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PubMed1977

Matching under concurrent fixed-ratio variable-interval schedules of food presentation.

Four pigeons were exposed to concurrent fixed-ratio, variable-interval schedules of food presentation. The fixed-ratio requirement was either 25, 50, 75, or 100 responses, with the variable-interval schedule parameter held constant at 4 minutes. A delay time was imposed between a changeover from one schedule to the other and subsequent food availability. The delay time was varied at each ratio requirement over four values; no delay, 0-second delay, 1.5-second delay, and 5.0-second delay. As the fixed-ratio requirement or the delay time increased, a greater proportion of the total responses and time spent responding occurred under the variable-interval schedule relative to the proportion of food deliveries under that schedule. Neither relative overall response rate nor relative time spent responding equalled the relative frequency of food presentation, as would be predicted by a linear "matching" model. Rather, these data were described by power functions with slopes of approximately 1.0 and intercepts greater than 1.0. In the terms of Baum's (1974) analysis, these deviations from linear matching represent bias in favor of responding under the interval schedule. Bias, as reflected in the intercept of the power function, was greater for the ratio of time than the ratio of responses.

Journal Article↗
PubMed2001

The general matching law describes choice on concurrent variable-interval schedules of wheel-running reinforcement.

Six male Wistar rats were exposed to concurrent variable-interval schedules of wheel-running reinforcement. The reinforcer associated with each alternative was the opportunity to run for 15 s, and the duration of the changeover delay was 1 s. Results suggested that time allocation was more sensitive to relative reinforcement rate than was response allocation. For time allocation, the mean slopes and intercepts were 0.82 and 0.008, respectively. In contrast, for response allocation, mean slopes and intercepts were 0.60 and 0.03, respectively. Correction for low response rates and high rates of changing over, however, increased slopes for response allocation to about equal those for time allocation. The results of the present study suggest that the two-operant form of the matching law can be extended to wheel-running reinforcement. 'I'he effects of a low overall response rate, a short Changeover delay, and long postreinforcement pausing on the assessment of matching in the present study are discussed.

Animals↗
PubMedDate not supplied

Cesium-134 and strontium-85 in strawberry plants following wet aerial deposition.

The understanding of the processes that control the behavior of radionuclides in crops can support policymakers to take actions to protect the environment and safeguard human health. Data concerning the behavior of radionuclides in fruits are limited. Strawberry (Fragaria x ananassa Duchesne) plants were contaminated on the aboveground part by sprinkling an aqueous solution of 134Cs and 85Sr at three growing stages: predormancy, anthesis, and beginning of ripening. Intercepted activity was more affected by the posture and physical orientation of leaves rather than by leaf area or biomass. Fruit interception ranges from 0.2 to 1.2% of the sprinkled activity. Translocation coefficients from leaf to fruit are on the order of 10(-4) for 134Cs and 10(-5) for 85Sr. Translocation reaches its highest intensity between anthesis and ripening. If deposition occurs when plants are bearing fruits, the fruit activity will be affected by the activity initially deposited on the fruit surfaces. This is important for 85Sr as it is not translocated in the phloem. The loss of the dead leaves at the resumption of growth causes high plant decontamination, but a fraction of both radionuclides remains in the storage organs, roots, and shoots, which is retranslocated to fruits in the following spring. The values of the environmental half-time, t(w), after deposition at predormancy are 114 d for 134Cs and 109 d for 85Sr. Cesium-134 tends to be allocated to fruits, while 85Sr remains in leaves and crowns. Translocation of radionuclides to roots results in soil contamination.

Cesium Radioisotopes↗
PubMed1999

Accidental iatrogenic intoxications by cytotoxic drugs: error analysis and practical preventive strategies.

