Blood Rheology in Post-Thrombotic Syndrome — A Pilot Study

Patients suffering from post-thromobotic syndrome are compared to controls in terms of ex-vivo measurements to quantify the rheological behavior of blood: blood and plasma viscosity, haematocrit, red cell aggregation, red cell filterability, erythrocyte sedimentation rate (ESR), plasma fibrinogen. The results show that plasma viscosity, red cell filterability, ESR and fibrinogen are significantly changed indicating a lack of blood fluidity in post-thrombotic disease. It is suggested that the rheological deficit and the venous pathology both contribute to a disturbed microcirculation in the affected limb.

Limited Blood Fluidity as a Contributory Factor of Venous Stasis in Chronic Venous Insufficiency

Patients with chronic venous insufficiency were compared to matched controls in terms of blood and plasma viscosity, haematocrit, blood cell filterability, red cell aggregation, fibrinogen and ESR. The results show that in chronic venous insufficiency plasma viscosity and red cell aggregation are elevated, while blood cell filterability is reduced. Furthermore, the venous blood flow velocity (as determined by Doppler technique) correlates inversely with both plasma viscosity and red cell aggregation. We conclude that the systematic rheological abnormality increases the resistance to venous blood flow and may represent a contributory factor of venous stasis in this disorder.

Fibrinogen and viscosity as risk factors for subsequent cardiovascular events in stroke survivors

OBJECTIVE

To investigate whether abnormalities in blood viscosity predict a poor prognosis for subsequent cardiovascular events in stroke survivors.

DESIGN

Nested case-control study among a cohort of survivors of a first stroke, followed for an average of 2 years. Patients with a second stroke, myocardial infarction, or cardiovascular death were matched with patients who did not have such events (control patients).

SETTING

Buchberg-Klinik, Bad Tölz, Germany, a specialized center for stroke rehabilitation.

PATIENTS

A total of 625 consecutive patients. Twenty-one patients (3.5%) were lost to follow-up. Sixty pairs were matched.

MEASUREMENTS

Native and hematocrit-standardized blood viscosity at three shear rates, hematocrit, plasma viscosity, fibrinogen, erythrocyte sedimentation rate, total leukocyte count, and the matching variables.

RESULTS

Eighty-five patients had a second stroke, myocardial infarction, or died due to a cardiovascular event. Patients with re-events had higher blood viscosity and fibrinogen levels than the control patients. In the 60 matched pairs, the mean of the paired differences between patients with re-events and control patients was 5.03 mPa.s (95% CI, 1.262 to 8.941; P = 0.01) for native blood viscosity at shear rate 0.7 s-1, for plasma viscosity, 0.044 mPa.s (CI, 0.006 to 0.083; P greater than 0.02), and for fibrinogen, 0.056 g/L (CI, 0.010 to 0.101; P greater than 0.02). Odds ratios were significantly increased only for plasma viscosity (odds ratio, 2.86; CI, 1.06 to 8.43) and fibrinogen (odds ratio, 3.67; CI, 1.31 to 11.69).

CONCLUSIONS

Hyperfibrinogenemia is an independent risk factor for cardiovascular events in stroke survivors. Intervention trials with fibrinogen lowering measures may be warranted.

A viscometric method of measuring plasma fibrinogen concentrations

A technique based on deducing the viscosity of serum from that of plasma was compared with the commonly used Clauss method. The two methods correlated closely (r = 0.914). The reproducibility of the viscometric method was slightly poorer than the Clauss technique at low fibrinogen concentrations, equal to that at medium fibrinogen concentrations, and marginally better at high concentrations. Fibrinogen can therefore be measured reasonably accurately with the viscometric method, and can be recommended as an alternative for laboratories possessing a viscometer.

Can rheologic variables be of prognostic relevance in arteriosclerotic diseases?

The hypothesis that blood rheology is of prognostic value in patients with arteriosclerotic diseases was tested in a prospective study of 843 patients at a rehabilitation clinic. They were tested for blood serum and plasma viscosity, hematocrit, fibrinogen, red cell aggregation and deformability, erythrocyte sedimentation rate, white cell count, cholesterol, and triglycerides. End points were defined as a second stroke or myocardial infarction or cardiovascular death within two years of the initial examination. Patients suffering such end points as compared with matched pairs (n = 74; matching criteria: identical manifestation of arteriosclerosis, identical sex and similar age and risk factors) had significantly higher native blood viscosity (p = 0.002), red cell aggregation (p = 0.01), serum viscosity (p = 0.01), fibrinogen (p = 0.02), and cholesterol (p = 0.01). It is concluded that rheologic factors are associated with the prognosis in patients with arteriosclerotic diseases.

Impaired blood rheology: a risk factor after stroke?

