Biorheology

This study investigates the influence of haematocrit, fibrinogen concentration and fibrinogen availability (amount of fibrinogen per red blood cell) on erythrocyte sedimentation. The Westergren technique was applied to blood samples from 36 subjects and to their blood manipulated to haematocrits of 10, 20, 30 and 40%. Readings were taken every 10 minutes for 300 minutes. Previous studies indicate that erythrocyte sedimentation occurs in three phases. In this study, we show that haematocrit has little influence on either the rate of fall of particles in the first phase ( $m_{1}$ ) or the duration of the first phase. This is also true for fibrinogen availability and for fibrinogen concentration at low haematocrits. At high haematocrits $m_{1}$ increases with fibrinogen concentration. The rate of fall of rouleaux during phase 2 ( $m_{2}$ ) and ESR $_{60}$ both decrease exponentially with haematocrit and increase linearly with fibrinogen concentration. While $m_{2}$ is more closely correlated to fibrinogen availability than to fibrinogen concentration or to haematocrit, this is not the case for ESR $_{60}$ . Thus haematocrit, fibrinogen concentration and fibrinogen availability are more important to the velocity of sedimentation in the second phase than to the sedimenting velocity during phase 1 or to the duration of phase 1.

We have previously proposed the osmofiltration method based on a modified Hanss hemorheometer to analyze distributions of erythrocytes in their ability to pass through membrane filters with 3 $\mu$ m pores. Upon decrease in medium osmolality ( $u$ ) the erythrocyte volume increases. When cell volume becomes $V=V_{\mathrm{cr}}$ at $u=u_{\mathrm{cr}}$ , such cell loses its ability to pass through a 3 $\mu$ m pore. The flow rate of erythrocyte suspension containing cells with different $u_{\mathrm{cr}}$ through a filter gradually decreases with decreasing medium osmolality. This rate becomes zero at some $u=\Omega$ , when the number of non‐filterable cells in the applied sample approaches the number of pores in filter. Experimental determination of the dependencies of the filtration rate on medium osmolality for various hematocrit values allows to obtain $\Omega$ for each hematocrit and, thereby, to assess the distribution of erythrocytes in $u_{\mathrm{cr}}$ . Here, we propose a simplified version of this method, which allows screening of the erythrocytes in heterogeneous suspensions for the distribution in $u_{\mathrm{cr}}$ by measuring $\Omega$ for only two hematocrit values, 0.1% and 1%. Applications of the proposed method are exemplified by analysing the erythrocyte populations of healthy donors, of patients with microspherocytosis, hemochromatosis and normal erythrocyte populations in an acidic environment.

A new capillary system was developed, incorporating infrared sensors, which allowed the determination of whole blood viscosity over a wide range of shear stresses. Flow conditions were defined by the geometry of the capillary and the sample pressure head. Whole blood was considered to be a power law fluid and a modified Mooney’s formula was used for the calculation of the related invariants. The new viscometer proved to be very simple in use, requiring one run, had a short measuring time and utilised a small test sample volume. However it can be used for whole blood viscosity measurements only at medium and high shear stresses.

The size of liquid crystalline domains formed in partially dried giraffe saliva is found to be an order of magnitude greater than that previously documented for slug pedal mucus. A correlation between (a) intrinsic liquid crystalline domain size and (b) the scale of surface topography over which the mucus is required to provide lubrication is postulated. The scale of mucus microstructure can be related, via a simple model, to two significant material constants: the elastic constant $K$ for distortion of molecular alignment in the liquid crystalline state, and the anchoring energy $I$ at the liquid crystal/substrate interface. In turn, the quantity $K$ is expected to depend on fundamental molecular characteristics of the constituent mucin, such as molecular weight and degree of glycosylation. The possibility that observations of mucus microstructure might serve as a diagnostic tool for mucus defects at the molecular level is suggested.