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Biomedical subjects

D Tremblay

Publications and source records attributed to D Tremblay.

At least 19 recordsLinked to original sources
PubMed2000

Seed misplacement and stabilizing needles in transperineal permanent prostate implants.

BACKGROUND AND PURPOSE: Seed misplacement occurring in transperineal permanent implants contributes to the degradation in dose coverage. It has been suggested that needles could be used to immobilize the prostate and help reduce misplacement. This study investigates the effects of parallel stabilizing needles on seed misplacement. MATERIALS AND METHODS: A group of ten patients implanted with stabilizing needles was compared with a group of 20 patients implanted without stabilization. Measurements were performed on the displacement of individual seeds and needles. The needle measurements are: insertion angle, the ratio of post-implant over pre-implant lengths and the clustering tendency, a measure of relative misplacement among the seeds of the same needle. RESULTS: No difference was observed in seed misplacement. No difference was observed in needle insertion angle, a measure which was expected to improve with the use of stabilizing needles. CONCLUSION: None of the expected effects from the use of parallel stabilizing needles have been observed. This method of prostate contention appears to be without benefits. Seed misplacement is most pronounced along the insertion axis and is caused by friction between prostatic tissues and implantation needles. Reducing friction could be a promising alternative to prostate contention in trying to reduce misplacement.

Algorithms↗
PubMed1999

Local failure is responsible for the decrease in survival for patients with breast cancer treated with conservative surgery and postoperative radiotherapy.

PURPOSE: The aim of the present study was to evaluate the role of local failure (LF) in the survival of patients treated with lumpectomy and postoperative radiotherapy and to investigate whether LF is not only a marker for distant metastasis (DM) but also a cause. METHODS: Charts of patients treated with breast conservative surgery between 1969 and 1991 were reviewed retrospectively. There were 2,030 patients available for analysis. The median duration of follow-up was 6 years. A Cox regression multivariate analysis was performed using LF as a time-dependent covariate. RESULTS: Local control (LC) was 87% at 10 years. Local failure led to poorer survival at 10 years than local control (55% v 75%, P < .00). In a Cox model, local failure was a powerful predictor of mortality. The relative risk associated with LF was 3.6 for mortality and 5.1 for DM (P < .00). In patients with LF, the rate of DM peaked at 5 to 6 years, whereas it peaked at 2 years for patients with LC. The mean time between surgery and DM was 1,050 days for patients without LF and 1,650 days for patients with LF (P < .00). CONCLUSION: Our results show that local failure is associated with an increase in mortality. The difference in the time distribution of distant metastasis for LF and LC could imply distinct mechanisms of dissemination. Local failure should be considered not only as a marker of occult circulating distant metastases but also as a source for new distant metastases and subsequent mortality.

Actuarial Analysis↗
PubMed1997

DHEA-S selectively impairs contextual-fear conditioning: support for the antiglucocorticoid hypothesis.

The authors had reported that glucocorticoids play a selective role in fear conditioning. The adrenal steroid dehydroepiandrosterone (DHEA) has been reported to act as a functional antiglucocorticoid. If DHEA has antiglucocorticoid properties, then its effects on fear conditioning might resemble those produced by adrenalectomy. The authors now report that chronic exposure to high levels of dehydroepiandrosterone sulfate (DHEA-S; converted in vivo to DHEA) produced the same pattern of results as adrenalectomy. Specifically, treatment with DHEA-S impaired contextual fear conditioning 24 hr after conditioning but not immediately after conditioning, and like adrenalectomy, DHEA-S had no effect on auditory-cue fear conditioning. Preexposure to the context before drug treatment eliminated the amnestic effects of DHEA-S, suggesting that, like adrenalectomy, DHEA-S exerted its effect by interfering with the construction of a contextual memory representation. Thus, DHEA appears to act as a functional antiglucocorticoid in the processes that mediate learning and memory.

Acoustic Stimulation↗
PubMed1997

A new penumbra generator for electron fields matching.

