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PubMed2000

Analytical and diagnostic performance of troponin assays in patients suspicious for acute coronary syndromes.

BACKGROUND: The controversy whether there is a clinically significant difference between troponin T (cTnT) and troponin I (cTnI) in regard to predictive value and cardiac specificity is still ongoing. METHODS: We evaluated enzyme-linked immunosorbent assay systems for cTnI and cTnT in patients with acute coronary syndromes and multiple control groups to define threshold values for risk stratification and compare their predictive value. RESULTS: In 312 patients with noncardiac chest pain, cTnI levels were below the detection limit of 0.2 microg/L and cTnT levels were 0.011 [0.010-0. 013] microg/L. In patients with end-stage renal failure (n = 26) and acute (n = 38) or chronic (n = 16) skeletal muscle damage, median concentrations were 0.20 [0.20-0.35], below the detection limit, and 0.20 [0.20-0.25] for cTnI, and 0.04 [0.01-0.10], 0.011 [0.005-0.025], and 0.032 [0.009-0.054] microg/L for cTnT. In patients with acute coronary syndromes (n = 1130), maximized prognostic value for 30-day outcome (death, infarction) was observed at a threshold level of 1.0 microg/L for cTnI (29.0% positive) and at 0.06 microg/L for cTnT (35. 0% positive). Significant differences in the area-under-the-curve values were observed between cTnI and cTnT (0.685 vs. 0.802; p = 0. 005). For both markers, the area-under-the-curve values did not increase with the second (within 24 h after enrollment) or third (48 h) blood draw. CTnI showed a less strong association with 30-day outcome than cTnT. When cTnI was put in a logistic multiple-regression model first, cTnT did add significant information. CONCLUSION: By using the defined threshold values and the employed test systems, single testing for cTnI and cTnT within 12 h after symptom onset was appropriate for risk stratification. Despite the lower cardiac specificity for cTnT, it appears to have a stronger association with the patients' outcome, whereas, as previously shown, the ability to identify patients who benefit from treatment with a GP IIb/IIIa receptor antagonist is similar.

Acute Disease↗
PubMed2006

Setting nutrient thresholds to support an ecological assessment based on nutrient enrichment, potential primary production and undesirable disturbance.

The EU Water Framework Directive recognises that ecological status is supported by the prevailing physico-chemical conditions in each water body. This paper describes an approach to providing guidance on setting thresholds for nutrients taking account of the biological response to nutrient enrichment evident in different types of water. Indices of pressure, state and impact are used to achieve a robust nutrient (nitrogen) threshold by considering each individual index relative to a defined standard, scale or threshold. These indices include winter nitrogen concentrations relative to a predetermined reference value; the potential of the waterbody to support phytoplankton growth (estimated as primary production); and detection of an undesirable disturbance (measured as dissolved oxygen). Proposed reference values are based on a combination of historical records, offshore (limited human influence) nutrient concentrations, literature values and modelled data. Statistical confidence is based on a number of attributes, including distance of confidence limits away from a reference threshold and how well the model is populated with real data. This evidence based approach ensures that nutrient thresholds are based on knowledge of real and measurable biological responses in transitional and coastal waters.

Classification↗
PubMed2006

Do oncologists believe new cancer drugs offer good value?

BACKGROUND: Substantial debate centers on the high cost and relative value of new cancer therapies. Oncologists play a pivotal role in treatment decisions, yet it is unclear whether they perceive high-cost new treatments to offer good value or how therapeutic costs factor into their treatment recommendations. METHODS: We surveyed 139 academic medical oncologists at two academic hospitals in Boston. We asked respondents to provide estimates for the cost and effectiveness of bevacizumab and whether they believed the treatment offered "good value." We also asked respondents to judge how large a gain in life expectancy would justify a hypothetical cancer drug that costs $70,000 a year. Using this information, we calculated implied cost-effectiveness thresholds. Finally, we explored respondents' views on the role of cost in treatment decisions. RESULTS: Ninety academic oncologists (65%) completed the survey. Seventy-eight percent stated that patients should have access to "effective" care regardless of cost. Implied cost-effectiveness thresholds, derived from the bevacizumab and hypothetical scenarios, averaged roughly $300,000 per quality-adjusted-life-year (QALY). Only 25% of oncologists felt that bevacizumab offered "good value." CONCLUSIONS: A majority of academic oncologists stated that cost does not influence their clinical practice, nor should it limit access to "effective" care. Yet respondents did not consider all effective drugs to be of good value. Implied cost-effectiveness thresholds were $300,000/QALY--a value higher than the $50,000 standard often cited. A subset of oncologists were sensitive to cost, believing it should factor into clinical decisions. These findings reflect the ongoing controversies within the medical community as expensive new therapies enter the system.

