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Biomedical subjects

B M Sayers

Publications and source records attributed to B M Sayers.

13 recordsLinked to original sources
PubMed1979

A model of left ventricular function in the denervated heart.

A model has been formulated for the function of the denervated left ventricle. Using the model it is possible to generate realistic waveforms for aortic flow, aortic pressure, left ventricular volume and left ventricular pressure over a wide range of simulated haemodynamic conditions. The effect of changes in contractile state is introduced through the concept of left ventricular pumping capacity. Model results compare well with similar data obtained from denervated hearts in open-chest dogs anaesthetized with halothane under positive pressure ventilation. Simulation of changes in contractile state shows excellent agreement with data published by previous investigators.

Animals↗
PubMed1979

Implementing a computer-based electro-oculographic analysis system.

Electro-oculographic recordings of caloric-induced nystagmus were conducted in a number of normal and disordered subjects. On the basis of the results, implementation of a clinical measuring system is considered; this is based on the interbeat interval, selected in view of its favourable sensitivity and stability. Two stages of processing are involved; first, the determination of the interbeat intervals, second the analysis. The first stage has been implemented off-line on a general purpose computer and also, in on-line mode, by special purpose electronics. The second stage requires computer analysis. We have used the rank magnitude sequences of interbeat intervals as the basis of the analysis.

Adult↗
PubMed1979

Pattern analysis in the study of infantile diarrhoea and other epidemiological problems.

The patterns imposed on records of epidemiological variables by spatial, temporal, and other factors demand a special approach for their identification, characterization, and interpretation. Over the last 10 years, a methodology based on pattern analysis has been developed and put to the test in elucidating selected epidemiological problems. The aim of this approach is to link the pattern or its detailed features to factors likely to be important in understanding the origins of the disease and the mechanisms underlying its occurrence; such knowledge may in turn suggest methods that can be used to control the disease. Pattern analysis provides a battery of techniques that can greatly enhance the cost-effectiveness of epidemiological investigations. To exemplify these techniques, the applications of pattern analysis in the study of the infantile diarrhoeal complex and in elucidating the epidemic spread of wildlife rabies are described. Some other examples are mentioned briefly and comments are made on the more important techniques available.

Animals↗
PubMed1978

Analysis of the occurrence of anencephalic stillbirths in the Fylde Peninsula, 1956--1967.

Computer-based statistical signal methods have been applied to the analysis of case-occurrence time and location data from a 12-year complete series of anencephalic stillbirths in the Fylde peninsula of Lancashire. In the absence of any certainty about causative or contributory factors in these occurrences, the primary questions are if the underlying process is Poisson, or if there is evidence of a seasonal influence, and if any regional differences or communicable factors can be identified. With the limited case numbers (124) most small-sample statistical tests were not sufficiently informative. But using pattern and print-process analysis methods and simulation techniques, further elucidation is possible; for example, it is shown that a seasonally rate-modulated Poisson process is a reasonable model for case occurrences in the southern region, but not in the north, for which a different process must apply and where some evidence exists of clustering of preferred inter-event intervals. It is concluded in particular, that there is a regional dependence, with seasonal factors, of the process underlying case occurrences, and in general, that signal analysis methods are useful in the interpretation of small-sample spatio-tempered epidemiological data.

Anencephaly↗
PubMed1978

Objective specification of the incremental weight variable in weanling diarrhoeal disease of infants.

The objective specification of the second variable (body weight) measured in an epidemiological field study of weanling diarrhoeal disease of infants has been approached by computer-based pattern analysis, complementing previous studies of the diarrhoeal signal of daily defaecation count (DS). The weight data are available for 64 weeks in a subset of 50 out of 139 infants in the study. A weekly incremental weight signal (IWE) was estimated by successively differencing each new observed weight with a smoothed version of the previous value. Variable latency of the different features of this variable precludes the formation of an average-profile by coherent averaging the ensemble of records; a feature-analysis method based on statistical trend analysis was therefore developed. Features of the resulting IWE average profile can be linked to weanling events, transient diarrhoeal episodes, and typical post-neonatal shifts in level of the diarrhoeal signal. The results are consistent with the view that both nutritional and infectious factors operate in most deviations from typical behaviour seen in individual IWE records. In all the infants having an abnormally low (64 week) weight gain, a sustained abnormal DS elevation can be recognized in the 7-15 week period, with recurrent diarrhoeal episodes (type P2, as previously classified) during the 45-60 week period; both abnormalities were associated with substantial effects on weight gain. But individual P2-diarrhoeal episodes occurring before about 40 weeks of age could be linked only to small, quickly-compensated effects on incremental weight.

