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Biomedical subjects

N B Grover

Publications and source records attributed to N B Grover.

70 records · Page 4Linked to original sources
PubMed1975

The influence of cardiopulmonary bypass on the size of human platelets.

Large and small platelets are present in the bloodstream in nearly equal proportions and comprise about 30 per cent of the normal platelet population. The assumption that cardiopulmonary bypass may alter this platelet population distribution was investigated. Platelet volume distribution curves during and after cardiopulmonary bypass were examined in 12 patients undergoing various intracardiac operation by an electronic particle-sizing apparatus based on the Coulter counter. Mean platelet volume (MPV) was 8.6 +/- 0.7 cubic microns prior to cardiopulmonary bypass. Ten minutes after commencement of cardiopulmonary bypass the MPV decreased to 85 per cent of control levels. A further decrease, reaching a plateau at 75 per cent of prebypass MPV, was reached after 50 minutes on bypass. MPV returned to 87 per cent of prebypass levels 2 hours after discontinuation of cardiopulmonary bypass. Since it is known that platelet count is markedly reduced on cardiopulmonary bypass, a simultaneous 25 per cent decrease in MPV can be explained only by a highly selective disappearance of the large platelets from the circulation. As the larger platelets are younger and functionally more potent than the smaller ones, the selective disappearance of large platelets may thus provide an explanation for the observed alteration in platelet adhesiveness caused by cardiopulmonary bypass.

Blood Cell Count↗
PubMed1972

Electrical sizing of particles in suspensions. 3. Rigid spheroids and red blood cells.

The processes involved during the passage of a suspended particle through a small cylindrical orifice across which exists an electric field are investigated experimentally for an approximate prolate spheroid in the form of two tangent, rigid spheres (ragweed pollen particles) and for fresh, human red blood cells. Oscillograms of current pulses produced by both types of particles are presented and discussed in terms of particle shape and orientation and the effects of the hydrodynamic field. It is concluded that all the particles enter the orifice with their major axes aligned parallel to the orifice axis (electric field), but that during their passage some are rotated by the hydrodynamic field. Cells with their equatorial plane perpendicular to a radius of the orifice change their orientation with respect to the electric field as they are rotated, the others do not; only in the former case is there any deformation. It is shown that the bimodal or skewed size distributions can be explained on this basis, and that size (shape factor x volume) is actually a normally distributed variable (P > 95%). The average size of samples from 10 healthy adults was found to be 102.7 mu(3) with a coefficient of variation of 1.8%. For a volume of 87 mu(3), this corresponds to a shape factor of 1.18, an axial ratio (assuming a perfect oblate spheroid) of 0.26, and an equivalent major axis of 8.6 mu. The effect of high electric fields on red cell size distributions is mentioned.

Adult↗
PubMed1969

Electrical sizing of particles in suspensions. I. Theory.

The processes involved during the passage of a suspended particle through a small cylindrical orifice across which exists an electric field are considered in detail. Expressions are derived for the resulting change in current in terms of the ratios of particle to orifice volume and particle to suspending fluid resistivity, and particle shape. Graphs are presented of the electric field and of the fluid velocity as functions of position within the orifice, and of the shape factor of spheroids as a function of their axial ratio and orientation in the electric field. The effects of the electric and hydrodynamic fields on the orientation of nonspherical particles and on the deformation of nonrigid spheres is treated, and the migration of particles towards the orifice axis is discussed. Oscillograms of current pulses produced by rigid, nonconducting spheres in various orifices are shown and compared with the theoretical predictions.

Biophysical Phenomena↗
PubMed1969

Electrical sizing of particles in suspensions. II. Experiments with rigid spheres.

Experimental verification is provided for the theoretical expressions (see preceding article, I. Theory) describing the electrical processes that take place during the passage of an aqueous suspension of rigid, nonconducting spheres (ragweed pollen) through an orifice across which there exists an electrical field, for a large range of orifice dimensions; the instrumentation developed is considered in some detail. The effective length of an orifice as deduced from conductivity measurements is shown to be essentially the same as that predicted theoretically. Absolute volume distributions are presented of a suspension of polystyrene latex spheres as determined electrically (mean 11.17 mu(3), c. v. 4.2%) and with an electron microscope (mean 11.01 mu(3), c. v. 4.1%). Conflicting experimental results reported in the literature are discussed.

Biophysical Phenomena↗
PubMed1966

Anisometric transport of ions and particles in anisotropic tissue spaces.

The results of time-lapse measurements and electron microscopic observations on the diffusion of histological dyes, colloidal particles, and heavy metal salts in excised chicken breast tendon are reported. In all cases, the transport was found to be anisometric, the extent of the spreading being much greater parallel than perpendicular to the collagen fibers. The diffusion of colloidal gold was shown to be governed by a random diffusion process, with coefficients of 3 to 5 x 10(-7) and 1 to 2 x 10(-7) cm(2)/sec for the parallel and perpendicular directions, respectively; the anisotropy was attributed to steric hindrance. In the diffusion of uranyl nitrate, a sharp boundary appeared at the leading edge of the diffusate and advanced at a rate proportional to the square root of time. Electron micrographs showed uranyl nitrate clusters localized in space on the surface of the collagen fibrils and tightly bound to the polar amino acid regions of the macromolecule. A model was proposed involving diffusion with attrition, and predicted a sharp boundary advancing proportionally to the square root of time and to the 0.65 power of the initial diffusate concentration. Application of the model to the experimental results for uranyl nitrate gave a diffusion coefficient of 10 x 10(-7) and 4 x 10(-7) cm(2)/sec for the parallel and perpendicular directions, respectively, and a possible explanation of this large difference was advanced. The importance of anisometric transport in anisotropic tissues was indicated.

Animals↗