OBJECTIVES: Drug errors are quite common. Many of them become harmful only if they remain undetected, ultimately resulting in injury to the patient. Errors with cytotoxic drugs are especially dangerous because of the highly toxic potential of the drugs involved. For medico-legal reasons, only 1 case of accidental iatrogenic intoxication by cytotoxic drugs tends to be investigated at a time, because the focus is placed on individual responsibility rather than on system errors. The aim of our study was to investigate whether accidental iatrogenic intoxications by cytotoxic drugs are faults of either the individual or the system. The statistical analysis of distribution and quality of such errors, and the in-depth analysis of contributing factors delivered a rational basis for the development of practical preventive strategies. METHODS: A total of 134 cases of accidental iatrogenic intoxication by a cytotoxic drug (from literature reports since 1966 identified by an electronic literature survey, as well as our own unpublished cases) underwent a systematic error analysis based on a 2-dimensional model of error generation. Incidents were classified by error characteristics and point in time of occurrence, and their distribution was statistically evaluated. The theories of error research, informatics, sensory physiology, cognitive psychology, occupational medicine and management have helped to classify and depict potential sources of error as well as reveal clues for error prevention. RESULTS: Monocausal errors were the exception. In the majority of cases, a confluence of unfavourable circumstances either brought about the error, or prevented its timely interception. Most cases with a fatal outcome involved erroneous drug administration. Object-inherent factors were the predominant causes. A lack of expert as well as general knowledge was a contributing element. In error detection and prevention of error sequelae, supervision and back-checking are essential. Improvement of both the individual training and work environment, enhanced object identification by manufacturers and hospitals, increased redundancy, proper usage of technical aids, and restructuring of systems are the hallmarks for error prevention. CONCLUSIONS: Errors follow general patterns even in oncology. Complex interdependencies of contributing factors are the rule. Thus, system changes of the working environment are most promising with regard to error prevention. Effective error control involves adapting a set of basic principles to the specific work environment. The work environment should allow for rectification of errors without penalty. Regular and ongoing intra-organisational error analysis needs to be an integral part of any error prevention strategy. However, it seems impossible to totally eliminate errors. Instead, if the environment guarantees timely error interception, most sequelae are avoided, and errors transform into a system-wide learning tool.

Antineoplastic Agents↗
PubMed1995

Effects of inhibitors of ouabain-sensitive Na+, K(+)-ATPase and Li+ ions on the neuromuscular transmission of the frog.

The effect of blockade of ouabain-sensitive alpha 2 and alpha 3 (neural type) isozymes of Na+, K(+)-ATPase was investigated on frog neuromuscular preparations by recording the frequency augmentation-potentiation (FAP) of the endplate potential, an electrophysiological and neuropharmacological technique to analyze the drug actions on the release process of the readily releasable transmitter quanta. Erythrosin B, which was thought to selectively inhibit the neural type Na+, K(+)-ATPase, pivoted the log-linear FAP relation counterclockwise without altering the intercept on the ordinate. Chlormadinone had a similar action. An increase in the concentration of extracellular K+ ions pivoted the FAP relation clockwise with a concomitant upward shift of the intercept on the ordinate, and low K+ Ringer's solution produced an inverse effect. In contrast, Li+ ions shifted the FAP relation upwards dose-dependently leaving its slope unchanged. Cinnarizine, a blocker for inositol-1,4,5-trisphosphate-induced Ca2+ release, and 5,5'-dimethyl-1,2-bis(2-amino-phenoxy)ethane-N,N,N',N'-tetraacetic acid, a specific intracellular Ca2+ chelator, significantly antagonized the potentiating action of Li+. The ouabain-sensitive neural type Na+, K(+)-ATPase isozyme, which is abundant in neural tissues, seems to play an important role in stimulation frequency-dependent modulation of the quantal transmitter release such as FAP.

Adrenal Cortex Hormones↗
PubMed1991

Correlations of in vivo beta-cell function tests with beta-cell mass and pancreatic insulin content in streptozocin-administered baboons.

