Effects of viscosity on cerebral blood flow after cardiac arrest.

OBJECTIVES: To determine blood viscosity in adult comatose patients treated with mild therapeutic hypothermia after cardiac arrest and to assess the relation between blood viscosity, cerebral blood flow, and cerebral oxygen extraction. DESIGN: Observational study. SETTING: Tertiary care university hospital. PATIENTS: Ten comatose patients with return of spontaneous circulation after out-of-hospital cardiac arrest. INTERVENTION: Treatment with mild therapeutic hypothermia for 24 hours followed by passive rewarming to normothermia. MEASUREMENTS AND MAIN RESULTS: Median viscosity at shear rate 50/s was 5.27 mPa · s (4.29-5.91 mPa · s) at admission; it remained relatively stable during the first 12 hours and decreased significantly to 3.00 mPa · s (2.72-3.58 mPa · s) at 72 hours (p < 0.001). Median mean flow velocity in the middle cerebral artery was low (27.0 cm/s [23.8-30.5 cm/s]) at admission and significantly increased to 63.0 cm/s (51.0-80.0 cm/s) at 72 hours. Median jugular bulb saturation at the start of the study was 61.5% (55.5-75.3%) and significantly increased to 73.0% (69.0-81.0%) at 72 hours. Median hematocrit was 0.41 L/L (0.36-0.44 L/L) at admission and subsequently decreased significantly to 0.32 L/L (0.27-0.35 L/L) at 72 hours. Median C-reactive protein concentration was low at admission (2.5 mg/L [2.5-6.5 mg/L]) and increased to 101 mg/L (65-113.3 mg/L) in the following hours. Median fibrinogen concentration was increased at admission 2,795 mg/L (2,503-3,565 mg/L) and subsequently further increased to 6,195 mg/L (5,843-7,368 mg/L) at 72 hours. There was a significant negative association between blood viscosity and the mean flow velocity in the middle cerebral artery (p = 0.0008). CONCLUSIONS: Changes in blood viscosity in vivo are associated with changes in flow velocity in the middle cerebral artery. High viscosity early after cardiac arrest may reduce cerebral blood flow and may contribute to secondary brain injury. Further studies are needed to determine the optimal viscosity during the different stages of the postcardiac arrest syndrome.

Fetal aortic distensibility, compliance and pulse pressure assessment during the second half of pregnancy.

The objective of the study was to measure fetal aortic pulse wave velocity and lumen diameter waveforms and subsequently calculate local distensibility, compliance and pulse pressure. A dedicated algorithm for optimizing lumen diameter assessment from radiofrequency ultrasound data is described. Biplane raw data were obtained from a matrix array transducer. We evaluated 83 confirmed, normally developing pregnancies at 22-38 wk. Fetal aortic pulse wave velocity (PWV, m/s) = 0.047 × gestational age (wk) + 1.241, and the distensibility coefficient (1/kPa) = 1/(1.04 × PWV(2)). The logarithm of the local compliance index (mm(2)/kPa) and the pulse pressure (kPa) were both linearly related to gestational age as 0.022 × GA (wk) - 0.343 and 0.012 × GA (wk) + 0.931, respectively. In conclusion, fetal aortic elastic properties can be derived from phase-sensitive radiofrequency data and multiline diameter assessment. Future studies may shed further light on the developmental origins of vascular health and disease.

On-line blood viscosity monitoring in vivo with a central venous catheter, using electrical impedance technique.

Blood viscosity is an important determinant of microvascular hemodynamics and also reflects systemic inflammation. Viscosity of blood strongly depends on the shear rate and can be characterized by a two parameter power-law model. Other major determinants of blood viscosity are hematocrit, level of inflammatory proteins and temperature. In-vitro studies have shown that these major parameters are related to the electrical impedance of blood. A special central venous catheter was developed to measure electrical impedance of blood in-vivo in the right atrium. Considering that blood viscosity plays an important role in cerebral blood flow, we investigated the feasibility to monitor blood viscosity by electrical bioimpedance in 10 patients during the first 3 days after successful resuscitation from a cardiac arrest. The blood viscosity-shear rate relationship was obtained from arterial blood samples analyzed using a standard viscosity meter. Non-linear regression analysis resulted in the following equation to estimate in-vivo blood viscosity (Viscosity(imp)) from plasma resistance (R(p)), intracellular resistance (R(i)) and blood temperature (T) as obtained from right atrium impedance measurements: Viscosity(imp)=(-15.574+15.576R(p)T)SR ((-.138RpT-.290Ri)). This model explains 89.2% (R(2)=.892) of the blood viscosity-shear rate relationship. The explained variance was similar for the non-linear regression model estimating blood viscosity from its major determinants hematocrit and the level of fibrinogen and C-reactive protein (R(2)=.884). Bland-Altman analysis showed a bias between the in-vitro viscosity measurement and the in-vivo impedance model of .04 mPa s at a shear rate of 5.5s(-1) with limits of agreement between -1.69 mPa s and 1.78 mPa s. In conclusion, this study demonstrates the proof of principle to monitor blood viscosity continuously in the human right atrium by a dedicated central venous catheter equipped with an impedance measuring device. No safety problems occurred and there was good agreement with in-vitro measurements of blood viscosity.

