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Biomedical subjects

J D Fenwick

Publications and source records attributed to J D Fenwick.

At least 37 records · Page 2Linked to original sources
PubMed1999

Severe ovarian hyperstimulation syndrome following salvage of empty follicle syndrome.

We report a case of severe ovarian hyperstimulation syndrome (OHSS) following a rescue of empty follicle syndrome (EFS). This suggests that the risk of developing OHSS remains unaltered even in the presence of EFS. The case supports the possibility of obtaining oocytes that fertilize and cleave normally after a second dose of human chorionic gonadotrophin (HCG) and a repeat oocyte retrieval. It supports the suggestion that the follicles are not necessarily empty in EFS. It demonstrates further that OHSS cannot be prevented by aspiration of follicular fluid and patients with large numbers of follicles and EFS must be warned of this potential complication.

Adult↗
PubMed1998

Spectral reconstruction of clinical megavoltage photon beams and the implications of spectral determination on the dosimetry of such beams.

An analysis technique, based on simulated annealing, is described which is employed to derive megavoltage photon beam spectral information from narrow beam attenuation measurements. Megavoltage photon beam spectra have been determined using this technique for linear accelerators from different manufacturers, and different models from individual manufacturers at a range of energies from nominal 6 MV to nominal 25 MV. All of the photon beams included in the study are in routine clinical use. The subsequent effects on dosimetry of employing derived primary spectra to specify beam quality are examined. The results suggest that the quality index TPR(20)10 may be insensitive to beam quality changes for high-energy beams in the range of 15 MV to 25 MV. Although the quality index may be insensitive as a beam quality specifier at these higher qualities, the actual difference in the calculated dose delivered using derived spectra as the quality specifier rather than TPR(20)10 is likely to be small, the results obtained indicating a difference of between 0.2% and 0.7% in the calculated dose delivered.

Biophysical Phenomena↗
PubMed1998

Predicting the radiation control probability of heterogeneous tumour ensembles: data analysis and parameter estimation using a closed-form expression.

A closed-form formula describing the tumour control probability (tcp) of a heterogeneous collection of tumours has been obtained by analytically averaging the homogeneous double-exponential tcp formula over inter-tumour distributions of clonogen radiosensitivity, density and repopulation rate, tumour volume and dose. The formula can be straightforwardly and relatively quickly fitted to clinical data, yielding radiobiological parameter values for use in tcp modelling. The formula was fitted to published tcp data which catalogued tumour control records grouped by dose and tumour volume, and treatment duration. Fitted parameter values, confidence intervals and goodness-of-fit statistics were determined. The sets of parameter values obtained are unique only to within a scaling factor. The formula provides non-rejectable fits to data which grouped tcp by dose and volume when radiosensitivity parameters take values close to laboratory estimates, the fitted volume dependence parameter, however, taking rather high values. Good fits are obtainable with the intuitively reasonable volume parameter value of one, but with radiosensitivity values around one-third of their laboratory estimates. Non-rejectable fits to data which grouped tcp by dose and treatment duration may be obtained with radiosensitivity and repopulation rate parameters lying close to laboratory estimates.

Breast Neoplasms↗
PubMed1996

Absorption of radiocaesium by sheep after ingestion of contaminated soils.

The absorption of 137Cs by sheep following ingestion of contaminated soil was studied using an established dual isotope method. Two agricultural soils were studied: an alluvial gley contaminated by discharges to the sea from the Sellafield Reprocessing Plant, and a lowland organic soil that had been artificially contaminated. Values of the true absorption coefficient of radiocaesium of 0.19 +/- 0.03 and 0.03 +/- 0.01, respectively, were obtained for these soils. This implies that availability of soil-associated radiocaesium for uptake following ingestion is up to about 20% of that when the activity is incorporated in vegetation. These results have been compared to estimates of availability made using an in-vitro approach described previously and found to be in good agreement. However, comparison with in-vitro data obtained for an upland peat indicated that absorption from some upland organic soils could be greater than from the lowland organic soil.

Absorption↗
PubMed1994

Comparison of stable isotopes and radioisotopes in the measurement of iron absorption in healthy women.