Academic Medical Centers↗
PubMed2005

ECG-gated 16-MDCT of the coronary arteries: assessment of image quality and accuracy in detecting stenoses.

OBJECTIVE: The aim of this study was to investigate image quality and diagnostic accuracy in detecting coronary artery lesions using a 16-MDCT scanner. MATERIALS AND METHODS: Thirty-seven patients (28 men, nine women) underwent unenhanced helical CT and MDCT angiography of the coronary arteries. After patients received oral beta-blocker medication, CT scans were obtained during a single breath-hold with a 16-MDCT scanner using ECG-gating (0.75-mm collimation, 2.8-mm table feed/rotation, 0.42-sec rotation time). The image quality was assessed in terms of artifacts and segment visibility by two reviewers. Stenosis severity was compared with the results of conventional invasive coronary angiography. RESULTS: The data evaluation of the image quality was based on a total of 488 segments, of which 380 segments were considered to have diagnostic image quality. One hundred eight segments (22.1%) could not be sufficiently evaluated because of severe calcifications (35 segments) and motion artifacts (73 segments). The mean calcium score (Agatston score equivalent [ASE]) was 524.3 +/- 807.6. Twenty-eight (75.7%) of the 37 patients had an ASE of less than 1,000 (mean ASE, 90.8 +/- 152.3 [SD]), and nine (24.3%) patients had an ASE of 1,000 or greater (mean ASE, 1,761.0 +/- 637.6). For detecting lesions 50% or greater (without any exclusion criteria), the overall sensitivity, specificity, positive predictive value, and negative predictive value were 59%, 87%, 61%, and 87%, respectively. When limiting the number of patients to those with a calcium score of less than 1,000 ASE, the threshold-corrected sensitivity for lesions 50% or greater was 93%; specificity, 94%; positive predictive value, 68%; and negative predictive value, 99%. CONCLUSION: In patients with no or moderate coronary calcification, MDCT of coronary arteries using 16-MDCT technology allows the reliable detection of coronary artery stenoses with high diagnostic accuracy. Obtaining an initial unenhanced scan was found to be mandatory to avoid performing useless examinations in patients with severe calcifications.

Adrenergic beta-Antagonists↗
PubMed1998

Gas exchange threshold as a predictor of severe postoperative complications after lung resection in mild-to-moderate chronic obstructive pulmonary disease.

Low exercise capacity is considered predictive for postoperative complications or death after thoracic and general surgery. However, in recent literature no agreement has been found about the predictive cut-off values for preoperative exercise parameters. The aim of this work was to investigate whether peak oxygen consumption (V'o2) and noninvasive anaerobic threshold (AT) determined by gas exchange threshold (GET) can be reliable preoperative predictors of mortality and morbidity after lung resection in patients with mild-to-moderate (forced expiratory volume in one second (FEV1) > 50% predicted) chronic obstructive pulmonary disease (COPD). Fifty tour COPD patients were studied before lung surgery: 12 had severe complications, 16 had mild and 26 had no complications. Peak V'O2 sensitivity and specificity in predicting severe postoperative complications were 41.6% and 95.5% respectively (using 75% of the predicted value as cut-off), while for GET they were 91.6% and 97.6% respectively (using 14.5 mL.kg-1.min-1 as cut-off value). Only one patient (3.5%) with a peak V'O2 > 20 mL.kg-1.min-1 suffered severe complications. On the other hand 11 out of the 26 patients (42.3%) with peak V'O2 < 20 mL.kg-1.min-1 had serve complications. In patients with peak V'O2 < 20 mL.kg-1.min-1, 11 out of 12 (91.6%) with a GET < or = 14.5 mL.kg-1.min-1 suffered severe complications, whereas 15 out of 15 (100%) with a GET > 14.5 mL.kg-1.min-1 showed no or mild complications. In conclusion, peak oxygen consumption values > 20 mL.kg-1.min-1 can be considered a safe upper cut-off limit for pulmonary resection. In patients with a peak oxygen consumption value < 20 mL.kg-1.min-1, gas exchange threshold determination can improve significantly the predictivity of a cardiopulmonary test for severe complications and must be routinely considered.

Adult↗
PubMed2005

Integrating chemical and biological criteria.

