Whole blood viscosity and erythrocyte deformability are related to endothelium-dependent vasodilation and coronary risk in the elderly. The prospective investigation of the vasculature in Uppsala seniors (PIVUS) study.

It has previously been shown that a high hemoglobin value, a major determinant of whole blood viscosity (WBV), predicts cardiovascular events. One putative mechanism might be an impaired endothelial function. Erythrocyte deformability is another rheologic feature of the erythrocyte being of importance for the flow properties of the blood, especially in the capillaries. The present study evaluates the relationships between blood viscosity, erythrocyte deformability assessed as erythrocyte fluidity (EF), coronary risk and endothelial vasodilatory function. In the population-based PIVUS study (1016 subjects aged 70); endothelium-dependent vasodilation (EDV) was evaluated by the invasive forearm technique with acetylcholine given in the brachial artery and the brachial artery ultrasound technique with measurement of flow-mediated dilatation (FMD). WBV, plasma viscosity (PV) and EF were measured in a random sample of 573 subjects. WBV and PV were positively and EF negatively related to Framingham risk score. EDV was inversely related to both whole blood and plasma viscosity. FMD was not related to any rheologic variable. In multiple regression analyses WBV and EF were significantly related to EDV independently of gender, hypertension, smoking, hypercholesterolemia, obesity and diabetes. Acetylcholine-induced vasodilation in the forearm, but not FMD, was negatively related to whole blood viscosity and positively related to EF independently of traditional risk factors in elderly subjects, indicating a pathophysiological link between impaired hemorheology and coronary risk.

Brain tissue oxygen monitoring: a study of in vitro accuracy and stability of Neurovent-PTO and Licox sensors.

OBJECT: Periods of brain tissue ischemia are common after severe head injury, and their occurrence and duration are negatively correlated with outcome. Accurate and reliable measurement of brain tissue oxygenation (B(ti) pO(2)) may be a key to improve patient outcome after severe head injury. Knowledge of stability and accuracy of the B(ti) pO(2) systems is crucial. We have therefore conducted a bench test study of new Neurovent-PTO (NV) and Licox (LX) oxygen tension catheters to evaluate the sensor accuracy, response time to different oxygen tensions, response to temperature changes and long-term stability. METHODS: For all experiments five new fluorescent NV sensors and five new electrochemical LX sensors were used. The catheter probes were placed into a container filled with a buffer solution. The solution was equilibrated with five high precision calibration gases. The accuracy of the probes was recorded after an equilibration period of 20 min in O(2) concentrations of 5, 10, 20, 30 and 40 mmHg at 37.0 +/- 0.2 degrees C. The probe response to an increase in temperature from 37.0 degrees C to 38.5 degrees C to 40.0 degrees C in two different gases with O(2) concentrations of 10 and 20 mmHg were analysed. We also recorded the time for reaching 90% of a new oxygen concentration level when switching from one concentration to another. Finally, to test if there was a time-dependant drift in pO(2) recordings, all sensors were left in 10 mmHg O(2) solution for 10 days, and recordings were taken every 24 h. RESULTS: In all gas concentrations, NV and LX sensors measured pO(2) with high accuracy and stability in vitro (mean differences from calculated values were for NV 0.76-1.6 mmHg and for LX -0.46-0.26 mmHg). Both sensors showed a shorter response time to pO(2) increase (for NV 56 +/- 22 s and for LX 78 +/- 21 s) compared to pO(2) decrease (for NV 131 +/- 42 s and for LX 215 +/- 63 s). NV pO(2) values were more stable for changes in temperature, while LX sensors showed larger standard deviations with increasing temperature (the difference from the calculated values in 19.7 mmHg O(2) at 40 degrees C were for NV probes between 0.5 and 1.7 mmHg and LX between -2.3 and 1.9 mmHg). Both sensors gave stable results with low standard deviations during long-term (10 days) use, but with a slight elevation of measured pO(2) levels by time. CONCLUSIONS: Both NV and LX were accurate in detecting different oxygen tensions, and they did not deviate over longer recording times. However, LX needed a significantly longer time to detect changes in pO(2) levels compared to NV. Furthermore, LX probes showed an increased standard deviation with higher temperatures.

Shear stress in the common carotid artery is related to both intima-media thickness and echogenecity. The Prospective Investigation of the Vasculature in Uppsala Seniors study.

It has previously been shown that the degree of shear stress (SS) in the carotid artery is related to both plaque occurrence and intima-media thickness (IMT). Since the echogenecity also is an important feature of plaques, we investigated if a reduced shear stress also is related to the echolucency of plaque and the intima-media complex. In the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS) study, a population-based study of 1016 subjects aged 70, left common carotid artery diameter, IMT, the grey scale median (GSM) of the intima-media complex (IM-GSM) and the blood flow velocity were measured by ultrasound. Occurrence of plaque was noted, and the echogenecity of the plaques was visually estimated by the Gray-Weale classification. Shear stress was inversely related to both IMT and IM-GSM (p=0.0084 and p=0.003, respectively), independently of gender and coronary risk, estimated by the Framingham risk score. Shear stress was lower in subjects with carotid plaque (44% of the sample) than in those without (p=0.0013), and was inversely related to the echogenecity in the subjects with plaque (p=0.0092), independently of gender and coronary risk. A low shear stress in the common carotid artery was associated with both a thick IMT and an echolucent intima-media complex. A similar picture was seen when overt plaques were evaluated, suggesting that shear stress is of importance for both the extent and composition of atherosclerosis.

Hemorheological and hemodynamic changes in predialysis patients after normalization of hemoglobin with epoetin-alpha.

OBJECTIVE: Changes in blood viscosity and total peripheral resistance may contribute to increased blood pressure during partial correction of renal anemia with erythropoietin. An increase in hemoglobin level is followed by decreases in cardiac output and left ventricular mass. We examined how normalization of hemoglobin in predialysis patients affects both hemorheological and hemodynamic variables. MATERIAL AND METHODS: Twelve moderately anemic predialysis patients (hemoglobin 115.9+/-7.8 g/l) received epoetin-alpha with the aim of achieving a normal hemoglobin level (135-160 g/l). Hemorheological variables were measured using rotational viscometry. Cardiac index was determined by means of Doppler echocardiography. RESULTS: After 48 weeks, the hematocrit level had increased from 37.9%+/-3.0% to 47.0%+/-3.1% (p<0.0001). Blood viscosity increased from 3.84+/-0.33 to 4.59+/-0.4 mPa x s (p<0.001). Blood viscosity standardized to a hematocrit level of 45% and a plasma viscosity of 1.31 mPa x s did not change. Plasma viscosity, erythrocyte aggregation tendency and erythrocyte fluidity remained unchanged. The cardiac index decreased from 2.64+/-0.57 to 2.19+/-0.72 l/min/m(2) (p<0.05). The total peripheral resistance index increased from 3270+/-985 to 4013+/-1046 (dyn x s/cm(5))m(2) (p<0.05). Blood pressure remained constant, but the amount of antihypertensive medication used increased by 30%. CONCLUSIONS: Hemoglobin normalization in predialysis patients raised blood viscosity and total peripheral resistance due to an increase in hematocrit level, without other consistent hemorheological changes. Antihypertensive therapy had to be increased in many patients to maintain an acceptable blood pressure. The cardiac index was reduced, which may have prevented further development of left ventricular hypertrophy.