Platelet transfusion therapy: platelet concentrate preparation and storage.
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Blood Donors↗
Biomedical subjects
L Tarassenko
Publications and source records attributed to L Tarassenko.
Impedance imaging in the newborn.
We have been investigating the use of electrical impedance methods for the study of cerebral haemodynamics in the newborn for many years. Of particular interest has been the early detection of intraventricular haemorrhage, which is a major cause of death or handicap in low birthweight infants. Several problems exist in obtaining representative impedance measurements from the newborn, most notably movement artefact, respiratory-based modulation and a blood-flow related pulsatile component. Movement artefact is by far the most significant problem; in order to perform long-term monitoring we have developed an effective algorithm for rejection of corrupted data. To remove the respiratory component, which can be 1-2% of the impedance measurement, we link to the output of a respiratory monitor (standard in intensive care units) as a means of synchronising measurements to a fixed point in the respiratory cycle. Similarly, to remove the blood-flow pulsatile component, measurements are gated from the R-wave of the recorded ECG. Our total system consists of a front-end measurement system that passes image data over a serial link to a host computer. Data storage, image reconstruction and display is performed on the host, which can be any of a wide range of personal computers. The front-end contains the impedance measurement circuit, electrode switching electronics and a microprocessor for control, and is of a sufficiently small size to fit into the incubator next to the baby. Incorporating a microprocessor into the front-end produces a very flexible system that has many benefits, including: asynchronous operation from host, 'intelligent' pre-processing of measurements, command driven operation from host, etc. Software development for the front-end is performed on the host with program down-load for interactive debugging. Details of the front-end electronics and software, system performance, preliminary clinical results and other application areas of the impedance imaging technique to the care of the newborn are presented.
Cerebral Hemorrhage↗
Use of digital techniques to process cerebral electrical impedance signals in the new born.
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Cerebrovascular Circulation↗
Cerebral haemodynamics in newborn babies studied by electrical impedance. Preliminary results.
We report studies in which the amplitude of the cardiac-synchronous change in transcephalic impedance, delta Z, has been used in the investigation of cerebral haemodynamics in newborn babies. Three clinical situations, in which cerebral blood flow might be expected to change, have been studied. The impedance signal, delta Z, decreased in size during a tension pneumothorax, increased slightly with feeding, and, during an exchange transfusion of an asphyxiated baby, there was a consistent increase in the size of the signal during infusion of blood and a decrease in size as blood was withdrawn. This method may be useful for the continuous study of cerebral haemodynamics in the preterm baby over prolonged periods.
Cerebrovascular Circulation↗
The effect of varying LED intensity on pulse oximeter accuracy.
Most pulse oximeters automatically alter the intensity of their light-emitting diodes (LEDs) according to the absorption of the finger, toe or earlobe to which they are attached. This paper investigates the effect of changing LED intensity on pulse oximeter accuracy. Our results show that the peak wavelength of a red LED typically increases by 8 nm as its intensity is increased ten-fold. To determine whether this shift introduces a significant error, a simple theoretical model based on the Beer-Lambert law is used. The model predicts that a 10:1 change in LED intensity results in a 2.5% error at 50% arterial oxygen saturation (SpO2). At high saturations (SpO2 greater than or equal to 85%) the model predicts little loss of accuracy and thus any effect due to changes in LED intensity will be apparent only at low saturations.
Equipment Design↗
Neural networks.
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Neural Networks, Computer↗