Correlation between blood rheological properties and red blood cell indices(MCH,MCV,MCHC) in healthy women

1 Introduction

From hemodynamic point of view blood is a two-phase suspension of formed elements where cells are suspended in plasma which is an aqueous solution of organic molecules, proteins and salts. The viscosity of blood depends on the existing shear forces and is determined by hematocrit, plasma viscosity (PV), Red Blood Cell (RBC) aggregation and the bio-mechanical properties of RBCs [4]. Deformability describes the ability of RBCs to change shape in response to deforming forces which not only improves their flow properties but also protects against cell disruption under bulk flow conditions and in the microcirculation when passing through capillary vessels as small as 3 μm in diameter in particular [2]. Early during erythropoiesis, the number of cell organelles is reduced to a minimum through extrusion of the nucleus, endoplasmic reticulum and mitochondria ensuring optimal plasticity of the cellular membrane. Variability of cell morphology may involve a change in cell curvature, uniaxial deformation or area expansion [4]. Under physiological conditions the deforming force is predominantly exert from outside the cell by fluid shear stress. However, it may be generated in the cell itself, caused by a change of the osmotic milieu [8], by formation of rigid fibers of cytoplasmic hemoglobin S, such as in sickle cell anemia [6], or by increased density of the intracellular fluid mainly as a result of hemoglobin-concentration and -properties [10]. The extent, vector and mode of deformation depend on the magnitude, rate and direction of the exposed stress. While RBCs behave as elastic bodies, and thus the shape change is reversible when the deforming forces are removed [7] they also exhibit viscous behavior so they respond as a viscoelastic body as well. Internal viscosity, viscoelastic properties and surface area to volume ratio are the main determinants of RBC deformability [14]. Plastic changes of the RBC membrane may be irreversibly upon exposure to excessive shear forces or in pathologic conditions associated with numerous diseases such as metabolic Syndrome, diabetes mellitus [12], iron deficient anemia [23], hemoglobinopathy [5, 13], pre-eclampsia/HELLP-Syndrome [18], and autoimmune disease. Changes in RBC indices, e.g. mean corpuscular volume (MCV), corpuscular hemoglobin content (MCH) of erythrocytes, as well as mean hemoglobin concentration of the erythrocyte mass were found to correlate with impaired RBC deformability in effected patients.

In a first step it was the aim of this community based study to investigate the association between blood rheological parameters and RBC deformability in particular and RBC indices in otherwise healthy mid-age women prior to elective gynaecological surgery.

2 Patients and methods

3 Results

This is a cross-sectional observational study. During the study period from June 2014 to December 2014 a total of 286 healthy women (age: 46.5±17.6 y; BMI: 25.5±5.2 kg/m²) were eligible for inclusion into this prospective evaluation. All the operations were indicated due to benign and non-infectional elective gynaecological illnesses, mainly one-day surgery: 58% hysteroscopy and laparoscopy; 26% dilatation and curettage of the uterus; 16% hysterectomy. The patients‘ characteristics are presented in Table 1.

4 Discussion

The combination of a high degree flexibility of the erythrocyte membrane (viscoelasticity), in the presence of a low intracellular fluid viscosity and a high surface area/cell volume ratio provides optimalconstellation for maximal cell deformability in the microcirculation or passing through the spaces between the endothelial cells of the splenic sinusoids smaller than 3μm in diameter [4]. Biconcave discoid geometry of RBCs with a major diameter of 8 μm and MCV of about 90 fL (89,77 fL in our study) under normal conditions results in a 40% greater mean surface area (SF) of about 140μm² compared to that of a spherical cell shape of the same MCV which allows uniaxial deformation [4]. Hemoglobin-concentration and its biochemical properties primarily determine intracellular fluid viscosity which is about 7 mPa s and which as such has no elastic behavior [4]. Our results confirm a close relation between RBC deformability and MCV, and although correlation coefficients between 0.128 and 0.214 were within in a narrow range, significantly highest correlation was found when RBCs were exposed to moderate to high shear forces, which approximately corresponds to the shear stress found in the splenic sinusoids. Moreover, the reliance of RBC deformability on MCHC could be clearly demonstrated, whereas increasing MCHC went along with a continuous reduction in RBC deformability, which was most pronounced during high shear stress exposure. The role of MCV on the impact of RBC deformability has been impressively shown in patients with macrocytosis greater than 97 fL (mean: 115.9±5.2 fL) where elongation indices for RBCs were significantly higher compared to normocytic controls at low, moderate and high shear stress test conditions (r = 0.548; p <  0.01) [22]. The trend towards improved RBC deformability in extreme sized RBCs in vitro may be limited when passing through very narrow vessel in vivo. MCV reduces with the aging of RBC while rigidity increases which likely is a main cause of their clearance in the spleen. Bosch et al. [3] could demonstrate reduced deformability in the fraction of older RBCs characterized by increased MCHC and lower MCV which is in line with our observation. Numerous study have shown reduced RBC deformability in patients with hemoglobinopathia such as sickle cell anemia [5, 13] or thalassemia [20]. However, reduced deformability associated with these diseases unlikely is the result of anemia itself but rather is caused by impaired viscoelasticity of the membrane through generation of rigid fibers of HbS that distort and damage the cytoskeleton and membrane in sickle cell anemia, alternatively by attachment of unstable globin precipitates to the membrane that induce oxidation of the skeletal proteins in thalassemia. Vaya et al. [23] found significantly lower deformability of RBC - using same ektacytometric technics as in our trial - in 50 patients with iron deficiency anemia compared to age- and sex- matched healthy controls. Correlation analyzes between RBC-indices and -deformability was not performed, but compared to healthy subjects anemia was characterized by significantly lower MCV and MCHC as well. It is unclear to what extend each indices represents a dominating effector of reduced RBC deformability in iron deficient anemic patients.

Blood rheological results in our trial were closely related with the age of women. While RBC aggregation and PV were also correlated with BMI, the latter had no effect on RBC deformability in women of this trial whose mean BMI was 25.5 kg/m² which is in the range of moderate overweight according to WHO (25–30 Kg/m²) [15]. The influence of obesity on hemorheology has been addressed in a number of trials and while a trend towards increased viscosity was found in most of them, improvement in hemorheological parameters after weight loss and treatment with low calorie diet was reported as well [9, 16]. A recent trial reconfirmed significant correlation between BMI and whole blood viscosity, hematocrit, Pv and RBC aggregation. As in our trial BMI in these patients was 27.54±0.34 kg/m² indicating moderate overweight whereas RBC rigidity was indifferent for high and low BMIs as well [21].

The results of the current trial based on notable number of apparently healthy women show close relation between RBC deformability, MCV and MCHC which is age dependent but independent of the BMI in mid-age women with normal to moderate increased weight. The results of all blood rheological parameters indicate an age dependent increase in blood viscosity.