Search PubMed⌕ Search

Biomedical subjects

D R Williams

Publications and source records attributed to D R Williams.

At least 217 records · Page 12Linked to original sources
PubMed1986

Higher order color mechanisms.

Evidence supporting the existence of higher order color mechanisms, that is, ones beyond the previously identified second stage mechanisms is presented. This evidence includes a reanalysis of the data of Krauskopf et al. [Vision Res. 20, 1123-1131 (1982)] on the desensitizing effects of viewing chromatically modulated fields, new experiments on a generalized version of the "transient tritanopia" experiment of Mollon and Polden [Phil. Trans. R. Soc. Lond. 278, 207-240 (1977)] and results on the relationship between discrimination and detection of brief color changes.

Animals↗
PubMed1986

Sodium and potassium intakes in a representative population sample: estimation from 24 h urine collections known to be complete in a Cambridgeshire village.

1. A representative sample of eighty men aged 25-44 years from a Cambridgeshire village, each carried out one 24-h urine collection which was analysed for sodium, potassium, creatinine and urea content. The completeness of the collections was verified using oral doses of p-aminobenzoic acid (PABA; the PABA check test). 2. In the seventy-one collections shown to be complete, the average 24 h excretion of Na was 172 mmol and the average 24 h excretion of K was 74 mmol. 3. Fifty-one of these men's wives also made complete 24 h collections. The average content of these was 128 mmol Na and 61 mmol K. 4. Self reports and creatinine index would have identified as incomplete only 29 and 14% respectively of collections so judged by PABA. 5. Average excretion of 150 mmol Na/d was similar to estimated intakes of 140-167 mmol/d from the National Food Survey (Bull & Buss, 1980).

4-Aminobenzoic Acid↗
PubMed1986

Treatment and follow-up of patients with epilepsy in two general practices.

The continuing care of people with epilepsy in two general practices was investigated by means of case note review and interviews with patients. It was found that 98% (56 out of 57) of patients were receiving anticonvulsant drugs. Despite the prescription of drugs, however, only 64% (25 out of 39) of those patients interviewed were receiving regular follow-up and three of the patients receiving no surveillance had suffered recent fits. Many of the patients had experienced no fits for several years and it was considered that anticonvulsant therapy could have been stopped in some cases. It is recommended that a system be devised to ensure that all epileptic patients on anticonvulsants see their general practitioner at least yearly.

Adolescent↗
PubMed1986

Risk factors for undescended testis.

The hypothesis that undescended testis is caused by an excess of maternal oestrogen in pregnancy has been tested indirectly in a case-control study comparing mothers of boys with undescended testis (83) and mothers of normal boys (129) born on the same day. The study concentrated on the gestation of the boys, but also investigated the mother's previous obstetric history and postnatal events in the boys. The hypothesis predicted that there should be an excess of nausea, vomiting and hypertension in mothers of cases, but in fact the pregnancies of the case and control mothers were similar in all respects except one. The exception was the increased liability of the mothers of cases to threatened abortion. Mothers of cases also had an increased tendency to miscarry in previous conceptions, a reduced number of deliberate terminations and evidence of decreased fertility. An alternative hypothesis is suggested which would explain these findings. This is that placental function is impaired in the gestation of affected boys and the secretion of human chorionic gonadotrophin is reduced. This leads to changes in fetal testicular function and possible maldescent. Those born with undescended testis were more likely to present to a general practitioner with illness in the first three years after birth and this difference was mainly due to asthma, eczema, jaundice and feeding difficulties.

Adult↗
PubMed1986

Non-optical aids.

Non-optical aids help patients deal with everyday problems where sight is impaired. A review of the many non-optical devices is discussed including relative size devices, writing and communication aids, posturing and positioning aids, illumination control and non-optical sensory substitution devices. An extensive appendix is provided listing sources of many non-optical aids.

Blindness↗
PubMed1986

Management of postconization cervical stenosis by laser vaporization.

