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Changes in cerebral blood flow (CBF) can be assessed directly with xenon clearance (XeC) or indirectly by measuring changes in middle cerebral artery blood velocity (Vmca) with transcranial Doppler (TCD). The aim of this study was to compare the changes in CBF and Vmca following caffeine ingestion. Nineteen patients (age 48-86, recovering from an acute(More)
Middle cerebral arterial blood velocity (MCAv) response to spontaneous and manipulated changes of arterial blood pressure (ABP) was studied in eight subjects using a linear autoregressive with exogenous input (ARX) model. ABP and MCAv were measured non-invasively by photoplethysmograph and transcranial Doppler ultrasound, respectively. Data were recorded at(More)
BACKGROUND Caffeine is present in a variety of beverages and food and is widely consumed. In a previous study of patients recovering from an acute ischaemic stroke using transcranial Doppler ultrasound we demonstrated a fall in middle cerebral artery blood velocity of 12% following ingestion of 250 mg caffeine. The aim of this study was to investigate if(More)
PURPOSE Raised intracranial pressure (ICP) is a potentially treatable cause of morbidity and mortality but tools for monitoring are invasive. We sought to investigate the utility of the tympanic membrane displacement (TMD) analyser for non-invasive measurement of ICP in children. METHODS We made TMD observations on normal and acutely comatose children(More)
Although the assessment of dynamic cerebral autoregulation (CA) based on measurements of spontaneous fluctuations in arterial blood pressure (ABP) and cerebral blood flow (CBF) is a convenient and much used method, there remains uncertainty about its reliability. We tested the effects of increasing ABP variability, provoked by a modification of the thigh(More)
Transcranial Doppler ultrasonography measures cerebral blood flow velocity (CBFv) of basal intracranial vessels and is used clinically to detect stroke risk in children with sickle cell anaemia (SCA). Co-inheritance in SCA of alpha-thalassaemia and glucose-6-phosphate dehydrogenase (G6PD) polymorphisms is reported to associate with high CBFv and/or risk of(More)
OBJECTIVE To measure cerebral blood flow before and after intra-aortic balloon counterpulsation (IABC) in patients at high risk of developing delayed cerebral ischaemia after aneurysm surgery following subarachnoid haemorrhage. METHODS Six prospectively selected patients at high risk of developing delayed ischaemia had elective IABC after clipping of(More)
Despite advances in modelling dynamic autoregulation, only part of the variability of cerebral blood flow velocity (CBFV) in the low frequency range has been explained. We investigate whether a multivariate representation can be used for this purpose. Pseudorandom sequences were used to inflate thigh cuffs and to administer 5% CO2. Multiple and partial(More)
Blood flow to the brain is controlled by a number of physiological mechanisms that respond to changes in arterial blood pressure, arterial CO2 levels and many other factors. Assessing the integrity of this control system is a major challenge. We report on repeatability of measures based on single and multiple input models during spontaneous and enhanced(More)
The assessment of cerebrovascular regulatory mechanisms often requires flexibly controlled and precisely timed changes in arterial blood pressure (ABP) and/or inspired CO2. In this study, a new system for inducing variations in mean ABP was designed, implemented and tested using programmable sequences and programmable controls to induce pressure changes(More)