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PubMed1991

High-performance liquid chromatographic (HPLC) analysis of oligomeric components of the spermicide nonoxynol-9.

The commercially available Nonoxynol-9 spermicide is a multicomponent mixture of oligomers. When Nonoxynol-9 was separated by normal phase gradient HPLC, 17 components were shown to exist in the commercial mixture. These oligomeric components follow a Poisson distribution around the most abundant oligomer, EO 8 (11.7%). Select oligomers were isolated by preparative HPLC (Rt = 19.6, 34.0, 45.6, 51.2, 61.6, and 79.2 min) and purified by HPLC. These were identified by FAB-MS and NMR to be the oligomers EO 3, EO 6, EO 8, EO 9, EO 11, and EO 16, respectively.

Chromatography, High Pressure Liquid↗
PubMed1996

Tmax: an unconfounded metric for rate of absorption in single dose bioequivalence studies.

PURPOSE: While peak drug concentration (Cmax) is recognized to be contaminated by the extent of absorption, it has long served as the indicator of change in absorption rate in bioequivalence studies. This concentration measure per se is a measure of extreme drug exposure, not absorption rate. This paper redirects attention to Tmax as the absorption rate variable. METHODS: We show that the time to peak measure (Tmax), if obtained from equally spaced sampling times during the suspected absorption phase, defines a count process which encapsulates the rate of absorption. Furthermore such count data appear to follow the single parameter Poisson distribution which characterizes the rate of many a discrete process, and which therefore supplies the proper theoretical basis to compare two or more formulations for differences in the rate of absorption. This paper urges limiting the use of peak height measures based on Cmax to evaluate only for dose-dumping, a legitimate safety concern with any formulation. These principles and techniques are illustrated by a bioequivalence study in which two test suspensions are compared to a reference formulation. RESULTS: Appropriate statistical evaluation of absorption rate via Tmax supports bioequivalence, whereas the customary analysis with Cmax leads to rejection of bioequivalence. This suggests that the inappropriate use of Cmax as a surrogate metric for absorption rate contributes to the unpredictable and uncertain outcome in bioequivalence evaluation today.

Absorption↗
PubMed1999

A comparison of methods for estimating individual pharmacokinetic parameters.

Characteristics of the methods for estimating individual pharmacokinetic parameters are compared both theoretically and numerically. The methods examined represent the range of most of modern methods and include the ordinary least squares, iteratively reweighted least squares, extended least squares, generalized least squares, maximum quasi-likelihood and its extended scheme, and minimum relative entropy methods. When the function representing the mean itself is used as a variance function, which may be then related to a Poisson distribution, the iteratively reweighted least squares estimator and maximum quasi-likelihood estimator are both identical to that of the minimum relative entropy method. These methods work by minimizing a kind of relative entropy between observed data and corresponding theoretical values. Furthermore, these methods guarantee agreement between the sum of the observed values and the estimate of the sum. This relation does not hold in general for the other estimators. The sum can, in a sense, be viewed as an approximation of the area under the curve. In addition, it is shown by numerical study that these methods are robust against the misspecification of the variance model and work as effectively as such sophisticated methods as the extended least squares, generalized least squares, and maximum extended quasi-likelihood methods. These sophisticated methods require complicated numerical optimization techniques and should be used only in cases where the estimation of the variance function is demanded. In the other cases, the method of minimum relative entropy or its equivalent is sufficient or even preferable for estimating individual pharmacokinetic parameters.

Computer Simulation↗
PubMed2003

Predicting the spread of herbicide resistance in Australian canola fields.

A common concern expressed about the commercial release of transgenic canola into cropping systems is the risks of unwanted gene flow between varieties. Experimental data is emerging that answers some of the theoretical questions that have been posed when considering gene flow on a landscape scale. This study developed models that utilise some of this published data in an attempt to quantify the spread of transgenes in a commercial farming system. The models, which included bootstrapping the empirical data and three mathematical simulations, were compared with each other and the published data. One of the mathematical models estimated average resistance frequency by imposing a Poisson distribution around the published mean value for a single transgenic field surrounded by conventional canola fields and the other two were derived from the theory that pollen flow decreased with distance in the form of a log decay curve. The predictions of all models suggested that the average frequency of resistance occurring from pollen flow in neighbouring canola fields, even when multiple transgenic fields are adjacent to the conventional fields, are likely to be below the current internationally accepted thresholds for contamination.

