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Biomedical subjects

A Purvis

Publications and source records attributed to A Purvis.

31 records · Page 2Linked to original sources
PubMed1995

A composite estimate of primate phylogeny.

This paper presents an estimate of the phylogeny of all 203 species of primate. The composite tree is derived by applying a parsimony algorithm to over a hundred previous estimates, and is well resolved, containing 160 nodes. The ages of over half the clades in the tree have been estimated from information in the literature. Bootstrapping has been used to indicate the degree of certainty associated with each clade. The tree will be a useful framework for comparative biologists and shows which areas of primate phylogeny are still only sketchily known.

Algorithms↗
PubMed1995

Macroevolutionary inferences from primate phylogeny.

We apply new statistical methods to a recent estimate of the phylogeny of all living primate species to test a range of models of cladogenesis. Null models in which probabilities of speciation and extinction do not differ among contemporaneous lineages are not consistent with the phylogeny. We present evidence that the net rate of cladogenesis (speciation rate minus extinction rate) increased in the lineage leading to the Cercopithecidae (Old World monkeys), and that there have been further increases in some lineages within that family. Such increases suggest the occurrence of clade selection, although we have not identified the selected trait or traits. There is no evidence that the net rate of cladogenesis is a function either of how many primate lineages are already present or of time. Intriguingly, three other clades--Strepsirhini, Platyrrhini and Hominoidea--appear to have had very similar rates of clade growth, in spite of their great biological differences.

Animals↗
PubMed1995

Comparative analysis by independent contrasts (CAIC): an Apple Macintosh application for analysing comparative data.

CAIC is an application for the Apple Macintosh which allows the valid analysis of comparative (multi-species) data sets that include continuous variables. Comparison among species is the most common technique for testing hypotheses of how organisms are adapted to their environments, but standard statistical tests like regression should not be used with species data. Such tests assume independence of data points, but related species often share traits by common descent rather than through independent adaptation. CAIC uses a phylogeny of the species in the data set to partition the variance among species into independent comparisons (technically, linear contrasts), each comparison being made at a different node in the phylogeny. There are two partitioning procedures--one used when all variables are continuous, the other when one variable is discrete. The resulting comparisons can be analysed validly in standard statistical packages to test hypotheses about correlated evolution among traits, to estimate parameters such as allometric exponents, and to compare rates of evolution. Previous versions of the package have already been used widely; this version is simpler to use and works on a wider range of machines. The package and manual are freely available by anonymous ftp or from the authors.

Data Interpretation, Statistical↗
PubMed1993

Relations between song repertoire size and the volume of brain nuclei related to song: comparative evolutionary analyses amongst oscine birds.

Song and brain structure are compared amongst 41 species of oscine birds by using the method of independent evolutionary contrasts. We find a significant correlation between the relative volume of the song control centre, the high vocal centre (HVC), and the number of song types typically found in the repertoire. Relative HVC volume is not correlated with the number of different syllable types per song bout. The relative volume of a second song nucleus, area X, is not significantly correlated with either measure. Relative HVC volume is uncorrelated with relative volume of the hippocampus, a brain area involved in other forms of memory. This is the first evidence for repeated independent evolution of an association between complexity of learned song and the relative volume of one of the song control nuclei though to be involved in song learning.

Animals↗
PubMed1992

Healing by wire.

Explore the source record for details and available documents.

Diffusion of Innovation↗
PubMed1992

Warm-up rates during arousal from torpor in heterothermic mammals: physiological correlates and a comparison with heterothermic insects.

This study examines the relationship between warm-up rate, body mass, metabolic rate, thermal conductance and normothermic body temperature in heterothermic mammals during arousal from torpor. Predictions based on the assumption that the energetic cost of arousal has been minimised are tested using data for 35 species. The observation that across-species warm-up rate correlates negatively with body mass is confirmed using a comparative technique which removes confounding effects due to the non-independence of species data due to shared common ancestry. Mean warm-up rate during arousal correlates negatively with basal metabolic rate and positively with the temperature difference through which the animal warms, having controlled for other factors. These results suggest that selection has operated to minimise the overall energetic cost of warm-up. In contrast, peak warm-up rate during arousal correlates positively with peak metabolic rate during arousal, and negatively with thermal conductance, when body mass has been taken into account. These results suggest that peak warm-up rate is more sensitive to the fundamental processes of heat generation and loss. Although heterothermic marsupials have lower normothermic body temperatures and basal metabolic rates, marsupials and heterothermic eutherian mammals do not differ systematically in warm-up rate. Pre-flight warm-up rates in one group of endothermic insects, the bees, are significantly higher than predictions based on rates of arousal of a mammal of the same body mass.

Animals↗
PubMed1991

Reach out and cure someone.

A new 900 number offers medical advice by phone, but can it replace a family physician's personal touch?

Ethics, Medical↗
PubMed1991

Comparative methods for explaining adaptations.

The ways that taxonomic differences in morphology, behaviour or life history are related to each other and to differences in lifestyle have been used regularly to test ideas about the selective forces involved in their evolution. Such comparative tests have been transformed recently by using increased statistical rigour. The realization that the statistical model against which comparisons are made is a model of how evolution proceeds, forms the basis of a new generation of comparative tests that are grounded properly on phylogenetic reconstruction.

Adaptation, Physiological↗
PubMed1986

Postal survey of bronchoscopic practice by physicians in the United Kingdom.

In 1983 a postal survey of the bronchoscopic practice of chest physicians in the United Kingdom produced a 90% response rate. Two hundred and thirty one physicians were carrying out bronchoscopy; they had performed about 40 000 bronchoscopies in the preceding year, 87% of these being fibreoptic procedures with topical anaesthesia. The mortality rate of fibreoptic bronchoscopy was 0.04%, with a 0.12% incidence of major complications. Transbronchial biopsy carried both an appreciably higher mortality rate of 0.12% and a major complication rate of 2.7%. There is wide variation in the use and choice of sedative drugs for fibreoptic bronchoscopy. Many of the drug combinations could be criticised on pharmacological grounds. The mean dose of lignocaine was 342 mg, most operators exceeding the usual maximum recommended dose; but adverse reactions were rare. Routine supplemental oxygen was given by only 18% of bronchoscopists. Basic resuscitation equipment was often inadequate. Radiological screening was used for transbronchial lung biopsy by 53% of respondents and significantly reduced the incidence of pneumothorax from 2.9% to 1.8%. Both the number of bronchoscopies performed and the complication rate were higher than previous estimates. Bronchoscopists should re-examine their policy on drugs and safety precautions to minimise the risks of the procedure.

Anesthesia↗
PubMed1982

Inside the chart review.

The study on which this article is based was conducted at the University of North Carolina's Family Practice Center to analyze the content of teaching that occurred in the face-to-face chart review sessions. Data were collected from a sample of 276 chart reviews and processed by a microcomputer program that compiled reports of types of problems encountered by residents, topics of discussion pertinent to those problems, and learning needs defined as a result of those discussions. Reports were generated for faculty members nad residents, and summary reports were produced for the teaching encounters. This system of computerized data analysis can be used to identifying learning needs of residents and areas of teaching emphasis for faculty. The information can be used for educational planning and faculty development.

Clinical Competence↗