The hypothesis that blood rheology is of prognostic value in stroke patients was tested in a prospective study. A total of 523 patients in the rehabilitation phase of stroke (outside the acute phase reaction after stroke) were tested for blood, serum and plasma viscosity, haematocrit, fibrinogen, red cell aggregation and deformability, ESR, white cell count, cholesterol and triglycerides. Endpoints were defined as a second stroke (lethal or not) within 2 years after the initial examination. Patients suffering such endpoints exhibit elevated blood viscosity, red cell aggregation, plasma and serum viscosity, fibrinogen and cholesterol levels, compared to patients without endpoints. It is concluded that rheological factors are associated with the prognosis after a first stroke.

A double-blind trial of Dextran-haemodilution vs. placebo in claudicants

Haemodilution is often recommended for peripheral arterial disease, yet little data is available to support its clinical efficacy. This study was designed to prove or disprove the effectiveness of Dextran-haemodilution in intermittent claudication. Twenty claudicants with long, well-collateralized arterial occlusions were randomized into groups 1 and 2. Group 1 received isovolemic haemodilution with Dextran 40 (500 ml per session) during 3 weeks, which was followed by a wash-out period, followed by placebo treatments for 3 weeks. In group 2 this sequence was reversed. Pain-free and maximal walking distances were measured by standardized treadmill tests along with plethysmographic blood flow, Doppler pressures, haematocrit, blood and plasma viscosity as well as fibrinogen. Walking distances increased significantly by about 50% during haemodilution in both groups. This was paralleled by a fall in haematocrit and blood viscosity. All other variables remained constant. During placebo treatments there were no significant changes of any variable. The treatment was tolerated without complications. Thus Dextran-haemodilution seems safe and effective in selected peripheral occlusive arterial disease (POAD) patients. Potential responders might be identifiable before the start of therapy by angiographic investigations. The clinical effectiveness of Dextran 40 is comparable to that of hydroxyethyl starch 200 as reported in the literature.

Hemorheological effects of oral contraceptives

To determine the hemorheological effects of oral contraceptives, 50 healthy young women took no medication for 3 cycles. Subsequently they were randomized into group A and B. Group A took Diane-35, B took Microgynon each for 6 cycles. Finally 3 cycles without medication followed. Blood viscosity was quantified by ex vivo measurements of hematocrit, blood and plasma viscosity, red cell filterability, fibrinogen and colloid oncotic pressure. In group A fibrinogen rose at the end of the medication phase. In group B fibrinogen, blood and plasma viscosity increased on medication. The former 2 variables remained elevated even after discontinuation of the oral contraceptive. The data combined with those from the literature suggest that low-dose oral contraceptives lead to no biologically meaningful changes in blood rheology while higher doses induce limitations of blood fluidity which could be involved in the increment of cardiovascular risk by these medications.

Leucocyte aggregation in burned patients

Leucocyte aggregation describes one type of biophysical behaviour of white cells. To test whether this parameter is changed in burned patients, 15 burn victims were investigated immediately after admission into hospital. Cell counts and aggregation were measured and related to the prognosis of the injury. Compared with normal controls, burning injury is associated with higher white cell counts and enhanced leucocyte aggregation. Fatal injuries showed a (non-significant) tendency for higher aggregation values than survivors. There are significant positive correlations between white cell counts, maximal aggregation values and the burned body surface area. The results suggest that leucocyte aggregation is pathologically enhanced in response to burns. Possibly this alteration is of prognostic importance.

Placebo-controlled, double-blind trial of hemodilution in peripheral occlusive arterial disease

A number of uncontrolled trials has suggested that hemodilution is effective in peripheral occlusive arterial disease. This study was aimed at proving or disproving the efficacy of hemodilution by using a randomized, placebo-controlled, double-blind crossover design. Twenty-four stable claudicants with long, collateralized femoropopliteal obstructions were treated with isovolemic hemodilution with 500 mL of 10% hydroxyethyl starch 200 and sham dilutions. Three weeks of hemodilution lowered blood and plasma viscosity, as well as hematocrit, and increased resting blood flow and pain-free walking distance. Placebo treatments produced no such favorable changes. It is concluded that hemodilution therapy can be clinically effective in patients with arterial obstructions in the lower extremities. Hemodilution seems particularly promising under hemodynamic condition of low shear stresses in vivo.

Is increased plasma viscosity a risk factor for high blood pressure?

Data from several epidemiologic studies have suggested that, among other variables, hematocrit and fibrinogen may constitute risk factors for high blood pressure. As part of a population survey for cardiovascular risk factors, plasma viscosity and hemoglobin were measured. Blood pressure was determined under standardized conditions according to the recommendations of the AHA. A two-stage age-sex-stratified cluster sample of 5,312 persons, aged twenty-five to sixty-four years, was selected from a mixed urban/rural target population of 282,279 (total population approximately 533,000). A net response of 79.3% was achieved. Multiple logistic regression analyses including plasma viscosity, hemoglobin, body mass index, alcohol consumption, smoking behavior, and total serum cholesterol as independent variables were run controlling for both age and sex. Plasma viscosity appeared as a significant main effect in all analyses and demonstrated the strongest association with high blood pressure next to body mass index. Whether this association implies a causal relationship cannot be answered from cross-sectional data. However, even if plasma hyperviscosity represents a secondary phenomenon in hypertension, it might be of prognostic relevance. There is evidence that increased plasma viscosity may contribute to myocardial hypertrophy. Therefore hypertensives with impaired blood fluidity might constitute a subgroup at particular risk for cardiovascular complications. When antihypertensive drugs are selected, their influence on blood viscosity should be taken into account.

