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Biomedical subjects

M G Pepper

Publications and source records attributed to M G Pepper.

At least 19 recordsLinked to original sources
PubMed1995

Monitoring respiratory activity in neonates using diaphragmatic electromyograph.

The monitoring of the development of respiratory function in low-birth-weight or sick neonates is important in its overall treatment. The most direct approach to obtaining information on respiratory function is to monitor the activity of the diaphragmatic muscular system rather than measure the resultant change in lung volume or ventilator output, which cannot be guaranteed to be directly related to the neonate's own respiratory activity. The system was designed to assess the feasibility of monitoring respiratory activity in such neonates by measuring the diaphragmatic electromyograph. It is hoped that this system can be used to monitor the development of lung function and possibly, if reliability proves adequate, the synchronisation and control of ventilator assistance. To monitor the EMG, the dominant effect of the ECG was removed using a digital processor. Initial clinical measurements indicate that neonatal respiratory activity can be monitored by measuring the diaphragmatic EMG. Comparative measurements show the EMG method is faster in detecting the inspiratory phase of a breath. Measurements on ventilated neonates showed the presence of intermittent respiratory activity. It also is proposed that clinically relevant information may be deduced from the analysis of the morphology of the detected EMG waveform.

Diaphragm↗
PubMed1991

Noninvasive detection of ventricular wall motion by electromagnetic coupling. Part 1. Theory: the changes in the reflected impedance of a coil over a semi-infinite medium with properties ranging from lossy dielectric to a conductor.

Radiofrequency coils are used as sensors in various applications such as nuclear magnetic resonance (NMR) imaging and displacement cardiograms (DCGs). In most cases the impedance and the resonant frequency of the coil are monitored to provide the required information. The paper describes the changes in reflected impedance and in resonant frequency of a coil when it is placed near a medium with properties ranging from a lossy dielectric to a pure conductor. The theory of interaction between the coil and the medium is investigated and a model based on the use of vector potentials is developed. One prediction of the theory is that placing the coil over body equivalent saline (lossy dielectric) at 15 MHz results in an increase in the inductance of the coil and a resultant decrease in resonant frequency. This prediction was supported experimentally.

Electromagnetic Fields↗
PubMed1991

Noninvasive detection of ventricular wall motion by electromagnetic coupling. Part 2: Experimental: cardiokymography.

The cardiokymograph or displacement cardiograph (DCG) is a noncontacting device which senses movement of the heart throughout the cardiac cycle by the interaction of a radiofrequency (10-20 MHz) electromagnetic field, generated by a sensing coil, with the thorax. In the paper three different techniques of detecting this movement will be discussed: monitoring the changes in sensing resonant frequency (FM modulation), monitoring the changes in impedance of the coil at resonant frequency (AM modulation) and a new technique which monitors the changes in coil impedance at fixed frequency. The sensitivities of these three techniques will be compared. A simplified theory of the mode of coupling between the coil and the thorax will be studied in terms of a transformer model. Preliminary clinical measurements of anterior left and right ventricular motion will be given. The presence of higher-frequency features related to atrial motion and the opening and closing of the aortic and pulmonary values will also be described.

Electromagnetic Fields↗
PubMed1986

Evaluation of light sources and light guides for use in transurethral surgery.

An evaluation of the quality of light sources and guides was carried out in response to a demand that sufficient light intensity should always be available for transurethral procedures when bleeding occurs. A light monitor was developed for the rapid assessment of the source intensity and light guide transmission. A simple test protocol was also developed for routine assessment of the sources and guides and for evaluation of new sources and guides before purchase. The sources and guides were classified in order of merit and coded to permit the selection of those of the highest quality; this guarantees a satisfactory level of illumination during surgery.

Electronics, Medical↗
PubMed1984

An on-line ultraviolet radiation monitoring system for control of photosensitivity test dose.

A system has been developed to monitor and integrate on-line a small fraction of the monochromatic ultraviolet radiation directed at the skin from a phototest source, thus correcting for fluctuations in the irradiance. On completion of the required test dose, the exposure is terminated automatically. Radiation is reflected from a silica plate, housed in a skin applicator, onto a photodiode connected to an integrator. The variation of the reflectivity of the silica plate with wavelength and with incident angle was calculated. The reflectivity of the applicator with and without the silica plate in situ was studied experimentally. Measurements were made of the spatial distribution of irradiance from and across the face of the applicator. To calibrate the photodiode current, the absolute irradiance at the face of the applicator had to be measured with a wide angle detector. No significant deviation from a linear variation was observed between changes in the skin irradiance and changes in the photodiode current.

Humans↗
PubMed1984

A pre-set ultraviolet dose meter.

The design, construction and performance of an ultraviolet radiation (UVR) pre-set dose meter is described. The meter simultaneously displays irradiance, dose, and elapsed time, and incorporates a calibrated variable gain control to permit use with detectors of varying sensitivity. The meter has been developed to permit the automatic administration of UVR dose in photosensitivity testing. The UVR is generated by a Xenon lamp and delivered to the patient via a monochromator and liquid filled light guide. A beam-splitter in the light guide applicator diverts a small fraction (9%) of the UVR onto a photo-diode detector connected to the meter. When the dose recorded by the meter reaches the pre-set value the meter activates a solenoid which closes the monochromator exit slit shutter. This on-line control of the dose ensures that any fluctuations in irradiance are compensated so that the pre-set test dose is always administered to within the 1% accuracy of the instrument.

Humans↗
PubMed1983

A meter for ultraviolet dose and irradiance.

A compact, portable, battery-powered meter has been developed to monitor and to integrate ultraviolet irradiance. The meter has been designed to accept signals from either a thermopile or a solid-state (GaAsP) diode detector. A variable scale factor is provided to accommodate a range of different detector sensitivities. The measurable irradiance range is 100 microW cm-2 to 100 mW cm-2 and that of dose is 200 mJ cm-2 to 200 J cm-2. The meter can be operated manually or for a range of preset times. The irradiance, dose and elapsed times are displayed. Outputs from the preamplifier and from the scaling amplifier are available for interfacing the instrument with a computer or chart recorder. The meter has been designed to have an overall measurement uncertainty of the order of 1% in order to ensure that the major error contribution lies with the detecting devices.

Humans↗