Changes in blood rheology in patients with stable angina pectoris as a result of coronary artery disease

Blood Haemoglobin Concentration Is Directly and Independently Related with Pulse Wave Velocity, a Measure of Large Artery Stiffness

High haemoglobin level has been associated with metabolic syndrome, elevated blood pressure (BP), and increased mortality risk. In this cross-sectional study, we investigated the association of blood haemoglobin with haemodynamics in 743 subjects, using whole-body impedance cardiography and pulse wave analysis. The participants were allocated to sex-stratified haemoglobin tertiles with mean values 135, 144, and 154 g/L, respectively. The mean age was similar in all tertiles, while body mass index was higher in the highest versus the lowest haemoglobin tertile. The highest haemoglobin tertile had the highest erythrocyte and leukocyte counts, plasma C-reactive protein, uric acid, renin activity, and aldosterone. The lipid profile was less favourable and insulin sensitivity lower in the highest versus the lowest haemoglobin tertile. Aortic BP, cardiac output, and systemic vascular resistance were similar in all tertiles, while the pulse wave velocity (PWV) was higher in the highest versus the lowest haemoglobin tertile. In linear regression analysis, age (Beta 0.478), mean aortic BP (Beta 0.178), uric acid (Beta 0.150), heart rate (Beta 0.148), and aldosterone-to-renin ratio (Beta 0.123) had the strongest associations with PWV (p < 0.001 for all). Additionally, haemoglobin concentration was an explanatory factory for PWV (Beta 0.070, p = 0.028). To conclude, blood haemoglobin concentration had a small direct and independent association with a measure of large artery stiffness.

Analysis of Red Blood Cell Parameters in Dogs with Various Stages of Degenerative Mitral Valve Disease

Introduction

Although peripheral blood analysis has become increasingly automated, microscopy is the only available method for the diagnosis of anisocytosis and poikilocytosis. The aims of the study were to compare RBC volume data obtained with two different analysers and by manual assessment of smears and to compare this data between dogs in various stages of heart failure secondary to degenerative mitral valvular (DMV) disease. The impact of diuretic administration on RBC morphology was also assessed.

Material and Methods

Sixty-eight dogs, 56 in different stages of DMV disease and 12 as healthy controls, were studied. Impedance and flow cytometry haematological analyses were performed for each animal. Additionally, two smears were prepared for manual analysis. RBC structure, staining, and size differences were recorded.

Results

There were no significant differences between the blood morphological parameters assessed using haematological analysers nor between dogs receiving diuretic treatment and those not treated. Based on the manual smear, significantly higher erythrocyte anisocytosis was observed in the dogs with symptomatic DMV disease than in the control group.

Conclusion

Haematological analysers based on impedance and flow cytometry provide reliable and comparable morphological results in dogs with heart failure. However, microscopic assessment of blood smears is a more reliable tool to detect erythrocyte anisocytosis.

Quantitative Measurement and Evaluation of Red Blood Cell Aggregation in Normal Blood Based on a Modified Hanai Equation

The aggregation of red blood cells (RBCs) in normal blood (non-coagulation) has been quantitatively measured by blood pulsatile flow based on multiple-frequency electrical impedance spectroscopy. The relaxation frequencies f_c under static and flowing conditions of blood pulsatile flow are utilized to evaluate the RBC aggregation quantitatively with the consideration of blood flow factors (RBC orientation, deformation, thickness of electrical double layer (EDL)). Both porcine blood and bovine blood are investigated in experiments, for the reason that porcine blood easily forms RBC aggregates, while bovine blood does not. The results show that the relaxation frequencies f_c of porcine blood and bovine blood present opposite performance, which indicates that the proposed relaxation frequency f_c is efficient to measure RBCs aggregation. Furthermore, the modified Hanai equation is proposed to quantitatively calculate the influence of RBCs aggregation on relaxation frequency f_c. The study confirms the feasibility of a high speed, on-line RBC aggregation sensing method in extracorporeal circulation systems.

Significantly increased low shear rate viscosity, blood elastic modulus, and RBC aggregation in adults following cardiac surgery

Open heart surgeries are common for treating ischemic and heart valve disease. During cardiac surgery, cardiopulmonary bypass (CPB) can temporarily take over the function of heart and lungs. However, elevated red blood cell (RBC) aggregation may lead to the common side-effects such as microinfarction. We investigated blood physical properties changes and the correlation between blood microstructure, viscoelastic response and biochemical changes following surgery with CPB. We examined shear-rate dependent blood viscosity, elasticity and RBC aggregate size in the pre-surgery disease state, post-surgery state and long-term recovery state of cardiac surgical patients. Within a week following surgery, the patient hematocrit was significantly lower due to CPB. Despite lower RBC concentration, the RBC aggregate shape became larger and more rounded, which is correlated to the elevated plasma fibrinogen related to systemic inflammatory response. During the same period, the hematocrit-adjusted low shear rate viscosity increased significantly, as did the yield stress, indicating more solid-like behavior for blood. Six months to one year later, all the physical and biochemical properties measured returned to baseline.

Periodic and simultaneous quantification of blood viscosity and red blood cell aggregation using a microfluidic platform under in-vitro closed-loop circulation

To evaluate variations of blood circulating in closed loops, hemorheological properties including blood viscosity and red blood cells (RBCs) are quantitatively measured with independent in-vitro instruments after collecting blood from a closed loop. But, most previous methods require periodic blood collections which induce several problems such as geometric differences between the fluidic channel and the in-vitro method, hemodilution, storage time, and unspecific blood flow rates. To resolve these issues, in this study, blood viscosity and RBC aggregation of blood circulating within a closed loop are measured with a microfluidic platform periodically and simultaneously. To demonstrate the proposed method, in-vitro closed-loop circulation is established by connecting several components (peristaltic pump, air compliance unit, fluid divider, and reservoir) in series. In addition, to measure blood viscosity and RBC aggregation, a microfluidic platform composed of a microfluidic device, pinch valve, and syringe pump is created. During each period, blood viscosity and RBC aggregation are measured by monitoring blood flow at constant blood flow, and image intensity at stationary blood flow. The proposed method is first employed to evaluate the effect of hematocrits and dextran concentrations on the RBC aggregation and blood viscosity by using a syringe pump (i.e., specific blood flow-rate). The method is then applied to detect the blood viscosity and RBC aggregation under in-vitro closed-loop circulation (i.e., unspecific blood flow-rate). From these experimental demonstrations, it is found that the suggested method can be effectively used to monitor the RBC aggregation and blood viscosity under in-vitro closed-loop circulation. Since this method does not require periodic collection from closed-loop circulation or an additional procedure for estimating blood flow-rate with a syringe pump, it will be effectively used to monitor variations of blood circulating in extracorporeal bypass loops.

