Anthony A. Birch

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BACKGROUND AND PURPOSE The aim of this study was to test the hypothesis that the phase difference that occurs between an induced oscillation in blood pressure and the resultant oscillation in middle cerebral artery (MCA) flow velocity could reflect the competence of cerebral autoregulation. METHODS Fourteen volunteers performed 19 cycles of 10 seconds of(More)
A forced periodic variation in blood pressure produces a similar variation in cerebral blood velocity. The amplitudes and phases of the pressure and velocity waveforms are indicative of the dynamic response of the cerebral autoregulation. The phase of the velocity leads the pressure; the greater the phase difference the faster the autoregulation response.(More)
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)
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)
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)
The objective of this report is to highlight the potential for false pressure measurements from systems that combine intracranial pressure (ICP) measurement and ventricular drainage. If the ports of the drain become blocked to the extent that they present a high resistance to cerebrospinal fluid flow, then a significant pressure gradient between the inside(More)
The objective of this work was to determine if systematic differences exist between blood pressure time series measured by two non-invasive techniques. Cerebral blood flow autoregulation is often measured while a change in blood pressure is induced by deflation of thigh cuffs. To interpret the result a continuous measurement of arterial blood pressure is(More)
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. We made TMD observations on normal and acutely comatose children presenting to Kilifi(More)