Clinical Hemorheology and Microcirculation

The deformability of red blood cells (RBCs) is an important rheologic factor in the maintenance of normal blood flow in the microcirculation. Contrary to the well‐known relationship between hyperlipidemia and atherosclerosis, the relationship between RBC rheology and the serum lipid profile has remained controversial and obscure. Moreover, the correlation of high‐density lipoprotein (HDL)‐cholesterol and RBC deformability has not been fully understood. In the present cross‐sectional study of 139 apparently healthy subjects, we investigated whole‐cell deformability (filterability) of RBCs in relation to the lipid profile, using a nickel mesh filter with 3.2‐ \mu m pores. RBC filterability was independent of gender, age and serum levels of low‐density lipoprotein (LDL)‐cholesterol. The filterability was significantly proportional to the HDL‐cholesterol values ( r={} 0.382, p<{} 0.01), whereas it was inversely proportional to the triglyceride levels ( r=-0.259 , p<{} 0.01). These findings may provide new insight into the role of HDL‐cholesterol not only in preventing atherosclerotic progression but also in improving RBC filterability.

The aim of the present study is comparison of changes of principal hemorheological factors responsible for blood flow disorders in the microcirculation in patients with ischemic brain infarcts. It was found that in venous blood samples the erythrocyte aggregability (examined with a direct, highly sensitive, quantitative technique) was considerably more increased (by mean of 120%) than the blood plasma fibrinogen contents, blood plasma viscosity, and hematocrit which increased only by 23.7%, 7.4% and 3.6%, respectively, as compared to the same hemorheological factors in the healthy controls. These results led us to the following conclusion: among the other tests the enhanced erythrocyte aggregability, when measured with an appropriate technique, is the best diagnostic indicator of hemorheological derangements during development of the ischemic brain infarct.

The deformability of erythrocytes in Waldenström’s Macroglobulinemia (WM) patients are analysed by shear stress diffractometer in vitro. Erythrocytes obtained from blood samples of WM patients are subjected to well defined shear forces, varying from 0.3 to 60 Pa, and their corresponding elongation indexes generated by diffraction pattern of a laser beam are recorded. For comparison, equal number of samples from normal adult volunteers is also studied. The results show a shear dependent decrease in deformability index in WM patient samples. The decrease in deformability index of WM patients is significant at high shear forces ( > 12 Pa) when compared to those of normal samples whereas it is not significant at low shear forces. As the deformability of erythrocytes together with elevated plasma viscosity and enhanced erythrocyte aggregation may cause potential flow stagnation at microvasculature, these studies are clinically relevant.

Objective: Patients affected by obstructive sleep apnea syndrome (OSAS) have an increased risk of cardiovascular diseases such as stroke and myocardial infarction. The pathophysiological mechanisms leading to increased vascular risk are still matter of debate. A relative morning hyperviscosity could be one of the leading mechanisms of cardiovascular morbidity which is actually known to be especially high in the morning hours.

Methods: Whole blood viscosity (WBV) at seven shear rates, ranging from 0.47 to 118 sec ^{-1} , haematocrit (Hct), and plasma fibrinogen (F) concentration, were measured on venous blood samples in 12 patients with OSAS and in 8 healthy controls at 8–9 p.m. and at 7–8 a.m. the morning after. WBV values were normalized on Hct by the computation of the standardised normal deviate z on the normal database of the laboratory.

Results: No changes were observed in controls. Hct, F and normalized WBV (independently from Hct changes) significantly increased in the morning hours in OSAS patients.

Conclusions: Viscosity of whole blood increases in the morning in OSAS patients but not in healthy controls. This condition may be related to the increased susceptibility to cerebral ischemia in patients affected by OSAS, particularly evident in the early morning.

The original Westergren blood sedimentation technique was modified to assess leukocyte sedimentation properties. The relative change of leukocyte and erythrocyte counts was measured in the upper half section of blood column in vertically positioned sedimentation tubes in 10‐minute‐intervals for 60 minutes. During the first 20 minutes of gravity sedimentation, the leukocytes taken from critically ill patients showed upward flotation, however, healthy individuals’ leukocytes demonstrated slight sedimentation. The upward flotation rate of leukocytes seemed less dependent on erythrocyte sedimentation during the first 15 minutes of sedimentation time than after it. Based on this observation, the sedimentation properties of leukocytes were characterized by the leukocyte antisedimentation rate taken at the 15th minute of sedimentation time (LAR15). Erythrocyte aggregability index, plasma fibrinogen concentration and native leukocyte count did not correlate to LAR15 in healthy volunteers (n = 25) . However, LAR15 was correlated to leukocyte adherence (p <0.01) , to whole blood viscosity (p < 0.05) , to hematocrit (p < 0.05) and to the conventional erythrocyte sedimentation rate (p < 0.05) .