Evaluation of frequency and intensity of asymptomatic anisocytosis in the Japanese dog breeds Shiba, Akita, and Hokkaido

Microcytosis is observed in healthy Japanese breed dogs. The aim of the study was to evaluate the frequency and intensity of asymptomatic anisocytosis using a three-grade scale in Japanese dog breeds with special emphasis on the following indices: mean cell volume, mean cell haemoglobin, mean cell haemoglobin concentration, and red blood cell distribution width. The retrospective study included analyses of blood morphology and blood smear for clinically healthy Japanese dog breeds Shiba, Akita, and Hokkaido aged from 6 months to 14 years, performed as a part of preventative care. A total of 74 dogs of both sexes were qualified for the study. The group included both neutered and non-neutered animals (Akita – 17 females, 12 males, Shiba – 24 females, 18 males, Hokkaido – 2 females, 1 male). The blood smear revealed significant anisocytosis in 60.8% and mild anisocytosis in 28.4% of the tested dogs – 89.2% in total. Microcytosis was reported for 25.7% of the tested Japanese breed dogs. Reduced mean cell haemoglobin and mean cell haemoglobin concentration were diagnosed in 75.7% and 40.5% of dogs, respectively. Red blood cell distribution width as an anisocytosis indicator exceeded the norm in 12% of the tested dogs. Compared to mixed breed dogs, the Japanese breeds had a reduced mean cell volume, mean cell haemoglobin concentration and significant anisocytosis in the blood smear as well as a higher red blood cell distribution width indicator. Veterinarians should consider these differences when interpreting the results of morphological blood tests.

Comparison of the simple red blood cell adhesiveness/aggregation test with the laser-assisted optical rotational cell analyzer: Red blood cell aggregation in patients with coronary artery disease and a healthy control group

BACKGROUND

Red blood cell (RBC) aggregation influences blood flow properties, impacts blood microcirculation and consequently oxygen delivery. Different methods are established to determine RBC aggregation: under static conditions (i.e. the RBC adhesiveness/aggregation test (EAAT)) or under shear conditions (i.e. the laser-assisted optical rotational cell analyzer (LORCA)).

OBJECTIVE

Comparison of these two different methods in detecting the RBC aggregation of patients with coronary artery disease (CAD) and of healthy controls.

METHODS

RBC aggregation was quantified in peripheral venous blood of patients with CAD and healthy controls using EAAT and LORCA.

RESULTS

Both methods detected an increased RBC aggregation in patients with CAD compared to the healthy control group: the ratio of clot-free area to whole area (rCFA) detected with EAAT (15.65 vs. 11.30%), and aggregation index (66.33 vs. 53.90%), shear rate of disaggregation (SDA) (105.59 vs. 69.21 s-1), and upstroke/ttop (0.03 vs. 0.02 au/s) detected with LORCA device were increased, aggregation half time (detected with LORCA) was decreased (2.11 vs. 3.60 s). rCFA (EAAT) correlated with SDA (LORCA).

CONCLUSIONS

Both methods determine an increased RBC aggregation in patients with CAD. However, only one measurement parameter of the LORCA seems to reflect the same RBC aggregation properties as the EAAT.

Influences of two high intensity interval exercise protocols on the main determinants of blood fluidity in overweight men

BACKGROUND

Acute effects of continuous exercise on the markers of blood fluidity have been addressed in different populations and the changes are intensity related. However, the effect of different high intensity interval exercise (HIIE) on these variables is unclear.

OBJECTIVE

This study is designed to determine the effects of two different HIIE with different work/rest ratios but the same energy expenditure on the main determinants of blood fluidity.

METHODS

Ten overweight men (age, 26.3±1.7 yrs) completed two HIIE protocols on two separate occasions with one week intervening. The two HIIE encompassed performing: 1) 6 intervals of 2 min activity at 85% of VO2max interspersed by 2 min active recovery at 30% of VO2max (ratio 1 to 1, HIIE1/1), and 2) 6 intervals of 30 s activity at 110% of VO2max interspersed by 4 min active recovery at 40% of VO2max (ratio 1 to 8, HIIE1/8). Each exercise trial was followed by 30 min rest. Venous blood samples were obtained before exercise, immediately after exercise and after recovery and analyzed for blood and plasma viscosity, fibrinogen and red blood cell indices.

RESULTS

The HIIE1/1 protocol led to higher reduction (P < 0.01) in plasma volume changes compared to HIIE1/8 (9.9% vs 5.7%). Moreover, increases in blood viscosity, plasma viscosity, hematocrit, RBC count and mean arterial blood pressure observed following HIIE1/1 were significantly (P < 0.05) higher than HIIE1/8 ; whereas, the changes in fibrinogen concentration neither were significant in response to both trials nor were significantly different between two protocols (P > 0.05). However, the changes in all variables during exercise were transient and returned to the baseline levels after 30 min recovery.

CONCLUSIONS

It is concluded that the HIIE protocol with lower intensity and shorter rest intervals (higher work to rest ratio) clearly results in more physiological strain than HIIE with higher intensity but longer rest intervals (lower work to rest ratio) in overweight individuals, and that the work to rest ratio could be as important as exercise intensity when considering the hemorheological variables during HIIE.

Comparison of hemorheological changes in patients after acute coronary events, intervention and ambulatory rehabilitation

During the past decades, our group have investigated the hemorheological parameters (HPs) of more than 1,000 patients with various forms of ischemic heart disease (IHD). Our data indicate that HPs are altered in patients with IHD and the extent of the alterations is in good correlation with the clinical severity of the disease. Our findings have also proven that HPs play a critical role in the pathogenesis of myocardial ischemia.The lack of regular exercise is an important cardiovascular risk factor. Regular physical activity - as part of the cardiovascular rehabilitation training program (CRP) - is recommended for the treatment of IHD and the prevention of first or further cardiovascular events. To estimate the beneficial hemorheological effects of CRP, compared to patients after a coronary event or intervention and not participating in CRP, the data of four of our prospective studies (three non-CRP and one CRP-participating) were evaluated.Hematocrit (Hct), plasma and whole blood viscosity (WBV), Hct/WBV ratio significantly (p < 0.05) increased in the non-CRP groups during the 6-12 months follow-up, while in the CRP group they significantly decreased (p < 0.05). Red blood cell aggregation decreased in a much greater manner in the CRP group.Our results indicate that CRP has beneficial hemorheological effects and is able to reverse the deterioration of HPs after coronary events or intervention.

Hemorheological abnormalities and their associations with coronary blood flow in patients with cardiac syndrome X: a comparison between males and females

Aim:

The role of elevated whole blood viscosity (WBV) in the pathogenesis of atherosclerosis is well known. We sought to investigate the gender differences in the association between WBV, coronary blood flow and tissue oxygen delivery index (TODI) in cardiac syndrome X (CSX).