In 18 patients with symptomatic cervical stenosis after conization, laser vaporization of the stenotic segment was performed. Total relief of symptoms was achieved in 12 patients and partial relief in four. In seven cases there was no evidence of stenosis at follow-up, and in a further nine cases the degree of stenosis was less. In seven cases it was possible to visualize the squamocolumnar junction at follow-up. This had not been possible in any cases before the procedure. Vaporization using the carbon dioxide laser provides a useful conservative management technique for postconization stenosis.

Adult↗
PubMed1985

Aliasing in human foveal vision.

An improved laser interferometer allows forced choice contrast sensitivity measurements that are relatively unaffected by optical blurring in the eye. At spatial frequencies above about 60-70 c/deg, the regular bars of the interference fringe are no longer visible; observers report a pattern resembling zebra stripes centered on the line of sight. The characteristics of this pattern are consistent with the hypothesis that it is a moiré pattern resulting from aliasing by the foveal cone mosaic. Properties of this moiré pattern allow an assessment of the regularity of the foveal lattice, the spacing between cones, and the light-catching area of individual cones.

Form Perception↗
PubMed1985

Stereopsis with chromatic signals from the blue-sensitive mechanism.

Evidence is presented that the depth seen in dim violet targets superimposed on a bright yellow background is mediated solely by the blue-sensitive mechanism. In forced-choice experiments using these stimuli, observers could discriminate between crossed and uncrossed disparities when the targets were either figural or random dot stereograms. Stereo thresholds for a three bar target whose spatial parameters were adjusted for the B cone mechanism were on the order of 40 sec of arc, a value considerably smaller than the spacing between B cones. With the additional assumption that signals from the blue-sensitive mechanism do not contribute to luminance, these results confirm that purely chromatic signals have access to stereoscopic mechanisms.

Color Perception↗
PubMed1985

Hospital admissions of diabetic patients: information from hospital activity analysis.

Hospital admissions data for 1981 reveal that, for the population of East Anglia, 1.6% of hospital bed days were attributed to diabetes mellitus as the principal cause for admission. Admissions for diabetes without complications or with ketoacidosis or other coma accounted for about 60% of bed days while the other specified complications of diabetes accounted for the remainder. Admissions with diabetes as a subsidiary diagnosis accounted for 2.6 times as many bed days as those for which the disease was the principal diagnosis. Ischaemic heart disease or cerebrovascular disease was recorded as principal diagnosis significantly more often than would be expected from the general population experience, particularly for female diabetics. On an average day, 5.6% of beds were occupied by diabetic patients. The diabetic population of East Anglia used, on average, 5.1 hospital bed days per person year compared with 1.1 days for the non-diabetic population.

Diabetes Complications↗
PubMed1985

Glycaemic effects of bread and marmalade in insulin-dependent diabetes.

The glycaemic responses of 12 C-peptide negative insulin-dependent diabetics were studied following four breakfasts with different carbohydrate sources. Total energy content of the meals was the usual for each subject, carbohydrate supplying 55% and fat 32%. The meals comprised: wholemeal bread with margarine; white bread with margarine; marmalade made with sucrose, and cheddar cheese; and marmalade (22% of total energy) on wholemeal bread with margarine. The study demonstrated powerfully that there were no statistically significant or clinically relevant differences between the meals in post-prandial glucose peak elevation, or in incremental area under the blood glucose curve to 120 mins. On these grounds, sucrose, in amounts considered acceptable to the general population, need not be prohibited from diabetic diets.

Adult↗
PubMed1985

The treatment of cervical intraepithelial neoplasia by laser vaporization.

Of 711 women with cervical intraepithelial neoplasia (CIN) treated by laser vaporization 675 (95%) remain colposcopically and cytologically free from disease after a median follow-up of 20 months. Thirty-six patients needed other forms of treatment to eradicate suspected residual disease. One patient presented with invasive carcinoma of the cervix 34 months after treatment with the carbon dioxide laser. It is concluded that in selected cases laser vaporization is an effective method of treating pre-invasive disease of the cervix.