Australia↗
PubMed1999

Reading population codes: a neural implementation of ideal observers.

Many sensory and motor variables are encoded in the nervous system by the activities of large populations of neurons with bell-shaped tuning curves. Extracting information from these population codes is difficult because of the noise inherent in neuronal responses. In most cases of interest, maximum likelihood (ML) is the best read-out method and would be used by an ideal observer. Using simulations and analysis, we show that a close approximation to ML can be implemented in a biologically plausible model of cortical circuitry. Our results apply to a wide range of nonlinear activation functions, suggesting that cortical areas may, in general, function as ideal observers of activity in preceding areas.

Brain Mapping↗
PubMed2002

Indistinguishable photons from a single-photon device.

Single-photon sources have recently been demonstrated using a variety of devices, including molecules, mesoscopic quantum wells, colour centres, trapped ions and semiconductor quantum dots. Compared with a Poisson-distributed source of the same intensity, these sources rarely emit two or more photons in the same pulse. Numerous applications for single-photon sources have been proposed in the field of quantum information, but most--including linear-optical quantum computation--also require consecutive photons to have identical wave packets. For a source based on a single quantum emitter, the emitter must therefore be excited in a rapid or deterministic way, and interact little with its surrounding environment. Here we test the indistinguishability of photons emitted by a semiconductor quantum dot in a microcavity through a Hong-Ou-Mandel-type two-photon interference experiment. We find that consecutive photons are largely indistinguishable, with a mean wave-packet overlap as large as 0.81, making this source useful in a variety of experiments in quantum optics and quantum information.

Journal Article↗
PubMed2005

Dental procedures can be undertaken without alteration of oral anticoagulant regimen.

DATA SOURCES: Medline provided the primary data source with references from identified articles being reviewed for additional studies. The Cochrane Collaboration database was also searched and a search performed of cited references. STUDY SELECTION: Clinical studies, in English, examining perioperative management of patients receiving long-term oral anticoagulant (OAC) therapy were selected. DATA EXTRACTION AND SYNTHESIS: Data were extracted regarding management strategy, thrombo-embolic events and bleeding complications, and type of surgical or invasive procedure. Event rates were reported as number of patients experiencing the event divided by number of patients at risk. Binomial and Poisson distributions were used to calculate 95% confidence intervals (CI). RESULTS: A total of 31 reports were identified and concluded to be of generally poor quality. For studies reporting thrombo-embolic events, 29 events occurred in 1868 patients (1.6%; 95% CI, 1.0-2.1) of which seven were strokes (0.4%; 95% CI, 0.0-0.7). Major bleeding while receiving OAC was reported to be rare for dental procedures (occurring in four out of 2014 individuals), arthrocentesis (in none out of 32), cataract surgery (none out of 203), and upper endoscopy or colonoscopy with or without biopsy (no occurrences in 111 patients). For the other invasive and surgical procedures reviewed, OAC needs to be withheld and a suitable personalised perioperative management strategy instigated. A guideline, based on the limited evidence available, for the perioperative management of anticoagulation for procedures requiring discontinuation of OAC is presented. CONCLUSIONS: Certain surgical or invasive procedures can be undertaken in patients who are taking OAC therapy without alteration of their regimen. For procedures requiring discontinuation of OAC, personalised management strategies are required. More rigorous studies are needed to better inform this debate.

Comment↗
PubMed1999

A model for population growth of laboratory animals subjected to marker-assisted introgression: how many animals do we need?

This study provides methods for calculating the mean and variance of the number of animals with the desired genotype in each backcross generation for a marker-assisted introgression experiment. The ultimate goal is to produce animals which are homozygous for the desired loci. The methods have been developed specifically for experiments with inbred lines. The model assumes a Poisson distribution for litter size, and is similar to that used in stochastic versions of population dynamics models. Certain biological parameters must be specified as well as parameters under the control of the breeder. These methods can be utilized in designing an experiment to determine the number of founder animals required, given the number of animals required at the completion of the backcross process and vice versa. Consideration is given to minimizing the total amount of genotyping over the entire experiment, by varying the number of times each backcrossed male is used. In addition, an outline is given for an adaptive design that allows for changes in male usage to be made during the experiment.

