility, we estimate the electrophoretic charge on the aggregate to be about 1000 or about 20 electrophoretic charges for each heparin monomer. The electrophoretic light-scattering measurements also indicate that the aggregate scattering species have very similar surface charge densities resulting from the aggregates being formed from heparin molecules.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemistry, Pharmaceutical↗

PubMed1983

Issues for informed consent.

Informed consent from a cytapheresis donor is the culmination of a complex decision making process during which the blood collecting agency presents sufficient information to enable the donor to make a free choice whether or not to donate. The institution bears the responsibility for providing all information relevant to the donor's decision, whether favorable or unfavorable. At no other stage of its contact with the donor can a collecting agency discharge its public trust more meaningfully. Thus, informed consent is not only the greatest altruistic expression from the unrelated volunteer donor, or the expression of deepest commitment to the family for the related donor, it is also the fullest expression of the value which the institute places on the autonomy of the donor. The foundation upon which the concept of informed consent rests has been laid by law, medicine, government, ethics, and religion. Although the procedures accompanying the informed consent process appear bureaucratic, they should be viewed as the components of a remarkable, dynamic process. The consent of a donor to undergo cytapheresis is an eloquent statement of the value he or she places on the importance of another human being's life.

Blood Component Removal↗

PubMed1977

Kinetic dielectric decrements and conducting liquids.

We have calculated influence of ion migration on the measured dielectric constant of an electrolyte solution. The solvent is assumed to be a viscous, incompressible, polarizable liquid continuum having a finite dielectric relaxation time, while the ion is a rigid, impenetrable body. The decrement in the static permitivity of the solution with respect to the pure solvent is shown to be proportional to the product of solvent dielectric relaxation time and conductivity of the solution, with an additional contribution arising from viscous relaxation in the solvent.

Electric Conductivity↗

PubMed1977

Kinetic polarization deficiency in electrolyte solutions.

The prediction and experimental confirmation of a previously unsuspected kinetic effect occurring in electrolyte solutions are presented herein. Kinetic polarization deficiency may be described as a reduction, with respect to the pure solvent, in the static permittivity of the solution; the decrement in epsilon0 is shown to be proportional to the product of the dielectric relaxation time of the solvent and the low frequency conductivity of the solution. The kinetic ion-solvent interaction affects the capacitive admittance in two closely related ways: as an ion migrates, the surrounding volume elements of the liquid tend to rotate according to the laws of hydrodynamics, and although dielectric relaxation tends to restore an equilibrium polarization appropriate to the local electric field, this adjustment is not instantaneous; rather it lags behind by the dielectric relaxation time. Conversely, the force that an external field exerts on an ion does not develop its full strength instantly because the ion is driven partly by the external field and partly by the polarization that develops in response to the applied field, the polarization field evolving with a time constant that is the relaxation time for the orientation of solvent dipoles.

Electrolytes↗