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Biomedical subjects

K J Reynolds

Publications and source records attributed to K J Reynolds.

18 recordsLinked to original sources
PubMed2005

The comparison of different feed forward neural network architectures for ECG signal diagnosis.

The electrocardiograms (ECGs) record the electrical activity of the heart and are used to diagnose many heart disorders. This paper proposes a two-stage feed forward neural network for ECG signal classification. The research is aimed at the design of an intelligent ECG diagnosis tool that can recognise heart abnormalities while reducing the complexity, cost, and response time of the system. A number of neural network architectures are designed and compared for their ability to classify six different heart conditions. Two network architectures based on one stage and two stage feed forward neural networks are chosen for this investigation. The training and testing ECG signals are obtained from MIT-BIH database. The network inputs are comprised of 12 ECG features and 13 compressed components of each heart beat signal. The performance of the different modules as well as the efficiency of the whole system is presented. Among different architectures, a proposed multi-stage network named NET_BST possesses the highest recognition rate of around 93%. Therefore, this network proves to be a suitable candidate in ECG signal diagnosis systems.

Algorithms↗
PubMed2004

Reducing power line interference in digitised electromyogram recordings by spectrum interpolation.

Interference from power lines (50 or 60 Hz) is the largest source of extraneous noise in many bio-electric signals and is within the bandwidth of many such signals. In this study, two different methods were compared for their efficacy in removing 50 Hz noise added to surface electromyogram (EMG) signals free of power line interference. The first was a simple second-order recursive digital notch filter. The second was an approach called spectrum interpolation, in which it is assumed that the magnitude of the original 50 Hz component of the EMG signal can be approximated by interpolation of the amplitude spectrum of the signal. When the spectrum was based on records containing an integer number of cycles of 50 Hz interference, and the frequency resolution was finer than 1 Hz, spectrum interpolation performed similarly to, or significantly better than, the notch filter (p < 0.01). It was also possible to make spectrum interpolation more robust than the notch filter. The Pearson squared correlation coefficient r2 between clean signals and signals processed using the notch filter was reduced from 0.98 to 0.65 when the interference frequency was increased by 0.5 Hz, but r2 for spectrum interpolation at 0.2 Hz resolution was only reduced from 0.99 to 0.85 if spectral values between approximately 49.5 and 50.5 Hz were modified by interpolation.

Artifacts↗
PubMed2002

Learning to apply effective cricoid pressure using a part task trainer.

An anatomically-correct model of a larynx inside a head and neck model was constructed so that the location, direction and amount of force applied to the neck could be measured. Fifty trained staff from three general hospitals were then asked to apply cricoid pressure on the model. None was able to state the force that should be applied (30 N), and only five (10%) actually applied cricoid pressure effectively. After training using the model, 45 (90%) applied cricoid pressure correctly (p < 0.001). This study demonstrates that improved training in cricoid pressure is needed and supports earlier researchers who suggested that this can be achieved using simulators.

Anesthesiology↗
PubMed2000

When are we better than them and they worse than us? A closer look at social discrimination in positive and negative domains.

This article argues that in-group favoritism occurs on positive and negative dimensions only when the dimensions of comparison provide an appropriate and meaningful basis for self-other definition, that is, when traits comparatively and normatively fit in-group-out-group categorizations. Three studies are reported in which groups were evaluated on positive or negative traits that varied in their degree of normative fit to in-group and out-group identity. In line with predictions, fit rather than stimulus valence was the crucial determinant of (a) in-group favoritism and (b) absolute level of differentiation between groups. Implications of the findings for explanations of positive-negative asymmetry and broader understandings of intergroup discrimination are discussed.

Adult↗
PubMed1997

Tendon organ sensitivity to steady-state isotonic contraction of in-series motor units in feline peroneus tertius muscle.

1. Measurements have been made of the sensitivity of tendon organs to steady-state, isotonic contractions of single and groups of in-series motor units in the peroneus tertius muscle of the cat hindlimb. 2. Linear relationships were found between the Ib afferent discharge and the contractile tension generated by tetanic stimulation of single motor units. These relationships held for the fast, fatiguable (FF) units and for all but the lowest tensions generated by the slow (S) and some fast, fatigue resistant (FR) units. The sensitivity of the organs was independent of the contractile properties of the units. 3. Groups of three motor units were stimulated isotonically at low rates (around 30 Hz), but asynchronously to produce a smooth tension profile. Again, linear relationships pertained between the discharge rate and the tension, and the sensitivity was the same for different motor unit types. 4. Under isotonic conditions, therefore, the tendon organs showed linear responses to the tension with similar sensitivities, indicating that tendon organs may have the capacity to signal faithfully steady-state contractile tensions.

Afferent Pathways↗
PubMed1997

Advances in capillary electrochromatography.

Capillary electrochromatography (CEC) is a hybrid between capillary electrophoresis and high performance liquid chromatography (HPLC) that has gained popularity in recent years. CEC uses an electrically driven flow to transport the solutes through the chromatographic column. Separation can be achieved by differential partition between two phases, differential electromigration, or a combination of these two. Herein, the main features of CEC are presented, including basic principles and a literature overview on different practical approaches used.

Chromatography, High Pressure Liquid↗
PubMed1997

Spectral pattern of neonatal cerebral blood flow velocity: comparison with spectra from blood pressure and heart rate.