Animals↗
PubMed1998

p53-mediated transcription induces resistance of DNA to UV inactivation.

A possible role of p53-dependent transcription in the induction of DNA repair was explored by transfecting a UV-irradiated chloramphenicol acetyl transferase (CAT) reporter plasmid (pRGC.FOS.CAT), containing a minimal FOS promoter driven by a consensus p53 binding site, into a p53 negative-mouse cell line [(10)1]. When a p53-expressing plasmid (pSV.p53) was cotransfected into these cells, CAT expression levels persisted even after prolonged UV irradiation. In comparison, CAT expression from pSV2.CAT, which lacks a p53-responsive element in its SV40 promoter, dropped off much more precipitously after UV irradiation in the absence or presence of WT p53 expression. A similar sharp drop was observed with three other constructs when the reporter gene was under the control of the ras, beta-actin or fos promoter. Mouse cells (A1-5) that constitutively express a temperature-sensitive mutant (135 AV) of mouse p53 also generated, at 32 degrees C, higher levels of enzyme expressed from UV-irradiated pRGC.FOS.CAT than from UV-irradiated pSV2.CAT. The frequency of cyclobutane pyrimidine dimers in UV-irradiated pRGC.FOS.CAT was determined with T4 endo V, and the probability of having an undamaged CAT coding strand was calculated by the Poisson distribution for various times of UV-irradiation. The observed relative CAT expression levels from irradiated pSV2.CAT and pRGC.FOS.CAT in the absence of p53 were consistent with those numbers. These results show that WT p53-mediated transcription directs a resistance of the transcribed DNA to UV inactivation and reactivates the reporter gene. Furthermore, some single point substitution mutants of p53 that maintain a near normal ability to activate transcription had lost their ability to extend CAT gene expression after UV irradiation. Conversely, other mutants with reduced transcriptional activity retained this ability. This indicates that although resistance to UV inactivation is transcriptionally-dependent, these two activities are genetically distinct. These data, taken together, suggest that the transcription of UV-damaged DNA by a p53-dependent process promotes its repair.

Actins↗
PubMed2003

Long-term outcome and mortality after transsphenoidal adenomectomy for acromegaly.

OBJECTIVE: Acromegaly has long been associated with increased mortality but few long-term follow-up data are available in patients treated for this disease. We therefore studied a group of 103 patients who underwent transsphenoidal adenomectomy for acromegaly between 1970 and 1999 and were followed for one to 30 years. DESIGN AND PATIENTS: A retrospective chart review was performed on 103 patients living in the province of Quebec, Canada. Mortality data were obtained by hospital charts, contact with the patient's family or death certificates. Stringent biochemical criteria were used to define remission (random GH < 2.5 microg/l, or GH nadir after an oral glucose load is < 1 microg/l and IGF-I within the normal range) and patient survival in the group in remission and the group with persistent disease were compared to survival of the population of Quebec, Canada, using the probabilities of the Poisson distribution. RESULTS: There were four deaths in the perioperative period, one of which was directly related to surgery. Initial remission was obtained in 82% of microadenomas, 60% of macroadenomas and 24% of invasive adenomas. The long-term (> or = 10 years) remission rate for surgery alone was 52%. A second transsphenoidal surgery, radiation therapy and/or octreotide were used in a subset of patients with persistent disease. Long-term remission was obtained in 63% of patients. Five (mean age, 64 years) of the 57 patients in remission died; this rate did not differ significantly from the mortality rate expected in the general population (P = 0.18). Thirteen (mean age, 59.8 years) of the 34 patients with persistent disease died; this rate was significantly higher than that expected in the general population (P = 0.008). CONCLUSIONS: Our observations confirm that uncontrolled acromegaly increases mortality compared to the general population and that mortality rates similar to the general population are restored once remission is induced.