We present a system to derive benchmarks for protection of aquatic organisms that, as chemical criteria, promotes regulation of contaminants and, as biological criteria, focuses on an endpoint that adequately represents species abundance. The proposed method utilizes quantile regression to quantify the decline in maximum number of organisms with increasing contaminant concentrations. This limiting function then is applied to project the contaminant concentration associated with a threshold number of organisms. The threshold value is defined according to the study's objective and level of desired protection. Here, we defined it as 0.8 x 90th quantile of the number of organisms in samples from reference sites. We use the proposed system to derive taxon-specific, field-based effect concentrations (FECs) for copper and zinc in Ohio, USA, rivers and streams. Comparisons of results with respective chronic values suggest that only the draft criteria for copper are adequately protective. Projected zinc FECs were far lower than respective estimates of chronic values. The FECs likely are less sensitive to impacts of confounding factors because high numbers of organism in samples are observed when negative effects of other stressors are absent or minimal. We discuss other advantages, limitations, and potential applications of the proposed system.

Benchmarking↗
PubMed2002

Assessment of guidelines for limiting exposures to emf using methods of probabilistic risk analysis.

Allowable limits of human exposure to radiofrequency fields commonly include a "factor of safety," typically between 10 to 50, which is somewhat arbitrary. The broad objective in our work is to assess radiofrequency exposure limits, hazard thresholds, and safety factors using methods of probabilistic risk analysis. We focus our analysis on the variables affecting peak radiofrequency specific energy absorption rate (SAR) values in the brain from digital mobile telephones operating at approximately 900 MHz. As SAR is defined as a product of positive random variables, it is not unreasonable to assume that SAR has a lognormal distribution. Our analysis of component SAR variables such as conductivity and permittivity of grey brain matter and radiated field strengths using experimental and numerical modeling data strongly supports our hypothesis that SAR values are distributed lognormally. It then follows that the probability that the SAR exceeds a certain threshold can be derived directly and is shown to be very low for handset SARs relative to presently allowable standard limits.

Electromagnetic Fields↗
PubMed1989

Formation of unique structure in polypeptide chains. Theoretical investigation with the aid of a replica approach.

A replica approach analogous to that used in spin glass systems is implemented to study the configurational space of a heteropolymeric model of protein with a quenched, disordered sequence of links in the limit of a large number of link types. It is shown that there exists a threshold value of chain heterogeneity which separates two qualitatively different types of behavior. For a low degree of heterogeneity the protein globule is like a homopolymer in a collapsed state without definite chain folds: an exponentially large number of folds make a significant contribution to the partition function in this regime. After the threshold heterogeneity has been overcome, the chain freezes drastically but without latent heat; few (approx. 1) frozen states with definite chain folds are thermodynamically dominant in this state. The relation of these results to thermodynamic aspects of protein folding is discussed.

Mathematics↗
PubMed2004

Mercury persistence in indoor environments in the Amazon region, Brazil.

We evaluated the indoor atmospheric Hg contamination in gold trade shops in two Brazilian cities of the Legal Amazon area using the Spanish moss (Tillandsia usneoides, Bromeliaceae) as a sentinel species. Plants inside plastic cages were exposed to a controlled atmosphere to evaluate the rate of Hg retention over time and then distributed in several stores with different characteristics to enable a relative comparison. Hg concentrations were determined by cold vapor atomic absorption spectrophotometry. Plants exposed in active stores with good air circulation exhibited lower levels. Ex-gold trade shops that were kept closed for long periods exhibited higher values. Stores that have been restored before being transformed into new businesses exhibited lower values than nonrestored ones. Direct measurements suggest that indoor Hg air concentrations were below the threshold limit recommended by the World Health Organization to occupational exposure; nevertheless, restoring ex-gold trade shops could ensure a healthier working environment.

Air Pollution, Indoor↗
PubMed2004

Estimating and comparing reduction in HIV-1 RNA in clinical trials using methods for interval censored data.

The magnitude of reduction in HIV-1 RNA levels provides an important complement to the end point based on the percentage of patients achieving HIV-1 RNA levels below a threshold value. Analyses and interpretation of this end point, however, is difficult due to the lower limit of quantification. Crude methods of analyzing HIV-1 RNA data provide biased estimates of the HIV-1 RNA reduction. Censored methods that take into account the censoring of HIV-1 RNA measurements by the limit of quantification greatly improve the analysis of HIV-1 RNA reduction end points. It was shown, however, that when there is a high percentage of censoring, those methods can overestimate HIV-1 RNA reduction. We suggest going a step further, considering that HIV-1 RNA reduction is left-censored by the limit of quantification and right-bounded by the HIV-1 RNA levels at baseline. We then suggest using nonparametric and parametric methods introduced for interval-censored data to analyze such data. A convenient feature of the methodology is the ability to easily handle missing HIV-1 RNA data, although some assumptions are required. For instance, the HIV-1 RNA reduction can be estimated using the so-called "missing = failure" scenario. Graphic procedures to check the validity of using parametric methods are described. The methods are discussed and illustrated with data of 2 recent clinical trials. Surprisingly, it was found that the log10 transformation of the HIV-1 RNA reduction was not appropriate in our data.

