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Biomedical subjects

R W Hiorns

Publications and source records attributed to R W Hiorns.

At least 19 recordsLinked to original sources
PubMed2002

Distinctive features of age-specific fertility profiles in the English-speaking world: common patterns in Australia, Canada, New Zealand and the United States, 1970-98.

The paper seeks to identify common features in the fertility patterns of the English-speaking world and provide a model basis for comparison of fertility between countries and over time. Attention is focused on the heterogeneity within the fertility patterns of Australia, Canada, New Zealand, and the United States, similar to that reported earlier for the UK and the Irish Republic. The recent age-specific fertility patterns of these countries display a marked 'bulge' in fertility of women under age 25. A mixture model with two-component Hadwiger functions provides a suitable fit. The heterogeneity thus suggested is related to the proportion of births outside marriage. Additionally, there is some evidence that, in the United States, and lesser extent in New Zealand, this heterogeneity in fertility patterns may be explained by ethnic difference in the timing and number of births.

Australia↗
PubMed1999

Recent European fertility patterns: fitting curves to 'distorted' distributions.

Recent patterns of fertility in Europe show marked differences between countries. Recent United Kingdom and Irish fertility curves show 'distortions' in terms of a 'bulge' in early age fertility, distinct from the smoother curves of other European countries. These patterns may not be adequately described by mathematical functions used by previous studies to model fertility curves. A mixture model with two component distributions may be more appropriate. The suitability of the simple and mixture Hadwiger functions is examined in relation to the fertility curves of a number of European countries. While the simple Hadwiger model fits recent period age-specific fertility distributions for some countries, others which display a 'bulge' in early age fertility distributions for some countries, others which display a 'bulg' in early age fertility require a mixture Hadwiger model. Some of the parameters of the Hadwiger models appear to be related to familiar demographic indices. The simple and mixture Hadwiger models appear useful in describing and comparing fertility patterns across European countries.

Europe↗
PubMed1996

Meteorological factors and the time of onset of chest pain in acute myocardial infarction.

Analysis of the time of onset of chest pain in 2254 patients with a myocardial infarction admitted to a coronary care unit in Leicester during a 10-year period shows an association with temperature and humidity. During both the most cold and humid times of the year, the relationship is a strong one. A generalized linear model with a log link was used to fit the data and the backward elimination selection procedure suggested a humid, cold day might help to trigger the occurrence of myocardial infarction. In addition, cold weather was found to have a stronger effect on the male population while those men aged between 50 and 70 years were more sensitive to the effect of high humidity.

Chest Pain↗
PubMed1992

Modelling of changes in the corneal endothelium after cataract surgery and penetrating keratoplasty.

Long term changes in endothelial cell density were monitored in three groups of patients after surgery. One group underwent uncomplicated cataract surgery, one group complicated cataract surgery which eventually progressed to corneal decompensation, and one group penetrating keratoplasty. A mathematical model is presented which describes endothelial cell loss after surgery as an exponential decay process towards an asymptote with constant rate of cell loss over time. When fitted to the data from the three groups there is excellent agreement in each case. Discriminant analysis techniques were applied to model predictions to assess the likelihood of late corneal decompensation after surgery. From measurements of endothelial cell density before and after surgery we were able to correctly assign patients undergoing cataract surgery to decompensation or non-decompensation groups in 85.7% and 92.7% of cases respectively.

Cataract Extraction↗
PubMed1991

Clustering of ipsilateral cortico-cortical projection neurons to area 7 in the rhesus monkey.

The distribution within individual cytoarchitectonic areas of the cells of origin of ipsilateral cortico-cortical fibres to area 7 of the parietal lobe of the monkey has been studied. After injections of horseradish peroxidase into area 7, labelled cells in a variety of cortical areas were plotted and their distribution along the length of the cortex analysed. Significant clustering of labelled cells was seen wherever their numbers were sufficient for meaningful statistical analysis. In most cases, further analysis using correlation techniques revealed a significant banding of labelled cells across the cortex. Typical bands varied from 500-800 microns in width, and formed an irregular branching and rejoining pattern across the cortex. The intra-area distribution of cortico-cortical projection neurons is comparable to the distribution of neurofibrillary tangles in the cortex in Alzheimer's disease.

Alzheimer Disease↗
PubMed1990

Immunogenetic correlates of susceptibility to infection with Heligmosomoides polygyrus in outbred mice.

Outbred MF1 mice were characterized with respect to their susceptibility to infection with Heligmosomoides polygyrus (Nematoda) on the basis of faecal egg counts after 8 weeks of repeated infection (50 larvae/week). Selective breeding for resistance and susceptibility was carried out over 3 generations. The H-2 type of a sample of the mice was determined, and antigen recognition assessed on the basis of Western blots against adult and larval H. polygyrus homogenate. The selective breeding programme yielded very strong evidence for the heritability of susceptibility to infection. The results were consistent with a model of single gene control with resistance dominant over susceptibility. The presence of the H-2k haplotype was significantly associated with susceptibility, as was the recognition of a 17 kDa antigen in blots against both larval and adult worm homogenate. The proportion of mice phenotypically susceptible to infection, the proportion bearing the H-2k haplotype, and the proportion recognizing the 17 kDa antigen, were all approximately 0.25.