Methods:

Forty-six CSX patients and 14 healthy volunteers were enrolled. The coronary flow parameters were obtained with transthoracic Doppler echocardiography and WBV was measured (at high-shear and low-shear rates of 300s-1 and 5s-1, respectively) using a scanning capillary tube viscometer. TODI was determined from the ratio of hematocrit to WBV measured at a low-shear rate of 5s-1.

Results:

In male patients, the mean diastolic coronary flow velocity (CFV) and diastolic velocity time integral (VTI) were significantly decreased compared to control group (all p<0.05) and the WBV showed significant negative correlation with peak systolic CFV (r = −0.559 at 300s-1, r = −0.438 at 5s-1), mean systolic CFV (r = −0.577 at 300s-1, r = −0.488 at 5s-1), systolic VTI (r = −0.576 at 300s-1, r = −0.530 at 5s-1) and diastolic VTI (r = −0.553 at 300s-1, r = −0.551 at 5s-1) (all p<0.01). Meanwhile, although female patients showed no significant relationships between WBV and coronary flow parameters, TODI were significantly decreased compared to the control group (3.64 ± 0.34 vs. 4.07 ± 0.38%/centipoises (cP), respectively, p=0.008).

Conclusion:

Our study suggests that there are gender-related differences in the pathogenesis of microvascular angina and gender-specific approaches for CSX patients might be needed.

Hybrid System for Ex Vivo Hemorheological and Hemodynamic Analysis: A Feasibility Study

Precise measurement of biophysical properties is important to understand the relation between these properties and the outbreak of cardiovascular diseases (CVDs). However, a systematic measurement for these biophysical parameters under in vivo conditions is nearly impossible because of complex vessel shape and limited practicality. In vitro measurements can provide more biophysical information, but in vitro exposure changes hemorheological properties. In this study, a hybrid system composed of an ultrasound system and microfluidic device is proposed for monitoring hemorheological and hemodynamic properties under more reasonable experimental conditions. Biophysical properties including RBC aggregation, viscosity, velocity, and pressure of blood flows are simultaneously measured under various conditions to demonstrate the feasibility and performance of this measurement system. The proposed technique is applied to a rat extracorporeal loop which connects the aorta and jugular vein directly. As a result, the proposed system is found to measure biophysical parameters reasonably without blood collection from the rat and provided more detailed information. This hybrid system, combining ultrasound imaging and microfluidic techniques to ex vivo animal models, would be useful for monitoring the variations of biophysical properties induced by chemical agents. It can be used to understand the relation between biophysical parameters and CVDs.

Microfluidic-based speckle analysis for sensitive measurement of erythrocyte aggregation: A comparison of four methods for detection of elevated erythrocyte aggregation in diabetic rat blood

Biochemical alterations in the plasma and red blood cell (RBC) membrane of diabetic blood lead to excessive erythrocyte aggregation (EA). EA would significantly impede the blood flow and increase the vascular flow resistance contributing to peripheral vascular diseases. In this study, a simple microfluidic-based method is proposed to achieve sensitive detection of hyperaggregation. When a blood sample is delivered into the device, images of blood flows are obtained with a short exposure time for a relatively long measuring time. A micro-particle image velocimetry technique was employed to monitor variation of the flow rate of blood as a function of time. Given that EA formation in the channel creates clear speckle patterns, the EA extent can be estimated by calculating a speckle area (ASpeckle) through a normalized autocovariance function. The hematocrit effect is assessed by comparing optical images transmitted through blood samples. EA variations caused by dextran treatment are quantitatively evaluated using characteristic time (λSpeckle) obtained by fitting the variations of ASpeckle. Other indices including number of RBCs in an aggregate (NRBC), characteristic time of erythrocyte sedimentation rate (λESR), and aggregation index estimated from ultrasound signals (AIEcho) are determined under different EA conditions using conventional techniques. The four different methods are applied to diabetic blood samples to compare their indices under hyperaggregation conditions. It is found that the proposed method can detect variation of EA reasonably, compared with conventional measurement techniques. These experimental demonstrations support the notion that the proposed method is capable of effectively monitoring the biophysical properties of diabetic blood.

Exercise-induced changes in inflammatory processes: Implications for thrombogenesis in cardiovascular disease

Sedentary lifestyle is a risk factor and a strong predictor for chronic disease and premature death. Low-grade inflammation has been proved a key player in the pathogenesis of cardiovascular disease. Inflammatory processes have been also involved in maintaining the balance between coagulation and fibrinolysis. In addition, an inverse linear dose-response relation between physical activity and mortality risks has also been reported. However, the favorable effects of structured exercise programs and the independent contribution of physical activity to cardiovascular risk are still under investigation. In response to heavy exercise, interleukin-6 (IL-6) is secreted by contracting skeletal muscles, followed by an acute reactant release of C-reactive protein (CRP). Both CRP and IL-6 can stimulate monocyte tissue factor production, provoke platelet hyperreactivity, promote fibrinogen biosynthesis, and enhance microparticle formation and erythrocyte aggregability, thus triggering prothrombotic state. By contrast, regular exercise and physical activity are protective against all-cause mortality through suppressing pro-inflammatory cytokine production, enhancing anti-inflammatory mediators and antioxidant development, and promoting fibrinolytic activity. Low-load resistance exercise also plays an advantageous role in thrombogenesis by reducing inflammatory processes and potentiating fibrinolytic features. In the present review article, we provide an overview of the impact of different modes and intensities of physical activity on vascular inflammation and thrombogenesis.

Viscoelasticity of blood and viscoelastic blood analogues for use in polydymethylsiloxane in vitro models of the circulatory system

The non-Newtonian properties of blood are of great importance since they are closely related with incident cardiovascular diseases. A good understanding of the hemodynamics through the main vessels of the human circulatory system is thus fundamental in the detection and especially in the treatment of these diseases. Very often such studies take place in vitro for convenience and better flow control and these generally require blood analogue solutions that not only adequately mimic the viscoelastic properties of blood but also minimize undesirable optical distortions arising from vessel curvature that could interfere in flow visualizations or particle image velocimetry measurements. In this work, we present the viscoelastic moduli of whole human blood obtained by means of passive microrheology experiments. These results and existing shear and extensional rheological data for whole human blood in the literature enabled us to develop solutions with rheological behavior analogous to real whole blood and with a refractive index suited for PDMS (polydymethylsiloxane) micro- and milli-channels. In addition, these blood analogues can be modified in order to obtain a larger range of refractive indices from 1.38 to 1.43 to match the refractive index of several materials other than PDMS.