Clinical Trials as Topic↗
PubMed1983

Intensity discrimination with cochlear implants.

Intensity difference limens were measured for various frequencies and intensities of sinusoidal and pulsatile electrical stimulation in monkeys with electrodes implanted in the scala tympani, scala vestibuli, modiolus, or middle ear. Difference limens decreased, as a function of initial stimulus intensity, from values of 1.5-3 dB near threshold to as low as 0.5 dB near the upper limit of the dynamic range. If sensation level was held constant, difference limens decreased as a function of frequency up to about 500 Hz, and then remained constant. They were similar across a variety of electrode placements and separations if differences in threshold and dynamic range were taken into account. However, difference limens measured in severely damaged ears were slightly smaller than those in moderately damaged ears. The near miss to Weber's law, characteristic of acoustic difference limens, was not seen with electrical stimuli. Differences limens for electrical stimuli were roughly one-half those for acoustic stimuli; thus, part of the deficit in dynamic range for electrical stimulation compared with acoustic stimulation is countered by the smaller intensity differences limens for electrical stimuli.

Acoustic Stimulation↗
PubMedDate not supplied

Hearing in adult-onset diabetes mellitus.

Hearing acuity and otologic symptoms were examined in 200 patients with adult-onset diabetes mellitus. Data were analyzed according to sex and age and were compared with values of other documented studies; values were within normal limits except in two instances. Speech testing revealed that median speech reception thresholds and median discrimination scores were at the lower limits of normal. Hearing loss and otologic problems did not occur with any increased frequency in patients with adult-onset diabetes mellitus.

Adult↗
PubMed1997

Diagnostic value of tests that discriminate between exudative and transudative pleural effusions. Primary Study Investigators.

STUDY OBJECTIVE: To (1) determine appropriate decision thresholds and diagnostic accuracies for pleural fluid (PF) tests that discriminate between exudative and transudative pleural effusions, and (2) evaluate the quality of the primary investigations. DESIGN: Formal meta-analysis of studies that report the diagnostic value of pleural fluid tests. SETTING: Data collected from international academic medical centers. PATIENTS: Hospitalized patients undergoing thoracentesis for pleural effusions. INTERVENTIONS: Primary investigators were requested to transmit original data from patients described in their studies. MEASUREMENTS AND RESULTS: Eight primary studies described 1,448 patients with one or more of the following tests: protein (P)-PF, P-PF/serum ratio (R), bilirubin (BILI)-R, lactate dehydrogenase (LDH)-PF, LDH-R, cholesterol (C)-PF, C-R, and albumin gradient. We found that all eight tests had similar diagnostic accuracies when evaluated by receiver operating characteristic (ROC) analysis except for BILI-R, which was less diagnostically accurate. Decision thresholds determined by ROC analysis differed from previously reported values for LDH-PF (>0.45 upper limits of normal) and C-PF (>45 mg/dL). Paired and triplet test combinations tended to have higher diagnostic accuracies compared with individual tests, but examination of the odds ratios with 95% confidence intervals did not identify a clearly superior test combination. Limitations of the primary studies presented a high likelihood of bias affecting their results. CONCLUSIONS: Several strategies exist for clinicians in utilizing PF tests to classify effusions as exudates or transudates but accurate interpretations of these test results will require better designed studies.

Albumins↗
PubMed2001

Determination of tumor markers in serum. Pitfalls and good practice.

The determination of tumor markers may have consequences for the patients' treatment, which requires special attention to the analysis and to the expression of the results. In addition to the factors usually dealt with in the pre-analytical phase (identification, quality and storage of the sample) and in the analytical phase (interference, endogenous antibodies, hook effect), we must consider factors such as normal values (which depend heavily on the used techniques), threshold values defining other characteristics (sensitivity, specificity, positive and negative predictive value) and kinetics. Knowledge of the limitations of the tumor marker analysis, in particular tumor markers for non-cancerous diseases leading to possible increases (false positives), is also indispensable. All of this led to the definition of guidelines for good practice, including the design of quality control, rules for requesting, validation and interpretation of results, and the setting up of a serum library.

Antibodies↗
PubMedDate not supplied

Protection goals for residents in the vicinity of civil airports.