Adolescent↗
PubMed1985

Influence of following context on perception of the voiced-voiceless distinction in syllable-final stop consonants.

This paper reports acoustic measurements and results from a series of perceptual experiments on the voiced-voiceless distinction for syllable-final stop consonants in absolute final position and in the context of a following syllable beginning with a different stop consonant. The focus is on temporal cues to the distinction, with vowel duration and silent closure duration as the primary and secondary dimensions, respectively. The main results are that adding a second syllable to a monosyllable increases the number of voiced stop consonant responses, as does shortening of the closure duration in disyllables. Both of these effects are consistent with temporal regularities in speech production: Vowel durations are shorter in the first syllable of disyllables than in monosyllables, and closure durations are shorter for voiced than for voiceless stops in disyllabic utterances of this type. While the perceptual effects thus may derive from two separate sources of tacit phonetic knowledge available to listeners, the data are also consistent with an interpretation in terms of a single effect; one of temporal proximity of following context.

Adult↗
PubMed1985

Performance of a quality-assessment scheme for blood glucose meters in general practice.

We describe our experience with a quality-assessment scheme for Glucometer users in General Practice based on simultaneous blood samples taken on filter paper strips and posted to the laboratory. The accuracy of results from these blood glucose meters outside the laboratory was below generally accepted laboratory standards; 30% of results fell outside +/- 20% of the laboratory value. Only 58% of the filter paper strips sent out were returned for analysis, suggesting a lack of awareness of the benefits and importance of such a scheme by the G.P. Glucometer users.

Blood Glucose↗
PubMed1985

Visibility of interference fringes near the resolution limit.

The contrast sensitivity of the visual system to interference fringes has been measured in the range from 10 to 65 cycles/deg with a forced-choice psychophysical procedure. Masking produced by the spatial-noise characteristic of coherent fields was avoided by diluting the interferometric field with a fixed amount of uniform, incoherent light. The loss of contrast sensitivity between 10 and 60 cycles/deg ranged from 0.85 to 1.5 log units depending on the observer. Despite these individual differences, the mean contrast sensitivity for six observers at 60 cycles/deg was more than a factor of 8 higher than the most sensitive previous estimates, suggesting that the neural visual system is much more sensitive to fine detail than previously believed. The most sensitive observer required only 4% contrast to detect a 60-cycle/deg interference fringe. Even the shallow interferometric contrast-sensitivity functions reported here are too steep to be explained solely by scattered light at the retina. It is argued that the optical properties of the photoreceptor mosaic make a negligible contribution to the contrast-sensitivity loss between 0 and 60 cycles/deg, and neural factors must be implicated.

Adult↗
PubMed1984

Metal binding by pharmaceuticals. Part 4. A comparative investigation of the interaction of metal ions with hydralazine, prizidilol and related compounds.

The metal complexing properties of two antihypertensive drugs, hydralazine (1-hydrazinophthalazine) and prizidilol (a hydrazinopyridazine), and some related ligands, have been studied using potentiometry, elemental analysis, spectrophotometry and computer simulation. The coordination chemistry of 1-hydrazinophthalazine and the hydrazinopyridazines is similar in that Ca(II), Mg(II), and Mn(II) complexes are not formed, whereas Zn(II), Cu(II) and Fe(II)/Fe(III) complexes are produced. Both kinds of ligand react with Fe(II) to form a brightly coloured tetrazene complex which is insoluble for hydralazine but soluble for prizidilol. Computer simulation studies indicate that the most prevalent metal complex of prizidilol in blood plasma is [Fe2+(Priz-)H+]2+ but that this only forms at very high drug concentrations. It is concluded that prizidilol is unlikely to have any direct effects on the metabolism or distribution of the trace elements listed here.

Chelating Agents↗