Search PubMed⌕ Search

Biomedical subjects

L Tarassenko

Publications and source records attributed to L Tarassenko.

30 records · Page 2Linked to original sources
PubMed1992

Quantitative optical determination of the viability of platelet concentrates.

An optical method to assess platelet viability in platelet transfusion concentrates has been developed which is based on the observation that healthy, discoid platelets transmit more light in shear flow than aged, spherical cells. Using a specially designed glass channel, the rise in transmission of light through platelet samples with agitation is referenced against a measurement of transmission without flow. Referencing the measurements may minimize the effects of red blood cell contamination, as well as other variations among platelet packs such as plasma characteristics and plastic container variability. At an optimal frequency of agitation, the ratio of the transmission of light with agitation to that of the sample at rest is found to correlate highly with the concentration of discoid platelets, r = 0.92 to 0.95 (P less than 0.001), for light sources including a HeNe laser and two LEDs. Using this index, the discoid platelet counts of twelve platelet packs are estimated and compared with manual counts. The mean difference between the two methods was 0.009 x 10(9) discoid platelets ml-1 with a standard deviation of 0.11 x 10(9) cells ml-1. We conclude that the method may be applied to the development of a non-invasive device to monitor the concentration of viable, discoid platelets in storage.

Blood Platelets↗
PubMed1992

An optical method for the determination of platelet count in platelet samples contaminated with red blood cells.

We present a simple photometric method to determine the total concentration of platelets present in a sample independently of red blood cell concentration. Standard optical density curves for platelet samples ranging in concentration from 0 to 1.5 x 10(9) cells/ml and contaminated with red blood cells ranging in concentration from 0 to 0.03 x 10(9) cells/ml are determined. A study of the absorbance spectra of red blood cells and platelets suggests that by calculating the absorbance difference between two wavelengths, an estimate of red blood cell concentration can be made. Then, in the second step of this two-step method, the individual absorbance measurements at the two wavelengths are matched to the standard values determined previously to derive an estimate of platelet concentration. In a trial of 62 unknown platelet samples contaminated with red blood cells, the standard deviation for the error in platelet count was 0.16 x 10(9) cells/ml with a mean difference of 0.011 x 10(9) platelets/ml. We conclude that our method may be useful in laboratories not equipped with electronic cell counters as well as in applications such as the development of noninvasive measurements of platelet concentration in platelet transfusion packs.

Erythrocytes↗
PubMed1991

In vitro investigation of the factors affecting pulse oximetry.

The effect of a number of physiological parameters on pulse oximetry accuracy has been investigated in an in vitro model. We have found that above 50% saturation, pulse oximeters will not be affected by variations in haematocrit, blood flow rate, tissue blood content and pulse amplitude. At low saturations, however, it is known that the accuracy of pulse oximeters decreases and our in vitro results suggest how this may be corrected.

Blood Flow Velocity↗
PubMed1991

Temperature dependence of led and its theoretical effect on pulse oximetry.

Ambient temperature is known to affect the emission spectrum of a light-emitting diode (LED). This study has investigated the effect of changes in ambient temperature on the emission spectra of two LED with peak emission wavelengths similar to those used in pulse oximetry. There was a 5.5-nm increase in the peak wavelength for a 660-nm LED, and a 7.8-nm increase in the peak wavelength for a 950-nm LED as temperature increased from 0 to 50 degrees C. Using a simple theoretical model based on the Beer-Lambert law, the effect of these shifts in wavelength on pulse oximeter accuracy was examined and found to be negligible over the temperature range studied.

Electrodes↗
PubMed1991

Absorption and multiple scattering by suspensions of aligned red blood cells.

The analytical theory of multiple scattering [J. Opt. Soc. Am. 60, 1084 (1970)] permits predictions of scattering patterns by homogeneous suspensions of aligned and randomly oriented particles. Predictions for randomly oriented particles have been tested previously. Using an optical system involving a He-Ne laser and suspensions of red blood cells, we tested the theory's predictions for scattering by suspensions in two distinct alignments. The qualitative effects of cell alignment on light scattering are consistent with those predicted, although measured differences in scattering between the two alignments exceed those predicted. We conclude that the theory may provide an optical means of distinguishing particle orientation in multiple scattering suspensions.

Absorption↗
PubMed1988

Quantitative analysis of immunological reactions on silicon surfaces by multiple-angle Brewster angle reflectometry.

An optical biosensing instrument has been developed for the quantitative analysis of immunological reactions on biochemically sensitized surfaces. It is based on the measurement of reflectance changes of polarized laser light incident on high refractive index substrates at angles close to the pseudo-Brewster angle. Multiple-angle Brewster angle reflectometry (MABAR) has been used to investigate the binding of anti-human serum albumin (a-HSA) to human serum albumin (HSA) coated silicon surfaces. The concentration dependence and reaction kinetics of antibody-antigen complex formation have been studied using red and green He-Ne laser light. A significant increase in sensitivity has been observed with green light.

Antibodies↗
PubMed1987

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↗
PubMed1983

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↗
PubMedDate not supplied

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↗
PubMedDate not supplied

Neural networks.

Explore the source record for details and available documents.

Neural Networks, Computer↗