Clinical Hemorheology and Microcirculation

Blood rheology is influenced by metabolism and nutrition. We investigated this issue in 41 elite athletes exercising 13±0.9 hr/wk (mean age: 23.9±0.67 yr; mean V_{O2 max}: 52.6±2.3 ml/min/kg body weight) with a standardised nutritional questionnaire suitable for sports medicine. Calorie intake (% of recommended intake) was negatively correlated with the RBC disaggregability threshold (r=−0.505, p=0.01). There were negative correlations between fibrinogen and protein intake (% of the total caloric intake r=−0.787, p=0.0008; amount in g/kg/day r=−0.597, p=0.03). Accordingly, the RBC disaggregability threshold was also correlated negatively with protein intake (r=−0.508, p=0.05). Lipid intake (g/kg/day) was negatively correlated with the RBC disaggregability threshold (r=−0.564, p=0.03) and positively to the hematocrit/viscosity ratio (r=0.531, p=0.03). Carbohydrate intake (g/kg/day) was positively correlated with whole blood viscosity (r=0.517, p=0.04) and negatively to the hematocrit/viscosity ratio (r=−0.4863, p=0.05). In addition fibrinogen was negatively correlated with hematocrit (r=−0.4129, p=0.036) and positively with a host of aggregation parameters (p<0.001). Therefore fibrinogen levels and red cell rheology exhibit correlations with the nutritional status in athletes. Low protein intake appears to be associated with (mildly) raised fibrinogen and aggregability, and low calorie intake is associated with lower RBC disaggregability.

Objective: To investigate if blood hyperviscosity in RA patients is due to a reduced erythrocyte deformability and, therefore, turning it into a reliable activity indicator, as well as a therapy follow‐up marker for this pathology.

Methods: (1) The haemorheological profile consisting of erythrocyte deformability, blood and plasma viscosity, and erythrocyte membrane fluidity was determined in 24 AR patients and 17 healthy controls. (2) A 4 year follow‐up was carried on in 16 patients monitoring blood viscosity, erythrocyte deformability and biochemical variables in relation to clinical assessment of disease activity (Disease Activity Score “DAS 28‐4”).

Results: Erythrocyte deformability and membrane fluidity were impaired in RA patients compared to controls (p<0.001). Blood viscosity was significantly increased and correlated with the cell rigidity index (r=0.85, p<0.0000) in RA patients. The follow‐up showed a good correlation between haemorheological parameters and DAS 28‐4 during disease evolution.

Conclusion: our results support the hypothesis that in RA, blood hyperviscosity is determined by deformability loss, which in turn is due to a membrane rigidization. This could evidenced that a widespread cell membrane damage is expressed through an impaired erythrocyte deformability, turning haemorheological parameters into reliable tools to study disease evolution. The follow‐up study enabled us to confirm that erythrocyte deformability is an efficient indicator of rheumatoid arthritis activity.

Raynaud's phenomenon is a paroxysmal and reversible vasospasm affecting generally the acral circulatory regions. The relevance of the hæ morheological alterations in these patients, as a source of ischæmic events has been neglected. The objective of the present work was to evaluate and correlate the rheological blood properties, some biochemical parameters, e.g., plasma fibrinogen and immunoglobulin levels, and periungual capillaroscopy. The explicative variables considered were: blood viscosity, plasma viscosity, erythrocyte rigidity index, plasma fibrinogen, erythrocyte sedimentation rate, erythrocyte aggregate size, erythrocyte aggregation rate and serum immunoglobulin (IgG and IgM). The response variable was the nailfold capillary pattern categorised as either normal or pathological. Fibrinogen, erythrocyte aggregation rate and IgM are significantly higher in patients with a pathological pattern in comparison with patients bearing a normal one. The statistical analysis enabled us the modelling of the pathological pattern occurrence probability in function of plasma fibrinogen. Consequently, 100 mg/dl plasma fibrinogen increase, increases twice the probability of presenting a pathological pattern. Therefore, we can conclude that high levels of fibrinogen in Raynaud's phenomenon patients are associated with impaired skin microcirculation assessed by periungual capillaroscopy.

Nephelometry technique was used to register the alterations of the scattering signal from a whole blood sample due to erythrocyte aggregates in stasis and under controlled shear stress. The measured parameters were: the characteristic times of linear and three‐dimensional aggregates formation, and the strength of aggregates of different types.

These parameters depend on the sample temperature in the range of 2÷50°C. Temporal parameters of the aggregation process strongly increase (by 3 times) at temperature 45°C. For samples of normal blood the aggregates strength parameters do not significantly depend on the sample temperature, whereas for blood samples from patients with cryoglobulinemia high increase of the strength of both three‐dimensional and linear aggregates and decrease of time of linear aggregates formation at low temperature of the sample (4°C) was observed. The difference of these parameters of the pathological blood from that of the normal at room temperature was quite opposite.

Possible reasons of such behavior of aggregation state of blood and explanation of the observed effects are suggested.

Background: Cutaneous microcirculation shows a distinctive spatiotemporal inhomogeneity. Therefore provocation tests are necessary to receive significant and reproducible data. The present study investigated the effect of localized cutaneous vascular alteration, like in psoriasis vulgaris, on different parameters of reactive hyperemia (peak capillary blood cell velocity [pCBV], postocclusive reactive hyperemia [PRH%], and time to peak capillary blood cell velocity [tpCBV]).

Material and methods: Psoriatic plaques and normal skin on the contralateral side of 20 patients with psoriasis vulgaris were examined by Laser Doppler Anemometry. Capillary blood cell velocity was measured before suprasystolic occlusion and during postocclusive hyperemia.

