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PubMed1993

On the nature of things still going bang in the night: an analysis of residency training in trauma.

In the 1982 Presidential Address to the Society of University Surgeons, Trunkey reported on the inadequacy of surgical education in trauma care. His conclusions were based on American Board of Surgery operative experience data compiled from residents completing surgical training in 1980. The purpose of this study was to compare current resident operative experience in trauma surgery with the American Board of Surgery data from 1980. Yearly resident operative experience data obtained from the Residency Review Committee from 1987 through 1991 were analyzed. The relationship between the percentile rank and the number of operative cases was defined using linear regression. The percentile rank of residents performing a specified number of operative cases was computed using a linear regression coefficient. The results were then compared with previously published 1980 American Board of Surgery summary data. Resident operative experience in trauma surgery was stable over the 5-year period investigated and no significant trends were identified. Comparison of the data from 1980 to 1991 revealed that the percentage of residents performing less than ten cases decreased markedly, from 18% to 9%. Moreover, the percentage of residents claiming fewer than 50 cases declined from 86% to 29%. Based on this analysis, it appears that resident operative experience dramatically increased from 1980 to 1987 and has since remained stable. The reasons for this are unclear but undoubtedly involve the accuracy of reporting operative experience, Residency Review Committee operative trauma definitions, and the actual number of trauma surgery cases available for trainees.(ABSTRACT TRUNCATED AT 250 WORDS)

General Surgery↗

PubMed2005

Predicting fetal anemia by using reference centile charts for liver length, spleen perimeter and umbilical vein maximum flow velocity in Thai fetuses throughout gestation.

AIM: To create reference centile charts for liver length, spleen perimeter and umbilical vein maximum flow velocity (UVVmax) in Thai fetuses in order to predict fetal anemia in Thai fetuses. METHODS: The study was a prospective, cross-sectional study, carried out at the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Faculty of Medicine, Siriraj Hospital, Mahidol University. A total of 780 pregnant women between 13 and 40 weeks' gestation, who attended the antenatal clinic at Siriraj Hospital, Mahidol University, Bangkok, were recruited. Each fetus was measured only once for the purpose of this study. The mean and standard deviation (SD) were estimated at each week of gestation using linear regression modeling. A total of 752 fetuses were measured for fetal liver length, spleen perimeter and UVVmax. Linear regression models were fitted to estimate the mean 95% confidence interval for liver length, spleen perimeter and UVVmax at each gestational age. The centile charts of those parameters were also presented. CONCLUSION: Reference centile charts for fetal liver length, spleen perimeter and UVVmax of Thai fetuses were created.

Anemia↗

PubMed1988

Ultrasonic propagation properties (@ 100 MHz) in excessively fatty rat liver.

The effects on the ultrasonic propagation properties of livers of the addition of 1% orotic acid to rat diets were examined. In rats, dietary orotic acid exerts several effects on lipid metabolism; its overall consequence is that excessively high hepatic fat concentrations are built up over a short period of time, thus making this an ideal model to study the ultrasonic propagation properties as a function of sequential development of fatty liver. Over a 16-day period on the orotic acid diet, the supplemented rat liver lipid concentrations increased from a normal range of 2%-4% to the lower 20's%; hepatic water concentration decreased from a normal value of approximately 70% to approximately 50%; total protein concentration decreased slightly from a normal range of 17%-20% to 11%-16%; and rat liver weight increased from approximately 11 g to around 20 g. Ultrasonic attenuation coefficient and speed were assessed in liver tissue with the scanning laser acoustic microscope at 100 MHz. As hepatic lipid increased, ultrasonic attenuation at 100 MHz increased temporally from a normal range of 12-14 dB/mm to a maximum of 54 dB/mm and ultrasonic speed decreased from a normal range of 1553-1584 m/s to a minimum of 1507 m/s. Multivariant linear regression was used in the analysis of covariance to fit the least-squares estimates to the linear regression model. Strong correlates of ultrasonic speed with both water concentration and fat concentration in the liver were observed.