Body Weight↗
PubMed1977

The spatial correlation of fluctuations of the blood flow in forearm skin.

The oxygen tension at the skin surface, with the atmospheric oxygen supply excluded, may be measured polarographically on the human forearm. Under suitable environmental conditions, spontaneous fluctuations in skin surface oxygen tension can be recorded and these are the result of fluctuating blood flow in the superficial skin vessels. An array of separate cathodes in a single polarographic electrode assembly has been used to measure the fluctuations in blood flow which are occurring simultaneously at seven different points in the skin. Spectral analysis of a long recording of such fluctuations shows that most of the power is concentrated at the lower frequencies but does not reveal any clearly defined dominant frequency. It is clear, however, from inspection of the fluctuation patterns, that recurring bursts of activity occur with quite well-defined periodicities in the range of 30s to 5 min. There is a stronger correlation between the fluctuations occurring at points on the skin surface less than 1 mm apart than between points further apart, although there are clearly some components which are common to points separated by up to 5 mm which was the largest separation of cathodes used in these experiments. These observations are supported by the value of cross correlation coefficients between the channels. These results suggest that the observed fluctuations are the result of at least two factors. The first one is common to all the channels but the effect of this may be overridden by a second and more local one controlling the blood flow.

Arm↗
PubMed1977

The changes in configuration of the rib cage and abdomen during breathing in the anaesthetized cat.

1. The external surface of the rib cage and abdominal wall in anaesthetized cats was surgically exposed in order to record their movements cinematographically in spontaneous breathing and in paralysed cats, during artificial positive pressure ventilation. 2. Cine-stereophotography was used to allow the recording of the movements of a set of markers placed on the external surface of the trunk wall and the corresponding stereometric data were numerically and graphically processed into three-dimensional drawings. The cine-film frames corresponding to the phases of maximum inflation and deflation of the lungs were analysed to reveal the changes in configuration associated with the respiratory movements of the trunk wall. 3. The changes in shape of the diaphragm and the diaphragm and the displacements of the abdominal viscera between extreme inflation and deflation were recorded by X-ray photography. 4. During spontaneous inspiratory movements, the ribs rotated outwards and rostrally about the costovertebral joints, bringing about an increase in the transverse dimensions of the cage all along its length; these movements were accompanied by a clear-cut caudad displacement of the sternum, caused by the straightening of the costal cartilages and by the widening of the angles defined at sternochondral joints between the sternum and each of the costal cartilages. 5. Neuromuscular blockade abolished muscle tone in the trunk wall, allowing the weight of the viscera markedly to deform its configuration. 6. The inspiratory rib movements of the paralysed animal during artificial inspiration were similar to those during spontaneous breathing but the movements of the sternum were inverted and showed small cranial displacements. 7. The loss of muscular tone under neuromuscular blockade made the abdominal wall more compliant than the rib cage to the positive lung pressure and allowed greater mobility of the viscera with consequent distortion of the shape of the diaphragm. 8. The role of rib cage muscle tone in meeting requirements of purely configurational character in such a shell-like structure is discussed in relation to the optimal mechanical performance of the diaphragm.

Abdominal Muscles↗
PubMedDate not supplied

Fully objective ERA by phase spectral analysis.

A method of ERA using the Vertex potential is presented which is entirely objective. The result is given by means of a statistical evaluation which is derived automatically. The method is based on pattern analysis of the V-potential, the technique relying essentially on analysis of the phase spectrum of the appropriate Fourier components.

Acoustic Stimulation↗
PubMedDate not supplied

Pattern analysis of auditory-evoked EEG potentials.

A pattern analysis approach to the detection of auditory evoked potentials in the EEG is reported. Pattern aspects of individual post-stimulus responses have been examined first through their correlation coefficients using the suprathreshold average evoked potential as a reference pattern, and second by the ensemble distribution of phase values of Fourier spectral components, employed to characterise signal pattern. The correlation study indicated that suprathreshold stimuli act to increase the reference pattern similarity of individual records. Individual harmonic phase values are distributed approximately uniformly for unstimulated EEG, but were demonstrated to be increasingly aggregated for increasingly suprathreshold stimuli. It is proposed that a fully objective audiometric technique can be based on a phase-spectral technique.

Acoustic Stimulation↗