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Biomedical subjects

J E Saunders

Publications and source records attributed to J E Saunders.

At least 55 records · Page 3Linked to original sources
PubMed1989

Inter-subject variability in the metabolism of proguanil to the active metabolite cycloguanil in man.

1. The metabolism of proguanil to the active metabolite cycloguanil has been evaluated in 135 British Troops and 26 Kenyan schoolchildren. 2. Large inter-subject variability was observed in both plasma and urinary concentrations of proguanil and cycloguanil after standard doses of drug. 3. Based on the ratio of proguanil to cycloguanil (P/C) in urine the British troops formed a non-normal distribution. 90% of the population formed a discrete distribution with P/C ranging from 0.5 to 9.0 while the remaining 10% were scattered throughout the distribution to an extreme value of 39. A similar pattern of variability was observed using P/C from a 6 h plasma sample. 4. This variability was due to differences in the ability of individuals to metabolise proguanil to cycloguanil. 5. Thirteen schoolchildren who had experienced malaria during prophylaxis with proguanil and thirteen matched controls each received proguanil (100 mg). We could not discriminate between the two groups based on P/C ratio in either a 6 h plasma or 0-6 h urine sample.

Adolescent↗
PubMed1987

Physical characteristics of Dornier extracorporeal shock-wave lithotriptor.

Measurements of the pressure, noise, and radiation dose levels from a Dornier lithotriptor are reported. The distribution of the peak pressure around the treatment focus was investigated, and the highest pressures were found to occur within an elongated volume. Within the treatment room, noise levels of 80-90 dB were produced during each shock wave, rising to 95 dB by the patient's head. Ear protection for the staff and patient is recommended, and careful room design is necessary to minimize the sound disturbance to adjacent quarters. Measurements of the radiation skin dose received by patients from the x-ray localization system were relatively high and ranged from 2-55 cGy (rad), with a mean of 12 cGy. The operator needs to be aware of these high doses and should take precautions to minimize them.

Ear Protective Devices↗
PubMed1987

Pressure waveforms generated by a Dornier extra-corporeal shock-wave lithotripter.

Pressure waveforms in the acoustic field generated by a Dornier (HM3) shock-wave lithotripter have been measured using a bilaminar shielded PVDF membrane hydrophone in water. Using these waveforms, values of the peak-positive (p+) and peak-negative pressure (p-) at various positions in the field have been estimated. At the focus, p+ is 38.6 MPa (standard deviation = 9.0 MPa) and p- is 10.1 MPa (standard deviation = 1.0 MPa) at 20 kV discharge potential and an electrode separation in the range 1.3 to 2.4 mm. The peak-positive pressure is found to fall to 50% (-6 dB level) at about 60 mm either side of the focus on the major axis of the reflector and on a 10 mm radius circle around the focus in the focal plane. A shot-to-shot variation of +/- 25% in p+ is attributed to the inherent variability of the electrical discharge which may result in changes in the exact position and strength of the acoustic field. The results reported are considered to be more accurate than those of previous measurements due to the relatively flat frequency response of this type of hydrophone.

Acoustics↗
PubMed1987

Acoustic cavitation generated by an extracorporeal shockwave lithotripter.

Evidence is presented of acoustic cavitation generated by a Dornier extracorporeal shockwave lithotripter. Using x-ray film, thin aluminum sheets, and relatively thick metal plates as targets, evidence of liquid jet impacts associated with cavitation bubble collapse was observed. The jet impact was violent enough to puncture thin foils and deform metal plates. Furthermore, numerous jet impacts were generated over a volume of greater than 200 cm3. It is likely that such violent cavitation will also occur in tissue, and observed biological effects (e.g. renal calculus disintegration and tissue trauma) may be related to cavitation damage.

Lithotripsy↗
PubMed1987

F-M 100-Hue total error scores have discrete values.

A proof is presented which shows that the total error scores derived from the Farnsworth-Munsell 100-Hue test are an integer multiple of 4. The one proviso for this relates to the way in which the first and last caps in a box are handled.

Color Perception Tests↗
PubMed1985

Essentiality of the active-site arginine residue for the normal catalytic activity of Cu,Zn superoxide dismutase.