Animals↗

PubMedDate not supplied

A comparison of colour duplex ultrasonography after transurethral alprostadil and intracavernous alprostadil in the assessment of erectile dysfunction.

This study aimed to investigate whether transurethral alprostadil could be used for the diagnosis of erectile dysfunction using colour duplex ultrasound. The ultrasonography results were compared after transurethral and intracavernous alprostadil administration in 20 patients with erectile dysfunction. There were no significant differences in the mean peak systolic velocities (PSVs) between the two routes of administration, but the mean end diastolic velocities (EDVs) showed significant differences, with patients treated with transurethral alprostadil having higher EDVs. Linear regression analysis of the PSVs reached following the two routes of administration showed a moderate relationship, but linear regression analysis of the EDVs showed no relationship. We concluded that transurethral alprostadil was an inappropriate vasoactive drug to use with colour duplex ultrasonography for the evaluation of patients with erectile dysfunction because it required a longer scan time and it was less effective and less reliable than intracavernous alprostadil at stimulating complete corporeal smooth muscle relaxation.

Adult↗

PubMed2003

The association between socioeconomic development at the town level and the distribution of dental caries in Brazilian children.

OBJECTIVE: To investigate the association between dental caries among children in the state of São Paulo, Brazil, and town-level indices of socioeconomic development. METHODS: We examined 15 385 oral-examination records from children aged 5 or 6 years old from 129 towns and cities in the state of São Paulo. We studied two outcomes: (1) the mean number of decayed, missing, and filled deciduous teeth (dmft index) and (2) the care index, which is the proportion of decayed teeth that have already been filled. The explanatory variables were the child development index, human development index, illiteracy rate among subjects older than 20 years, household income, Gini coefficient, insufficient income, fluoridated water supply, number of dentists per 10 000 inhabitants, number of dentists in the public service per 10 000 inhabitants, and number of weekly hours of dentist work in the public service per 10 000 inhabitants. Multiple linear regression models were fitted to the two outcome variables (dmft index and care index). RESULTS: The multiple linear regression analysis showed that a higher dmft index was associated with a low child development index, a high illiteracy rate, and an unfluoridated water supply. The child development index was significantly associated with the care index, and the number of dentists in the public service per 10 000 inhabitants showed borderline statistical significance. CONCLUSIONS: Our results indicate that town-level indices of socioeconomic status are significantly correlated with caries indices. Our results also emphasize the beneficial effect that fluoridating water has on reducing the prevalence of dental caries and the fact that strategies for treating and preventing oral diseases should be emphasized within the context of overall health promotion for children.

Adolescent↗

PubMed2004

[Inadequate erythropoietin production (epo) in patients with multiple myeloma].

