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Biomedical subjects

A M Webb

Publications and source records attributed to A M Webb.

15 recordsLinked to original sources
PubMed2005

The determination of the size and shape of buried InAs/InP quantum dots by transmission electron microscopy.

Bright-field, diffraction-contrast imaging in the transmission electron microscope has been applied to the determination of the diameter and height populations of a single layer of buried, pure, InAs/InP quantum dots (QDs). Plan-view diffraction contrast from the QDs was observed to increase significantly when the sample was tilted away from the [001] growth direction to near the [111] zone-axis orientation. This added contrast was a result of contributions to the displacement of atoms in a direction perpendicular to the electron beam arising from strain in the growth direction. Since the strain in the growth direction was about an order of magnitude larger than the strain perpendicular to the growth direction, as the sample is tilted away from the [001] zone-axis condition, the larger strain component increases the projected strain thereby increasing the QD contrast in the image. For the sample studied, both of the populations for the QD diameter and the image contrast were observed to be multimodal with the seven peaks in the contrast distribution correlating with seven distinct populations of QDs each differing in height by one monolayer (ML), from 3 to 9MLs. An analysis of the theoretically expected and experimentally observed standard deviations in the Gaussian fits to the QD diameter and height distributions provided an additional constraint in the selection of the optimal model for the multimodal distributions.

Journal Article↗
PubMed1999

Persistently high plasma morphine-6-glucuronide levels despite decreased hourly patient-controlled analgesia morphine use after single-dose diclofenac: potential for opioid-related toxicity.

UNLABELLED: We studied the time course of clinical and pharmacokinetic effects after the rectal administration of diclofenac 100 mg in seven patients using patient-controlled morphine (PCA) on the first postoperative day after major spinal surgery. Plots of plasma diclofenac concentrations and pain intensity difference (PID) demonstrated counterclockwise hysteresis consistent with distribution to a central effect compartment such as the central nervous system. Mean +/- SEM (range) maximum PID and its timing were 62%+/-10% (32%-98%) and 309+/-20 (210-360) min after the administration of diclofenac, respectively. Minimal respiratory rates were significantly slower after the administration of diclofenac (P < 0.001), occurring at 197+/-51.9 (60-360) min; arterial desaturations occurred in two patients without oxygen therapy. Plasma morphine and morphine-6-glucuronide (M6G) concentrations interpolated to the average time of minimal respiratory rate indicated decreases of 23%+/-13% (0%-79%) and 1%+/-9% (0%-32%) from their respective starting values. Plasma M6G concentrations were significantly different from baseline only 420 and 480 min after the administration of diclofenac. The potential opioid-sparing effects of a nonsteroidal antiinflammatory drug added during PCA morphine use may not be manifest for several hours. During this lag, plasma concentrations of M6G may reach and remain at levels high enough to increase the risk of respiratory depression and other opioid side effects for hours. IMPLICATIONS: Plasma concentrations of morphine, morphine-6-glucuronide, and diclofenac were measured postoperatively after a single dose of rectal diclofenac 100 mg was added to morphine patient-controlled analgesia. Peak analgesia occurred 309 min and respiratory depression 197 min after diclofenac administration. Morphine consumption had decreased by 20%, but concentrations of the active metabolite morphine-6-glucuronide were unchanged. Vigilance is recommended in patients receiving patient-controlled analgesia opioids and nonsteroidal antiinflammatory drugs.

Administration, Rectal↗
PubMed1997

Intrauterine contraceptive devices and antigestagens as emergency contraception.

Although the Yuzpe regimen of emergency contraception is the one most commonly used, there are alternatives. Copper-containing intrauterine devices are very effective and can be inserted for at least 5 days after unprotected intercourse and sometimes longer. They may, however, transmit pre-existing infection into the upper genital tract and cause discomfort when being fitted. Progestogen-only emergency contraception appears, from WHO studies, to be a useful adjunct to current therapies. Mifepristone has been studied in various doses and has been shown to be very effective but is not yet commercially available. Health services should provide a full range of methods including emergency contraception by appropriately trained people in an acceptable environment.

Contraceptives, Oral, Synthetic↗
PubMed1996

Evidence-guided prescribing of combined oral contraceptives: consensus statement. An International Workshop at Mottram Hall, Wilmslow, U.K., March, 1996.