1. Stable isotope methods are being used to investigate the absorption of dietary iron. In order to be certain that this new methodology is accurate, we have compared results obtained using stable isotopes and inductively coupled plasma mass spectrometry with those determined using a radioisotope and whole body counting. 2. The stable isotope 54Fe (2.8 mg) was given to 10 healthy non-pregnant women. Six women received the isotope in aqueous form, and four took it with a meat meal. The 54Fe served as a carrier for 10 ng of the radioisotope 59Fe. An ampoule (200 micrograms) of the isotope 57Fe or 58Fe was then given intravenously, and in serum samples taken over the next 10 h the ratios of the stable iron isotopes were measured by inductively coupled plasma mass spectrometry and the oral iron absorption was calculated. This was then compared with the results obtained by using a whole body counter to measure (on day 0 and day 14) the gamma-activity emitted by the radioisotope. 3. The mean iron absorption measured by both methods ranged from 8% to 45%. Measurement of the post-absorptive serum enrichment of the stable isotopes provided estimates of absorption from both aqueous and food iron which were similar to that yielded by whole body counting, the mean difference being -1.5% (95% confidence interval -5.2 to 2.1%). Absorption estimated by stable isotopes exhibited the same inverse relationship with the serum ferritin level (body iron stores) to that known to exist with whole body counting.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Intercomparison of whole-body counters using a multinuclide calibration phantom.

Whole-body counters in the UK have been compared using a multinuclide anthropomorphic phantom. A standard Bush phantom was modified by inserting channels into the long axis of each section. Radionuclide sources sealed in a urea-formaldehyde polymer were then inserted into the channels to simulate distributions of radioactivity in a human. The phantom was taken to 10 whole-body counters in the UK and estimates of 134Cs, 137Cs and 40K were obtained both separately and as mixtures. Results showed close agreement between the median estimates and the known activities. The technique also allowed diagnosis of particular problems in calibration for several of the counters.

Calibration↗
PubMed1990

The influence of furosemide on plasma elimination and urinary excretion of drugs in standardbred horses.

A study of the effects of intravenous administration of either 150 mg or 250 mg of furosemide to standardbred mares pre-treated with other drugs was undertaken to determine whether a unique pattern of drug elimination into urine and from plasma for each compound occurred. Furosemide significantly reduced the plasma concentrations of codeine compared to control 2-6 h after furosemide administration. In contrast, the plasma concentrations of theophylline, phenylbutazone, pentazocine, guaifenesin and flunixin were not markedly altered by furosemide. In the case of acepromazine, clenbuterol and fentanyl, the data generated were insufficient to state with certainty whether or not furosemide affected the plasma concentrations of these three drugs. A significant reduction was noted in the urinary concentrations of guaifenesin, acepromazine, clenbuterol, phenylbutazone, flunixin, fentanyl and pentazocine within 1-4 h of furosemide administration. The urinary concentrations of theophylline remained reduced as long as 8 h after furosemide injection. Furosemide administration to horses pre-treated with codeine resulted in depression of urinary morphine concentrations 2-4 h and 9-12 h after furosemide injection. A lower furosemide dose (150 mg) produced changes in drug urinary excretion and plasma elimination equivalent to the higher dose (250 mg). It is evident that furosemide affects the urinary and plasma concentrations of other co-administered drugs but not in a predictable fashion, which limits the extrapolation of these results to as yet untested drugs.

Acepromazine↗
PubMed1989

Evaluation of recent experience in hypoglossal-facial nerve anastomosis in the treatment of facial palsy.

This evaluation of recent experience of hypoglossal-facial nerve anastomosis in ten patients who had undergone acoustic neuroma resection, indicates that this procedure may have a role to play in the treatment of this disfiguring condition. Facial symmetry at rest is satisfactory in the majority of patients, who suffered little long term deficit from the loss of their hypoglossal nerve. This procedure is ideally suited to otolaryngological practice.

Adult↗
PubMed1988

Fluid dynamics during bronchoalveolar lavage.