Anaemia is the most common haematological complication in patients with malignant diseases. It is found in 60%-90% of cases with multiple myeloma. The pathogenesis of this hypoproliferative, normochromic, normocytic anaemia is complex. Results from clinical studies which evaluate the efficacy of recombinant human erythropoietin (rHuEpo) refer to the possibility that patients with multiple myeloma independently of renal function could have Epo deficiency. Based on this finding, the aim of the study was to evaluate the erythropoietin production in patients with multiple myeloma in order to define clinical conditions of Epo deficiency and thereby enable rational use of this expensive drug. 42 patients with multiple myeloma were examined. The control group consisted of 25 patients with iron deficiency anaemia. 14 healthy volunteers represented the so-called "normal" control. The adequacy of Epo production was estimated from the graphic representation of the linear regression between Epo and haemoglobin (Hb) in the control group, as well as from O/PEpo ratio as a measure of the degree of adequacy of Epo production (O -- observed Epo value, P -- predicted Epo value from the regression equation of the control group). The erythropoietic activity was estimated from the graphic representation of the linear regression between soluble transferin receptors (sTfR) and Hb in the control group, as well as from O/PsTfR ratio, as a measure of the degree of adequacy of erythropoietic activity (O -- observed sTfR value, P -- predicted sTfR value from the regression equation of the control group). Significant inverse correlation between Epo and Hb was found in patients with multiple myeloma but preserved renal function, which was not the case in patients with renal insufficiency. 43% of patients without renal insufficiency and 85% of patients with renal insufficiency had inadequate Epo response to anaemia. In both patient groups (with and without renal insufficiency) instead of the expected inverse relationship between Hb and sTfR as in the control group, a positive correlation was found. 76% of patients had inadequate sTfR response to anaemia. There is a positive correlation between O/PEpo and O/PsTfR which is in favour of Epo driven erythropoiesis. O/PEpo and O/PsTfR in patients with multiple myeloma are significantly lower in comparison to the control group, which also points to the inadequacy of erythropoietin production, respectively erythropoietic activity. In conclusion, the results from this study show unambiguously that anaemia in patients with multiple myeloma appears because of decreased erythropoiesis as a consequence of bone marrow infiltration with malignant plasma cells as well as inadequate Epo production. Most probably, there are two forms of inadequate Epo production: one because of the renal insufficiency and the other that found in patients with anaemia of chronic diseases the mechanism of which is not clear.

Adult↗

PubMed2005

Erythropoietin production in patients with malignant lymphoma.

Lymphomas are a heterogenous group of malignant diseases. 30-50% of patients, even before chemo- and radiotherapy are begun have anemia. The pathogenesis of this anemia is multifactorial and still not completely clear. Newer investigations refer to a causality between the anemia in patients with lymphoma and the inappropriate erythropoietin production for the degree of anemia. Based on this finding, the aim of the study was to evaluate the erythropoietin production in patients with malignant lymphoma in order to define the clinical conditions of Epo deficiency and thereby enable rational use of this expensive drug. 27 patients with malignant lymphoma were examined. The control group consisted of 25 patients with iron deficiency anemia. 14 healthy volunteers represented the so-called "normal" control. The adequacy of Epo production was estimated from the graphic representation of the linear regression between Epo and hemoglobin (Hb) in the control group, as well as from the O/PEpo ratio as a measure of the degree of adequacy of Epo production (O - observed Epo value, P-predicted Epo value from the regression equation of the control group). The erythropoietic activity was estimated from the graphic representation of the linear regression between soluble transferrin receptors (sTfR) and Hb in the control group, as well as from the O/PsTfR ratio, as a measure of the degree of adequacy of erythropoietic activity (O - observed sTfR value, P - predicted sTfR value from the regression equation of the control group). Significant inverse correlation between Epo and Hb was found in patients with malignant lymphoma (r= -0.76, p < 0.001). 33% of patients had inadequate Epo response to anemia. O/PEpo in patients with malignant lymphoma is significantly lower in comparison to the control group, which also points to the inadequacy of erythropoietin production. There was a significant negative correlation between sTfR and Hb in patients with malignant lymphoma (r= -0.056, p < 0.001). Inadequate sTfR response to anemia have 76% of patients. The positive correlation between O/PEpo and O/PsTfR (r=0.79, p < 0.001) points out to a causality between the inadequacy of erythropoietin production and the inadequate erythropoiesis. In conclusion, results from this study show unambiguously that anemia in patients with malignant lymphoma appears because of decreased erythropoiesis as a consequence of bone marrow infiltration with lymphoma cells as well as inadequate Epo production. Most probably, the inadequate Epo production in patients with malignant lymphoma is as that seen in the anemia of chronic diseases whose mechanism is not clear.

Adult↗

PubMed1987

Phencyclidine pharmacokinetic scaling among species.