Exertional periodic breathing potentiates erythrocyte rheological dysfunction by elevating pro-inflammatory status in patients with anemic heart failure

BACKGROUND

Exertional periodic breathing (EPB) or anemia is associated with an adverse prognosis in advanced heart failure (HF). The disturbed rheological properties of erythrocytes may contribute to circulatory disorders. This study investigated whether EPB with/without anemia influences rheological/hemodynamic functions in patients with HF.

METHODS

According to the WHO criteria for anemia, 168 HF patients were divided into six groups: non (N)-anemic with (n=27)/without (n=56) EPB, light (L)-anemic with (n=17)/without (n=21) EPB, and moderate/several (M/S)-anemic with (n=21)/without (n=26) EPB groups. These HF patients and 30 healthy counterparts performed an incremental exercise test using a bicycle ergometer. Rheological and hemodynamic characteristics were determined by slit-flow ektacytometer and bioreactance-based device/near infrared spectrometer, respectively.

RESULTS

In the HF patients with EPB, both L- and M/S-anemic groups exhibited 1) higher plasma myeloperoxidase/interleukin-6 concentrations, 2) more blood senescent/spherical erythrocyte counts, 3) larger aggregability and smaller deformability of erythrocytes under shear flows, 4) higher systemic vascular resistance, which was accompanied by smaller amounts of blood distributed to cerebral/muscular tissues during exercise, 5) less VO(2peak) and ventilatory efficiency, and 6) lower Short Form-36 physical/mental component scores and higher Minnesota Living with HF questionnaire score than N-anemic group. Additionally, plasma myeloperoxidase/interleukin-6 levels were directly related to erythrocyte aggregability and inversely related to erythrocyte deformability. However, there were no significant differences in pro-inflammatory factors, rheological/hemodynamic properties, and aerobic capacity between L- and N-anemic groups in the HF patients without EPB.

CONCLUSION

EPB potentiates anemia-related rheological/hemodynamic dysfunctions by elevating pro-inflammatory status, reducing physical fitness in patients with HF.

Lack of association between Glu298Asp polymorphism and coronary artery disease in North Indians

Nitric Oxide (NO) is an important molecule carrying number of different functions in humans. Published studies suggest that it may inhibit several key steps involved in the pathogenesis of atherosclerosis. Inhibition or reduction of NO due to Glu298Asp polymorphism may accelerate atherosclerosis. The aim of this study was to determine whether Glu298Asp polymorphism is implicated in the pathogenesis of coronary artery disease (CAD) among North Indian population from the state of Uttar Pradesh, India. We selected 253 CAD patients and 174 healthy, normotensive, non-diabetic controls, which were matched for gender and ethnicity. The Glu298Asp (rs1799983) variant was detected by genotyping subjects, using a polymerase chain reaction followed by restriction fragment length polymorphism. There was no significant difference found in the genotypic and allelic frequencies between patients and controls. Our study indicated that Glu298Asp polymorphism does not play any critical role in the pathogenesis of CAD, at least in North Indian population.

Plasma and blood viscosity in metabolic syndrome

BACKGROUND AND AIM

The relationship between metabolic syndrome (MS) and blood and plasma viscosity has been scarcely investigated. In the present study we have evaluated the difference in blood and plasma viscosity between subjects with and without MS, in order to verify whether viscosity measurement can add more information on the overall cardiovascular risk connected with the presence of the MS.

METHODS AND RESULTS

Two hundred and sixty nine women and 520 men have been enrolled. Blood and plasma viscosity have been measured with a cone-plate viscometer equipped with a cp-40 spindle. MS has been defined according to the third report of the National Cholesterol Education Program, Adult Treatment Panel III. Eighty four women and 154 men fulfilled the criteria for MS. Hematocrit adjusted blood viscosity was higher in subjects with MS compared to those without the syndrome, both in males (shear rate 225 s(-1): 4.60+/-0.38 vs. 4.52+/-0.33 cP, p<0.01) and females (4.57+/-0.28 vs. 4.46+/-0.31 P, p<0.01). Blood viscosity was correlated with all components of MS but glucose, and after adjustment for them the difference between subjects with or without MS was completely abolished. Plasma viscosity was significantly higher only in females with MS.

CONCLUSIONS

These data demonstrate that blood viscosity is increased in subjects with MS, but the increase seems to depend on the metabolic alterations of the syndrome. The independent contribution of the rise in blood viscosity to the cardiovascular risk connected with the presence of MS seems therefore negligible. The increased plasma viscosity in females with MS needs further clarification.

Hematocrit is associated with carotid atherosclerosis in men but not in women

BACKGROUND

It is known that blood and plasma viscosities are associated with clinical manifestations of atherosclerosis, though evidence is not conclusive particularly in women.

OBJECTIVE

To verify whether hematocrit and blood and plasma viscosities are independently associated with carotid atherosclerosis and whether their measurement can improve the definition of the global coronary heart disease (CHD) risk.

METHOD

Eight hundred and ninety-two participants in a cardiovascular disease prevention campaign were examined with regard to conventional CHD risk factors (age, blood pressure, lipids, glucose, body mass index, waist/hip ratio, cigarette smoking and diabetes), hematocrit and blood and plasma viscosities. According to the degree of carotid atherosclerosis, investigated by echo-Doppler, participants were divided in three groups: those without atherosclerosis, those with a low degree of atherosclerosis and those with a high degree of atherosclerosis.

RESULTS

In men, age, blood pressure, intima-media thickness (IMT), hematocrit (47.4+/-3.7%, 47.8+/-3.7%, 48.4+/-3.7%, P<0.05) and blood viscosity (4.69+/-0.51 cP, 4.77+/-0.55 cP, 4.82+/-0.51 cP, P=0.05) increased with increasing degree of carotid atherosclerosis. In women, age, blood pressure, total cholesterol and low-density lipoprotein-cholesterol, IMT and plasma viscosity (1.42+/-0.12 cP, 1.44+/-0.11 cP, 1.46+/-0.13 cP, P<0.05) increased with increasing carotid score. Analysis of covariance (ANCOVA) showed that after adjusting for hematocrit, blood viscosity was no longer different in the three groups. In discriminant analysis, hematocrit, among the hemorheological variables investigated, was independently associated with carotid score in men (F=3.66, P<0.05). Neither hematocrit nor blood and plasma viscosities were significantly associated with carotid score in women.

CONCLUSION

These findings suggest that in men, both hematocrit and blood viscosity are related to carotid atherosclerosis but hematocrit would appear to have an independent effect over and above that mediated by viscosity.

The role of whole blood viscosity in premature coronary artery disease in women

BACKGROUND

Impaired hemorheology has been demonstrated in atherosclerotic disease and has shown a relationship with classical risk factors. Blood viscosity (eta), being the ratio of shear stress over shear rate, is an important parameter of hemorheology. In women with premature coronary artery disease (CAD), the underlying risk factors are a matter of debate and the role of whole blood viscosity in its pathogenesis has not been documented.

