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Biomedical subjects

D E Maynard

Publications and source records attributed to D E Maynard.

At least 19 recordsLinked to original sources
PubMed1997

A dual coordinate system finite difference method for forward and inverse solutions of the volume conductor problem in neurology.

Finite difference methods for the volume conductor problem have used a single coordinate system for the mesh and made approximations of Laplace's equation. This method is simple but has two major problems. Firstly, to deal with boundary conditions properly, the normal potential gradient at the boundary must be known. However it is complicated to compute at a curved surface point. Secondly, for an inverse solution the equation on a curved boundary is difficult to reverse since more than one inner mesh node appears in the approximation equation for each surface point. The new method developed in this paper is a dual coordinate system. One system serves as a frame mesh, the other is a sub-coordinate system in which surface points become mesh points (regular nodes). The equation at each surface point is then directly reversible since only one inner point appears in the equation. The forward solution is applied to both centric and eccentric bone models and uses the conventional successive over-relaxation (SOR) method. Noise is added to this solution for input to the inverse procedure which is a direct step-in non-iterative method. Low pass filtering was effective in reducing the effects of noise. In the examples given, only one coordinate subsystem is used but, for complex shape boundaries, multiple subsystems would be necessary.

Action Potentials↗
PubMed1987

The hydro-electroencephalogram, a novel method of EEG recording.

A novel method is described of recording EEG by means of electrodes in de-ionised water in which the scalp is immersed. It permits large numbers of closely packed electrodes to be connected quickly both in the plane of the scalp and three-dimensionally. A common reference potential can be derived from the whole immersed scalp. The technique should be suitable for the practical application of mathematical methods of source location where large numbers of electrodes are required.

Brain↗
PubMed1986

The effect of halothane on cerebral electrical activity. An assessment using the cerebral function analysing monitoring (CFAM).

Recordings of cerebral electrical activity were obtained using the cerebral function analysing monitor from eight unpremedicated patients anaesthetised with increasing concentrations of halothane in oxygen. The amplitude of the processed EEG increased at one and decreased at two minimal alveolar concentrations. The frequency distribution of the weighted EEG signal showed a linear increase of delta activity with a corresponding decrease in beta activity with increasing concentrations of halothane.

Action Potentials↗
PubMed1986

Anaesthesia with ICI 35,868 monitored by the cerebral function analysing monitor (CFAM).

Ten patients who received bolus doses of the cremophor formulation of ICI 35,868 were monitored using the Cerebral Function Analysing Monitor (CFAM). Visual inspection of the traces obtained showed an easily recognizable pattern which was associated with an increasing depth of anaesthesia. Statistical analysis showed a high correlation between venous blood levels of the drug and changes recorded by the CFAM, although there was marked inter-patient variation. It is suggested that this variation is due to the effect of a time-lag between changes in drug concentration in the brain and venous blood.

Adult↗
PubMed1984

Changes in cerebral electrical activity measured by the Cerebral Function Analysing Monitor following bolus injections of thiopentone.

Seven premedicated patients were anaesthetized with thiopentone administered incrementally every 180 s while cerebral electrical activity was recorded with the Cerebral Function Analysing Monitor (CFAM). Arterial blood samples were collected at 40, 90 and 165 s after each bolus of thiopentone for the measurement of plasma total and bound thiopentone concentrations. The correlation between free thiopentone concentration and the CFAM representation of mean electroencephalogram (EEG) amplitude was -0.78 (P less than 0.001), excluding values following the first two boluses. Beta band percentage activity was inversely related (r = 0.70-0.90; P less than 0.05- less than 0.001) and delta directly related (r = 0.76-0.86; P less than 0.05- less than 0.001) to log of free thiopentone concentration, including all values. The closest correlations (beta, r = 0.88, P less than 0.001; delta r = 0.80, P less than 0.001) were found at 90 s after each bolus.

Adolescent↗
PubMed1984

The cerebral function analysing monitor. Initial clinical experience, application and further development.

The cerebral function analysing monitor is a development of the cerebral function monitor. It produces a more detailed analysis of the electroencephalogram (EEG) amplitude and analyses the frequency of the waveforms into standard beta, alpha, theta and delta bands. It can analyse the EEG from two input channels, produce traces of the standard EEG, and compute visual, auditory, somato sensory and brain stem evoked potentials.

Anesthesia, General↗
PubMed1984

The effect of nitrous oxide on cerebral electrical activity.

Recordings of cerebral electrical activity produced by the cerebral function analysing monitor ( CFAM ) were obtained from nine healthy volunteers breathing increasing concentrations of N2O in O2. Concentrations of 30 and 50% N2O produced significant reductions in CFAM trace amplitude. Withdrawal of N2O resulted in an increase in amplitude with an initial increase above the control level. There were no consistent changes in the frequency distribution of the weighted electroencephalographic signal with increasing concentrations of N2O.