In vivo beta-cell function tests are used increasingly in humans during the preclinical phase of insulin-dependent diabetes mellitus (IDDM), but the severity of the beta-cell loss responsible for the abnormalities seen in these tests is unknown. We have measured several physiological beta-cell function tests--fasting plasma glucose, glucose disappearance constant, fasting insulin, acute insulin responses to arginine (AIRarginine) and glucose (AIRglucose), and glucose potentiation of AIRarginine (delta AIRarginine/delta G) and two direct objective measurements (pancreatic insulin content [PIC] and quantitative beta-cell mass)--in adolescent male baboons (Papio anubis/cyanocephalus). We have correlated in vivo measurements obtained within 3 days after the animals were killed with in vitro estimates of PIC and beta-cell mass in 15 animals, (2 nondiabetic requiring insulin treatment and 13 after varying doses of streptozocin to induce degrees of beta-cell damage ranging from normoglycemia to severe hyperglycemia). There was a strong linear correlation between beta-cell mass and PIC (r = 0.79, P less than 0.001). Physiological measures of beta-cell function were significantly correlated with both PIC and beta-cell mass. The correlations between physiological measures and beta-cell mass were linear and intercepted the beta-cell mass axis at 0.15-0.2 g, suggesting that in vivo measures of beta-cell function approach 0 when there is still approximately 40-50% of the beta-cell mass detectable histologically. With PIC, the linear correlations intercepted the axes close to 0. These findings provide considerable validity to the measurements of beta-cell function used in preclinical IDDM in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Reassessment of glucose effectiveness and insulin sensitivity from minimal model analysis: a theoretical evaluation of the single-compartment glucose distribution assumption.

Minimal model analysis with the frequently sampled intravenous glucose tolerance test provides an effective way to measure two important metabolic parameters in vivo under non-steady-state conditions: glucose effectiveness (SG) and insulin sensitivity (SI). Two questions regarding the validity of SG and SI have recently emerged. First, SG from the minimal model is suspected to be overestimated. Second, the occurrence of SI values indistinguishable from zero ("zero-SI") is not negligible in large clinical studies, and its physiological meaning is uncertain. In this study, we examined the significance of the assumed single-compartment glucose distribution embedded in the minimal model on the estimation of SG and SI. A more accurate two-compartment model was constructed by incorporating insulin action on hepatic glucose output and uptake into a previously validated construction. The two-compartment results were compared with the one-compartment minimal model results. It was shown that the one-compartment assumption contributes to a systematic deviation of SG (slope = 0.54, y-intercept = 0.014 min[-1]; n = 195 simulations). However, SG from the minimal model was linearly correlated to SG determined from the two-compartment model (r = 0.996). The one-compartment assumption also contributed to the occurrence of zero SI values for insulin-resistant subjects. A similar linear relationship was found between SI estimated by both the minimal model and the two-compartment model (slope = 0.58, y-intercept = -0.57 x 10[-4] min[-1] per pU/ml, r = 0.998). In conclusion, SG and SI from the minimal model are not necessarily equivalent to values emanating from the more accurate two-compartment model. However, the very high correlation between one- and two-compartment results suggests that the minimal model-derived SG and SI are dependable indexes of in vivo glucose effectiveness and insulin sensitivity. Minimal model analysis' advantages of simplicity, minimal invasiveness, reasonable reflection of non-steady-state glucose kinetics, and cost-effectiveness could in many cases outweigh the structural bias introduced by the model simplification.

Blood Glucose↗
PubMed1998

Determining true glomerular filtration status in newly presenting type 2 diabetic subjects using age and sex adjustment.

OBJECTIVE: To determine age- and sex-adjusted reference ranges (ASARRs) for glomerular filtration status using data from nondiabetic subjects and to apply these to newly presenting type 2 diabetic subjects. RESEARCH DESIGN AND METHODS: Glomerular filtration rate corrected for body surface area (cGFR) was determined using a radionuclide (51Cr-EDTA) method in 75 non-diabetic subjects (37 men, 38 women) and 219 type 2 diabetic subjects (157 men, 62 women). The 95% constant reference ranges (CRRs) were calculated as mean nondiabetic cGFR+/-1.96 SD. The 95% ASARRs were calculated by Altman's method from the nondiabetic cGFR versus age regression residuals for both male and female subjects. RESULTS: Using Altman's method, the intercepts, but not the gradients, of the cGFR versus age regressions were significantly different between male and female subjects (intercept difference [95% CI] 8.2 [1.3-15.1], gradient difference -0.4 [-1.1 to 0.3]). Fitting a common gradient, 95% ASARRs for normofiltration were found to be from 123.9 - (0.89 X age) to 181.7 - (0.89 x age) for male subjects, and from 116.0 - (0.89 X age) to 173.2 - (0.89 X age) for female subjects. The 95% CRR for normofiltration was 70.2-138.1 ml x min(-1) x (1.73 m)(-2). When applied to the diabetic cGFRs, the CRRs and ASARRs gave, respectively, 17% (37/219) versus 21% (46/219) hyperfiltrators and 83% (181/219) versus 79% (172/219) normofiltrators. Using the ASARRs, 14 normofiltrators (6 men, 8 women) were reclassified as hyperfiltrators (change [n/total n] [95% CI] 8% [14/181] [4-12]), and 5 hyperfiltrators (5 men, 0 women) were reclassified as normofiltrators (change 14% [5/37] [5-30]). CONCLUSIONS: We conclude that age and sex adjustment are essential to assess glomerular filtration status.