Interspecies pharmacokinetic parameters (y) for phencyclidine [1-(1-phenylcyclohexyl)piperidine] were correlated with body weight (B) using linear regression and the allometric equation of the form y = aBx (which also may be written as the linear regression equation, log y = x log B + log a). The data were obtained from previously reported pharmacokinetic studies in mammals (i.e., humans, monkey, dog, rat and mouse) and new pharmacokinetic data for the pigeon. The animal body weights ranged from 32.5 to 77,000 g and included 6 animal species from 2 vertebrate classes. The pharmacokinetic parameters correlated with body weight were T1/2 (T1/2 = 126B0.32, r2 = 0.799), volume of distribution (V beta = 10B0.96, r2 = 0.966) and systemic clearance (CLs = 50B0.64, r2 = 0.891). In addition, clearance values were multiplied by the maximum lifespan potential (MLP) of each animal and correlated with body weight [CLs X MLP = (3.3 X 10(5))B1.0, r2 = 0.991]. This helped normalize for species differences in systemic clearance, which correlated with species longevity. These allometric equations should provide the information for scaling phencyclidine pharmacokinetic data among diverse species.

Animals↗

PubMed1980

[Evaluation in vitro of the local anesthetic effect by means of the dose/stabilization effect curve].

The effect "in vitro" and "in vivo" of local anesthetics is normally evaluated at fixed time or considering the time required to obtain a per cent effect. We have attempted to estimate the dose/effect correlation at steady state using "in vitro" preparation of sciatic nerve-trunk of frog. Such an experiment is possible only if the concentrations of drugs tested are lower than those used in previous methods, so as not to inhibit the nerve fibres completely. The drugs tested were: lidocaine, procaine, promethazine and imipramine. Using linear regression analysis, it is possible to compare both the DE50 of the drugs tested and slopes of linear regression. In this manner we can better characterize the pharmacodynamic properties of local anesthetics.

Anesthetics, Local↗

PubMed2006

Data analysis of kinetic modelling used in drug stability studies: isothermal versus nonisothermal assays.

PURPOSE: Kinetic modelling was applied to predict the stability of cholecystokinin fragment CCK-4 in aqueous solution, which was analyzed by isothermal and nonisothermal methods using a validated stability indicating HPLC method. METHODS: The isothermal studies were performed in the temperature range 40 to 80 degrees C at pH 12 and ionic strength 0.01 M as constants, whereas nonisothermal stability studies were performed using a linear increasing temperature program, heating rate 0.25 degrees C/h and a temperature interval 40-82 degrees C. The isothermal studies require two-step linear regression to estimate the parameters, resulting in a well-defined confidence interval. Nonisothermal kinetic studies require nonlinear or linear regression by previous transformation of data to estimate the parameters. In this case, the two most popular approaches, derivative and integral, were used and compared. RESULTS: Under isothermal conditions, an apparent first-order degradation process was observed at all temperatures. The linear Arrhenius plot suggested that the CCK-4 degradation mechanism was the same within the studied temperature range, with quite large uncertainties due to the small number of degrees of freedom based only on the scatter in the plot, and giving an estimated shelf life at 25 degrees C of 35.2 days. The derivative approach yields high variability in the Arrhenius parameters, since they are dependent on the number of polynomial terms chosen, so several statistical criteria were applied to select the best model. The integral approach allows activation parameters to be calculated directly from experimental data, and provides results in good agreement with those of the traditional method, but have the advantage that the uncertainty in the final result directly reflects the goodness of fit of the experimental data to the chosen kinetic model. The application of the bootstrap technique to estimating confidence limits for the Arrhenius parameters and shelf life is also illustrated, and shows there is no difference between the asymptotic and bootstrap confidence intervals. CONCLUSIONS: Nonisothermal studies give us fast and valuable information about drug stability, although their potential for predicting isothermal behaviour is conditioned by the data analysis method applied.

Drug Stability↗

PubMed2006

Transcutaneous monitoring of partial pressure of carbon dioxide in the elderly patient: a prospective, clinical comparison with end-tidal monitoring.