AIM

To investigate the association of whole blood viscosity with premature CAD in women, with complaints suggestive of angina pectoris.

METHODS

Eighty-eight women (mean age 53 years) were divided into two groups, those with a high likelihood of CAD (LIKELI+) and those with a low likelihood of CAD (LIKELI-), based on medical history and technical investigations. Assessment of risk factors comprised smoking, diabetes mellitus, arterial hypertension, left ventricular hypertrophy (LVH), systolic and diastolic blood pressures, total low-density lipoprotein (LDL)- and high-density lipoprotein (HDL)-cholesterol, triglycerides, body mass index, menopause, hormone replacement therapy, uric acid and creatinine, and predicted 10-year cardiovascular risk according to the Framingham study was calculated. Whole blood viscosity was determined at 37 degrees C using a rotational cone-and-plate viscosimeter.

RESULTS

Baseline characteristics did not differ significantly between the groups except for antiplatelet therapy (P=0.001), prevalence of diabetes mellitus (P=0.002), predicted 10-year cardiovascular risk (P=0.007), essential hypertension (P=0.02), LVH (P=0.03) and smoking habits (P=0.04). LIKELI+ women had a significantly higher whole blood viscosity at all shear rates compared with LIKELI- women (P<0.05). All blood viscosities measured from 25 to 125 s(-1) were highly significantly (P<0.0001) correlated with eta(250s(-1)). Univariate correlates with eta(250s(-1)) comprised triglycerides (P=0.006) and haematocrit (P=0.026). Binary logistic multivariate regression analysis for high likelihood of CAD revealed that only presence of arterial hypertension (P<0.0001) was predictive. Multiple regression analysis demonstrated that haematocrit (P=0.001) and likelihood of CAD (P=0.01) were the only significant determinants of eta(250s(-1)).

CONCLUSION

In this study, blood viscosity did not appear as an independent risk factor for the prediction of premature CAD in women. Viscosity may act as a marker of CAD or of classical risk factors.

Improvements in blood rheology after cardiac rehabilitation and exercise training in patients with coronary heart disease

OBJECTIVES

Our purpose was to examine the effect of cardiac rehabilitation and exercise training on blood rheology in patients with coronary heart disease (CHD). Although increased blood and plasma viscosity have been associated with an increased risk of CHD, the effects of cardiac rehabilitation and exercise training on blood rheology in patients with CHD are uncertain.

METHODS

We assessed whole blood effective viscosity (mu), hematocrit standardized blood viscosity (mu45)), red blood cell transport efficiency (tau(rbc)), and plasma viscosity (PV) in 23 nonsmoking patients with CHD before and after a phase II cardiac rehabilitation and exercise training program. In addition, we compared the group data with the data of a healthy reference group of 10 subjects.

RESULTS

Patients with CHD had significantly elevated mu (3.35 +/- 0.35 cp vs 3.06 +/- 0.19 cp, P <.05) and mu45 (3.51 +/- 0.29 cp vs 3.12 +/- 0.06 cp, P <.001) and reduced tau(rbc) (12.7% +/- 1.0% x cp(-1) vs 14.2% +/- 0.7% x cp(-1), P <.001) compared with healthy subjects. After rehabilitation, patients with CHD had reductions in PV (1.85 +/- 0.18 cp vs 1.77 +/- 0.11 cp, P <.01) and mu45 (3.58 +/- 0.22 cp vs 3.39 +/- 0.22 cp, P <.0001) and an increase in tau(rbc) (12.4% +/- 0.8% x cp(-1) vs 13.2% +/- 0.9% x cp(-1), P <.0001).

CONCLUSIONS

Cardiac rehabilitation improves blood rheology in patients with CHD by reducing mu45 and PV and elevating tau(rbc). These improvements may contribute to the increased functional capacity and reduced morbidity and mortality that is associated with participation in cardiac rehabilitation and exercise programs.

Intravenous immunoglobulin-related acute coronary syndrome and coronary angiography in idiopathic thrombocytopenic purpura--a case report and literature review

In acute coronary syndromes, GPIIb/IIIa platelet inhibitors have demonstrated a reduction in recurrent myocardial ischemia. Conversely, one might expect that enhancing platelet activity in patients in acute coronary syndromes would have the opposite effect. We report a patient with idiopathic thrombocytopenic purpura (ITP) that had recurrent myocardial ischemia associated with administration of intravenous immunogloblin (IVIG). Literature is reviewed.

Parameters of red blood cell aggregation as correlates of the inflammatory state

To identify clinically relevant parameters of red blood cell (RBC) aggregation, we examined correlations of aggregation parameters with C-reactive protein and fibrinogen in unstable angina (UA), acute myocardial infarction (AMI), and bacterial infection (BI). Aggregation parameters were derived from the distribution of RBC population into aggregate sizes (cells per aggregate) and changing of the distribution by flow-derived shear stress. Increased aggregation was observed in the following order: UA, AMI, and BI. The best correlation was obtained by integration of large aggregate fraction as a function of shear stress. To differentiate plasmatic from cellular factors in RBC aggregation, we determined the aggregation in the presence and absence of plasma and formulated a "plasma factor" (PF) ranging from 0 to 1. In AMI the enhanced aggregation was entirely due to PF (PF = 1), whereas in UA and BI it was due to both plasmatic and cellular factors (0 < or = PF < or = 1). It is proposed that clinically relevant parameters of RBC aggregation should express both RBC aggregate size distribution and aggregate resistance to disaggregation and distinguish between plasmatic and cellular factors.

Combined leukocyte and erythrocyte aggregation in patients with acute myocardial infarction

OBJECTIVES

To determine whether the increased aggregability of both white and red blood cells previously reported in acute myocardial infarction (aMI) correlates with each other.

DESIGN

Cross-sectional study comparing two groups of patients and a group of healthy controls.

SETTING

A tertiary university affiliated hospital (Intensive Cardiac Care Unit and Department of General Internal Medicine).

PATIENTS

Consecutive patients with aMI, patients with chest pain and no infarction, and healthy controls.

MEASUREMENTS AND RESULTS

We adapted a simple slide test and image analysis to reveal the state of both leukocyte and erythrocyte adhesiveness/aggregation in the peripheral blood of patients with aMI. A significant (P=0.0001) increment in the aggregation of both cellular populations was noted in 48 patients with aMI as opposed to the 141 patients with ischemic heart disease and no infarction and in 45 matched controls. In addition, a significant correlation was noted between the various variables of the leukocyte and erythrocyte adhesiveness/aggregation tests.

