1987 Volume 9 Issue 1 Pages 48-53
It is generally accepted that an increase in whole blood viscosity (WBV) in a range of low shear rates is due mainly to the aggregation of red blood cells (RBC), but that at the shear rates over 55-60/sec, the aggregation of RBC has little concern with WBV. At the higher shear rates, WBV is regulated by hematocrit (Ht), plasma viscosity (PV) and RBC deformability. Therefore, it appears to be possible to estimate an index of RBC deformability by eliminating the participation of Ht and PV from WBV.
The purpose of the present study was to obtain indices of RBC deformability by calculating from the values of WBV, PV and Ht. WBV and PV were measured in 40 healthy subjects and 17 patients with cerebral infarction with a cone-plate viscometer (Tokyo Keiki Co.) at the shear rates of 75.5 and 377.5/sec. Ht was measured with the capillary tube method. In order to apply the RBC-deformability index to a wide range of Ht and PV, the following procedures were performed : Ht in each sample was altered by removing or adding autologous plasma (PV being constant), and PV was changed by partial replacement of the plasma with physiological saline by two steps (Ht being constant).
Results were summarized as follows; 1) From the measurements in normal subjects, an extremely significant correlation was obtained between Ht and relative viscosity (WBV/PV) with an equation of Y=e0.0286X-0.0094 (n=112, r=0.992, p<0.001). Since WBV/PV expresses the contribution of the red cells (Ht and RBC deformability) to blood viscosity, the deviation of measured relative viscosity from this regression line in percent was thought to be an index of red cell deformability (% (WBV/PV)). 2) When plasma of each sample was diluted with physiological saline, WBV was lineally decreased in every case. A significant positive correlation (n=80, r=0.949, p<0.001) was also obtained between PV and %WBV, which was the percent deviation of individual WBV from the point of same Ht on the standard exponential curve obtained from the healthy subjects (n=112, r=0.988, p<0.001). The deviation from the regression line of this correlation was regarded as another index of RBC deformability (RD-Index), since the contribution of Ht and PV was mathematically eliminated from WBV. 3) The multiple regression analysis on the contribution of the rheologic factors to WBV showed that both the coefficients of determination of Ht, PV and % (WBV/PV), and Ht, PV and RD-Index to WBV were close to 1.0 (0.996 0.998) in both healthy subjects and patients with cerebral infarction. 4) The correlation of these two indices of red blood cell deformability was significant not only in healthy subjects (n=40, r=0.917, p<0.001) but in patients with cerebral infarction (n=17, r=0.944, p<0.001). 5) There was a significant correlation between MCHC (mean corpuscular hemoglobin concentration) and RD-Index, i.e. the higher the MCHC, the poorer the RBC-deformability was.
The results obtained from the present study suggest that these two indices appropriately indicate the RBC deformability.