Acromegaly↗
PubMed1999

The certification of a reference material for the evaluation of methods for the enumeration of Bacillus cereus.

A reference material containing Bacillus cereus was certified by the Community Bureau of Reference (BCR) for its number of colony-forming particles (cfp) in 0.1 ml reconstituted capsule solution. To this end, a batch of approximately 15,000 capsules was produced and tested for its homogeneity and stability. The variation in the number of cfp between capsules (homogeneity) was not found to be significantly different from a Poisson distribution. Stability was tested for extended periods at storage temperature (-20 degrees C) and at various higher temperatures up to 37 degrees C for 4 weeks to simulate transport conditions. Only at 37 degrees C did a small but significant decrease in the number of cfp occur. At -20 degrees C, no decrease in the number of cfp was observed over a period of about 4 years. For certification, 12 laboratories determined the number of cfp on two agars: Mannitol Egg-Yolk Polymyxin agar (MEYP, incubated at 30 degrees C) and Polymyxin pyruvate Egg-yolk Bromothymol blue Agar (PEMBA, incubated at 37 degrees C). The certified geometric mean value on MEYP after 24 h of incubation was 53.4 cfp 0.1 ml-1 of the reconstituted capsule solution (95% confidence interval 51.7-55.2) and on PEMBA, 55.0 (95% confidence interval 52.8-57.4). Based on these certified values, user tables were constructed specifying the 95% confidence limits when testing a smaller number of capsules, as would be done in individual laboratories. Based on the information on homogeneity, stability and the certification study, the BCR decided to certify the material as CRM 528.

Bacillus cereus↗
PubMed2003

Cardiac resynchronization and implantable cardioverter defibrillator therapy: preliminary results from the InSync Implantable Cardioverter Defibrillator Italian Registry.

The aim of this study was to evaluate ventricular arrhythmias occurring in recipients of the InSync ICD for the primary and secondary prevention of sudden death. The InSync ICD was implanted in 142 patients (128 men; mean age 65 +/- 10 years) with heart failure (mean NYHA functional Class 3.0 +/- 0.7) and wide QRS (mean 159 +/- 33 ms). The underlying etiology was ischemic in 55%, idiopathic in 33%, and valvular or hypertensive cardiomyopathy in 12% of patients. The numbers of arrhythmic episodes/100 patient-months was computed with their 95% CI, assuming a Poisson distribution. Implants were performed in 48 (34%) patients who did not have an ACC/AHA guidelines Class I indication for ICD therapy. A total of 104 patients were compliant for follow-up visits. During a 9-month median (range 0.1-24) follow-up of 104 compliant patients, 19 experienced a total of 94 ventricular arrhythmias, all successfully interrupted or self-terminated, with a median number of two separate episodes, corresponding to a rate of 10 episodes/100 person-month (95% CI 8-12). A rate of 12 episodes/100 person-months (95% CI 10-15) was measured in the subgroup of patients with ACC/AHA class I indications, versus two episodes/100 person-months (95% CI 1-5) in the remainder of the population. Among 12 deaths, 9 were due to heart failure, 1 to a non-cardiovascular cause, and 2 to unknown causes. The implantation of ICD in heart failure patients has been prominently extended to primary prevention. Patients without standard ICD indications experienced life-threatening arrhythmic events. The impact of ICD combined with cardiac resynchronization therapy on arrhythmic profile, mortality, and costs in this subgroup of patients need to be more precisely studied, with a particular focus on the various types of underlying heart disease.

Adult↗
PubMed2000

Increased risk of secondary cancers in patients with primary cutaneous T cell lymphoma.