A series of related studies were designed to investigate and quantify the degree of fluid exchange between the lung segment and the interstitium or pulmonary circulation that occurred during a standardized bronchoalveolar lavage (BAL). In 5 subjects undergoing a 3 x 60 ml BAL, the dilution of introduced fluid was calculated at approximately 25% using both technetium colloid and methylene blue. Thus, there was a total dilution volume of about 225 ml. In the same experiment, tritiated water was incorporated into the introduced fluid, and the degree of dilution of tritium in the aspirate was compared with that of the other 2 markers. The dilution of tritium was greater than anticipated, suggesting that around 55 ml of water had effluxed from the lung segment during BAL. The total fluid gain by the segment during BAL was thus approximately 100 ml (44% of the dilution volume), although the contribution of fluid resident in the lung prior to BAL to this volume was not known. The 3 x 60 ml BAL procedures were performed in a further 5 patients 12 h after they had received tritiated water orally. The concentration of urea, a putative "endogenous marker" of dilution, was assayed simultaneously in plasma and aspirate. From these values the fluid normally resident in the lung segment was calculated to contribute at most about 2% to the total aspirated volume. A median of 39% of the 85 ml aspirated was calculated to have come from the circulation or surrounding interstitium by simultaneous measurements of the concentrations of tritium in plasma and lavage aspirate.(ABSTRACT TRUNCATED AT 250 WORDS)

Body Water↗
PubMed1987

Presence of salicylic acid in standardbred horse urine and plasma after various feed and drug administrations.

Plasma and urinary levels of salicylic acid were examined in Standardbred mares after administration of various feeds, containing different compositions of hay. In addition, horses were administered acetylsalicylic acid orally and methyl salicylate topically. Elevated salicylic acid levels were observed in horse urine and plasma in animals fed lucerne hay. The plasma and urinary elimination of salicylic acid exhibited a diurnal pattern which was related to the type of feed and the feeding schedule. Within 24 h after oral administration of acetylsalicylic acid, plasma and urine salicylic acid levels were consistent with residual levels observed after feeding lucerne hay. Elimination of salicylic acid was rapid and complete, with a half-life between 5 and 7 h. Topical administration of methyl salicylate (8.4 g) produced elevated urinary salicylic acid levels for 6 h. A smaller dose of methyl salicylate (3.4 g) did not elevate plasma or urine salicylic acid levels above those observed following administration of lucerne hay.

Administration, Oral↗
PubMed1986

Static and sequential dynamic scintigraphy of the tibia following fracture.

Eighty patients who had sustained a fracture of the tibial shaft were studied by scintigraphy using technetium-99m labelled methylene diphosphonate (99Tcm MDP) and a gamma camera. Static scintigrams were obtained in the early stages following injury and examined for the presence of 'cold spots' which may indicate loss of blood supply to fracture fragments; these were found in 10 per cent of cases but did not bear any definite relationship to the normal progression of union. Sequential dynamic scintigrams were obtained at intervals up to 20 weeks after fracture to determine whether a pattern of uptake of tracer could be identified which correlated with the subsequent progression of union, but no significant difference was observed between fractures healing promptly (less than 20 weeks) and those in which healing was delayed (greater than 20 weeks).

Adolescent↗
PubMed1986

Splenunculectomy in thrombocytopenic purpura.

In six patients with thrombocytopenic purpura not cured by splenectomy platelets fell to less than 150 X 10(9)/l within six weeks of splenectomy. They 'failed to respond'. Two underwent splenunculectomy without improvement. Splenuculectomy offered little chance of improvement to published cases who failed to respond but may well be helpful after true relapse.

Child↗
PubMed1982

Vitamin B12 absorption from the gut does not decline with age in normal elderly humans.

In 37 elderly subjects undergoing measurement of whole body retention of 58Co-B12 at 7 and/or 14 days it was observed that significant (greater than 5%) retention of an inert non-absorbable marker (51CrCl3) occurred at 7 days in 23% of subjects and at 14 days in 8% of subjects. In view of the substantial retention of marker at 7 days it is suggested, therefore, that 14-day measurements of B12 retention are more appropriate than 7-day measurements in the elderly. Whole body retention of vitamin B12 at 14 days was measured in 51 healthy elderly subjects. Results obtained did not correlate with age, between 60 and 96 years, and were no different from results obtained from younger subjects in previously reported studies. It is concluded that vitamin B12 absorption, per se, does not decline with age.

Aged↗