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Biomedical subjects

M Richards

Publications and source records attributed to M Richards.

At least 91 records · Page 5Linked to original sources
PubMed1999

Reduced gap strains induce changes in bone regeneration during distraction.

A bilateral New Zealand white rabbit model of distraction osteogenesis (DO) was used to investigate the relationship between strain environment and bone regeneration during limb lengthening. In seven (n = 7) rabbits, a stiffener was applied to the fixator on one side to reduce strains within the gap tissue after lengthening was completed. Animals were euthanized six days later and their distraction zones were harvested and analyzed for changes in new bone volume and architecture. Nonlinear finite element analyses (FEA) were performed to predict changes in the gap strain environment. FEA results predicted a nearly uniform sevenfold decrease in average strain measures within the distraction zone. No change in total average new bone volume and significant decreases in both bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) were observed in tibiae in which gap strains were reduced experimentally, compared to contralateral controls. These results suggest that fixator stiffening influenced the architecture but not the amount of newly formed bone. This animal model of distraction might be used to study the mechanisms by which strain fields affect events in bone repair and regeneration, such as cell proliferation, precursor tissue differentiation, and altered growth factor and nutrient delivery to tissues.

Animals↗
PubMed1999

Differential localization of inhibin subunit proteins in the ovine testis during fetal gonadal development.

Inhibins and activins are dimeric proteins that are involved in cell proliferation, apoptosis, and differentiation in a number of systems and have previously been detected in fetal testes of many species. This study used immunohistochemistry to examine the localization of inhibin alpha-, betaA-, and betaB- subunits during ovine testicular development from days 40-135 of gestation. Localization of inhibin betaA- and betaB-subunit messenger RNAs was confirmed by in situ hybridization. The results showed that there was differential localization of inhibin alpha-, betaA-, and betaB-subunits to specific cells in the ovine fetal testis from 40 days of gestation. All three inhibin subunits were present in Sertoli cells throughout gestation, whereas the rete epithelium and gonocytes did not express inhibin alpha-subunit. These data suggest that the fetal Sertoli cells have the capacity to produce all forms of inhibins and activins, i.e. inhibin A and B, and activins A, AB, and B, whereas the rete testis epithelial cells can only synthesize activin A. In the interstitium, the fetal Leydig cells expressed all three inhibin subunits, but this was restricted to the period between 40 and 90 days of gestation. Thereafter, inhibin alpha-subunit immunoreactivity was not observed in fetal Leydig cells, which suggests that only activin ligands are produced by Leydig cells during late gestation. Collectively, the data demonstrate that fetal ovine testes have the potential to produce the full repertoire of inhibins and activins from very early in testicular differentiation. The distinct and restricted localization of the various subunits to specific cells suggests that specific dimeric proteins have particular roles in the development and function of the fetal testis.

Animals↗
PubMed1999

Temporal and spatial characterization of regenerate bone in the lengthened rabbit tibia.

A rabbit model of bilateral tibial lengthening was used to investigate temporal and spatial changes in new bone volume and architecture during regenerate bone formation. Tibiae were lengthened 9.0 mm at 0.75 mm/day after a 6-day latency period. Animals were euthanized at four time points, and new bone volume and architecture within the distraction gap were assessed by microcomputed tomography and histomorphometry. New bone formation began before day 18 postsurgery and increased markedly between day 18 (completion of distraction) and day 24. This period of high bone formation activity might therefore be optimal for biologic and mechanical interventions aimed at enhancing bone regeneration. Regions of both endochondral and intramembranous bone formation were observed throughout the consolidation period. Significant increases in bone volume fraction were observed early in the consolidation period and were attributed to significant increases in trabecular thickness. This suggested that increased mineral density in the gap tissue with time was a consequence of increased osteoblast activity and associated trabecular thickening. New bone formation was shown to be highly oriented toward the distraction axis throughout lengthening. More bone formed consistently in lateral and proximal regions of the distraction gap, perhaps due to improved blood supply or progenitor cell availability in these areas. No differences in trabecular architecture were detected between regions having more or less bone volume, suggesting that bony tissue differentiation in all regions of the distraction gap was similar. Homotypical variations in measures of bone architecture were small; thus, these outcome variables seem appropriate for determining the effects of biological and mechanical interventions on bone regeneration in this animal model.

Animals↗
PubMed1998

A comparison of temperature measurements using three ear thermometers.