The rheological properties of human leukocytes (WBCs) have been studied using the micropipette aspiration and the filtration technique. Partial micropipette (i.d. 2.8–4.5 \mu m) aspiration of individual leukocytes under constant aspiration pressure of 8 mm H _{2} O and measurement of the aspirated length as a function of time (creep experiments) according to the Evans model have been carried out and the apparent viscosity \mu_{\mathrm{app}} was estimated. In the filtration experiments, using the Hemorheometer, the Index Rigidity of Leukocytes, ILR, was also estimated. The apparent viscosity \mu_{\mathrm{app}} of normal PMN and MNC was significantly different p< 0.05) , while the LYM and PMN had no statistical difference (p<0.5) . The leukocytes of the cell line HL‐60 were more rigid than the normal PMN (p <0.01) , while the PMN from patients with type II diabetes mellitus were more rigid than the normal PMN (p < 0.005) . The results of IRL showed similar differences among all of the leukocyte subpopulations. Comparison of these findings suggests a possible relationship between ILR and \mu_{\mathrm{app}} which in this case is: \mathrm{ILR} = 598 + 0.54\ \mu_{\mathrm{app}}\ (r = 0.986 , p ‐value 0.0003).

To evaluate how creatine influences erythrocyte deformability, we determined its effect on erythrocyte filterability in 9 subjects with insulin dependent diabetes (IDDM) without complications, 14 diabetics with uremia and 10 non‐diabetic controls. The short‐term incubation (15 min at 37 {}^{\circ} C) of diabetic erythrocytes with 3 mM creatine improved cell filterability (assessed according to the Reid method) from IDDM subjects without complications by 28.4% and that from diabetics with uremia by 18.9%. No rheological effect of creatine was found in erythrocytes from non‐diabetic controls. However, a significant protective effect against erythrocyte filterability impairment induced by treatment of red blood cells from non‐diabetic controls with hydrogen peroxide was observed with 3 mM (p < 0.04) and 5 mM (p < 0.01) creatine, respectively. Measurement of the thiobarbituric acid (TBA) reactivity was used to assess hydrogen peroxide induced formation of malondialdehyde (MDA). We found that creatine inhibits hydrogen peroxide‐induced erythrocyte MDA‐formation in a dose dependent manner by 20.4%, 22.3% and 41.4% for 1, 3 and 5 mM creatine, respectively. These results suggest that creatine by its ability to inhibit erythrocyte lipid peroxidation may contribute to the maintenance of normal cell deformability.

The efficacy of three weekly interventions with hypervolumetric hemodilution of a new preparation of hydroxyethyl starch (HES 100/0.5, 10%, C2/C6 substitution ratio of 6.5) on pain‐free walking distance of patients with peripheral arterial occlusive disease (PAOD) stage IIb on the Fontaine classification was investigated. In addition quantitative data on the pharmacokinetic properties of this HES preparation, and it’s impact on hemorheology, hemostasis and homeostasis were shown.

Ten patients were included according to a predefined protocol, and treated openly with 500 ml HES 100/0.5 10% on nine occasions over 18 days.

Pain‐free walking distance, the main outcome measure, showed a mean increase of 82 m ( + 60%). Hematocrit decreased 4 percentage points on average (5.5 percentage points one hour after interventions). Plasma viscosity dropped 5% on average with significant changes immediately after interventions only in patients whose baseline values had been equal to or above the 2 s reference area. Erythrocyte aggregation decreased by 16% in the course of treatment (8% immediately after interventions), systolic blood pressure by 13%, and total protein by 7%. Complement showed a trend towards lower values ( - 20%), and creatinine, pH and urine viscosity remained unchanged. Apart from complement changes, all reductions mirrored the dilution effects.

As to pharmacokinetics, serum mean molecular weight distribution was very similar to that of the infusion. A minor adverse drug reaction (light, spontaneously disappearing pruritus) was observed in one case.

Previous studies suggest that early loss of membrane might account for the shortened life‐span of neonatal red blood cells (RBC). The elastic area compressibility modulus describes the force required to achieve a defined expansion of the membrane and is thus a suitable intrinsic material property to describe mechanical stability of the RBC membrane. We studied RBC in eight cord blood samples (representing fetal blood), ten 5‐day old full‐term neonates and seven healthy adults. The RBC were suspended in hypotonic buffer solution and investigated using a modification of the micropipet technique by Evans et al. Cord blood RBC ( 204 \pm 33 dyn/cm) and neonatal RBC ( 209 \pm 11 dyn/cm) showed a 25% lower elastic area compressibility modulus than adult cells ( 278 \pm 26 dyn/cm; p <0.05 ). Thus, less force was necessary for expansion of neonatal RBC membrane. We conclude that neonatal RBC are more susceptible to mechanical damage of their membrane than adult cells.