Based on extensive and detailed reviews the present paper suggests evaluation criteria for aircraft noise for the prediction of noise effects and for the protection of residents living in the vicinity of (newly constructed or extended) civil airports. The protection concept provides graded evaluation criteria: Critical loads indicate noise loads that shall be tolerated only exceptionally during a limited time. Protection Guides are central evaluation criteria for taking actions to reduce noise immission. Threshold values inform about measurable physiological and psychological reactions due to noise exposures where long term adverse health effects are not expected. Evaluation criteria are provided for various protection goals, for hearing, communication and sleep, for the avoidance of annoyance and of suspected cardiovascular diseases. As protection of the residents is understood as a dynamic process, these criteria must be repeatedly tested and adapted to new scientific findings.

Aircraft↗
PubMed1984

The implication of concentration/response studies of tricyclic antidepressants for psychiatric research and practice.

The action of a drug is mediated by the attainment of an appropriate concentration at an effector site. However, the mechanisms of action of TCA's are complex, with multiple effector sites mediating multiple actions. If a well-defined concentration/response relationship can be demonstrated for a given response, it follows that the responsible drug/effector site interaction is likely to be rapidly reversible. If the effective concentration range is narrow, this may help to identify the particular action responsible for a given response, or to test whether beneficial responses in different settings are mediated by a similar underlying mechanism. The clinical value of defining concentration/response relationships derives from the identification of thresholds of efficacy, and of the limits beyond which the risk of toxicity outweighs the probability of therapeutic gain. The question of what constitutes the 'concentration', and what is meant by 'response' are discussed. Concentration depends upon absorption, distribution, metabolism, concomitant drug administration and elimination. The relative merits of biological, chemical, radioimmuno- and radioreceptor-assays, and the various sources of error which can render measures of concentration inconclusive, are discussed. With regard to the study of the antidepressant response to TCA's the problems involve issues of diagnosis, of trial design, of dosage, of data analysis, as well as response assessment. Given the range of methodological difficulties which have often not been adequately controlled, it is all the more remarkable that broadly consistent concentration/response relationships have been defined for the TCA's.

Antidepressive Agents, Tricyclic↗
PubMed1997

Evaluation of indoor air quality using the decibel concept. Part I--proposal of new units.

Weber-Fechner's law concerning the perception of sound by man with time expressed as a logarithmic function can also be used for the odour constituent used in the evaluation of indoor air quality in buildings. A new unit dB (odour) based on the concentration of Total Volatile Organic Compounds (TVOC) is proposed as it is currently the basis for determining the air change rate. On the Psycho-Physical Scale according to Yaglou, the weakest odour that can be detected by the human small sensors is equal to one and corresponds to the lower limit of percentage dissatisfaction (PD) of 5.8% and a threshold concentration (TVOC) of 50 micrograms/m3-0 dB (odour). The upper limit is determined by the initial value of toxicity TVOC-25,000 micrograms/m3-135 dB (odour). Optimal values corresponding to PD = 20% (according to EUR 14449 EN) and admissible values corresponding to PD = 30% (see Table 3) are proposed, therefore the same values used to evaluate noise can be used to evaluate air quality and additionally the contribution of individual constituents (at present acoustic and odour) to the overall quality of the environment can be ascertained. The determination of the required volume of fresh air for ventilation and air-conditioning systems according to the new principles is the subject of the Part II of this paper.

Acoustics↗
PubMed1997

Evaluation of indoor air quality using the decibel concept. Part II-ventilation for acceptable indoor air quality.

Weber-Fechner's law concerning the perception of sound by man with time expressed as a logarithmic function can also be used for the odour constituent used in the evaluation of indoor air quality in buildings. A new unit dB (odour) based on the concentration of Total Volatile Organic Compounds (TVOC) is proposed as it is currently the basis for determining the air change rate. On the Psycho-Physical Scale according to Yaglou, the weakest odour that can be detected by the human smell sensors is equal to one and corresponds to the lower limit of percentage dissatisfaction (PD) of 5.8% and a threshold concentration (TVOC) of 50 micrograms/m3-0 dB (odour). The upper limit is determined by the initial value of toxicity TVOC -25,000 micrograms/m3-135 dB (odour). Optimal values corresponding to PD = 20% (according to EUR 14449 EN) and admissible values corresponding to PD = 30% (see Part I of this paper) are proposed, therefore the same values used to evaluate noise can be used to evaluate air quality and additionally the contribution of individual constituents (at present acoustic and odour) to the overall quality of the environment can be ascertained.

Acoustics↗