Abutment of two or more electron fields to irradiate extended areas may lead to significant dose inhomogeneities in the junction region. This paper describes the geometric and dosimetric characteristics of a device developed to modify the penumbra of an electron beam and thereby improve the dose uniformity in the overlap region when fields are abutted. The device is a Lipowitz metal block placed on top of the electron applicator's insertion plate and positioned to stop part of the electron beam on the side of field abutment. The air-scattered electrons beyond the block increase the penumbra width from about 1.4 to 2.7-3.4 cm with an SSD of 100 cm. The modified penumbra is broad and almost linear at all depths for the 9 and 12 MeV electron beams used in this study. Film dosimetry was used to obtain beam profiles and isodose distributions of single modified beams and matched fields of 9 and 12 MeV as well as matched fields of both energies. Computer simulation was used to optimize the skin gap to be used and to quantify the dose uniformity as a function of the field separation for both modified and nonmodified beams. Results are presented for various field configurations. Without the penumbra generator, lateral setup errors of 2-3 mm may introduce dose variations of 20% or more in the junction region. Similar setup errors cause less than 5% dose variations when the penumbra generator is used to match the fields. The potential of the technique for the irradiation of curved surfaces is presented. A possible method for implementing the modified penumbra into a conventional treatment planning system is evaluated.

Electrons↗
PubMed1997

A selective role for corticosterone in contextual-fear conditioning.

The contribution of corticosterone to contextual- and auditory-cue fear conditioning was examined. Adrenalectomized rats showed reduced contextual-fear conditioning when tested 24 hr after conditioning; however, neither immediate contextual- nor auditory-cue fear conditioning was impaired. Contextual-fear conditioning in adrenalectomized rats with corticosterone replacement during the 4-day interval separating surgery and conditioning matched the level of controls. Moreover, rats exposed to the context prior to adrenalectomy showed normal long-term contextual-fear conditioning. Corticosterone replacement administered after the conditioning episode also negated the effects of adrenalectomy. Thus, corticosterone's role in fear conditioning is selective: It appears to contribute to the neural processes that support the consolidation of a long-term memory representation of the context.

Acoustic Stimulation↗
PubMed1996

Optimization of permanent 125I prostate implants using fast simulated annealing.

PURPOSE: Treatment planning of ultrasound-guided transperineal 125I permanent prostatic implants is a time-consuming task, due to the large number of seeds used and the very large number of possible source arrangements within the target volume. The goal of this work is to develop an algorithm based on fast simulated annealing allowing consistent and automatic dose distribution optimization in permanent 125I prostatic implants. METHODS AND MATERIALS: Fast simulated annealing is used to optimize the dose distribution by finding the best seed distribution through the minimization of a cost function. The cost function includes constraints on the dose at the periphery of the planned target volume and on the dose uniformity within this volume. Adjustment between peripheral dose and the dose uniformity can be achieved by varying the weight factor in the cost function. RESULTS: Fast simulated annealing algorithm finds very good seed distributions within 20,000 iterations. The computer time needed for the optimization of a typical permanent implant involving 60 seeds and 14 needles is approximately 15 min. An additional 5 min are necessary for isodose distribution computations and miscellaneous outputs. CONCLUSION: The use of fast simulated annealing allows for an efficient and rapid optimization of dose distribution. This algorithm is now routinely used at our institution in the clinical planning of 125I permanent transperineal prostate implants for early stage prostatic carcinoma.

Algorithms↗
PubMed1994

Intake, digestibility, and ruminal degradability of shredded hay.

Thirty-two Outaouais intact male lambs averaging 39.1 kg were assigned randomly to a 2 x 2 factorial arrangement of treatments consisting of two forages and two methods of harvesting to determine intake and digestibility. The four treatments fed during the experiment consisted of alfalfa and timothy hays harvested with either a prototype mat maker or a conventional mower conditioner. Hays were fed for ad libitum intake for the entire experiment, and data on digestibility and intake were collected for 9 d after a 21-d adaptation. Ruminal degradability of DM, N, and ADF of hays was estimated with two fistulated cows using nylon bags incubated up to 96 h. Harvesting with the prototype mat maker compared with the conventional mower generally increased intake and digestibility of alfalfa and timothy hays. Ruminal degradability of DM and the potentially degradable fraction of DM and ADF was higher when hay was harvested with the prototype mat maker than with the conventional mower. The increased digestibility of hay harvested with the prototype mat maker could be explained by the increased digestibility in the rumen because harvesting with the prototype mat maker increased the potentially degradable fraction of DM and ADF. These results suggest that the digestible energy content of hay was increased by shredding.

Analysis of Variance↗
PubMed1993

Pooling plasmas for a rapid answer in pharmacokinetic studies: application to a bioequivalence study of hydrocortisone tablets.