Animals↗
PubMed1988

Genetic and morphometric variances in three human populations.

Data from three human populations were used to investigate the putative relationship between genetic and morphological variances. There was no evidence to support the hypothesis that individuals heterozygous at a small number of marker loci are more often near the mean for anthropometric characters than are homozygotes. In one population (Otmoor), apparent support for the hypothesis was due to the confounding factors of correlations between anthropometric traits and population subdivision. It is unlikely that such relationships can be detected by intrapopulation comparisons because of the low association between measured and total heterozygosity.

Adult↗
PubMed1986

Heligmosomoides polygyrus (Nematoda): the dynamics of primary and repeated infection in outbred mice.

The population dynamics of Heligmosomoides polygyrus were studied in outbred male MF1 mice subject either to primary or repeated experimental infection. Little variability in susceptibility was observed between mice, but heterogeneity increased with both duration and intensity of primary infection; this result indicates that there are differences in parasite survival between hosts. The rate of parasite-induced host mortality was 4 X 10(-4) per parasite per host per parasite lifespan. The mortality rates of male and female larvae during their development in the intestinal wall were estimated as 0.033 and 0.021 per parasite per day respectively, and estimates of the expected lifespans of the adult male and female parasites in primary infection of 11.22 and 9.92 weeks were obtained. Approximately 40% of female worms were observed in copula at any one time, although this proportion was significantly depressed in hosts harbouring fewer than 50 parasites and during the first four weeks of infection. Parasite fecundity was markedly age-dependent; each female worm produced approximately 31,000 eggs during its lifespan. No density dependence in either worm survival or fecundity in primary infection was apparent. The only detectable effect of worm density was in association with spatial distribution in the intestine; high levels of infection were associated with a posterior shift in the location of a proportion of the parasite population. Characterization of the dynamics of primary infection allowed predictions to be made about the expected dynamics of repeated infection. The comparison of predicted results and observed data revealed unequivocal epidemiological evidence for the density-dependent regulation of parasite population growth during repeated infection, affecting both parasite survival and parasite fecundity. The results also demonstrated the existence of two types of host individual in which the dynamics of repeated infection were markedly different. It is concluded that immunological differences between mice (possibly under genetic control) may be responsible for the observed effects; approximately 25% of MF1 mice seem unable to generate any protective immunity against H. polygyrus, whereas 75% become almost completely refractory to reinfection. This experimental system could be used for quantitative investigation of the impact of acquired immunity and genetic heterogeneity on helminth population dynamics. Both are of obvious relevance with respect to the control of infections of medical and veterinary significance.

Animals↗
PubMed1986

Faecal egg counts and nematode fecundity: Heligmosomoides polygyrus and laboratory mice.

The results are presented of an experimental investigation of the relationship between faecal egg counts and worm burden in outbred MF1 mice infected with Heligmosomoides polygyrus (Nematoda). The sex-ratio of the adult parasites was found to be significantly female biased, but independent of parasite burden. Evidence was also found to suggest a significant association between parasite density and mating success. The linear logarithmic relationship (gradient of approximately 2) between the variance and mean of repeated egg counts from individual mice could not be disrupted by controlled experimental conditions, and is therefore concluded to be an inherent feature of the biology of helminth-host interactions. A significant positive association was detected between host faecal output and parasite fecundity; further investigation of the cause of this association is now required. Average faecal production was found to be inversely related to worm burden. In combination, the above two factors account partly, but not completely, for the observed density dependence in the absolute rate of parasite egg production. Two epidemiological consequences of the relationship between faecal production and parasite fecundity are discussed. First, absolute rates of egg production can only be estimated by temporal egg counts (epd). Secondly, measurements of egg production/g of faecal material (epg) are more reliable indicators of worm burden than measurements of epd. Both faecal output and worm fecundity respond as might be predicted to a period of host food deprivation; faecal egestion and measurements of epd are significantly depressed, and measurements of epg are significantly increased. The data are consistent with the hypothesis that egg production and faecal output are causally associated, but that other factors relating to parasite density also influence egg production. Of the possible causes for the high variability in parasite egg production between mice harbouring low number of worms, the most likely explanation seems to be host heterogeneity (possible genetic in origin). This is discussed in relation to similar patterns observed in data collected from human populations in areas of endemic helminth infection.

Analysis of Variance↗
PubMed1986

Pseudophakic bullous keratopathy: relationship with endothelial cell density and use of a predictive cell loss model. A preliminary report.

Patients involved in a clinical trial of cataract surgery who developed pseudophakic bullous keratopathy were studied. They did not differ from the trial population as a whole with respect to their age or pre-operative endothelial cell density. Bullous keratopathy occurred within a narrow range of endothelial cell density. Examination of endothelial cell loss profiles over four years of follow-up after cataract surgery, in patients who developed bullous keratopathy and others, suggested that there was a predictable pattern. A mathematical model is described which gave good agreement between predicted and measured endothelial cell density. The model is now being used to identify parameters which may predict susceptibility to development of bullous keratopathy.