STUDY OBJECTIVE: To evaluate the accuracy and precision of estimation of partial pressure of carbon dioxide (Pa(CO2)) using end-tidal or transcutaneous CO2 (TcP(CO2)) measurements during mechanical ventilation in the elderly patient. DESIGN: A prospective, observational study was conducted. SETTINGS: The study was done in the anesthesia department of a university hospital. PATIENTS: Seventeen anesthetized, mechanically ventilated patients older than 60 years were studied. INTERVENTIONS AND MEASUREMENTS: During standard sevoflurane anesthesia, and after proper calibration and an equilibration time of 30 minutes with stable hemodynamic and respiratory variables, arterial (Pa(CO2)), end-tidal (Pet(CO2)), and transcutaneous (TcP(CO2)) CO2 partial pressures were determined. In each patient, 1 to 5 sample sets (Pa(CO2), Pet(CO2), and TcP(CO2)) were obtained. MAIN RESULTS: A total of 45 sample sets were obtained from the patients studied. The Pa(CO2) values ranged between 21 and 58 mm Hg. The Pa(CO2) - Pet(CO2) tension gradient was 6 +/- 5 mmHg (95% confidence interval, -3 to 16 mmHg), whereas the Pa(CO2) - TcP(CO2) tension gradient was 2 +/- 4 mmHg (95% confidence interval, -6 to 9 mmHg) (P = 0.0005). The absolute value of the difference between Pa(CO2) and Pet(CO2) was 3 mm Hg or less in 7 of 45 sample sets (15%), whereas the absolute value of the difference between Pa(CO2) and TcP(CO2) was 3 mm Hg or less in 21 of 45 sample sets (46%) (P = 0.003). Linear regression analysis for TcP(CO2) versus Pa(CO2) showed a slope of 0.84 (r(2) = 0.73), whereas the linear regression analysis for Pet(CO2) versus Pa(CO2) showed a slope of 0.54 (r(2) = 0.50). CONCLUSION: Transcutaneous monitoring of CO(2) partial pressure gives a more accurate estimation of arterial CO(2) partial pressure than does Pet(CO2) monitoring.

Aged↗

PubMed1992

Shape of the relationship between hypertension and the rate of progression of renal failure in autosomal dominant polycystic kidney disease.

The effect of hypertension on the rate of progression of renal failure was analyzed in 26 patients with autosomal dominant polycystic kidney disease relating the slopes of progression (linear regression of the reciprocal serum creatinine on time) with the average mean arterial pressure, systolic and diastolic pressure, derived over the entire follow-up period for each patient. Hypertension was found in 19 of the 26 patients. Using simple linear regression, there was no significant correlation between the two variables in any case. Using polynomial regression (quadratic and cubic), this relationship fits a sigmoid (for diastolic pressure) or a negative parabolic curve (for mean arterial pressure and systolic pressure); i.e. the lowest and the highest values of mean arterial pressure and systolic pressure were associated with faster rates of progression. Thus, an appropriate model to study this relationship is not the linear but the polynomial regression.

Adult↗

PubMed2005

Influential observations in weighted analyses: examples from the National Longitudinal Survey of Children and Youth (NLSCY).

This paper highlights the impact of survey weights on model fit in multiple linear regression with specific reference to the National Longitudinal Survey of Children and Youth (NLSCY) and provides recommendations for the treatment of influential observations. Multiple linear regression was used to estimate the association between child and family factors in the preschool years and vocabulary development at school age. Analyses were performed with and without survey weights. The model fit was assessed by examining the distribution of the studentized residuals and the change in the regression coefficients that would occur if an observation were removed. Two summary measures of influence, Dffits and Cook's D are reported. The models were refit excluding influential observations. Weighting of the linear model resulted in previously non-influential observations having an undue influence on the estimation of the regression parameters in the weighted model. The influential observations were driven primarily by the size of the survey weight as opposed to unusual values of x and y. Researchers working with large national health surveys such as the NLSCY and the National Population Health Survey (NPHS) are advised to include a detailed influence analysis before any final conclusions are made.