Following anecdotal and research-based reports of inaccuracies encountered with the use of ear thermometers in patient care settings, this two-phase study was designed to compare the accuracy of three ear thermometers when used in a multioperator environment. The within-subject variation (limits of agreement) in ear temperature measurements obtained with the three ear thermometers in a multioperator condition by using an oral temperature reference standard ranged from +/- 1.25 degrees F to 1.85 degrees F. In multioperator, multisubject patient care environments using a pulmonary artery catheter core temperature as the reference standard, the limits of agreement for ear temperature measurements obtained with the three different ear thermometers ranged from +/- 2.19 degrees F to 2.85 degrees F. These results suggest that there is substantial variation in ear measurements and raise questions about the use of ear thermometers when there are multiple personnel taking temperatures, as occurs in hospital-based clinical practice environments. Handedness of the operator, position of the patient, and the ear used for measurement did not produce clinically significant variability in ear temperature measurements.

Adult↗
PubMed1998

Fatigue in patients with cancer.

This paper reviews current knowledge regarding cancer-related fatigue assessment, prevalence, mechanisms and management. Most quality of life questionnaires contain at least some items pertaining to fatigue and a number of more specific self-assessment tools have now also been developed. As a results, there is a growing body of literature which documents the extent and severity of fatigue in cancer populations. Unfortunately most of these studies are uncontrolled and do not, therefore, provide an accurate estimate of the prevalence or severity of cancer fatigue relative to that found in the general population. Data from controlled studies are limited and the results are conflicting. Cross-sectional studies suggest that fatigue is the result of a combination of physical and psychological causes. Although no one treatment is proven to alleviate cancer-related fatigue a number of strategies show therapeutic promise.

Cachexia↗
PubMed1998

Evaluation of the mechanical environment during distraction osteogenesis.

Physical forces have been hypothesized to direct the process of bone regeneration during distraction osteogenesis. However, despite significant clinical experience, relatively little is known about how the mechanics of distraction influence bone formation. This study investigated net fixator forces and strains in the distraction callus during bilateral lengthening of tibiae in New Zealand White rabbits. Distractions yielded a classic viscoelastic response with a sharp increase in fixator force, followed immediately by significant relaxation. Tension acting on mesenchymal gap tissue caused by distraction was estimated to reach more than 30 N by the time full lengthening was achieved. Average maximum cyclic strains within the distraction zone during ambulation were estimated to be 14% to 15% and supported by the results of fluoroscopic imaging. Paradigms for fracture healing have hypothesized that such strains are incompatible with new bone formation. The documented clinical success of distraction osteogenesis at stimulating large volumes of new bone suggests that other mechanisms that warrant additional investigation may be at work during distraction.

Animals↗
PubMed1998

Trisomy 21 associated transient neonatal myeloproliferation in the absence of Down's syndrome.

Although usually associated with Down's syndrome, transient neonatal myeloproliferation (TMD) can occur in the absence of a constitutional trisomy 21. This report describes two such cases, both of whom had a trisomy 21 restricted to clonal cells. Unlike in previous such reported cases, spontaneous morphological, cytogenetic, and molecular remission in both cases was followed by re-emergence, in one case, of an evolved clone with a more malignant phenotype which required pharmacological intervention. Awareness that trisomy 21 bearing leukaemia in the neonatal period can be transient even in the absence of Down's syndrome is important to prevent unnecessary treatment. Equally, such cases require indefinite follow up as a proportion may have a recurrence which may require treatment.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1998

Infant nutrition and cognitive development in the first offspring of a national UK birth cohort.

Several studies show a modest beneficial effect of breastfeeding on cognitive development after controlling for sociodemographic confounders. It is still unclear, however, to what extent this is due to the nutritional advantage of breast milk or to environmental influences associated with breastfeeding. We compared verbal ability scores at age 8 years in 511 first-born offspring of the National Survey of Health and Development who were ever or never breastfed, adjusting for paternal occupation, maternal education, maternal cognitive performance, attendance at nursery school, and maternal age at birth of the participant. A positive association between breastfeeding and cognitive performance was found but this was no longer the case after adjusting for either paternal occupation, maternal education, or maternal cognitive performance in turn. In contrast, an association between breastfeeding and cognitive function was not found for mothers of these offspring. Breastfeeding was increasingly associated with a non-manual social class across the generations although it remains unclear how this might mediate the effect of breastfeeding on cognitive performance.

Adult↗