Aged↗
PubMed1985

Sizes of neurons in the primate lateral geniculate nucleus during normal development.

Measurements of cell area have been made in the lateral geniculate nuclei (LGNs) of 18 normal rhesus monkeys aged from 8 days to fully adult. There is much less variability between individual animals than had been thought from measurements of undeprived cells in experimental animals following visual deprivation. It is therefore possible to make reliable comparisons of cell size between different animals. There is no change in size of cells in the parvocellular laminae between 8 days of age and adulthood, although cells in the magnocellular laminae grow a little. In the primate, unlike the cat, the period of maximum sensitivity to visual deprivation does not correspond to a period of rapid cell growth in the LGN.

Age Factors↗
PubMed1985

Effects of monocular closure at different ages on deprived and undeprived cells in the primate lateral geniculate nucleus.

This study has examined the effects of monocular visual deprivation on cells in the lateral geniculate nucleus of the primate by comparing the sizes of cells in deprived and undeprived LGN laminae of experimental rhesus monkeys with those of cells in the corresponding laminae of normal animals. A number of conclusions may be drawn from this comparison: monocular visual deprivation has major effects on cells in the undeprived LGN laminae and these vary with age at closure; the initial effect of monocular closure from birth is to cause marked hypertrophy of undeprived parvocellular cells with little shrinkage of the deprived parvocellular cells, whereas late monocular closure (after 2 months of age) causes marked shrinkage of both undeprived and deprived parvocellular cells; following monocular closure at birth, the LGN abnormality continues to evolve until at least 3 months of age, with a marked parallel shrinkage affecting both deprived and undeprived parvocellular cells. The initial hypertrophy of the undeprived cells is reversed and the deprived cells become smaller than normal; cells in the monkey LGN are sensitive to visual deprivation until about 1 year of age, much later than previously thought. Visual experience, however, modifies this sensitivity so that the effects of monocular visual deprivation are both qualitatively and quantitatively different at different ages; there are important differences between the susceptibility of cells in the magnocellular and parvocellular laminae to visual deprivation; and actual shrinkage of cells to markedly below normal size occurs and the smaller size is not simply failure of growth.

Age Factors↗
PubMed1985

Effect of reopening an eye after a period of monocular deprivation on sizes of neurons in the primate lateral geniculate nucleus.

Following monocular closure shortly after birth the deprived eye of 4 rhesus monkeys was reopened at different times. Following long-term recovery, cells in the undeprived laminae of the lateral geniculate nucleus of these animals were of normal size and those in the deprived laminae were markedly shrunken. Comparisons with animals monocularly deprived for similar periods indicate, however, that in 3 of these animals the undeprived parvocellular cells would have been markedly hypertrophied at the time of reopening the deprived eye, and in two of the animals, little shrinkage of the deprived parvocellular cells would have occurred by this time. Both undeprived and deprived parvocellular cells have therefore undergone marked shrinkage after the deprived eye had been reopened. The parallel shrinkage of deprived and undeprived parvocellular cells which occurs following closure at birth thus appears to be a consequence of the initial abnormalities produced by monocular closure rather than a direct result of the continuing lack of visual input to one eye.

Animals↗
PubMed1985

Anatomical correlates of the distribution of the pathological changes in the neocortex in Alzheimer disease.

The numbers and distribution of the neurofibrillary tangles and neuritic plaques have been determined in several areas of the neocortex in brains affected by various degrees of severity of Alzheimer disease. The homotypical cortex of the "association" areas of the temporal, parietal, and frontal lobes are severely involved, whereas the motor, somatic sensory, and primary visual areas are virtually unaffected. The neurofibrillary tangles are mainly in the supra- and infragranular layers, particularly in layers III and V. In all areas except area 18 in the occipital lobe, there are approximately twice as many tangles in layer V as in layer III. The tangles are arranged in definite clusters, and those in the supra- and infragranular layers are in register. The neuritic plaques occur in all layers but predominantly affect layers II and III and do not show clustering. These data on the severity of the pathological involvement in different areas of the neocortex and the laminar distribution and the clustering of the tangles support the suggestion that the pathological changes in Alzheimer disease affect regions that are interconnected by well-defined groups of connections and that the disease process may extend along the connecting fibers. The invariable and severe involvement of the olfactory areas of the brain in this disease is in striking contrast to the minimal changes in the somatic sensory and primary visual areas and raises the possibility that the olfactory pathway may be initially involved.

Aged↗
PubMed1981

Cell sizes in the lateral geniculate nucleus of normal infant and adult rhesus monkeys.

Measurements of mean cell area have been made in the lateral geniculate nuclei of 16 normal rhesus monkeys as a control for changes following visual deprivation. There is little variability between animals and no significant growth between 8 days of age and adulthood in the parvocellular laminae. The magnocellular laminae show more variability and some continuing growth after 8 days of age.

Aging↗