Modelling of impaired cerebral blood flow due to gaseous emboli

Bubbles introduced to the arterial circulation during invasive medical procedures can have devastating consequences for brain function but their effects are currently difficult to quantify. Here we present a Monte-Carlo simulation investigating the impact of gas bubbles on cerebral blood flow. For the first time, this model includes realistic adhesion forces, bubble deformation, fluid dynamical considerations, and bubble dissolution. This allows investigation of the effects of buoyancy, solubility, and blood pressure on embolus clearance. Our results illustrate that blockages depend on several factors, including the number and size distribution of incident emboli, dissolution time and blood pressure. We found it essential to model the deformation of bubbles to avoid overestimation of arterial obstruction. Incorporation of buoyancy effects within our model slightly reduced the overall level of obstruction but did not decrease embolus clearance times. We found that higher blood pressures generate lower levels of obstruction and improve embolus clearance. Finally, we demonstrate the effects of gas solubility and discuss potential clinical applications of the model

Report of Seminar on Estate Planning

Reports from the UK/CLE Seminar on Estate Planning held July 19-20, 1974

Report of Third Annual Seminar on Estate Planning

Reports from the UK/CLE Third Annual Seminar on Estate Planning held July 23-24, 1976

Transcranial Doppler (TCD) measurement of brain tissue pulsations generated by the major cerebral arteries: an in vitro study

Doppler ultrasound can be used to investigate brain tissue motion. The objective of this study was to construct a physiologically realistic vascular phantom of the brain to help elucidate invivo findings. A silicone cerebrovascular replica based on MRI data was incorporated into a flow circuit generating pulsatile flow (total 434ml/min, 60bpm) of a blood mimicking fluid. An electrical circuit analogue approach was used to achieve a 74:26 split of flow between the anterior and posterior circulations, pressure of ~90mmHg, and realistic flow rates in the major vessels. A polyvinyl-alcohol material mimicked the brain tissue. Ultrasound data were recorded from the phantom using a Spencer Technologies TCD system and analysed 'in house' to estimate tissue pulsation amplitude throughout the cardiac cycle. Properties of the tissue mimic were comparable to brain (speed of sound 1630m.s-1 , density 1.06kg.m-3 , Young’s Modulus 8kPa). Maximum displacements were ~250μm in the phantom (cf. ~200μm in healthy volunteers). Displacement/time curves were similar to in-vivo curves and the phantom helped elucidate features such as phase shifts and asymmetry. In conclusion, the phantom mimics tissue motion due to vessel pulsation, excluding ventricular flow, tissue perfusion and intracranial pressure. It is suitable for studying brain tissue pulsation and helps interpretation of in-vivo findings