CONCLUSIONS

The significant correlation between the aggregability of white and red blood cells in patients with aMI is suggestive of there being a commonly shared adhesive protein(s). The prompt identification of patients with increased aggregation might have clinical and therapeutic implications.

The genesis of atherosclerosis and risk factors: a review

Atherosclerosis constitutes the most common medical and surgical problem. This can be manifested clinically as stroke, coronary artery disease, or peripheral vascular disease. In the present review the microscopic appearance of the normal arterial wall, the definition of atherosclerosis and the five theories of atherogenesis are described. These are: the lipid theory, the hemodynamic theory, the fibrin incrustation theory, the nonspecific mesenchymal hypothesis and the response to injury hypothesis. Based on the above theories the sequence of events in atherogenesis is analyzed. The classification of the atherosclerotic lesions according to Stary (types I-VI) and their characteristics appear in a table. The epidemiology and the role of the following risk factors are presented in detail: age, sex, lipid abnormalities, cigarette smoking, hypertension, diabetes mellitus, physical inactivity, alcohol consumption, obesity, and hemostatic factors. In addition, less common genetically determined associations like homocystinuria, Tangier disease, Hutchinson-Gilford syndrome (progeria), Werner's syndrome, radiation induced atherosclerosis and the implications of Chlamydia pneumoniae on the arterial wall are discussed.

Venous dysfunction and the change of blood viscosity during head-up tilt

The precise stimulus that induces vasovagal syncope is still unclear. We have previously demonstrated that the peripheral distribution of blood volume (venous pooling) is a strong predictor of tilt induced vasovagal reaction. We hypothesized that an increase in venous pooling during tilt accentuates the measured increase in blood viscosity. This hypothesis is based on the previously demonstrated increase in venous pressure and subsequent increase in transcapillary fluid transudation during tilt. The increased blood viscosity, in turn, increases vascular shear rate, which may alter the vasoconstrictive and other cardiovascular responses to decreased preload. We measured blood viscosity (supine and tilt) in 56 patients with a history of orthostatic intolerance (37 with venous pooling [VP] and 19 without venous pooling [non-VP]). VP and non-VP were separated into subgroups based on blood pressure and heart rate response to tilt. There was a positive correlation between blood viscosity and plasma aldosterone in the supine. In the group as a whole, neither supine blood viscosity nor its increase during tilt differed between VP and non-VP. However, the tilt induced increase of blood viscosity was significant only in patients with tilt provoked tachycardia plus normal blood pressure response in VP group. We suggest that the increase of blood viscosity in this group led to the normal blood pressure response. The positive correlation between supine blood viscosity and supine plasma aldosterone indicates that the normal blood pressure response in this group possibly was via stimulation of the renin-angiotensin-aldosterone system.

Whole-blood viscosity and the insulin-resistance syndrome

BACKGROUND

In a previous study we found that elevated blood viscosity was linked to the insulin resistance syndrome, and we proposed that high blood viscosity may increase insulin resistance. That study was based on calculated viscosity.

OBJECTIVE

To determine whether directly measured whole-blood viscosity was related to the insulin-resistance syndrome in the same way as calculated viscosity had been found to be.

METHODS

Healthy young men were examined with the hyperinsulinemic isoglycemic glucose clamp technique, and we related insulin sensitivity (glucose disposal rate) to other metabolic parameters and to blood viscosity. We established a technique for direct measurement of whole-blood viscosity.

RESULTS

There were statistically significant negative correlations between glucose disposal rate and whole-blood viscosity at low and high shear rates (r = -0.41, P = 0.007 for both, n = 42). Whole-blood viscosity was correlated positively (n = 15) to serum triglyceride (r = 0.54, P = 0.04) and total cholesterol (r = 0.52, P = 0.05), and negatively with high-density lipoprotein cholesterol (r = -0.53, P = 0.04) concentrations. Insulin sensitivity index was correlated positively to high-density lipoprotein cholesterol (r = 0.54, P = 0.04) and negatively to serum triglyceride (r = -0.69, P = 0.005) and to total cholesterol (r = -0.81, P = 0.0003) concentrations.

CONCLUSIONS

The present results demonstrate for the first time that there is a negative relationship between directly measured whole-blood viscosity and insulin sensitivity as a part of the insulin-resistance syndrome. Whole-blood viscosity contributes to the total peripheral resistance, and these results support the hypothesis that insulin resistance has a hemodynamic basis.

Whole blood viscosity, blood pressure and cardiovascular risk factors in healthy blood donors

Whole blood viscosity contributes to the total peripheral resistance and has been suggested to be a risk factor for cardiovascular disease. Whole blood viscosity was measured using a direct technique in 105 healthy blood donors and in addition to establishing our reference values, the relationship to blood pressure and other cardiovascular risk factors was assessed. Whole blood viscosity correlated with systolic blood pressure (r = 0.29, p = 0.003), cholesterol (r = 0.21, p = 0.034), cholesterol/HDL cholesterol ratio (r = 0.33, p = 0.01), triglycerides (r = 0.37, p < 0.0005), body mass index (r = 0.29, p = 0.003) and waist-hip ratio (r = 0.30, p = 0.002). Subjects with systolic blood pressure > 130 mmHg (n = 16) had higher whole blood viscosity (p = 0.017) than those with lower blood pressure. Whole blood viscosity was significantly lower in women (n = 52) than in men at all shear rates (0.045 > p > 0.001). These results suggest that even in a population of healthy normotensive blood donors of a wide age range and either gender, there are positive correlations between directly assessed whole blood viscosity and a number of the components of the metabolic cardiovascular syndrome including systolic blood pressure, weight and blood lipids.

Hyperhomocysteinemia, hyperfibrinogenemia, and lipoprotein (a) excess in maintenance dialysis patients: a matched case-control study