Two methods of plasma pooling in pharmacokinetic studies are described. The first method allows the estimation of the average plasma profile of all subjects receiving a given dose or formulation, with at most as many assays as there are time points. The second method allows to estimate the individual AUCs of all subjects with only a single assay for each drug administration. These techniques were successfully employed to predict the final results of a bioequivalence study of two formulations of hydrocortisone 10 mg tablets. Plasma pooling methods can provide early partial information on the results of pharmacokinetic studies. They can be most useful in bioequivalence studies, where early estimates of the average curves and individual AUCs can lead to a decision not to proceed with all the assays, if bioequivalence appears unlikely. The pooling methods may also have useful potential applications in Phase I ascending dose-tolerance studies and in the field of pharmacokinetic studies in small animals. Further studies are necessary to test these methods in order to gain more information on their reliability in the decision-making process in these fields as well as in bioequivalence studies.

Adult↗
PubMed1993

Milk yield, intake, and blood traits of lactating cows fed grass silage conserved under different harvesting methods.

Thirty-two Holstein cows (8 primiparous) were assigned to negative control or to one of three treatments to assess three forage harvesting and conservation techniques. Forage was harvested as low moisture silage by either a cylinder-type forage harvester, a self-loading forage harvester, or a round baler. Treatment diets were fed from wk 4 to 15 of lactation and consisted of silages harvested by the respective methods supplemented with concentrate at 1.1% of BW. Unsupplemented silage harvested by a cylinder-type forage harvester was used as a control. Daily DMI was higher for cows fed supplemented heap silage cut with either a cylinder-type forage harvester (23.7 kg) or a self-loading forage harvester (22.6 kg) than for cows fed the control (20.0 kg) or supplemented round bale silage (20.1 kg). Milk yield was highest for cows fed supplemented heap silage cut with a cylinder-type forage harvester (26.6 kg/d) and lower for those fed supplemented heap silage cut with a self-loading forage harvester (22.7 kg/d) or the control (20.8 kg/d). Milk composition and digestibilities of DM, N, ADF, and energy were similar among treatments. Postfeeding NEFA concentration decreased more for control cows than for those fed supplemented silage, which was related to greater BW loss. The high milk yield for cows fed supplemented heap silage cut with a cylinder-type forage harvester could be related to a high DMI and low BW gain.

Animal Nutritional Physiological Phenomena↗
PubMed1991

Pharmacokinetics and metabolism of nilutamide.

Data are available on the pharmacokinetics and metabolism of nilutamide in the rat, dog, and human (normal volunteers and patients with advanced prostatic carcinoma). Studies using 14Carbon-nilutamide, radioimmunoassay, and high-performance liquid chromatography (HPLC) are reviewed. In the rat, bioavailability by the oral route was complete. The majority of the plasma radioactivity was unchanged nilutamide up to six hours, t1/2 was seven hours, and clearance was 150 mL/hour/kg body weight. Metabolism studies identified 6 urinary metabolites. The major metabolites result from reduction of the nitro group initially to an hydroxylamine (17%) and then to a primary amino (26%) group. In normal volunteers the compound was rapidly absorbed, displayed linear kinetics over a dose range of 100-300 mg, and declined slowly in plasma with a terminal phase t1/2 of forty-three to forty-nine hours. In studies in 12 patients with advanced (Stage D) prostatic carcinoma, single-dose kinetics after 14C-nilutamide and kinetics with repetitive twice-daily dosing of two to seven weeks were measured. Terminal phase plasma t1/2 of unchanged nilutamide was 56 +/- 19 hours and of total radioactivity 87 +/- 27 hours (mean +/- SD). Area under the curve of plasma radioactivity was 23 to 38 percent unchanged nilutamide. Urinary excretion of radioactivity was slow and incomplete because the collection time was not long enough in regard to t1/2 (mean after 5 days, 62 +/- 10%) and consisted almost entirely of metabolites. Steady-state plasma levels of nilutamide were reached in about two weeks. It can be concluded that in humans, unlike other species, plasma decay of nilutamide is very slow. Elimination is almost exclusively by metabolism. Single-daily dosing is appropriate. Hepatic impairment could be expected to prolong plasma decay; renal impairment is likely to have little effect.

Adult↗
PubMed1990

Pharmacokinetics of cefodizime administered intravenously as a single-dose (1.0 and 2.0 g) to healthy adult volunteers.