As putative etiologic factors of primary cutaneous T cell lymphomas may have a general cancerogenic effect, we wanted to assess the risk of secondary malignancies in 319 patients diagnosed with histopathologically verified cutaneous T cell lymphomas and reported to the Finnish Cancer Registry during the years 1953-95. Standardized incidence ratios were defined as the ratio of observed to expected numbers of cases. To obtain the expected numbers of cancer, age-, sex-, and period-specific Finnish incidence rates were applied to the appropriate person-years under observation. Ninety-five percent confidence intervals were calculated assuming a Poisson distribution. For the whole period, we detected 36 secondary cancers whereas 26 were expected (standardized incidence ratios 1.4, 95% confidence intervals 1.0-1.9). The overall risk of lung cancer was significantly increased (standardized incidence ratio was 2.7, 95% confidence intervals were 1.4-4.8); and in particular small-cell lung cancer showed high standardized incidence ratios (standardized incidence ratio was 8.5, 95% confidence intervals were 2.8-20). Also, the risk of lymphomas was elevated (standardized incidence ratios for Hodgkin and non-Hodgkin lymphomas combined were 7.0, 95% confidence intervals were 1.9-18). The incidence of other cancers was similar to the national ratios. An increased risk of secondary cancers and in particular small-cell cancer of the lung and lymphomas among patients with primary cutaneous T cell lymphoma is demonstrated. In clinical practice, lung cancer and lymphomas must be kept in mind when following up patients with cutaneous T cell lymphomas.

Adolescent↗
PubMed2003

Glomerulonephritis and malignancy: a population-based analysis.

BACKGROUND: An association between glomerulonephritis and malignant tumors has previously both been found and discarded in clinical series, but to our knowledge never has been tested in a population-based setting. METHODS: The Danish Kidney Biopsy Registry includes all kidney biopsies performed from 1985. Using a unique personal identification number, each person in the registry to the National Population Registry and the Danish Cancer Registry were linked. Cancer occurrence after the biopsy was compared in patients with morphological, glomerular diseases with that of the general Danish population, taking into account sex, age, calendar period and time since biopsy, and the 95% confidence interval (95% CI) for the observed-to-expected rates was calculated, assuming a Poisson distribution. Cancer occurrence was stratified to <1 year, 1 to 4, and >or=5 years after a biopsy. RESULTS: A total of 102 de novo cancers were found in 1958 patients. These cancers represent a two- to threefold excess of the expected number at <1 and 1 to 4, but not >or=5 years after a biopsy. Non-Hodgkin's lymphomas were observed six to eight times more than expected. Cancer excess was seen in glomerulonephritides with a known or suspected virus etiology. CONCLUSIONS: The excess cancer rate could be the result of underlying undiagnosed tumors whose antigens have initiated glomerulonephritis, or the immunosuppressive therapy that initiated or energized tumor cells. Based on the findings in our study, there is some support for an association to persistent viruses causing first the glomerulonephritides and then the malignancies, perhaps through a common pathogenesis. This calls for other studies to be done that are specifically designed to investigate this issue, with more data on patient characteristics and confounders.

Female↗
PubMed1991

Sampling errors and the precision associated with counting very low numbers of white cells in blood components.

Attention to the accurate and precise measurement of the white cell (WBC) content of transfused products has risen in response to awareness of the potential benefits of WBC-depleted components and the development of technical capabilities to produce these components. The techniques thus far reported have focused on the reliability of detecting a WBC, provided it is present in the test system. The likelihood of selecting a WBC from the product of interest for counting in the analytical system--that is, the sampling error--must also be considered. The occurrence of a WBC in a WBC-depleted component is a rare event and may be modeled with the binomial or the Poisson distribution. Several assay techniques were analyzed by using these distribution models to determine the confidence intervals of the WBC content. The 95-percent confidence intervals spanned more than 2 logs10 for some methods at 3 x 10(5) WBCs per product. It is concluded that the reporting of WBC content for research provides not only the estimate of the mean but also a confidence interval for this estimate. Quality control procedures should be designed to verify that the WBC content is less than the targeted amount and should provide an associated statement of confidence.

Blood Platelets↗
PubMed2003

Increasing blood availability by changing donation patterns.