Maintenance dialysis patients experience an exceedingly high incidence of arteriosclerotic cardiovascular disease (CVD) events that are poorly predicted by traditional CVD risk factor indices. We evaluated the prevalence of three non-traditional CVD risk factors, i.e. hyperhomocysteinemia, hyperfibrinogenemia, and lipoprotein (a) Lp(a)) excess, and combined hyperhomocysteinemia, hyperfibrinogenemia, and Lp(a) excess, in maintenance dialysis patients. Fasting total plasma homocysteine (Hcy), fibrinogen, Lp(a), glucose, and total and HDL cholesterol levels, and traditional CVD risk factor (i.e. glucose tolerance, smoking, hypertension, dyslipidemia) prevalences were assessed in 71 dialysis patients and 71 age, sex, and race matched Framingham Study controls free of clinical renal disease, with normal serum creatinine (< or = 1.5 mg/dl). Mean plasma Hcy 23.7 vs. 9.9 microM, P = 0.0001), fibrinogen (457 vs. 309 mg/dl, P = 0.0001), and Lp(a) (30 vs. 17 mg/dl, P = 0.0070) levels were substantially increased in the dialysis patients. Matched odds ratios (with 95% confidence intervals), dialysis patients/controls, for hyperhomocysteinemia, hyperfibrinogenemia, and Lp(a) excess, alone or combined, were markedly greater in the dialysis patients, with no evidence of confounding by the traditional CVD risk factors: hyperhomocysteinemia, 105.0 (29.9-368.9); hyperfibrinogenemia, 16.6 (6.6-42.0); Lp(a) excess, 3.5 (1.5-8.4); all three combined 35.0 (5.7-199.8). Given in vitro evidence that Hcy, Lp(a), and fibrinogen interact to promote atherothrombosis, combined hyperhomocysteinemia, hyperfibrinogenemia, and Lp(a) excess may contribute to the high incidence of vascular disease sequelae experienced by dialysis patients, which is inadequately explained by traditional CVD risk factors. Controlled, prospective studies of well-characterized maintenance dialysis cohorts are urgently required to substantiate this hypothesis.

Plasma viscosity increase with progression of peripheral arterial atherosclerotic disease

Increased blood and plasma viscosity has been described in patients with coronary and peripheral arterial disease. However, the relation of viscosity to the extent of arterial wall deterioration--the most important determinant of clinical manifestation and prognosis of the disease--is not well known. Therefore, the authors studied plasma viscosity as one of the major determinants of blood viscosity in patients with different stages of arterial disease of lower limbs (according to Fontaine) and its relation to the presence of some risk factors of atherosclerosis. The study encompassed four groups of subjects: 19 healthy volunteers (group A), 18 patients with intermittent claudication up to 200 m (stage II; group B), 15 patients with critical ischemia of lower limbs (stage III and IV; group C), and 16 patients with recanalization procedures on peripheral arteries. Venous blood samples were collected from an antecubital vein without stasis for the determination of plasma viscosity (with a rotational capillary microviscometer, PAAR), fibrinogen, total cholesterol, alpha-2-macroglobulin, and glucose concentrations. In patients with recanalization procedure local plasma viscosity was also determined from blood samples taken from a vein on the dorsum of the foot. Plasma viscosity was most significantly elevated in the patients with critical ischemia (1.78 mPa.sec) and was significantly higher than in the claudicants (1.68 mPa.sec), and the claudicants also had significantly higher viscosity than the controls (1.58 mPa.sec). In patients in whom a recanalization procedure was performed, no differences in systemic and local plasma viscosity were detected, neither before nor after recanalization of the diseased artery. In all groups plasma viscosity was correlated with fibrinogen concentration (r=0.70, P < 0.01) and total cholesterol concentration (r=0.24, P < 0.05), but in group C (critical ischemia) plasma viscosity was most closely linked to the concentration of alpha-2-macroglobulin (r=0.78, P < 0.01). These results indicate that in patients with peripheral arterial disease plasma viscosity increases with the progression of the atherosclerotic process and is correlated with the clinical stages of the disease.

Effect of low-dose oral triphasic contraceptives on blood viscosity, coagulation and lipid metabolism

The purpose of the study was to determine the relationship between hemorheological profile, i.e. blood viscosity, and other risk factors for cardiovascular and thrombotic diseases in women taking oral contraceptives and if blood viscosity may be considered a marker of cardiovascular risk in OC users. Plasma levels of coagulation parameters, serum lipids, blood viscosity and RBC deformability were determined in a group of 10 women taking OC vs. 10 controls. The blood parameters were evaluated before OC use and thereafter at 3 and 6 months. A significant change in the partial thromboplastin time, fibrinogen, HDL and apolipoprotein A-I was observed, while the other parameters remained unchanged. Plasma viscosity was significantly increased during OC treatment; whole blood viscosity and RBC deformability remained unchanged. However, although some parameters were significantly modified during OC treatment, all alterations remained within the normal range of laboratory values. The data confirm that low-dose triphasic OC therapy does not affect significantly the coagulation system, serum lipid metabolism and blood viscosity. Plasma viscosity measurement may be considered as a marker for monitoring women using OC because it is apparently the most sensitive parameter.

Clustering of cardiovascular risk factors: targeting high-risk individuals

Cardiovascular risk factors have traditionally been divided into 2 categories: modifiable risk factors (smoking, hypertension, elevated cholesterol, reduced high density lipoprotein cholesterol, and diabetes), and nonmodifiable risk factors (age, gender, and hereditary factors). However, more recent data indicate clustering of several metabolic and familial factors that are often related to each other. A pattern of lipoprotein abnormalities characterized by increased hepatic production of apolipoprotein B-containing lipoprotein particles, high blood pressure, visceral obesity, and peripheral insulin resistance are identified with increasing frequency in subjects with premature coronary artery disease (CAD). The metabolic substrates for many such disorders are being uncovered, and genetic analysis of affected kindred have, often with conflicting results, suggested associations with candidate genes. In the context of a multifactorial approach, aggressive treatment of lipoprotein disorders in high-risk individuals, or in the secondary prevention of cardiovascular diseases, has resulted in a decreased rate of progression of CAD and a marked reduction in clinical events. Further work in the field of hemostatic factors has shown that fibrinogen, activated coagulation factor VII, spontaneous platelet aggregation, and elevated levels of plasminogen activator inhibitor-1 (PAI-1), are all associated with CAD. There is a strong association between lipids (especially triglyceride-rich lipoproteins) and fibrinogen, PAI-1, and activation of factor VII. In addition, vascular function, especially endothelial cell physiology, has been shown to be compromised in the presence of multiple risk factors and to be improved with intensive therapy aimed at reducing risk factors, especially plasma lipoprotein levels. The implications for clinical practice are important. In the primary prevention of cardiovascular disease, proper risk stratification must be carried out with specific attention given to lifestyle changes. Cessation of smoking and changes in diet (both qualitative and quantitative), exercise, and serenity are often required. In the prevention of cardiovascular disease in subjects at high risk, or in the secondary prevention of CAD, a clear justification exists for aggressive lifestyle changes, often coupled with lipid-lowering therapy and adequate blood pressure control. Basic research is providing us with a better understanding of the molecular interactions between lipoproteins and hemostatic factors. It is becoming increasingly necessary to develop novel pharmaceutical agents with the combined ability to reduce atherogenic lipoprotein levels while also reducing susceptibility to thrombosis.

The role of platelets in essential hypertension

Recent research is helping us understand the complex interactions that occur between platelets and their environment. The several intracellular events that occur during platelet activation are being identified as ar their effects on other platelets, the endothelium and coagulation factors. Heightened platelet activation is seen early in essential hypertension and probably plays an important role in the initiation and progression of atherosclerosis and the disorders associated with it. This review identifies some of the changes in platelet structure and function in essential hypertension and their role in the pathogenesis of hypertensive vascular disease.

