Blood viscosity, blood pressure and carotid pathology

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Recent research resulted in new interpretation of the role of blood viscosity in vascular ... The assessed by Duplex ultrasound thicker intima-media and carotid ...
Series on Biomechanics, Vol. 25, No. 1-2 ( 2010), 76-82

Blood viscosity, blood pressure and carotid pathology in patients with cerebral infarctions I. Velchevaa, N. Antonovab, E. Titianovac, P. Damianova a

University Hospital of Neurology and Psychiatry, Medical University, Sofia 1113, Bulgaria; [email protected] b Institute of Mechanics and Biomechanics, Bulgarian Academy of Sciences c Clinic of functional diagnostics of nervous system, Military Medical Academy, Sofia, Bulgaria; [email protected]

_____________________________________________________________________________ Abstract The study aimed to assess the complex influence of blood viscosity and blood pressure on the neurosonographic morphological parameters in the common (CCA) and internal carotid arteries (ICA) in 32 patients with chronic unilateral cerebral infarctions (CUCI), 58 patients with risk factors (RF) for cerebrovascular disease (CVD) and 25 controls, additionally divided in subgroups with mean blood pressure (MBP) < 100 and ≥ 100. Hemorheological variables, including hematocrit (HT), whole blood (WBV) and plasma viscosity (PV) were examined. The diameters of the CCA and ICA, the intima-media thickness (IMT) of the vessel walls and the blood flow velocities were measured by color duplex scanning. Significant increase of Ht and WBV at wide range of shear rates in both patients` groups and of PV in the patients with RF for CVD in comparison to controls was found. Heterogenous atherosclerotic plaques, increased IMT and larger diameters of the CCA and ICA were measured. Significant correlations of Ht with IMT and of WBV with the carotid diameters predominating in the subgroups with MBP≥100 were revealed. The study confirmed the complex control of blood pressure and blood viscosity on both carotid wall and lumen, which is achieved through the tensile and wall shear stress. Keywords: blood viscosity, blood pressure, carotid arteries ______________________________________________________________________________________________

1. Introduction Recent research resulted in new interpretation of the role of blood viscosity in vascular pathology [1]. While in Poiseuille`s law its influence on blood flow was determined in rigid tubes, in the vascular system the leading role in the regulation of blood flow is assigned to the vascular endothelium, which controls both arterial tone and blood viscosity through secretion of mediators. The mediators can affect the blood rheological behavior deformability and aggregability of erythrocytes, leucocytes and platelets. Blood viscosity itself may influence the endothelium and vascular tone through alterations of wall shear stress, which in turn determines endothelial release of vasoactive nitric oxide and modulates the transcription of genes for nitric oxide synthase and other factors involved in vascular remodeling [2,3]. The shear stress was shown to be lower in carotid arteries with atherosclerotic plaques and intima-media thickening [4]. The assessed by Duplex ultrasound thicker intima-media and carotid plaques with morphological characteristics of complex heterogeneous hypoechoic plaques were related to vascular risk factors and predicted stroke risk [5,6]. Our previous studies showed positive correlations between hematoctit (Ht), whole blood viscosity (WBV) and blood pressure, predominantly diastolic and also with the intima-media thickness (IMT) of the common carotid arteries in patients with cerebral infarctions [7,8]. The present study aimed to assess the complex influence of blood viscosity and blood pressure on the neurosonographic morphological parameters in the common (CCA) and internal carotid arteries (ICA) in patients with chronic unilateral cerebral infarctions (CUCI) and with risk factors (RF) for cerebrovascular disease (CVD).

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I. Velcheva et al./ Blood viscosity, blood pressure and carotid pathology in patients with cerebral infarctions

2. Material and methods Included in the study were 32 patients with CUCI, 58 patients with RF for CVD and 25 clinically healthy subjects. Blood pressure, height and weight were measured and the body mass index (BMI) in kg/m2 and the mean blood pressure by the Wiggers` formula were calculated. According to the vascular risk the patients groups underwent additional relative subdivision into subgroups wth MBP < 100 and subgroups with MBP ≥ 100 (Table 1). Table 1 Clinical characteristic of the examined patients

N f/m Age range mean age BMI (kg/m2) SBP (mmHg) DBP (mmHg) MBP (mmHg) MBP≥100/ MBP