BACKGROUND: There is a declining margin between US blood collections and transfusions. Donation patterns were examined to characterize returning first-time donors and predict the impact on blood availability of decreasing the number of nonreturning donors. STUDY DESIGN AND METHODS: First-time donors giving between 1991 and 1994 were followed for 3 to 6 years. The impact of decreasing the number of nonreturning donors in a 12-month period was projected using the Poisson distribution to model the donation patterns of 539,063 donors who gave in 1995. Repeat donors were classified as "returning first-time" (gave a first-time donation within 12 months of their index donation), "established" (gave a repeat donation), and "inactive" (didn't donate in the 12 months before their index donation). RESULTS: A total of 49 percent of first-time donors did not return within 6 years. Returning first-time donors tended to be US born, white, and had more than a high school education. In 1995, 30 percent of donors were first time, 31 percent were established, 7 percent were returning first time, and 32 percent were inactive, giving 1.5, 2.4, 1.9, and 1.7 donations in 12 months, respectively. Reducing nonreturning donors by 5 percent could increase blood collections by 2.7 percent. Similarly, 15 or 25 percent reductions in nonreturns could increase collections by 8.6 or 16.0 percent, respectively. CONCLUSIONS: Most donors are not giving near the donation limit. A substantial increase in donations could be achieved by a relatively small decrease in donor nonreturn. Research is needed to understand why approximately half of first-time donors donate only once.

Behavior↗
PubMedDate not supplied

Temporal and spatial patterns of the clinical surveillance of BSE in France, analysed from January 1991 to May 2002 through a vigilance index.

Between 1991 and mid 2000, the surveillance of Bovine Spongiform Encephalopathy (BSE) in France was based solely on clinical surveillance through a Mandatory Reporting System. Since 2000, the implementation of active surveillance programmes using rapid tests, as a complementary tool targeted at dead and slaughtered cattle has shown that part of the BSE cases were not detected with the clinical surveillance. In order to obtain a better knowledge of the strength of the clinical surveillance, we analysed a vigilance index defined as the ratio of negative clinical suspicions to the cattle population in the region and period of interest. The temporal analysis of the vigilance index showed that it did not vary much between 1991 and 1999, increased sharply since 2000, and then decreased partly in 2001. The geographical analysis of the variations of the vigilance index was performed at the department level by comparing the observed number of negative clinical suspicions per department to the expected number, computed on the basis of the national average index and standardised on the production type of the cattle - dairy versus beef suckling cattle. As assumed, the data followed a Poisson distribution. We observed a high geographical variation of the vigilance index: ten departments out of 91 presented a significantly higher vigilance index than the national one, and four a significantly lower vigilance index. The vigilance index showed that the clinical surveillance was heterogeneous during the past twelve years, both in time and geographic location, in a range of one to ten. So the apparent trend in the BSE epidemic during this period as well as the differences in the spatial incidence of BSE have to be analysed with caution.

Animals↗
PubMedDate not supplied

Poultry, pig and the risk of BSE following the feed ban in France--a spatial analysis.

A spatial analysis was carried out in order to analyse the reason why the risk of Bovine Spongiform Encephalopathy (BSE) was spatially heterogeneous in France, during the period following the feed ban of Meat and Bone Meal to cattle. The hypothesis of cross-contamination between cattle feedstuff and monogastric feedstuff, which was strongly suggested from previous investigations, was assessed, with the assumption that the higher the pig or poultry density is in a given area, the higher the risk of cross-contamination and cattle infection might be. The data concerned the 467 BSE cases born in France after the ban of meat and bone meal (July 1990) and detected between July 1st, 2001 and December 31, 2003, when the surveillance system was optimal and not spatially biased. The disease mapping models were elaborated with the Bayesian graphical modelling methods and based on a Poisson distribution with spatial smoothing (hierarchical approach) and covariates. The parameters were estimated by a Markov Chain Monte Carlo simulation method. The main result was that the poultry density did not significantly influence the risk of BSE whereas the pig density was significantly associated with an increase in the risk of 2.4% per 10 000 pigs. The areas with a significant pig effect were located in regions with a high pig density as well as a high ratio of pigs to cattle. Despite the absence of a global effect of poultry density on the BSE risk, some areas had a significant poultry effect and the risk was better explained in some others when considering both pig and poultry densities. These findings were in agreement with the hypothesis of cross-contamination, which could take place at the feedstuff factory, during the shipment of food or on the farm. Further studies are needed to more precisely explore how the cross-contamination happened.

Animal Feed↗