There is a need to balance the provision of safe and effective contraception against the desire to avoid interventions which might unnecessarily restrict the availability of combined oral contraceptives (COCs). In March 1996, an international group of recognised authorities in their field met to review the available evidence concerning the effects of COCs and the value of various screening procedures in pre-menopausal women. Current scientific evidence suggests only two pre-requisites for the safe provision of COCs: a careful personal and family medical history with particular attention to cardiovascular risk factors, and an accurate blood pressure measurement. Further assessment is required only if a relevant personal or family history is disclosed or the blood pressure is elevated. Only a small minority of women will require this further assessment.

Contraceptives, Oral, Combined↗
PubMed1992

Comparison of Yuzpe regimen, danazol, and mifepristone (RU486) in oral postcoital contraception.

OBJECTIVE: To compare the effectiveness and acceptability of three regimens of postcoital contraception. DESIGN: Randomised group comparison of ethinyloestradiol 100 micrograms plus levonorgestrel 500 micrograms repeated after 12 hours (Yuzpe method); danazol 600 mg repeated after 12 hours; and mifepristone 600 mg single dose. SETTING: Community family planning clinic. SUBJECTS: 616 consecutive women with regular cycles aged 16 to 45 years. MAIN OUTCOME MEASURES: Number of pregnancies, incidence of side effects, and timing of next period. RESULTS: The raw pregnancy rates (with 95% confidence intervals) for the Yuzpe, danazol, and mifepristone groups were 2.62% (0.86% to 6.00%), 4.66% (2.15% to 8.67%), and 0% (0% to 1.87%) respectively. Overall, these rates differed significantly (chi 2 = 8.988, df = 2; p = 0.011). The differences between the mifepristone and Yuzpe groups and between the mifepristone and danazol groups were also significant. Side effects were more common and more severe in the Yuzpe group (133 women (70%)) than in either the danazol group (58 (30%)) or the mifepristone group (72 (37%)). The Yuzpe regimen tended to induce bleeding early but mifepristone prolonged the cycle. Three women bled more than seven days late in the Yuzpe group compared with 49 in the mifepristone group. CONCLUSIONS: Mifepristone was effective in reducing expected pregnancy rates and the Yuzpe method also had a clinical effect. Danazol had little or no effect. A further multicentre trial is needed.

Adolescent↗
PubMed1985

Glycosylated haemoglobin and glycosylated albumin in non-diabetic and diabetic mothers, and their babies.

Glycosylated haemoglobin (GHb), glycosylated albumin (GAlb), and blood glucose were measured from 283 non-diabetic, 7 insulin-dependent diabetic, and 5 gestational diabetic mothers, and in the cord blood of their babies. Significant correlation was found between mother and baby for GHb (r = 0.31) and GAlb (r = 0.42). However, GHb, GAlb and glucose concentration were significantly higher in maternal blood compared to cord blood (p less than 0.001). Only GAlb showed any difference between a pregnant and a non-pregnant population (p less than 0.001). All three parameters were significantly higher in the diabetic mothers compared to the non-diabetic mothers (p less than 0.001). No difference was found between the levels of GHb and GAlb in babies from these two groups. There was no difference in the level of GHb between gestational and insulin-dependent mothers although the latter showed a significantly higher blood glucose (p less than 0.05).

Adult↗
PubMedDate not supplied

Alternative treatments in oral postcoital contraception: interim results.

The study compares the effectiveness and acceptability of three regimes of postcoital contraception: 1) ethinylestradiol 100 micrograms/levonorgestrel 500 micrograms repeated after 12 hours (Yuzpe method); 2) danazol 600 mg repeated after 12 hours; and 3) RU486 600 mg single dose. Between 1 April 1990 and 15 October 1990, 215 women were selected and randomly allocated to the three treatment groups. One hundred and sixty eight were fully followed up, 35 ongoing and 8 lost to follow-up. All women had regular cycles and were aged 16-45 years. All treatments were given within 72 hours of unprotected intercourse and follow-up was until normal menstruation or diagnosis of pregnancy. beta-HCG was measured quantitatively where there was a suspicion of pregnancy. The data obtained show similar failure rates (Yuzpe 1/57, danazol 2/57, RU486 1/54) but more side-effects in the Yuzpe group (nausea 74.1%, vomiting 22.4%, breast tenderness 22.4%) than in the other two (danazol: nausea 31.6%, vomiting 3.5%, breast tenderness 19.3%) and (RU486: nausea 36.4%, vomiting 3.6%, breast tenderness 23.6%). There was one apparent allergic reaction in the danazol group. RU486 caused greater cycle disturbance, prolonging the cycle considerably. Initial results suggest that danazol and RU486 may be much more acceptable methods of postcoital contraception due to reduced side-effects and, in the latter case, single dose. Although numbers are small at present, the effectiveness of the newer methods appear similar to Yuzpe.

Abortifacient Agents↗