Results: Compared to normal skin psoriatic plaques showed a significant increase of peak capillary blood cell velocity (pCBV, normal skin: 0.89±0.23 mm/s, psoriatic plaque: 2.03±0.94 mm/s), resting capillary blood cell velocity (rCBV, normal skin: 0.43±0.12 mm/s psoriatic plaque: 0.72±0.20 mm/s) and postocclusive reactive hyperemia (PRH%, normal skin: 107%, psoriatic plaque: 180%). The time to peak capillary blood cell velocity (tpCBV) during reactive hyperemia did not change significantly.

Conclusion: In reactive hyperemia, changing of pCBV and PRH% combined with unaltered tCBV indicate a dysfunction of cutaneous microcirculation. In contrast acute closure of upper and lower arterial extremity show a changed tCBV with stable pCBV and PRH%.

The red blood ceIl (RBC) membrane forms tethers in response to shear forces acting on tiny membrane points. Tether formation depends on viscous and elastic membrane properties and has been used as indicator of membrane fragility. A micropipette technique was used to study time dependent tether formation and tether relaxation of individual RBC. Point attached RBC were aspirated at a negative pressure of −5 mm H₂O into a micropipette with an internal diameter of 7.8 μm. If tether formation occurred and the tether reached a length of approximately 16 μm, the pipette was carefully pulled back. The RBC left the orifice of the micropipette and the tether relaxed and pulled the main body of the RBC back to the attachment point. The relaxation of the tethers was exponential. The time constant for tether relaxation was 0.144 s which is similar to the time constant for recovery of entire RBC from extensional elastic deformation. Repeated tether formation and relaxation of the same RBC led to an earlier begin of tether formation and changed the behavior of tether growth, although the relaxation time did not change. We conclude that repeated tether formation decreases the resistance of the RBC membrane to form tethers upon given shear forces. Weakening of the membrane due to repeated plastic deformation may play a role in the membrane loss of circulating RBC during aging.

The circadian rhythm of stroke and myocardial infarction (MI) may be related to the circadian rhythm of melatonin, and erythrocyte deformability may be the key mechanism in this relationship. Therefore, this study has been performed to determine if there is a relationship between the pineal gland and melatonin and red cell deformability. Twenty‐eight rats underwent pinealectomy, pinealectomy plus melatonin administration (200 mg/kg), or no treatment (n=7 in each group). Erythrocyte deformability was determined using the filtration technique. The results are reported in mean (±SD) seconds: control: 1.45±0.44; pinealectomy (A): 1.55±0.16; pinealectomy (B): 1.34±0.26 and pinealectomy and melatonin: 2.56±0.69. Pinealectomy by itself did not cause any statistically significant change in erythrocyte deformability but the addition of melatonin significantly decreased it. These results suggest a relationship between melatonin and erythrocyte deformability. Further investigations may uncover the causes of the circadian rhythm of stroke and MI, which may help improve chronobiological therapies.

Leukocyte–endothelial interactions could have a pathogenic role in atherogenesis. Adhesion molecules expressed by endothelial cells, such as intercellular adhesion molecule 1 (ICAM‐1), interact with leukocyte integrins mediating the firm adhesion of leukocytes to endothelium which is followed by their transendothelial migration. The aim of our research was to evaluate polymorphonuclear leukocyte (PMN) integrin expression, at baseline and after activation, in a group of subjects with chronic vascular atherosclerotic disease (VAD). In 27 subjects with VAD we examined, at baseline and after in vitro activation with 4‐phorbol 12‐myristate 13‐acetate (PMA), the PMN integrin pattern (CD11a, CD11b, CD11c, CD18) using indirect immunofluorescence and a flow cytometer. At baseline VAD subjects showed an increase of CD11a and CD18 and a decrease of Cd11b and Cd11c as compared to normal subjects. After activation, in normal subjects, we found an increase in the expression of all integrins, while in VAD subjects we observed an increase of CD11b and Cd11c and a decrease of Cd11a and CD18. In VAD subjects, at baseline, the upregulation of Cd11a and CD18 may reflect PMN in vivo activation; after in vitro activation, the decrease of CD11a may be related to the lack of cytoplasmic deposits of this molecule, while CD18 might be internalized. The integrin behaviour pattern in chronic VAD deserves further investigation, considering that integrins are potential targets of therapeutical strategies, with the aim of preventing the atherosclerotic plaque progression and acute ischaemic events.

Red blood cells containing hemoglobin S are less deformable than normal erythrocytes and have a major effect on the viscoelasticity of blood. This alteration in rheology increases the impedance to flow, leading to an increase in RBC aggregation and reduction in oxygen saturation, which induces further sickling and occlusions in the microcirculation. Patients with sickle cell disease (SCD) can experience severe complications, such as acute pain and stroke. Automated red blood cell exchange transfusion, or erythrocytapheresis, is used in homozygous SCD (Hb SS) to replace sickled cells with normal cells, thereby decreasing the percentage of sickle hemoglobin (%Hb S) and maintaining a net balance in iron accumulation. These patients received monthly erythrocytapheresis with a goal to maintain a pre‐pheresis %Hb S at less than 30%. In this study, viscoelastic parameters were used to quantify the effectiveness of this therapy for six patients undergoing chronic erythrocytapheresis. Whole blood viscosity, elasticity and relaxation time at oscillatory strains of 0.2, 1 and 5, and hematocrit and %Hb S were measured prior to erythrocytapheresis and 15 minutes after completion and compared with normal reference values at the patient's hematocrit. This study confirms the beneficial effects on viscosity, elasticity, and relaxation time of erythrocytapheresis.