Fig 1.
Schematic drawing of the device and experimental setup that were used to measure blood conductivity.
(A) Cross-section of the PDMS chamber. (B) Shapes and sizes of the gold-plated electrodes on the bottom of the chamber. (C) The appearance of the measuring system. Blood samples are loaded into the chamber using a pipette. (D) Photograph of the experimental setup. Calibration using air. (E) Photograph of the measuring PDMS chamber with two planar electrodes.
Fig 2.
Schematic of the experimental setup that was used to obtain optical observations of blood sedimentation.
(A) Sony α900 digital camera with Carl Zeiss Vario-Sonnar lens. (B) Photograph of the micro-hematocrit capillary tubes in 5-place rack. Each capillary tube has an inner diameter of 1.2 mm and a length of 75 mm. (C) Photograph of the Sedi-Rate ESR System inside the light-tight box. Each plastic tube has a sedimentation scale of 200 mm and a bore of 2.55 mm.
Table 1.
Erythrocyte sizes and electrical properties.
Table 2.
Viscous properties of fluids, densities and velocity of sedimentation.
Table 3.
Notations for semi-empirical models of blood sedimentation.
Fig 3.
Theoretical model of the suspension of randomly oriented spheroidal particles.
Shell-ellipsoid model for suspension of erythrocytes.
Table 4.
Resistivity of human blood.
Fig 4.
Comparison of the effective medium theory and the experimental data.
Conductivities at various hematocrits (HCTs) were calculated using Eq 7. Our chamber with two planar electrodes was used to measure conductivity. Five samples of washed erythrocyte suspensions in pure plasma were prepared at HCT = 35, 45, 55, 62, and 98%.
Fig 5.
Time-dependent changes in blood conductivity during sedimentation.
Three samples of washed erythrocyte suspensions in pure plasma were prepared at hematocrit (HCT) = 35, 45, and 55%. (A) The conductivity of blood increased slightly during the first minute of observation and then decreased for more than 1.5 h. The conductivities of the disaggregated erythrocyte suspension were σ = 0.588, 0.468, and 0.355 S/m, at HCT = 35, 45, and 55%, respectively. The conductivity of the deposit on the bottom of the chamber was approximately 0.175 S/m at the end of the sedimentation, regardless of the initial HCT. (B) Initial changes in blood conductivity at HCT = 35%. The maximum value of the initial increase in conductivity was about 0.036 S/m at 18s. (C) The maximum value of the initial increase in conductivity was 0.028 S/m at 31 s (HCT = 45%). (D) The maximum value of the initial increase in conductivity was 0.027 S/m at 60 s (HCT = 55%).
Fig 6.
Influence of dextran and phosphate buffered saline (PBS) on changes in blood conductivity during sedimentation.
The plot presents a comparison of the changes in conductivity for three suspension of erythrocytes in (a) pure plasma, (b) PBS (pH = 7.4, 290 mOsmol/kg), and (c) dextran (425~575 kDa, 1 g/dl) solution in plasma. Each sample had a hematocrit = 45%. The inset presents the details of the initial stage of the change in conductivity.
Table 5.
Calculated erythrocyte settling velocities at different hematocrits.
Fig 7.
Sedimentation curve and change in the velocity of sedimentation with time for whole blood and a suspension of erythrocytes in phosphate buffered saline (PBS).
(A) Sigmoid sedimentation curve and change in the sedimentation velocity of whole blood. Suspension of washed erythrocytes in pure plasma, hematocrit (HCT) = 35%. (B) Linear growth of the pure PBS zone for the suspension of erythrocytes in PBS (pH = 7.4, 290 mOsmol/kg), HCT = 45%. The insets show capillary tubes with blood after 9190 s of sedimentation.
Fig 8.
Volume fraction profile and a simple model of erythrocyte sedimentation.
The height of the liquid column h remains constant in the process of sedimentation. The height of the plasma zone hp and the volume fraction at the bottom of the blood column both increase. The velocity of the boundary between the zones changes with time. (A) Experimental observation of variation of volume fraction profile during sedimentation. Suspension of washed erythrocytes in pure plasma, initial hematocrit = 38.5%. (B) Simplified model of erythrocyte sedimentation.
Fig 9.
Correlation between 60 min Westergren ESR test and rate of changes in blood conductivity.
EDTA-treated blood samples were prepared at different HCT and concentration of dextran or PBS. Each blood sample was loaded into the PDMS chamber and the Westergren tube at the same time.