Pieter Struijk

Evaluation of volume vascularization index and flow index: a phantom study

Three‐dimensional (3D) power Doppler ultrasonography provides indices to quantify moving blood within a volume of interest (e.g. ovary, endometrium, tumor or placenta). The purpose of this study was to determine the influence of ultrasound instrument settings on vascularization index (VI) and flow index (FI) at different flow velocities, using a specially built flow phantom with a small tube diameter.

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.

Blood pressure estimation in the human fetal descending aorta.

The objectives of this study were to estimate fetal blood pressure non‐invasively from two‐dimensional color Doppler‐derived aortic blood flow and diameter waveforms, and to compare the results with invasively derived human fetal blood pressures available from the literature.

Doppler flow velocity waveforms in the embryonic chicken heart at developmental stages corresponding to 5-8 weeks of human gestation

To obtain Doppler velocity waveforms from the early embryonic chicken heart by means of ultrasound biomicroscopy and to compare these waveforms at different stages of embryonic development.

On-line electrical impedance measurement for monitoring blood viscosity during on-pump heart surgery

Background: The viscosity of blood (η) as well as its electrical impedance at 20 kHz at high shear rate depends on hematocrit, temperature, concentration of macromolecules and red cell deformability. The aim of our study was to investigate the relation between viscosity and electrical impedance in a heart-lung machine-like set-up, because during on-pump heart surgery considerable viscosity changes occur. Methods: Blood of 10 healthy volunteers was examined under temperature variation between 18.5 and 37°C at four different levels of hemodilution. Blood viscosity was examined with a golden-standard technique, i.e. a Contraves LS 30 Couette viscometer, and the results were compared with measurements of the electrical resistivity (R) at 20 kHz by a specially designed device in series with the tubing system of a heart-lung machine. All measurements were performed at a shear rate of 87 s–1. Results: Using stepwise multiparameter regression analysis (SPSS) a highly significant correlation was found (r2 = 0.882) between viscosity (η) and resistivity (R). Adding the variables sodium ([Na+]) and fibrinogen ([Fibr]) concentration the coefficient of correlation further improved to r2 = 0.928 and the relation became: η = –0.6844 + 0.038 R + 0.038 [Na+] + 0.514 [Fibr]. All coefficients showed a statistical significance of p < 0. 001. Conclusions: Electrical impedance measurement is feasible in a heart-lung machine-like set-up and allows accurate continuous on-line estimation of blood viscosity; it may offer an adequate way to record and control viscosity changes during on-pump heart surgery.

Fetal heart rate and umbilical artery flow velocity variability in intrauterine growth restriction: a matched controlled study

To study heart rate and umbilical artery blood flow velocity variability in growth‐restricted fetuses and investigate the influence of the autonomic nervous system on these parameters.

Ultrasonic cervimetry to study the dilatation of the caudal cervix of the cow at parturition.

The objective of this study was to investigate the temporal changes in dilatation of the caudal cervix during induced calvings (n = 5). We used ultrasound cervimetry, allowing the continuous recording of the distance between a transmitting and receiving ultrasound crystal, which were implanted opposite to each other on the caudal rim of the cervix. We started recording between 19 and 21 h after injecting a prostaglandin analogue (PG) on day 272 of gestation. A fluid-filled catheter had been introduced transcervically between the fetal membranes and the uterine wall for measurements of intra-uterine pressure (IUP). While the characteristics of calving varied widely between the five animals, it appeared possible to divide the process of dilatation into four phases. During the latent phase, which lasted until 25-43 h after PG, no net gain in dilatation occurred. We found an acceleration phase (4.3-6.8 h), in which the dilatation rate speeds up (0.49-0.84 cm/h) in three of the cows. During the phase of maximum slope (lasting 0.5-4.8 h), we measured an even higher rate (1.47-8.48 cm/h), decreasing again during the deceleration phase (rate 0.24-2.28 cm/h) in four cows. The quality of the IUP measurements precluded us from continuously investigating the relationship between cervical dilatation and uterine contractions. However, short term simultaneous recordings revealed that the cervical opening changed momentarily in the absence of IUP during the latent phase, while during the phase of maximum slope, temporary changes of dilatation coincided with uterine contractions. We concluded that the method of ultrasound cervimetry used in this study provides a valuable way to study the process of cervical dilatation in parturient cows in vivo.

Umbilical venous volume flow and fetal behavioral states in the normally developing fetus

To determine the relationship between umbilical venous (UV) volume flow and fetal behavioral states 1F (quiet sleep) and 2F (active sleep) in normal pregnancies at 36–40 weeks of gestation.

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.

Comparison between color Doppler cineloop- and conventional spectral Doppler-derived maximum velocity and flow in the umbilical vein

To compare the umbilical venous flow velocity derived from color Doppler cineloop recordings with that derived from conventional spectral Doppler in normal pregnancies.