Adult↗
PubMed2002

Effect of background serum lithium concentrations on the accuracy of lithium dilution cardiac output determination in dogs.

OBJECTIVES: To assess the effect of increasing serum lithium concentrations on lithium dilution cardiac output (LiDCO) determination and to determine the ability to predict the serum lithium concentration from the cumulative lithium chloride dosage. ANIMALS: 10 dogs (7 males, 3 females). PROCEDURE: Cardiac output (CO) was determined in anesthetized dogs by measuring LiDCO and thermodilution cardiac output (TDCO). The effect of the serum lithium concentration on LiDCO was assessed by observing the agreement between TDCO and LiDCO at various serum lithium concentrations. Also, cumulative lithium chloride dosage was compared with the corresponding serum lithium concentrations. RESULTS: 44 paired observations were used. The linear regression analysis for the effect of the serum lithium concentration on the agreement between TDCO and LiDCO revealed a slope of -1.530 (95% confidence interval [CI], -2.388 to -0.671) and a y-intercept of 0.011 (r2 = 0.235). The linear regression analysis for the effect of the cumulative lithium chloride dosage on the serum lithium concentration revealed a slope of 2.291 (95% CI, 2.153 to 2.429) and a y-intercept of 0.008 (r2 = 0.969). CONCLUSIONS AND CLINICAL RELEVANCE: The LiDCO measurement increased slightly as the serum lithium concentration increased. This error was not clinically relevant and was minimal at a serum lithium concentration of 0.1 mmol/L and modest at a concentration of 0.4 mmol/L. The serum lithium concentration can be reliably predicted from the cumulative lithium dosage if lithium chloride is administered often within a short period.

Animals↗
PubMed1985

Information processing abilities and performance on two perceptual-motor tasks.

The purpose of this study was to investigate whether the hypothesized information-processing mechanisms, thought to be reflected by the slope and intercept of the regression of choice reaction time on stimulus information or information transmitted could account for performance on two novel laboratory tasks. In addition, analyses were performed to determine whether these theorized mechanisms represent stable within individual abilities or task specific capabilities. Analysis indicated that the slopes obtained from two different choice reaction time paradigms were unrelated while intercepts were moderately correlated. Examination of the pattern of zero-order correlations further showed that regression components were not meaningfully related to performance on either novel task, suggesting that knowledge of information-processing mechanisms, as assessed in choice RT paradigms, did not enhance the understanding of performance in more complex tasks.

Adolescent↗
PubMed1990

Sex differences and the role of figural complexity in determining the rate of mental rotation.

Two experiments were conducted to investigate the effects of figural complexity on the rate of mental rotation of 3-dimensional figures and to compare the performance of men and women. Complexity was manipulated in three ways: by changing the number of blocks in the figure (7 or 10), by altering the number of turns (2 or 3), and by using outline or solid figures. In the first study, these factors were manipulated between groups of subjects. Women showed steeper slopes than men, but none of the complexity variables affected either slope or intercept for the mental rotation function. In the second study, number of turns and number of blocks were manipulated within-subjects, using only the solid figures. There were significant sex differences in both slope and intercept, and the number of blocks affected the slope of the rotation function. In both studies, a small percentage of the subjects showed nonlinear functions relating angular rotation to response time. Although the women consistently showed slower rotation functions, rate of rotation did not relate either to figural complexity or to nonlinearity. The results suggest that the rate of mental rotation is not affected by figural complexity, at least at the levels used in the present study, and that men and women employ essentially similar strategies.

