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Biomedical subjects

P N Jones

Publications and source records attributed to P N Jones.

10 recordsLinked to original sources
PubMed1991

On collagen fibril diameter distributions.

Distributions of collagen fibril diameters, measured from electron micrographs, are compared using some of the common measures of the mean of the distribution. The role of mixture distributions in modelling these distributions is considered and a method of fitting such distributions to data observed in the form of histograms is described. The method is illustrated with six pairs of fibril diameter distributions used in assessing age and structural changes in various collagen samples from different species of animal. The extent of changes in diameter distributions is assessed in terms of the estimated means, variances and mixing proportions for the component distributions of the histograms in each pair.

Aging↗
PubMed1991

Fitting mixture distributions to phenylthiocarbamide (PTC) sensitivity.

A technique for fitting mixture distributions to phenylthiocarbamide (PTC) sensitivity is described. Under the assumptions of Hardy-Weinberg equilibrium, a mixture of three normal components is postulated for the observed distribution, with the mixing parameters corresponding to the proportions of the three genotypes associated with two alleles A and a acting at a single locus. The corresponding genotypes AA, Aa, and aa are then considered to have separate means and variances. This paper is concerned with estimating the parameters of the model, and their standard errors, by using an application of the EM algorithm. This technique also caters for the fact that the sensitivity measurements are only known to lie between the endpoints of certain intervals and that the exact measurement of the attribute is not possible.

Algorithms↗
PubMed1988

Asymmetrical pudendal nerve damage in pelvic floor disorders.

Differences in the left and right pudendal nerve terminal motor latencies have been observed in patients with pelvic floor disorders. Until now the mean value of the left and right pudendal latencies has been used as the index of pudendal neuropathy. In 22 patients of a group of 156 patients studied the pudendal nerve terminal motor latency was abnormally raised on one side only. These patients are thought to have pudendal neuropathy whether or not the mean value of the left and right pudendal latencies is also raised. This observation may have therapeutic implications.

Adult↗
PubMed1988

Fitting mixture models to grouped and truncated data via the EM algorithm.

The fitting of finite mixture models via the EM algorithm is considered for data which are available only in grouped form and which may also be truncated. A practical example is presented where a mixture of two doubly truncated log-normal distributions is adopted to model the distribution of the volume of red blood cells in cows during recovery from anemia.

Algorithms↗
PubMed1987

Relation between perineal descent and pudendal nerve damage in idiopathic faecal incontinence.

In 60 patients with idiopathic anorectal incontinence, without neurological disease, there was a significant relationship, shown by regression analysis, between the pudendal nerve terminal motor latency and the extent of perineal descent during straining (r 0.59; p less than 0.001), and the plane of the perineum on straining (r -0.61; p less than 0.001). These data are consistent with the suggestion that perineal descent can lead to stretch-induced damage to the perineal nerves in this condition.

Action Potentials↗
PubMed1987

Is paradoxical contraction of puborectalis muscle of functional importance?

Paradoxical contraction of the puborectalis muscle during simulated defecation straining (anismus) has been cited as a cause of constipation. The functional specificity of this phenomenon was evaluated in 79 patients, 50 with constipation, 21 with idiopathic perineal pain, and eight with solitary rectal ulcer syndrome. Electromyogram evidence of paradoxical puborectalis contraction was observed in 38 (76 percent), ten (48 percent), and four (50 percent) of these patients, respectively. All patients with solitary rectal ulcer syndrome had difficulty defecating; defecation was normal in all patients with perineal pain. These observations suggest that paradoxical contraction of the puborectalis muscle is not a specific finding, and that it is not the sole cause of constipation in patients with anismus.

Adolescent↗
PubMed1978

Bruising in cattle transported over long distances.

The relative susceptibility of cattle of different sexes to bruising was examined in five trials. In each trial there were three groups of cattle--bullocks, cows and mixed (bullocks and cows). The weight of bruised tissue trimmed from the carcases of the cows was significantly greater than that trimmed from the carcases of bullocks. The amount of bruising in cows, but not in bullocks, increased with increase in duration of journey. There was no evidence to suggest that differences in carcase weight or temperament, or "riding" of cows in oestrus were major contributing factors to the different levels of bruising.

Animals↗
PubMed1978

The duration of latent infection and functional immunity in droughtmaster and hereford cattle following natural infection with Babesia argentina and Babesia bigemina.

Tne Droughtmaster and 9 Hereford cattle were born in an enzootic babesiasis area and became naturally infected with Babesia argentina and B.bigemina during a 3 year period. They were then kept free of cattle ticks (Boophilus microplus) for the remainder of the experiment. Annually for the next 3 years their individual infection status with Babesia was determined by sub-inoculation of blood into splenectomised calves. At the end of this period the functional immunity of all cattle was challenged by blood inoculation of heterologous strains of B. argentina and B. bigemina. Infection with B. argentina persisted in all Herefords for 2 years and in 7 for 3 years after they had been freed of B. microplus. The number of Droughtmasters with detectable B. argentina infection progressively declined, and at the end of 3 years only 2 of 10 were still infected. No Herefords were shown to be infected with B. bigemina following 1 year's freedom from B. microplus but latent B. bigemina infection of at least 2 year's duration was demonstrated in one of the Droughtmasters. A marked degree of resistance was apparent in all cattle when they were challenged with an heterologous strain of B. argentina. There were no differences between the response to challenge of the Herefords and Droughtmasters nor between the reactions of cattle which had apparently naturally sterilised B. argentina infection and those which were still infected. The heterologous strain of B. bigemina produced parasitaemia in the majority of animals but only minimal fever and anaemia resulted with no significant differences between the breeds.

Age Factors↗
PubMed1976

Erythrocyte adenosine triphosphate levels in cattle infected with Babesia argentina.

Erythrocyte adenosie triphosphate (ATP) was estimated in 60 Droughtmaster cattle. The mean was 0.76 mumole/g haemoglobin; standard deviation +/- 0.18; range 0.41-1.45. ATP values were log normally distributed. Repeatability of ATP estimations was confirmed using 10 Hereford cattle. Animal variation in the estimates was double the sampling variation. No significant correlation between susceptibility to B. argentina and ATP was observed in 25 Droughtmaster and 5 Hereford cattle.

Adenosine Triphosphate↗