Adult↗
PubMed1984

Cerebral function monitor studies in neonates.

Cerebral function monitor (CFM) recordings were obtained from 107 neonates, considered by pediatricians to be neurologically normal on discharge from hospital. Maturational changes in sleep patterns for the tracings over the conceptional age range 30 to 43 weeks were quantified and the resulting EEG measures analyzed statistically. When tracings obtained from neonates of less than three weeks chronological age were considered, significant correlations were found with the weight of the neonate at the time of the recording. For tracings of premature neonates obtained at the mean chronological age of six weeks a relationship was found between EEG measures and Apgar scores. These results are discussed in relation to the mature neonatal EEG, and it is suggested that the CFM provides a simple additional method of assessment.

Apgar Score↗
PubMed1983

The cerebral function analysing monitor (CFAM). A new microprocessor-based device for the on-line analysis of the EEG and evoked potentials.

A description is given of a new microprocessor-based device for EEG analysis. The Cerebral Function Analysing Monitor (CFAM) analyses the EEG amplitude and frequency distribution. It produces a detailed plot of amplitude trends and separate traces of the percentage activity in each of the classical EEG frequency bands. Its clinical application was studied in five patients anaesthetized with thiopentone, and nitrous oxide and halothane in oxygen. During maintenance of anaesthesia, there was a gradual decrease in EEG amplitude and shift towards lower frequency EEG activity. Discontinuation of nitrous oxide resulted in a marked increase in EEG amplitude and an increase in alpha and beta band activity. Discontinuation of halothane resulted in smaller alterations in the CFAM trace. This device provides easily interpreted processed EEG data and merits further investigation.

Adult↗
PubMed1979

Intrapartum fetal monitoring with the cerebral function monitor.

We report a trial of the technical feasibility of monitoring the state of the fetal brain during labour using the Cerebral Function Monitor (CFM). This device was developed for long-term monitoring of the electroencephalogram (EEG). A tripolar scalp electrode allows removal of the fetal electrocardiograph (ECG) from the fetal EEG. Technically satisfactory recordings were obtained from 15 fetuses during labour for periods of up to 6 1/2 hours before delivery. There were alterations of CFM trace with fetal distress and also during general anesthesia for Caesarean section.

Anesthesia, General↗
PubMed1979

EEG processing by the Cerebral Function Monitor (CFM).

The Cerebral Function Monitor (CFM) is a machine designed to monitor EEG over long periods of time from hours to several days. It produces on a slow speed chart recorder a write-out of a processed EEG signal in parallel with a continuous measurement of electrode impedance. A description is given of the way in which the CFM processes both EEG and electrode impedance information. Some CFM applications are mentioned.

Brain↗
PubMed1979

Removal of EKG from fetal CFM recordings.

The monitoring of fetal EEG during labour can assist in identifying the effects on the fetus of anaesthetic and other drugs administered to the mother. Additionally it assists in detecting inadequate cerebral perfusion. One unsuccessful and one successful method are described of removing fetal EKG from the fetal EEG signal, so enabling the Cerebral Function Monitor to be used to monitor the fetal EEG. Examples of results are given.

Brain↗
PubMed1979

Development of the CFM: the Cerebral Function Analysing Monitor (CFAM).

Use of the Cerebral Function Monitor (CFM) to monitor anaesthetic procedures has led to improvements of design. A standard CFM can be modified to enable it to be controlled by a microprocessor. An altered chart output format is produced which incorporates both frequency information and a better indication of trends. Alpha-numerical information can be given on a visual display unit. The extended instrument, of which preliminary details are given, is called the Cerebral Function Analysing Monitor (CFAM).

Anesthesiology↗
PubMed1978

E.E.G. monitoring for the control of anaesthesia produced by the infusion of althesin in primates.

The continuous infusion of Althesin under electroencephalographic (e.e.g.) control provided a constant level of light anaesthesia for periods of 1--5.5 h during experimental brain hypoxia in spontaneously breathing baboons and Rhesus monkeys. Polygraphic records (respiration, heart rate, arterial pressure, cerebral venous sinus pressure, end-tidal gas concentrations) and also estimation of blood-gas tensions, pH, and concentrations of pyruvate and lactate demonstrated a steady physiological state. Various methods of e.e.g. monitoring were tested to establish an optimal assessment of depth of anaesthesia as a guide to the control of the rate of infusion of Althesin. A purpose-built modification of the Cerebral Function Monitor was found to give unequivocal recognition of changing depths of anaesthesia.

Alfaxalone Alfadolone Mixture↗