Red blood cell aggregability in patients with a history of leg vein thrombosis: influence of post-thrombotic treatment

Reversible aggregation of red blood cells (RBC) plays an important role in determining blood flow properties, and it is this aggregation which increases blood viscosity at low shear rates. The structure and sites of venous thrombi, as well as the fact that stasis is a major predisposing factor in venous thrombosis, suggest a strong association between vein thrombosis, slow blood flow and increased blood viscosity. RBC aggregation and disaggregation were measured (SEFAM erythroaggregameter, France) in 54 patients with a history of unexplained leg vein thrombosis. Results were compared to those of controls classified according to age. Increased RBC aggregability was observed in 41% of the patients, and the mean values indicated a significant elevation of RBC aggregability in patients when compared with controls (P < 0.05). Subgroups were compared to study the influence of thrombus recurrence and thrombosis type (deep versus superficial vein thrombosis) on the aggregation parameters. No significant difference was found between these subgroups. The use of compression stockings and veinotropic drugs tended to reduce the abnormalities in RBC aggregability (P < 0.05). An increase in RBC aggregability and in the shear resistance of RBC aggregates, by predisposing to circulatory stasis, is likely to contribute to the evolution and complications of leg vein thrombosis.

Relationship between hemorrheologic factors and insulin sensitivity in healthy young men

The present study aimed at testing a possible relationship between hemorrheologic factors, such as hematocrit, fibrinogen, and whole-blood viscosity, and insulin sensitivity in healthy humans. Twenty-one 21-year-old men were studied with the hyperinsulinemic euglycemic glucose clamp technique. We found statistically significant negative correlations between the glucose disposal rate (GDR) and calculated whole-blood viscosity at both high (r = -.55, P = .01) and low (r = -.51, P = .01) shear rates. We observed negative associations between GDR and fibrinogen (r = -.66, P = .002), GDR and hematocrit (r = -.63, P = .002), GDR and body mass index (r = -.51, P = .007), and GDR and resting heart rate (r = -.46, P = .04). Using stepwise multiple regression considering whole-blood viscosity, body mass index, mean arterial blood pressure, and heart rate as independent variables, we found that only whole-blood viscosity and body mass index were independent explanatory variables of the GDR. Together they accounted for 63% of the variability in the GDR in our subjects. These results suggest hemorrheologic, and therefore indirectly hemodynamic, factors as correlates to insulin sensitivity.

The role of fibrinogen as a cardiovascular risk factor

Several epidemiological studies have produced longitudinal data identifying fibrinogen as a major cardiovascular risk factor. Cross-sectional results show strong associations between fibrinogen and a variety of demographic variables, cardiovascular risk factors, or diseases. Clinical cohort studies demonstrate that fibrinogen might also be a risk factor for the sequelae of cardiovascular disease. Knowledge about the determinants of the plasma level of fibrinogen in health and disease is as yet incomplete. Understanding of the mechanisms leading to the atherothrombogenic action of fibrinogen is also fragmentary. Fibrinogen strongly affects blood coagulation, blood rheology and platelet aggregation; in addition fibrinogen and its metabolites have direct effects on the vascular wall. Finally, fibrinogen is a prominent acute phase protein. All of these phenomena might provide some insight into the pathophysiological mechanisms involved. It is concluded that fibrinogen represents a major, independent risk factor that should now be included into the cardiovascular risk profile.

The role of abnormalities in the anticoagulant and fibrinolytic systems in retinal vascular occlusions

The hemostatic mechanisms involve both an anticoagulant system to check the coagulation cascade and a fibrinolytic system to remove formed fibrin clots. Abnormalities of the hemostatic system or acquired abnormal hematological factors can produce a thrombophilic state which accounts for 15-28% of unexplained systemic vascular thrombosis in young patients. Similar abnormalities have recently been identified in some patients with retinal vascular occlusions. Screening of selected patients with retinal vascular occlusions may reveal additional ophthalmological patients with specific thrombotic syndromes.

Increased red cell aggregation in diabetes mellitus: association with cardiovascular risk factors

Red cell aggregation may be higher in diabetic patients and may predispose to cardiovascular disease. Red cell aggregation was measured by a simple photometric method in 122 diabetic patients and 100 matched control subjects, to determine its relationship to cardiovascular risk factors. Red cell aggregation was significantly increased in both Type 1 (4.3 +/- 1.3 vs 3.4 +/- 1.2, p < 0.002) and Type 2 diabetic patients (5.5 +/- 1.5 vs 3.2 +/- 1.3, p < 0.0001). In all diabetic patients aggregation correlated with triglycerides, VLDL, and inversely with HDL and in Type 2 diabetic patients also with body mass index, hypertension, and inversely with duration of diabetes. On multiple regression analysis, triglycerides and body mass index showed an independent association with red cell aggregation and in Type 2 diabetic patients smoking was also associated with increased red cell aggregation. It is concluded that increased red cell aggregation may be one mechanism by which some cardiovascular risk factors could promote cardiovascular disease in diabetes.

The possible role of hemorheology in atherothrombogenesis

Conventional risk factors predict only about 30-50% of incidental cases in cardiovascular diseases, which are still the leading cause of death in western societies. During the last decade, the importance of thrombosis as an essential mechanism in acute myocardial infarction (AMI) and stroke has been established. The introduction of thrombolysis has led to an impressive reduction in AMI case fatality and possibly also to a substantial amelioration of its prognosis. Evidence from experimental, clinical and epidemiological studies suggest, that several hemostatic and hemorheological factors (e.g., fibrinogen, Factor VII, plasma viscosity, hematocrit, red blood cell aggregation, total white cell count) might not only play an important role in the evolution of acute thrombotic events, but may also take part in the pathophysiology of atherosclerosis. An increasing number of studies reports altered hemostatic and hemorheological parameters to be associated with smoking, hyperlipoproteinemia, and high blood pressure, as well as with adverse dietary habits and other life-style factors. To date, their way of interaction with the atherosclerotic process is poorly understood. Hemorheological or hemostatic mechanisms that might promote thromboatherogenesis include the predisposition to thrombosis via a hypercoagulable state, the enhancement of atherosclerosis by fibrinogen and its metabolites, and finally the reduction of blood flow through various rheological effects (e.g., increase in plasma viscosity and red cell aggregation, or leukocyte activation). Future research should focus in more detail on the interrelationship between accepted risk factors and the hemostatic system as well as hemorheological parameters. Deeper insight into the mechanisms involved might lead to new preventive strategies as well as to therapeutic procedures in the management of atherosclerosis and associated thrombotic events.