Estimating the effect of gestational age on test performance of combined first-trimester screening for Down syndrome: a preliminary study.

OBJECTIVE: To establish how different methods of estimating gestational age (GA) affect reliability of first-trimester screening for Down syndrome. METHODS: Retrospective single-center study of 100 women with a viable singleton pregnancy, who had first-trimester screening. We calculated multiples of the median (MoM) for maternal-serum free beta human chorionic gonadotropin (free beta-hCG) and pregnancy associated plasma protein-A (PAPP-A), derived from either last menstrual period (LMP) or ultrasound-dating scans. RESULTS: In women with a regular cycle, LMP-derived estimates of GA were two days longer (range -11 to 18), than crown-rump length (CRL)-derived estimates of GA whereas this discrepancy was more pronounced in women who reported to have an irregular cycle, i.e., six days (range -7 to 32). Except for PAPP-A in the regular-cycle group, all differences were significant. Consequently, risk estimates are affected by the mode of estimating GA. In fact, LMP-based estimates revealed ten "screen-positive" cases compared to five "screen-positive" cases where GA was derived from dating-scans. CONCLUSION: Provided fixed values for nuchal translucency are applied, dating-scans reduce the number of screen-positive findings on the basis of biochemical screening. We recommend implementation of guidelines for Down syndrome screening based on CRL-dependent rather than LMP-dependent parameters of GA.

Jugular lymphatic sacs in the first trimester of pregnancy: the prevalence and the potential value in screening for chromosomal abnormalities.

OBJECTIVE: To investigate the prevalence of detectable jugular lymphatic sacs in a setting for first trimester screening for Down syndrome, and to evaluate the influence of jugular lymphatic sacs on the screening performance for chromosomal abnormalities. METHODS: A prospective single center study (Erasmus University Medical Center, Rotterdam, The Netherlands) over a period of one year (January 2003-February 2004). First trimester nuchal translucency measurement was performed in a study population of 415 fetuses. Additionally, the transversal plane with the spine and mandible was visualized to verify the presence of jugular lymphatic sacs. The jugular lymphatic sacs were measured anterior-posterior. The association between nuchal translucency and jugular lymphatic sacs was tested. RESULTS: Follow-up was complete in 406 cases (97.8%). Jugular lymphatic sacs could be visualized in 98 out of 415 (23.5%). The nuchal translucency thickness and the mean of the left and right jugular lymphatic sac were significantly correlated. CONCLUSION: The sonographic visualization of jugular lymphatic sacs significantly predicts chromosomal abnormalities, although nuchal translucency is a better predictor. Nuchal translucency and jugular lymphatic sacs are strongly correlated and therefore not applicable in a combination test.

Application of the magnitude-squared coherence function between uterine and umbilical flow velocity waveforms for predicting placental dysfunction: a preliminary study.

To examine whether the magnitude-squared coherence between uterine and umbilical blood flow velocity waveforms can, in conjunction with estimated fetal weight, uterine and umbilical pulsatility indices, fetal and maternal heart rates, diastolic notching and the amniotic fluid index, create a sensitive and specific model for the prediction of placental dysfunction. Binary logistic prediction models are created for preeclampsia, pregnancy induced hypertension and intrauterine growth restriction in a study group of 284 unselected midtrimester pregnancies. In each study group, the median value of derived parameters were compared with the uncomplicated pregnancy control group. The magnitude-squared coherence function between the uterine and umbilical flow velocity waveforms was found to be a statistically significant predictor of preeclampsia during the midtrimester of pregnancy. The magnitude-squared coherence did not improve the prediction of intrauterine growth restriction or pregnancy induced hypertension. The inclusion of magnitude-squared coherence as one of the prediction parameters may improve the early identification of pregnancies subsequently complicated by preeclampsia.