Child↗

PubMed2000

Life expectancy as an indicator of environmental health.

Whether or not life expectancy at birth is related to the quality of life as expressed by global economical, environmental and nutritional measures is the primarily studied question in this article. Two models, set of independent variables and multivariate analysis was performed. An attempt to estimate the role of studied variables in overall life expectancy was done, too. A descriptive, ecological study design was used. The population of 156 countries have been taken into account, using data from published databases [7, 9]. Access to safe drinking water, per capita gross domestic product, literacy, calories available as percentage of needs and per capita public health expenditures were taken as exposure, and compared with life expectancy at birth. A linear regression model was used to estimate the role of different exposures on life expectancy at birth. A correlation matrix for all variables and life expectancy at birth is presented in the article. Literacy and access to safe drinking water are statistically significant variables (p < 0.001) also after fitting a linear regression model. The correlation coefficient for the linear model was 0.8823 (R2 = 0.7784). Shares of years of life from overall life expectancy attributed to studied variables were 28.06, 9.42, 2.04 and 1.93% for literacy, access to safe drinking water, GDP and calories available as percentage of needs, respectively.

Educational Status↗

PubMed1987

Study of the selectivity of the impregnation of neurons by the Golgi method.

The selectivity of the impregnation of neurons by the Golgi method was examined by comparing Nissl-stained specimens with Golgi-stained specimens in terms of the somatic orientation, cross-sectional area, and long and short axes of the soma in the ventromedial hypothalamic nucleus (VMH) and lateral hypothalamic area (LHA) of 5-week-old rats. With regard to somatic orientation, we made comparisons directly between the Nissl distribution pattern and the Golgi pattern. The two distribution patterns did not differ significantly in either VMH or LHA (Smirnov test, P greater than 0.05). For somatic cross-sectional area and diameter (long and short), a mean value of every 10% of the total frequency was estimated for each histogram; the histogram was segmented into 10 percentile frequency domains, and a mean value for each domain was estimated. A linear regression was calculated between Golgi mean values and Nissl's at the same place. By use of the linear regression, all of the observed values on Nissl sections for somatic cross-sectional area and diameter were transformed into their corresponding Golgi values. The frequency distribution of these transformed Nissl values was compared with that of the actually observed Golgi values. There was a high degree of similarity between the two distribution patterns in all regions examined for long and short diameters as well as cross-sectional area of the soma (Smirnov test, P greater than 0.05). These findings suggest that the sampling of VMH and LHA neurons in the Golgi method used in the present study is similar to the corresponding sampling in Nissl preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

Fish biliary polycyclic aromatic hydrocarbon metabolites estimated by fixed-wavelength fluorescence: comparison with HPLC-fluorescent detection.

Fixed wavelength fluorescence (FF) was compared to high-performance liquid chromatography with fluorescence detection (HPLC-F) as an estimation of polycyclic aromatic hydrocarbon (PAH) exposure to fish. Two excitation/emission wavelength pairs were used to measure naphthalene- and benzo[a]pyrene (B[a]P)-type metabolites. Early nonmetabolite fluorescent peaks were negligible in HPLC chromatograms of bile of brown bullhead, white sucker, and common carp. Linear regression analysis of FF and HPLC-F data had r2 values between 0.89 and 1.00. Although the linear regression was significant, the absolute HPLC-F and FF values were not equivalent. HPLC-F values for B[a]P-type metabolites were always higher than those determined by FF. For naphthalene-type metabolites there was no consistent relationship between the HPLC-F and FF values. These inequivalencies were possibly due to the variable HPLC-elution patterns caused by the composition of metabolites and the unique fluorescent response exhibited in different solvent concentrations. Nevertheless, mean concentration estimates divided by the value obtained at the reference site were similar by both methods. The FF method can be used to estimate biliary PAH concentrations in these three species and allows PAH metabolites to become a routine measurement end point for environmental assessments.

