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P Dean

Publications and source records attributed to P Dean.

8 recordsLinked to original sources
PubMed1979

[Internal arteriovenous fistula in the antecubital region].

An assessment was made of the anterior cubital region as a vascular approach for primary and alternative dialysis. Reference is made to 36 fistulae in this area within 44 months' survival in the drawing of various conclusions with regard to surgical technique. End anastomosis of the median, cephalic or basilic vein laterally on the brachial or radial artery is recommended as a means of preventing or cutting down the more common complications associated with internal arteriovenous fitulae. The anastomosis should not exceed 6 mm in diameter. Complications led to loss of fistula function. In many cases, however, they did not prevent employment of the region for alternative approaches, such as superficialisation of the basilic vein or prosthesis.

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PubMed1979

Visual cortex ablation and thresholds for successively presented stimuli in rhesus monkeys: II. Hue.

Rhesus monkeys were trained to discriminate successively presented hues. The smallest difference they could reliably detect was determined before and after either inferotemporal ablation, or a lesion intended to remove as much as possible of prestriate area V4 (Zeki, 1973). As a group, the animals with lesions of V4 showed good but not perfect retention of their preoperative performance, and their thresholds were unaltered. The inferotemporal group showed no retention of the simplest successive task, red versus green, but after relearning their thresholds too were unaltered. It appears that animals without inferotemporal cortex can form precise internal representations of hues, and that the basis of the inferotemporal learning impairment may depend upon the nature of the stimuli to be discriminated.

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PubMed1979

Flow cytometry of mammalian sperm: progress in DNA and morphology measurement.

Variability in DNA content and head shape of mammalian sperm are potentially useful markers for flow cytometric monitoring of genetic damage in spermatogenic cells. The high refractive index and extreme flatness of the sperm heads produce an optical effect which interferes with DNA measurements in flow cytometers which have dye excitation and fluorescence light collection normal to the axis of flow. Orientation of sperm in flow controls this effect and results in coefficients of variation of 2.5% and 4.2%, respectively, for DNA measurements of mouse and human sperm. Alternatively, the optical effect can be used to generate shape-related information. Measurements on randomly oriented sperm from three mammalian species using a pair of fluorescence detectors indicate that large shape differences are detectable. Acriflavine-Feulgen stained sperm nuclei are significantly bleached during flow cytometric measurements at power levels routinely used in many flow cytometers. Dual beam studies of this phenomenon indicate it may be useful in detecting abnormally shaped sperm.

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PubMed1978

Visual acuity in hooded rats: effects of superior collicular or posterior neocortical lesions.

The visual resolution acuity of hooded rats was measured with an avoidance technique, using large, high contrast square-wave gratings of high mean luminance. Measurements were taken before and after ablation of either posterior cortex or the superior colliculus. The cortical lesions included both striate and temporal cortex, and caused retrograde degeneration throughout the dorsal lateral geniculate nucleus. Neither group showed signs of detecting even coarse square-wave gratings when first tested after operation. The animals with collicular lesions quickly relearnt, and their acuity was unaltered. After extensive training 3 out of 4 cortical animals relearnt to detect gratings, and their acuity was reduced to about one-third of its preoperative value. It seems likely that in rats the geniculocortical pathway carries sufficient information for the normal detection of high spatial frequencies. Whether a pathway from superior colliculus to neocortex via a thalamic relay also carries this information is uncertain.

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PubMed1978

Visual cortex ablation and thresholds for successively presented stimuli in rhesus monkeys: I. Orientation.

Rhesus monkeys were trained to discriminate gratings of different orientation presented one at a time. The smallest difference they could reliably detect was determined before and after removal of either inferotemporal, foveal prestriate or lateral striate cortex. Four animals with inferotemporal lesions had significantly higher thresholds after operation, which did not improve after extensive practice. Two monkeys with lateral striate ablation, and 1 out of 3 animals with foveal prestriate lesions were also impaired, but improved with practice. Monkeys without inferotemporal cortex may have imprecise internal templates for stimulus orientation, in accordance with the categorisation hypothesis of the inferotemporal defect.

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