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Biomedical subjects

S Meagher

Publications and source records attributed to S Meagher.

At least 19 recordsLinked to original sources
PubMed2006

Design and characterisation of a wall motion phantom.

Arterial wall motion is an essential feature of a healthy cardiovascular system and it is known that wall motion is affected by age and disease. In recent years, methods have been developed for measurement of wall motion with the intention of providing diagnostically useful information. An issue with all of these techniques is the accuracy and variability of both wall motion and derived quantities such as elasticity, which requires the development of suitable test tools. In this paper, a vessel wall phantom is described for use in ultrasound studies of wall motion. The vessel was made from polyvinyl alcohol (PVA) subjected to a freeze-thaw process to form a cryogel (PVA-C). The elastic modulus, acoustic velocity and attenuation coefficient varied from 57 kPa, 1543 m s(-1) and 0.18 dB cm(-1) MHz(-1) for one freeze-thaw cycle to 330 kPa, 1583 m s(-1) and 0.42 dB cm(-1) MHz(-1) for 10 freeze-thaw cycles. Wall motion was effected by the use of pulsatile flow produced from a gear pump. The use of a downstream flow resistor removed gross distortions in the wall motion waveform, possibly by removal of reflected pressure waves. However, a low amplitude 20 Hz oscillation remained, which is unphysiologic and thought to be caused by the vibration of the distended PVA-C vessel.

Arteries↗
PubMed2004

Determining zygosity in early pregnancy by ultrasound.

OBJECTIVES: First-trimester ultrasound can reliably determine chorionicity but not zygosity. We set out to investigate whether it may be possible to determine zygosity using ultrasound by noting the number of corpora lutea (CLs), structures which reflect ovulation. In the presence of a dichorionic twin pregnancy, the identification of one CL would suggest that twins are monozygotic whereas two CLs implies dizygosity. METHODS: This was a retrospective analysis of predominantly spontaneous twin pregnancies presenting for an early pregnancy ultrasound at 5-8-completed weeks of gestation. Placentation was correlated with presumed zygosity as predicted by the number of CLs present. RESULTS: Of 33 twin gestations, chorionicity was compatible in all cases with the predicted zygosity. In 15 cases one CL was seen and these were designated monozygotic. Of these, four were of monochorionic placentation and 11 dichorionic. The remaining 18 cases had two CLs and were presumed dizygotic; all were of dichorionic placentation. CONCLUSION: We propose a novel technique of zygosity determination during very early pregnancy which may have implications both clinically and in genetic research involving twins. However, this study requires further verification by comparing ultrasound results with DNA evidence taken after birth.

Corpus Luteum↗
PubMed2003

First-trimester diagnosis of micrognathia as a presentation of Pierre Robin syndrome.

We describe a case of first-trimester diagnosis of micrognathia. A transvaginal ultrasound scan performed at 13 weeks' gestation revealed an abnormal fetal facial profile consisting of a small mandible and a receding chin. A subsequent amniocentesis at 15 weeks' gestation revealed a normal karyotype. A morphology scan and subsequent postmortem examination at 19 weeks confirmed the first-trimester findings and revealed, in addition to the facial pathology, a complex cardiac abnormality and unilateral talipes equinovarus. These findings are consistent with the diagnosis of Pierre Robin syndrome.

Abortion, Induced↗
PubMed2003

Ultrasound prediction of risk of spontaneous miscarriage in live embryos from assisted conceptions.

OBJECTIVE: An accurate method to predict subsequent miscarriage in live embryos has not yet been established. This pilot study aimed to determine the most discriminatory ultrasound-based model for predicting spontaneous miscarriage after embryonic life was first detected in assisted conceptions. A method for estimating individual risk of miscarriage was developed. METHODS: This was a prospective cross-sectional survey of 322 live singleton embryos in women from an assisted reproductive technology program. Mean sac diameter (MSD), crown-rump length (CRL), embryonic heart rate (EHR), maternal age and gestational age at the first transvaginal scan detecting embryonic life (between 42 and 62 days) were observed. These variables were included in a multivariate model for predicting spontaneous miscarriage occurring prior to 20 weeks. MSD, CRL and MSD minus CRL were assessed in univariate logistic regression analyses. The global diagnostic accuracy of each model was compared directly using receiver-operating characteristics (ROC) curves. RESULTS: The multivariate model demonstrated the best ROC curve for predicting miscarriage (ROC area 0.87; 95% CI, 0.80-0.95). The separate univariate analyses had less diagnostic accuracy. In particular, MSD - CRL had a significantly smaller ROC area (0.65) than did the multivariate model (P < 0.01). CONCLUSIONS: The most discriminatory test for predicting spontaneous miscarriage in live embryos was a multivariate model, which allows estimation of individual risk levels.