Adult↗
PubMed1992

The repeatability and accuracy of ultrasound in measuring backfat of cattle.

Repeatability of ultrasound backfat measurements was determined on 217 cattle, and the association of ultrasound and carcass backfat measurements was evaluated with 580 animals. The correlation (repeatability) between consecutive ultrasound measurements was .975. Average difference between two ultrasound measures was .72 mm and error size was directly related (P less than .001) to the amount of backfat. Ultrasound measures averaged 8% (P less than .001) less than carcass measures. The average absolute difference between these two measures was 1.57 mm. Discrepancies were (P less than .001) larger when backfat was thicker; cattle with backfat measuring less than 10 mm averaged 1.43 mm absolute difference, whereas those with backfat greater than 10 mm averaged 1.89 mm. The variance of the discrepancies was partitioned into three components: ultrasound measurement error (14%), drift related to intercept and slope (15%), and residual (71%). The residual component may have represented errors in carcass measurement. In a subsequent trial with 175 cattle, average difference between ultrasound and carcass backfat measurements was reduced to 1.19 mm. Also, the slope and intercept virtually mimicked the isopach. Ultrasound measures can be more precise (minutely exact) and accurate (close to the true value) than carcass measures for assessing absolute backfat thickness in cattle. Elements of measurement protocol that may improve ultrasound technique are imparted in the manuscript.

Adipose Tissue↗
PubMed1994

Availability of amino acids for 10- to 20-kilogram pigs: lysine and threonine in soybean meal.

The availabilities of lysine and threonine in soybean meal for 10- to 20-kg pigs were determined in two experiments using slope-ratio methodology. In the first experiment, a basal diet formulated to contain 6 g of lysine/kg, but adequate in all other amino acids, was supplemented with 1, 2, or 3 g of lysine/kg from either soybean meal or L-lysine-HCl. Each of the seven diets was available on an ad libitum basis to six individually penned pigs (barrows:gilts, 1:1) from an initial weight of 9.9 kg until they reached a live weight of 20.8 kg. Daily feed intake was similar among diets. Common-intercept multiple linear regression of daily live weight gain and gain:feed ratio on dietary lysine level indicate slope ratios (soybean meal:lysine.HCl) of .85 and .88, respectively. In Exp. 2, a basal diet formulated to contain 4 g of threonine/kg was supplemented with .65, 1.30, 1.95, or 2.60 g of threonine/kg from either soybean meal or L-threonine. Each of the nine diets was available on an ad libitum basis to six individually penned pigs (barrows:gilts, 1:1) from 9.9 to 21.0 kg live weight. As in Exp. 1, daily feed intake was similar among the nine diets. The slope ratios (soybean meal:L-threonine) from common-intercept multiple regression analyses were .73 and .78 for daily weight gain and gain:feed ratio, respectively. Thus, the availabilities of lysine and threonine in soybean meal for young pigs were estimated to be 85 to 88% and 73 to 78%, respectively.

Animal Feed↗
PubMed1976

In vivo determination of the stress-strain relation of the human myometrium.

Smooth muscle is capable of responding by contraction to mechanical distension. Neither the structural basis for this phenomenon nor the theories of smooth muscle behavior are completely clear. A method is now described by which the contractile response to mechanical distension of the human uterine muscle in vivo is determined. The distension is enforced sinusoidally within the frequency range 0.005-2 Hz, by filling and emptying a rubber balloon introduced into the uterine cavity. A tonometric index of the myometrium is defined using Hook's law after the approximate evaluation of a contractile modulus and the tangential stress and strain in the inner layer of the uterine wall. The regression line of indices upon frequency is calculated and intercept and regression coefficient of the equation for basic conditions are compared with those obtained during administration of pharmacologically active agents. It is suggested that the differences in intercepts and regression coefficients be used as a measure of drug effect.

Adaptation, Physiological↗
PubMed1979

Emotional distress in morning-after pill patients.