Analysis of Variance↗

PubMed1994

Ambient ozone and crop loss: establishing a cause-effect relationship.

This paper provides the results of a retrospective mathematical analysis of the US NCLAN (National Crop Loss Assessment Network) open-top chamber data. Some 77% of the 73 crop harvests examined, showed no statistically significant yield differences between NF (non-filtered open-top chamber) and AA (chamberless, ambient air) treatments (no easily discernable chamber effects on yield). However, among these cases only seven acceptable examples showed statistically significant yield reductions in NF compared to the CF (charcoal filtered open-top chamber) treatment. An examination of the combined or cumulative hourly ambient O3 frequency distribution for cases with yield loss in NF compared to a similar match of cases without yield loss showed that the mean, median and the various percentiles were all higher (>/= 3 X) in the former in contrast to the latter scenario. The combined frequency distribution of hourly O3 concentrations for the cases with yield loss in NF were clearly separated from the corresponding distribution with no yield loss, at O3 concentrations > 49 ppb. Univariate linear regressions between various O3 exposure parameters and per cent yield losses in NF showed that the cumulative frequency of occurrence of O3 concentrations between 50 and 87 ppb was the best predictor (adjusted R2 = 0.712 and p = 0.011). This analysis also showed that the frequency distribution of hourly concentrations up to 87 ppb O3 represented a critical point, since the addition of the frequency distributions of > 87 ppb O3 did not improve the R2 values. In fact as the frequency of hourly O3 concentrations included in the regression approached 50-100 ppb, the R2 value decreased substantially and the p value increased inversely. Further, univariate linear regressions between the frequencies of occurrence of various O3 concentrations between 50 and 90 ppb and: (a) cases with no yield difference in NF and (b) cases with yield increase in NF compared to the CF treatment (positive effect) provided no meaningful statistical relationship (adjusted R2 = 0.000) in either category. These results support the basis that additional evaluation of the frequency of occurrence of hourly O3] concentrations between 50 and 87 ppb for cases with the yield reductions could provide a meaningful ambient O3 standard, objective or guideline for vegetation.

Journal Article↗

PubMed2006

Linear QSAR regression models for the prediction of bioconcentration factors by physicochemical properties and structural theoretical molecular descriptors.

The development of QSAR models useful for the prediction of fish bioconcentration factor (BCF) for a wide range of different chemical classes is crucial for the assessment and prioritisation of potentially persistent bioaccumulative and toxic substances. In this study we present QSAR models for BCF developed on a wide range of chemical structural classes of environmental and toxicological interest (such as dyes and various chlorinated and brominated compounds). The aim is to provide valid QSAR models, statistically validated for predictivity, for the prediction of BCF in general, but also for problematical chemical classes such as highly hydrophobic chemicals. Several descriptors, calculated by different commercially available software packages, have been employed in order to take into account relevant information provided by physicochemical properties (octanol/water partition coefficient and water solubility) and molecular features (structural and quantum-chemical molecular descriptors). The best descriptor subsets for the models were selected using the Genetic Algorithm-Variable Subset Selection strategy (GA-VSS) and calculations were performed by ordinary least squares regression. Starting from a data set of 640 compounds (logK(ow) range from -2.34 to 12.66), we developed linear QSARs, firstly for a data set of 620 compounds (logK(ow) range from -2.34 to 10.35) and secondly specifically for 87 highly hydrophobic chemicals (logK(ow) range from 6.00 to 10.35). All these models have been statistically validated (both internally by cross-validation and bootstrap and externally, by "a priori" splitting of available data by Kohonen Map-ANN in training and prediction sets) and their structural chemical domain has been verified by the leverage approach.

Animals↗