The cerebral blood flow velocity (CBFV) frequency spectra were studied in 106 premature and term newborns (gestational age range. 24-42 wk) and compared with the heart rate (HR) and mean arterial blood pressure (BP) spectra over the 0.005-0.5 Hz range. CBFV, BP, and HR were shown to have similar but not identical spectral patterns. Adjustment of a l/f model to these spectra produced highly significant fittings, but the residuals were not independent. This condition was met only by the CBFV and BP spectra over a limited frequency range (0.005-0.06 Hz). These results provide a characterization of the CBFV spectra for a much larger population of newborns than hitherto available, indicating that under certain conditions CBFV and BP might show the properties of chaotic systems. In infants without major complications, gestational age (GA) did not have a significant influence on the CBFV spectrum, whereas the spectral power to 0.5 Hz of both BP and HR was found to increase with GA. The spectral power increased over the first 24 h of postnatal life for all three variables: only CBFV showed a significant spectral change in the low frequency (LF, 0.02-0.08 Hz) range. A matched group comparison, adjusted for GA and postnatal age, indicated a reduction in CBFV LF power for term infants with birth asphyxia when compared with normal infants, which was not reproduced in the HR spectra.

Aging↗
PubMed1996

Effects of lead on growth plate chondrocyte phenotype.

Lead toxicity is a major public health problem in the United States. The skeleton serves as the major reservoir for ingested lead, where it is incorporated into bone matrix during calcification. While lead in bone has been considered inactive, mounting clinical and epidemiological data has shown a strong correlation between lead exposure and adverse effects on stature in children. These epidemiologic data suggest a direct effect of lead on skeletal development, but whether it reflects a systemic effect, a specific effect on osteoblasts, or an effect on the epiphyseal growth plate is as yet unclear. This study examined the effects of lead on parameters of cartilage biology in isolated chondrocytes. Changes in growth plate chondrocyte phenotype were assessed utilizing an established avian growth plate chondrocyte model. Low, sublethal doses of lead caused specific and significant effects on a number of important markers of growth plate chondrocyte phenotype, including suppression of alkaline phosphatase and both type II and type X collagen expression at the protein and mRNA levels, and a decrease in thymidine incorporation. In contrast, proteoglycan synthesis was stimulated relative to controls in lead-treated cultures, suggesting that the alterations in collagen and DNA synthesis and alkaline phosphatase activity are not due to cytotoxity. The data demonstrate important regulatory effects of lead on growth plate chondrocytes in cell culture and suggest an inhibitory effect on the process of endochondral bone formation. The growth plate may be one of the key target tissues accounting for the adverse effects of chronic lead exposure on skeletal development.

Animals↗
PubMed1995

Detection of mechanical changes to prosthetic heart valves by spectral analysis of valve closing sounds.

This study investigates the possibility of using spectral analysis of the closing sounds of a prosthetic heart valve to indicate minor changes to its mechanical state. Sounds are recorded in vitro in a large effectively anechoic tank of water, and the elastically mounted valve is actuated pneumatically within the water. This provides a noise-free environment for recordings. Analysis of the valve sounds is by spectral averaging and digital filtering, with each individual valve used to create its own filter. Results show that it is possible using this technique to detect reliably changes in the mechanical state of a valve, such as the addition of a small mass to the structure of the valve.

Acoustics↗
PubMed1995

Acoustic analysis of the closing sounds of implanted prosthetic heart valves.

Previous in vitro studies [K. J. Reynolds, Ph.D. thesis (1994); K. J. Reynolds and R. O. Stephen, J. Acoust. Soc. Am. 97, 60-68 (1995)] have shown that it is possible to detect minor mechanical changes to a prosthetic heart valve by acoustic analysis of the valve's closing sounds. This current study investigates the sounds produced by prosthetic valves implanted in patients. To reduce signal distortion at the thoracic surface, recordings were made with the patient submerged in water. Results show that stable reproducible averaged spectra can be obtained from implanted valves provided recording conditions are kept constant. The respiration cycle does not affect the recorded spectrum.

Acoustics↗
PubMed1993

The effect of dyshemoglobins on pulse oximetry: Part I, Theoretical approach and Part II, Experimental results using an in vitro test system.

Pulse oximeters are known to be inaccurate in the presence of elevated concentrations of carboxyhemoglobin and methemoglobin. This paper attempts to alleviate some of the confusion that exists between fractional and functional saturation, and to clarify the comparison of each with SpO2. A series of theoretical relationships between pulse oximeter reading (SpO2) and actual oxygen saturation (both fractional and functional) is derived using simple absorption theory. The theoretical relationships are checked using an experimental in vitro test system. This consists of a blood circuit containing a model finger, capable of simulating the pulsatile transmission signals through a real finger. Theoretical predictions and experimental results are compared and are found to agree well in the presence of carboxyhemoglobin, but less well with methemoglobin. Possible reasons are discussed.

Absorption↗
PubMed1992

In vitro performance test system for pulse oximeters.

An in vitro system was developed capable of testing the accuracy and reproducibility of pulse oximeter readings. The pulse oximeter probe receives signals through a pulsating blood cuvette. The development of the design of the cuvette is described. Using the final design (or 'model finger'), a comparison is made between readings from a Datex Satlite pulse oximeter (SpO2) and saturation values obtained by use of a multi-wavelength bench oximeter (SaO2). Linear regression analysis of the data gives SpO2 = 0.88 SaO2 + 11.2 (r = 0.979, p < 0.001).

Fingers↗
PubMed1992

Response of 10 pulse oximeters to an in vitro test system.

Pulse oximeters are often used in situations in which severe hypoxaemia may occur. We have developed an in vitro system to test the accuracy of pulse oximeter calibration. The probe of 10 different oximeters was attached to a model finger in an in vitro blood circuit, and pulse oximeter readings (SpO2) were compared with multi-wavelength in vitro oximeter readings (SO2) over a range of SO2 values from 50 to 100%. The oximeters tested varied widely in their accuracy and linearity. We conclude that the system can test the accuracy, reproducibility and linearity of response of pulse oximeter readings at low oxyhaemoglobin saturations.

Calibration↗
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↗
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↗