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Biomedical subjects

L Dintenfass

Publications and source records attributed to L Dintenfass.

At least 19 recordsLinked to original sources
PubMed1990

Blood as a near-"ideal" emulsion: a retrospective on the concept of the red cell as a fluid drop, its implications for the structure of the red cell membrane.

Although the question whether the red cell is fluid or solid has been discussed since 17th century, it was the author's measurement of the relative viscosity of blood in 1960's that supplied the first direct evidence that the red cell interior is fluid. Furthermore, through his application of the equations of Taylor and, later, Oldroyd, to this problem, it became evident that, for the red cell to exhibit fluid-drop-like behavior, the membrane must also be fluid. This led to his concept of the red cell membrane as a complex two-phase structure (lipoprotein micelles and two-dimensional protein networks) which was similar to the one accepted nearly a decade later. The requirements of the theory of ideal emulsions that the shear stress be transmitted into the cell interior via low viscosity membrane, are met in the later work of other investigators using the concept of a tank-treading membrane having viscoelastic properties. This paper reviews the original work of the author which led to the development of an equation for the relative viscosity of blood as a function of volume concentration, C: nr = (1 - TkC)-2.5, valid at shear rates above 180 sec-1, in which T is the Taylor factor which gives a measure of fluidity of the red cell, and k is a plasma trapping factor. Both T and k increase with increasing rigidity of the red cell. Finally, the effect of the membrane viewed as a complex two-phase fluid, on the rheology of the red cell is discussed.

Blood Viscosity↗
PubMed1990

A new outlook on body fluid viscosity and cell function: concluding remarks and discussion.

The area neglected so far in the fields of clinical and theoretical haemorheology is that of interaction between viscosity and chemical reactions in the cells. The reintroduction of teinochemical principle opens entirely new doors for investigation both in vitro and in vivo. Effect of extracellular fluid viscosity on synthesis (i.e. lipids) and on possible enzymatic and catalytic functions influences our opinion that haemorheology has to go back to fundamentals.

Animals↗
PubMed1989

Modifications of blood rheology during aging and age-related pathological conditions.

In principle there should not be any increase of blood viscosity factors (plasma viscosity, blood viscosity, aggregation of red blood cells, rigidity of red blood cells, dynamic thrombus formation) with aging in a healthy population. Such an increase would be due to pathological caused and not to aging per se. The pathological causes of the increase in the blood viscosity factors often observed in the elderly could be ascribed to the following: use of drugs (e.g. cigarette smoking); lack of exercise; unbalanced diet; psychological states such as anxiety and depression; presence of diseases such as heart disease or cancer or diabetes (although these disorders have the same effect in a younger population). The principal viscosity factors are explained, and their role in tissue perfusion, occlusions, infarctions and other disorders is described. This review will hopefully serve as an introduction to the studies of the haemorheology of aging. A counteraction of the elevation of blood viscosity factors might be helpful in ameliorating many diseases typical of aging, and should allow elderly people to remain active much longer.

Aging↗
PubMed1988

Aggregation of red cells in disease: some deductions and speculations based on results of "ARC" experiment on the space shuttle "Discovery" STS 51-C.

Experiment on STS 51-C in January 1985, carried out on blood samples obtained from patients with heart disease, diabetes, hyperlipidaemia and cancer showed that, under zero gravity, the morphology of red cell aggregates aggregates was normal, in contradistinction to the parallel and simultaneous observations under 1 g, which showed large and unorientated clumps of red cells. As such clumps could be considered of disadvantage in the microcirculation and tissue perfusion, the zero gravity observations were significant in a number of ways. In particular, a preliminary deduction (subject to further zero g experimentation) was that cell-cell interaction and adhesion are affected by zero gravity, and that most likely the microarchitecture of the cell membrane is modified; and that probably the receptors, their position and/or activity, are affected by zero gravity. Of particular interest could be a possible change in the properties of the discrete surface areas which respond preferentially to specific macromolecules (or ligands). There is a dissonance between these in vitro results and theoretical deductions on flow in the microcirculations by Oka, and as well of deductions on space sickness by Dintenfass, both assuming a disabling effect of zero g on the in vivo microcirculation. This dissonance should be explored, as effect of zero g might be different on blood flow in vivo and in vitro. However, the data available from the in vitro experiment suggest that studies in immunology and oncology might be enriched by zero gravity findings; and that studies under zero gravity might open a new avenue of research in these important fields.

Blood Viscosity↗
PubMed1985

Red cell aggregation in cardiovascular diseases and crucial role of inversion phenomenon.

Perfusion of the heart muscle remains an important area of studies fraught with great difficulties. An analogue of capillary system has been organized by using in vitro flow of blood from the heart patients in a slit-capillary photo-viscometer. The rate of aggregation of red cells and the morphology of aggregates have been observed and quantitated in representative cases. A possible role of the sludge-like aggregates is discussed from the viewpoint of the "inversion phenomenon" which amplifies resistance to flow as a function of rheology (rigidity or deformability) of cell aggregates and single cells. This pattern might be alike that of arterial spasm or can serve as a model for capillary occlusions. A description is given of the new instrument, the slit-capillary photo-viscometer, and stereological parameters obtained in macro- and micro-photography are included. Linear regressions of such parameters against stasis time are highly significant, showing correlation coefficient up to 0.99. These regressions can be compared for slopes and elevations observed in different blood samples, with significance up to 0.001.

Blood Viscosity↗
PubMed1978

Rigidity of red cells in essential hypertension.

Both viscosity of blood and the rigidity of red cells are of consequence in the mechanism of hypertension. While the details of this mechanism are still elusive, the evidence presented might open the way for a wider inquiry into the role of blood rheology in hypertension.

Blood Pressure↗
PubMed1977

Blood viscosity factors in evaluation of submaximal work output and cardiac activity in men.

Sixty-two male subjects, including patients with postmyocardial infarction, angina, other disorders, and normals, were studied by exercise testing on the bicycle ergometer, including exercise ECG, and by in vitro determination of blood viscosity, plasma viscosity, aggregation of red cells, and other factors. Significant correlations were found between the blood viscosity factors on the one hand, and different terms describing physical fitness and cardiac functions on the other. In all correlations an elevation of blood viscosity factors led to lower fitness or lower cardiac efficiency; and a decrease of blood viscosity (or plasma viscosity, or compound viscosity product) was associated with better fitness and higher cardiac efficiency. Similarly, ECG ST-segment depression was proportional to increase of blood viscosity factors. All these highly significant correlations were found within a very narrow range of hematocrits, while the hematocrit value itself was not significant in this study.

Adult↗