Viscidation of Blood during Short Term Bed Rest – Its Possible Importance in the Etiology of Deep Vein Thrombosis

Twelve male volunteers were submitted to strict bed rest. Before, 36 hours, and 84 hours after the start of immobilisation venous blood was drawn. Blood viscosity, haematocrit, plasma viscosity, red cell aggregation, red cell deformability, blood pressure, heart rate and body weight were determined. Results show marked haemoconcentration with significant elevations of blood viscosity, haematocrit, plasma viscosity and red cell aggregation during bed rest. Body weight declines by more than 1 kg. It is suggested that haemoconcentration reduces the fluidity of blood, which in turn decreases flow, thereby predisposing to venous thrombosis in clinical situations with bed rest

Changes in blood rheology of grossly obese individuals during a very low calorie diet

A group of grossly obese individuals were put on a 300 kcal diet for 15 days. Blood rheology was quantified by measuring blood and plasma viscosity, haematocrit, red cell aggregation and deformability, fibrinogen and ESR. After 15 days blood viscosity had decreased and red cell deformability increased. The results suggest that the rheological deficit in obesity can be partly normalized by low calorie diets.

Blood rheology associated with cardiovascular risk factors and chronic cardiovascular diseases: results of an epidemiologic cross-sectional study

As part of an epidemiologic cross-sectional study to determine cardiovascular (CV) risk factors in the population (total serum cholesterol, smoking, blood pressure, and body weight) hemoglobin (Hb) and plasma viscosity (PV) were measured. A two-stage cluster sample of 5,312 persons, aged twenty-five to sixty-four (available 5,069) was selected from a mixed urban-rural target population of 282,279 inhabitants, from which 4,022 (79.3%) participated in the study. Patients with chronic myocardial infarction (MI), cerebral infarction (CI), angina pectoris (AP), and peripheral arterial disease (PAD) were identified by questionnaire. The results show that there is no age or sex dependency of PV in healthy participants, while hemoglobin shows the well-known sex difference. In contrast, PV increases continuously with age in the total population. In men, increased PV is found in untreated hypertension, in hypercholesterolemia, and in smokers. In women, it is raised in hypercholesterolemia and in gross obesity. Male MI patients and patients of both sexes after CI in particular show statistically significantly elevated PV. Finally, in male patients with chronic AP or patients of both sexes with PAD, PV is elevated and a tendency to higher Hb values is seen. These results confirm smaller clinical trials suggesting that blood fluidity is pathologically altered in patients with CV risk factors or diseases. Since impaired blood fluidity may worsen the hemodynamic situation, in particular in patients with limited vasomotor reserve, hemorheologic parameters may be of prognostic relevance. Therapeutic implications of these findings should be considered.

Blood rheology in healthy cigarette smokers. Results from the MONICA project, Augsburg

To investigate the relationship between cardiovascular risk factors and the fluidity of blood, a random sample of the population consisting of 4022 persons ages 25 to 64 years was investigated for plasma viscosity, hemoglobin, and total serum protein. A total of 567 healthy nonsmokers and 287 healthy smokers were identified and compared. Plasma viscosity was found to be elevated in male smokers; this was related to both the degree and the duration of cigarette abuse. Plasma viscosity proved to be age-dependent in smokers, but did not change with age in nonsmokers. Total serum protein decreased with age in nonsmokers, while it did not change in smokers. Hemoglobin increased only in female smokers. These findings suggest that blood fluidity is jeopardized in smokers. In men the hemorheological deficit is mostly due to a rise of plasma viscosity, which, in turn, may be caused by an elevation of plasma fibrinogen levels. In women it is predominantly due to an increase in hemoglobin. These alterations in hemorheological variables may be a marker for increased cardiovascular risk in smokers and could reduce blood flow and hinder microcirculatory function.

Blood rheology in patients with transient ischemic attacks

A complete ischemic stroke is associated with a significant hemorheologic disturbance leading to a rise of the viscous component of the peripheral resistance. This abnormality represents a consequence of the acute event. Nonetheless, it could be causally related to ischemia. In an attempt to clarify this question, 26 patients suffering from transient ischemic attacks were compared with controls in terms of blood and plasma viscosity, hematocrit, blood cell filterability, and erythrocyte aggregation. In patients there was a significant impairment of blood fluidity comprising plasma viscosity, blood cell filterability, and erythrocyte aggregation, suggesting that the flow properties of blood are jeopardized even before an acute stroke. Most likely this is due to the underlying arteriosclerotic process. Our results open the way to speculating that hemorheologic mechanisms might predispose to the development of a stroke by decreasing cerebral blood flow. If this hypothesis were true, it would have important therapeutic implications.