Chemical modification of bovine and yeast Cu,Zn superoxide dismutases with phenylglyoxal diminishes the catalytic activities by greater than or equal to 98%, and treatment of these enzymes with butanedione plus borate leads to greater than or equal to 96% inactivation. The activity loss is accompanied by the modification of less than two arginine residues per subunit with no concomitant loss of Cu or Zn. The phenylglyoxal-modified enzymes require at least a 20-fold greater concentration of cyanide for 50% inhibition than do the corresponding native enzymes. Polyacrylamide-gel electrophoresis and activity staining of the phenylglyoxal-inactivated enzymes demonstrate that the residual activity is largely associated with modified forms that bear lower net positive charge than the native superoxide dismutases.

Arginine↗
PubMed1985

Displacement thresholds for motion detection under conditions of chromatic adaptation.

The smallest, continuous target displacement which is sufficient to cause a sensation of movement was measured under conditions of chromatic adaptation. The experiments were carried out for test target and background field wavelengths which selectively isolate the activity of the colour mechanisms of the human eye. The results show that, when target detection is largely mediated by the red or green colour mechanism, a target displacement of 2-3' in the foveal region is sufficient to cause a reliable sensation of movement. These displacement thresholds show only a small change as a function of target contrast or background retinal illuminance level. Similar results were obtained when the colour of the test target was the same as that of the background field (e.g. green, yellow or red), when no attempt was made to isolate a single colour mechanism. Test target and background wavelengths which isolate the activity of the blue colour mechanism yield displacement thresholds in the range 5-7' and show a stronger dependence on target contrast and background retinal illuminance level. The experiments were repeated at several eccentricities and the results show that, for a test target and background field of the same colour and under conditions which isolate the green or red spectral response mechanism, the minimum target displacement required for motion detection appears to increase in a manner similar to the centre-width receptive-field size of broad-band, centre--surround transient neurons in the rhesus monkey retina [De Monasterio and Gouras (1975) J. Physiol., Lond. 251, 167-195].(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Ocular↗
PubMed1984

An asymmetry in the optokinetic nystagmus response in normal individuals.

Optokinetic nystagmus (OKN) was induced by using a modified projector system to provide a moving pattern of irregular spots of light. A systematic electro-oculographic study of horizontal and vertical OKN for a series of stimulus velocities from 10 to 100 degrees s-1 was conducted on 10 healthy young subjects. It was found that the vertical responses, in particular to upward-moving stimuli, were less well sustained at velocities above 30 degrees s-1 than the horizontal responses. In view of these observations, care should be taken in the interpretation of OKN results clinically, and only when the response is absent in one direction or an extreme asymmetry is present should clinical significance be attached. This applies particularly for the vertical OKN responses. Clearly, the use of stimulus velocities below 40 degrees s-1 is advised and the standard suggested by Holm -Jensen and Peitersen [Acta oto-lar. 88, 110-116 (1968)] of a target moving at 20 degrees s-1 seems a reasonable choice.

Adult↗
PubMed1982

Discrimination and detection thresholds: the effect of observer criterion on the spatial properties of chromatic and achromatic mechanisms.

Spectral sensitivity functions were determined for structured test targets presented on a white background field. Data obtained for threshold detection of the targets are consistent with results obtained from previous studies which used unstructured test fields showing functions, with three maxima, dependent on opponent colour mechanisms. Data obtained from threshold discrimination measurements show a marked reduction in the blue sensitivity when 1 degree test targets are used. This effect decreases significantly when larger targets are used. A change of the observer's criterion can significantly alter the relative contributions of the achromatic and chromatic channels at threshold.

Color Perception↗
PubMed1981

Metabolism of ethanol by human bone marrow cells.

The ability of human bone marrow cells to metabolise has been studied. After incubation of suspensions of bone marrow cells with [1(-14)C] ethanol (0.1 mg/ml) for 1.5 h, radioactivity was present in the evolved CO(2) and in the cellular lipids. Only a part of the 14CO2 generated was dependent on the presence of contaminating blood cells in the marrow cell suspensions. These findings indicate that one or more cell types in the marrow are capable of oxidising ethanol to acetaldehyde and acetate. Our date raise the interesting possibility that the effects of chronic alcoholism on the bone marrow may not be caused by a direct action of ethanol, but may be related to some intracellular or extracellular changes resulting from the metabolism of ethanol within the marrow cells themselves.

Bone Marrow↗
PubMed1980

Flow rate determination using computed tomography.

A method of measuring flow in a large vessel by using a CT scanner is described. It has been shown that this is a simple, accurate and reproducible method in an experimental model. Possible clinical applications and limitations of this method of measuring flow are briefly considered.

Blood Flow Velocity↗