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.

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.

Mystery deepens--blood on the space-shuttle Discovery's flight STS 26 at zero gravity and some deductions or extrapolations.

The second "aggregation of red cells" experiment that was performed on the National Aeronautics and Space Administration's space-shuttle Discovery's flight STS 26 confirms the results that were obtained in 1985; however, some new features have come to light, in particular, the observation of a clot or thrombus which, so far, remains unexplained. An attempt has been made to link observations on the cell-to-cell interaction and blood viscosity under zero gravity to some of the problems that are facing astronauts and to some new dimensions in medical science.

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.

Experiment on "Discovery" STS 51-C: aggregation of red cells and thrombocytes in heart disease, hyperlipidaemia and other conditions.

The aim of this experiment was to study aggregation of red cells in the blood of patients with ischaemic heart disease, diabetes, hyperlipidaemia, and (silent) cancer, and in two normal donors. Reconstituted blood using IgG was also used. The instrument, the automated slit-capillary photo-viscometer (100 kg weight) was set on the middeck of the Space Shuttle. An analogous instrument was at the Kennedy Space Center. Blood was obtained from donors, anticoagulated, and adjusted to haematocrit of 30% using native plasma. Experiments took place at 25 degrees C, during which blood was forced to flow in the slit formed by two parallel glass plates. Macro and microphotography was carried out at specific intervals controlled by a computer. During stasis, lasting 6 minutes, aggregates (or clumps) of the red cells were formed. Results indicated that red cell aggregates do form under zero-G; that such aggregates are smaller than the ones obtained at one-G; that morphology is different, the zero-G showing rouleaux while one-G showing usual sludge-like clumps of red cells in all severe disorders. Platelets appeared to remain monodisperse under zero-G. Assuming that these data can be confirmed, one could suggest that zero-G affects cell-cell interaction, and may consequently influence the internal microstructure of the cell membrane and of the receptors, as well as their activity. Gravitational studies may thus open a new door on immunology and haematology in general.

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.

Execution of "ARC" experiment on space shuttle "Discovery" STS 51-C: some results on aggregation of red blood cells under zero gravity.

A project on "Aggregation of Red Cells" has been accepted by NASA in 1977. An automated slit-capillary photo-viscometer has been designed during 1979-1984, and its last version met NASA's space hazards requirements. The 'heart' of instrument is a set of two highly polished glass plates, spaced by a gap of 12.5 micrometers. An original drum-like infusion pump allows utilization of up to eight blood samples. During a sequential process, blood flows through the slit, and then stops to allow formation of aggregates. Micro- and macro-photography is carried out, and 500 photographs are obtained. Blood from normal donors and patients with history of ischaemic heart disease, colon cancer, juvenile-onset diabetes, hyperlipidaemia, etc., is anticoagulated and adjusted to haematocrit of 0.30 using native plasma. Samples are divided, and infused into the 'flight' and 'ground' instruments. Prior to experiment temp. is 5 degrees C; temp. during experiment is 25 degrees C. Experiments took place on 24-25 January 1985, on the middeck of space shuttle 'Discovery'. Subsequent results showed that red blood cells do not change shape under zero gravity; that aggregation of red cells does take place; that aggregates in pathologic blood show morphology of normal rouleaux under zero gravity, while identical blood shows clumps of red cells on the ground. The latter observation suggests that zero gravity might affect cell-to-cell interaction, and perhaps microstructure of the cell membrane. These aspects must remain however tentative till a confirmation by subsequent experiments can be obtained.

Experiment on aggregation of red cells under microgravity on STS 51-C.

Kinetics and morphology of aggregation of red cells were studied using automatic slit-capillary photo-viscometers, one situated on the middeck of the space shuttle 'Discovery', and the other in the ground laboratory at KSC. Experiments were run simultaneously, blood samples being adjusted to haematocrit of 0.30 using native plasma, at temp. of 25 degrees C, and anticoagulated by EDTA. Donors included patients with myocardial infarction, insulin-dependent diabetes, hyperlipidaemia and hypertension. Macro and microphotographs were obtained during flow and stasis. There was a striking difference in the morphology of aggregates formed in space and on the ground. Aggregates formed under zero gravity showed rouleaux formation, while the same blood samples showed severe clumping on the ground, in all patients blood. Normal blood showed rouleaux on the ground, but a random swarm-like pattern in space. The shape of the red cells remained normal under zero gravity.

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.

First haemorheological experiment on NASA space shuttle 'Discovery' STS 51-C: aggregation of red cells.

The 'secret' D.O.D. Mission on flight STS 51-C also carried nearly 100 kg of automated instrumentation of the Australian experiment on aggregation of red cells ("ARC"). The automated Slit-Capillary Photo Viscometer contained blood samples from subjects with history of coronary heart disease, cancer of the colon, insulin-dependent diabetes, etc., as well as normals. The experiment ran for nine hours, according to the program of its microcomputers. When shuttle landed and instrumentation recovered and opened in the presence of NASA quality control officers, it was obvious that experiment was a success. Tentative and preliminary results can be summarized as follows: red cells did not change shape under zero gravity; red cells do aggregate under zero gravity, although the size of aggregates is smaller than on the ground; the morphology of aggregates of red cells appears to be of rouleaux type under zero gravity, notwithstanding the fact that pathological blood was used. These results will have to be confirmed in the future flights. The background and history of development of the project are described, and put into context of our general haemorheological studies.

Measurement of Aggregation of Red Cells in space--a project for the NASA space shuttle.

Progress is described on the advanced stages in design of an instrument for the study of red blood cell aggregation and blood viscosity under near-zero gravity conditions. This paper gives a brief review of the experiment and its background and a description of the design of the instrument intended for space conditions. Summaries are given of solutions to some problems peculiar to a space experiment, particularly blood storage, microscope focusing, experiment control and data acquisition.