Abortion, Spontaneous↗
PubMed2001

Size and fluctuating asymmetry of morphometric characters in mice: their associations with inbreeding and t-haplotype.

Fluctuating asymmetry (FA), a ubiquitous type of asymmetry of bilateral characters, often has been used as a measure of developmental instability in populations. FA is expected to increase in populations subjected to genetic stressors such as inbreeding or environmental stressors such as toxins or parasites, although results have not always been consistent. We tested whether FA in four skeletal size characters and mandible shape was greater in a population of wild-derived mice reared in the laboratory and subjected to one generation of inbreeding (F = 0.25) versus that in an outbred group (F = 0.00). FA did not significantly differ between the inbred and outbred groups, despite the fact that these two groups differed dramatically in fitness under seminatural population conditions. As far as we know, this is the first study to evaluate the relationship between FA and inbreeding in wild house mice, and our general conclusion is opposite that of earlier work on laboratory inbred strains of mice and their hybrids. Size for two of the characters was significantly less in inbreds than in outbreds, however, and there was a significant difference between inbreds and outbreds in the signed differences of right and left sides in one character (humerus length). Some of the mice in both groups also were heterozygous or homozygous carriers of the t-complex. Because mice carrying this chromosome 17 variant are known to have reduced fitness, we also tested whether they had greater FA than mice carrying non-t-haplotypes. The overall level of a composite FA index calculated from all four characters was in fact significantly higher in the t-bearing mice. These combined results suggest that FA is not a generally sensitive proxy measure for fitness, but can be associated with fitness reductions for certain genetic stressors.

Analysis of Variance↗
PubMed2000

Male-male competition magnifies inbreeding depression in wild house mice.

The detrimental effects of inbreeding on vertebrates are well documented for early stages of the life cycle in the laboratory. However, the consequences of inbreeding on long-term survival and reproductive success (Darwinian fitness) are uncertain for vertebrates in the wild. Here, we report direct experimental evidence for vertebrates that competition increases the harmful effects of inbreeding on offspring survival and reproduction. We compared the fitness of inbred (from full-sib matings) and outbred wild house mice (Mus domesticus) in large, seminatural enclosures. Inbred males sired only one-fifth as many surviving offspring as outbred males because of their poor competitive ability and survivorship. In laboratory conditions, inbreeding had relatively minor effects on male reproductive success and no effect on survivorship. Seminatural conditions did not increase inbreeding depression for females, probably because females were not competing for any critical resources. The overall reduction in fitness from inbreeding was 57%, which is 4.5 times as great as previous estimates from the laboratory. These results have important implications for medicine, conservation, evolutionary biology, and functional genomics.

Animals↗
PubMed1998

Effect of intramural, subserosal, and submucosal uterine fibroids on the outcome of assisted reproductive technology treatment.

OBJECTIVE: To investigate the effect of subserosal, intramural, and submucosal fibroids on the outcome of assisted reproductive technology (ART) treatment. DESIGN: A retrospective comparative study. SETTING: A tertiary referral center for infertility. PATIENT(S): Treatment outcome of 106 ART cycles in 88 patients with uterine fibroids (33 subserosal, 46 intramural without cavity distortion, and 9 submucosal) was compared with that of 318 ART cycles in age-matched patients without fibroids. INTERVENTION(S): Controlled ovarian hyperstimulation and ART. MAIN OUTCOME MEASURE(S): Findings on transvaginal uterine ultrasonography performed before the initiation of treatment and pregnancy and implantation rates. RESULT(S): The pregnancy rates per transfer were 34.1%, 16.4%, 10%, and 30.1% in the patients with subserosal fibroids, intramural fibroids, submucosal fibroids and no fibroids, respectively. The implantation rates were 15.1%, 6.4%, 4.3%, and 15.7%, respectively. Both rates were significantly lower in patients with intramural fibroids than in those with subserosal fibroids or no fibroids. CONCLUSION(S): Pregnancy and implantation rates were significantly lower in the groups of patients with intramural and submucosal fibroids, even when there was no deformation of the uterine cavity. Pregnancy and implantation rates were not influenced by the presence of subserosal fibroids. Surgical or medical treatment should be considered in infertile patients who have intramural and/or submucosal fibroids before resorting to ART treatment.