The self-administered SCL-90 test was utilized to collect emotional distress data on 120 female patients requesting morning-after pill pregnancy interception. SCL prescores were significant in anxiety, guilt and depression factors. The 2-week post-treatment results showed a significant decrease in these factors. This test provides reliable measurement of emotional distress factors in gynecologic GYN patients. The results must be considered supportive for the use of DES interceptive therapy in spite of other clinical considerations relative to its safety.

Affective Symptoms↗
PubMed1993

The effect of caffeine on the accommodative response/accommodative stimulus function and on the response AC/A ratio.

Using a phoro-accommodometer, accommodation and convergence responses were measured for 17 experimental subjects before and after they ingested 200 mg caffeine. For 16 control subjects accommodation and convergence responses were determined at two test sessions separated by 45 min. For the experimental group, the accommodative response/accommodative stimulus (Ar/As) slope increased 0.05 D/D after ingestion of caffeine, and the response AC/A ratio decreased 3.05 delta/D. The y-intercept of the convergence response/accommodative response increased by 3.7 delta in the experimental group. These changes were statistically significant. For the control group, the differences in Ar/As slope, response AC/A ratio, and convergence response/accommodative response y-intercept between first and second test sessions were not statistically significant.

Accommodation, Ocular↗
PubMed1999

The effect of activity on the waking temperature rhythm in humans.

Nine healthy female subjects were studied when exposed to the natural light-dark cycle, but living for 17 "days" on a 27h day (9h sleep, 18h wake). Since the circadian endogenous oscillator cannot entrain to this imposed period, forced desynchronization between the sleep/activity cycle and the endogenous circadian temperature rhythm took place. This enabled the effects of activity on core temperature to be assessed at different endogenous circadian phases and at different stages of the sleep/activity cycle. Rectal temperature was measured at 6-minute intervals, and the activity of the nondominant wrist was summed at 1-minute intervals. Each waking span was divided into overlapping 3h sections, and each section was submitted to linear regression analysis between the rectal temperatures and the total activity in the previous 30 minutes. From this analysis were obtained the gradient (of the change in rectal temperature produced by a unit change in activity) and the intercept (the rectal temperature predicted when activity was zero). The gradients were subjected to a two-factor analysis of variance (ANOVA) (circadian phase/ time awake). There was no significant effect of time awake, but circadian phase was highly significant statistically. Post hoc tests (Newman-Keuls) indicated that gradients around the temperature peak were significantly less than those around its trough. The intercepts formed a sinusoid that, for the group, showed a mesor (+/-SE) of 36.97 (+/-0.12) and amplitude (95% confidence interval) of 0.22 degrees C (0.12 degrees C, 0.32 degrees C). We conclude that this is a further method for removing masking effects from circadian temperature rhythm data in order to assess its endogenous component, a method that can be used when subjects are able to live normally. We suggest also that the decreased effect of activity on temperature when the endogenous circadian rhythm and activity are at their peak will reduce the possibility of hyperthermia.

Adolescent↗
PubMed1999

Laser treatment of diabetic macular edema: comparison of ETDRS-level treatment with threshold-level treatment by using high-contrast discriminant central visual field testing.

Grid laser is recognized as an extremely effective treatment of diabetic macular edema, although it causes significant chorioretinal damage when applied and scars that expand with time. The purpose of this study is to compare the effects of two methods of grid laser photocoagulation for diabetic macular edema on high-contrast target discrimination in the central visual field. Grid laser photocoagulation with the Early Treatment Diabetic Retinopathy Study intensity burns has previously been shown to cause full retinal thickness burns. In this study, it produced severe destruction of paraxial vision, most marked at 2 degrees to 10 degrees from fixation. Grid laser using threshold-level burns, in contrast, appeared to produce some improvement in thresholded high-contrast vision at eccentricities from 2 degrees to 3 degrees outward, but failed to normalize visual parameters at these intercepts or at intercepts closer to fixation. Therefore, the recommendations are made (1) to use screening modalities other than biomicroscopic perception of retinal swelling to define earlier opportunities for intervention in the diabetic maculopathic process and (2) to use threshold or sub-threshold methods of laser grid photocoagulation for treating leakage and/or edema.

Adult↗