Cefodizime is a new third generation cephalosporin for parenteral use. The purpose of this study was to define the pharmacokinetic profile of cefodizime after intravenous dosing with 1.0 and 2.0 g in healthy adult volunteers. Concentrations in plasma were determined over a period of 34 h and in urine over 48 h, using high-pressure liquid chromatographic procedures. Cefodizime displays a long elimination half-life (3.5-3.7 h). Mean total clearance was 2.63 +/- 0.19 l/h and mean renal clearance was 1.37 +/- 0.15 l/h. Areas under the curve were 422 +/- 43 mg.h/l and 757 +/- 39 mg.h/l for 1.0 and 2.0 g respectively. The apparent volumes of distribution were 12.8 +/- 1.81 and 14.3 +/- 1.11. After 1.0 g administration the residual concentrations were 3.94 +/- 0.79 mg/l and 0.38 +/- 0.10 mg/l at 12 and 24 h, respectively; after 2.0 g administration the residual concentrations were 6.80 +/- 1.40 mg/l and 0.65 +/- 0.18 mg/l, at 12 h and 24 h. Cefodizime is mainly eliminated via the kidneys. This profile supports once-daily administration of cefodizime, when indicated in non-life-threatening infections.

Adult↗
PubMed1990

Pharmacokinetics of cefpodoxime in young and elderly volunteers after single doses.

Three pharmacokinetic studies involving single oral doses of cefpodoxime proxetil in healthy volunteers are reported. The first study was to determine the absolute bioavailability of cefpodoxime, the second was to study the relationship between the oral dose of cefpodoxime proxetil and pharmacokinetic parameters of cefpodoxime, and the third was to compare the pharmacokinetics of cefpodoxime in healthy young and elderly volunteers. Half the dose of cefpodoxime orally administered as cefpodoxime proxetil in tablet form reaches the systemic circulation, while 80% of the cefpodoxime absorbed is excreted unchanged in urine. The volume of distribution is large (32.3 l). The pharmacokinetics of cefpodoxime were linear in young and elderly subjects after 100 and 200 mg oral doses, which are those used therapeutically. The Cmax was about 1.4 mg/l (after 100 mg) and 2.6 mg/l (after 200 mg). Deviation from linearity appeared at 400 mg and the effect was confirmed at 800 mg. The differences between young and elderly subjects were negligible, with the exception of the half-life which increased by only 14%, from 2.67 to 3 h. Dosage adjustment is therefore not necessary in the elderly.

Administration, Oral↗
PubMed1990

Multiple dose pharmacokinetics of cefpodoxime in young adult and elderly patients.

Multiple dose pharmacokinetics of a new third-generation cephalosporin, cefpodoxime, were evaluated in adults (15, 18-60 years) and elderly adults (10, greater than or equal to 70 years), all out-patients suffering from acute lower respiratory tract infection. A dose of 200 mg cefpodoxime proxetil (expressed in mg cefpodoxime) was administered 12-hourly for seven to ten days and timed blood samples were evaluated on days 0, 3, 5, 6/7 and on the last day of treatment. Results showed that the pharmacokinetics in adult and elderly patients were comparable with those of healthy volunteers and with each other, with the exception of one elderly patient with severe renal impairment. Dosage adjustment of cefpodoxime proxetil does not therefore appear to be necessary in the elderly unless there is evidence of severe renal insufficiency.

Adolescent↗
PubMed1989

Inhibition of carbonic anhydrases in type I muscle fibers influences contractility.

We tested the effects of inhibiting the carbonic anhydrase activity of rat soleus and extensor digitorum longus muscles on the isometric contractile properties and the resistance to fatigue. SOL and EDL muscles from female rats were incubated in vitro in the presence of methazolamide, a specific inhibitor of carbonic anhydrase, before determining their contractile properties. Methazolamide had no effects on the contractile properties of the soleus muscle (10(-5) or 10(-3) M) and extensor digitorum longus (10(-3) M), except for the half-relaxation time of the soleus muscle which increased significantly. Values for half-relaxation time were significantly increased with both concentrations of the inhibitor. Muscles were then submitted to a fatigue protocol lasting 30 min. During the fatigue test, no significant difference was observed between control and 10(-5) M methazolamide soleus muscles. In presence of 10(-3) M methazolamide however, the soleus muscle showed a significantly increased resistance to fatigue compared with control preparations. No significant effect was observed with the extensor digitorum longus muscle exposed to 10(-3) M methazolamide. Results are discussed in terms of the presence of two different isoforms of carbonic anhydrase that may be associated with calcium uptake and energy metabolic processes, respectively.

Animals↗