Adult↗
PubMed1998

Physiological responses of deer mice (Peromyscus maniculatus) to infection with Capillaria hepatica (Nematoda).

Negative effects due to infection have not been documented for most natural host-parasite associations. I performed an infection experiment to measure the physiological consequences of infection by Capillaria hepatica in deer mice (Peromyscus maniculatus gracilis). Compared to their uninfected siblings, infected mice displayed increased serum concentrations of alkaline phosphatase and total proteins and reduced concentrations of albumin. Infected mice also had higher hematocrits and enlarged livers and spleens. There was no difference in swimming endurance between infected and control animals, possibly because mice did not perform at maximum aerobic capacity. Sex differences in alkaline phosphatase and albumin levels suggest that females are more sensitive to similar burdens of C. hepatica. Different hematocrit responses between mice from 2 localities suggest that historical associations can lead to evolutionary change in pathophysiology caused by this nematode. Further experiments would reveal whether these disturbances lead to reductions in host fitness.

Alkaline Phosphatase↗
PubMed1997

A microsatellite-based MHC genotyping system for house mice (Mus domesticus).

Major histocompatibility complex (MHC) genes are the most polymorphic loci known for vertebrates. Although this has been known for over two decades, the selective forces maintaining this genetic diversity are unclear. Efforts to study selection on these loci in nature have been hampered because no simple MHC typing systems are available. Here, we describe and evaluate a microsatellite-based MHC genotyping system for house mice (Mus domesticus). Thirty-five MHC-linked microsatellite loci were tested for amplification and scoring reliability, and 21 were deemed useful. These 21 loci were efficient at discriminating among nine serologically distinct MHC haplotypes, with 52% of microsatellite pairs providing 100% resolution. Since these microsatellite loci are scattered across the entire MHC region, they will be effective at detecting recombinant haplotypes. The number of alleles is higher for microsatellites inside the MHC than outside it, which presumably reflects genetic hitchhiking with MHC alleles under balancing selection. This microsatellite typing system now allows testing hypotheses about the nature of selection operating on MHC genes in natural populations of M. domesticus and other murid rodent species.

Alleles↗
PubMed1996

Early second-trimester determination of fetal gender by ultrasound.

Ultrasound identification assists in determining chorionicity in twins, in the interpretation of sex chromosome mosaicism and aneuploidy and in sex-linked conditions presenting after 14 weeks. This study addresses the frequency and accuracy of gender identification in a series of consecutive patients presenting for amniocentesis for genetic indications. Amniocentesis was performed at 14-20 weeks in 843 fetuses over a 5-year period. Ultrasound prediction of fetal gender was documented in 93.3% (770/843). The overall accuracy of diagnosis of fetal gender was 99.3% (765/770). Errors in diagnosis of gender were more likely to occur in the assessment of the female fetus. Such errors in diagnosis may be minimized by combining both tangential/transverse and sagittal views of the fetal perineum.

Amniocentesis↗
PubMed1995

Twin-twin transfusion syndrome: intraamniotic pressure measurement in the assessment of volume reduction at serial amniocenteses.

Two cases of severe twin-twin transfusion syndrome are described. In both, serial amniocenteses were followed by resolution of the disordered inter-twin haemodynamics with 4 intact term survivors. In all reports to date of aggressive reduction with or without successful outcome, volume reduction has been dictated by subjective or semiquantitative ultrasonic estimates of liquor volume. With the use of intraamniotic pressure estimation we describe a more rational basis for the removal of these large volumes of amniotic fluid.

Acute Disease↗