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PubMed1976

Sleep laboratory studies of flurazepam: a model for evaluating hypnotic drugs.

The results from six separate evaluations of flurazepam 30 mg in the sleep laboratory were combined to determine the effectiveness of the drug in inducing and maintaining sleep and its effects on sleep stages in a large sample of insomniac subjects. The combined studies provide a model from which a detailed profile of the effects of a hypnotic drug over short-, intermediate-, and long-term conditions can be thoroughly evaluated. Although sleep was significantly improved on the first night of flurazepam administration, peak effectiveness of the drug did not result until the second and third consecutive drug nights. Flurazepam continued to be effective in inducing and maintaining sleep with intermediate-and long-term drug use with only a slight loss of effectiveness with long-term use. Sleep was also significantly improved on the first and second nights of drug withdrawal. Carryover effectiveness of active metabolites of flurazepam from one drug night to the next drug night and to withdrawl nights is discussed. The clinical implications are discussed with regard to the time of peak effectiveness of the drug, dosage recommendations and schedule, minimizing possible effects of the drug on daytime performance, and the rationale and method for using drug holidays in the treatment regimen. With this comprehensive profile of the drug's actions, the physician is able to more rationally and effectively utilize the drug in treating the insomniac patient. With short-term administration, flurazepam produced a slight decrease in rapid eye movement (REM) sleep and an increase in REM latency. These effects were much more pronounced with intermediate-term drug administration, again possibly due to the accumulation of active metabolites. After withdrawal there was no rebound in REM sleep. Stages 3 and 4 sleep decreased progressively through short and intermediate drug administration. With initial withdrawal, there was a slight recovery in both sleep stages.

Anti-Anxiety Agents↗
PubMed1993

Impact of interpretation on associative freedom.

Seventy hours from the psychoanalytic case of Mrs. C, covering the full course of treatment, were scored for associative freedom, number of interventions, and a variety of clinical phenomena such as clarifications, interpretations, different forms of resistance, transference manifestations, and the like. Associative freedom significantly increased over the course of treatment and was significantly related to the number of analyst interventions per hour. The relationship was particularly strong in the latter stages of treatment. Three specific types of interventions were found to increase associative freedom in the latter stages of treatment. The effect of each type was found to influence both the session containing the interpretation and the next 3 sessions. This carryover effect was specific to the latter stages of the analysis.

Adult↗
PubMed2001

Carryover bias in visual assessment.

Carryover of stimuli in sequential judgments was studied for a visual assessment task involving estimation of the percentage cover of black circles on a white image. Seven image types with different levels of cover density were arranged in a sequentially balanced design in which each image type was preceded the same number of times by all image types. In the absence of carryover, when images were preceded by images with the same cover density, the response scores were well fitted by a power function of percentage cover with a mean exponent of 0.73 over subjects. Carryover took the form of an assimilation, so that the cover estimate for a target image was generally higher when preceded by an image with higher cover, and lower when preceded by an image with lower cover. However, the magnitude of the carryover effect showed little evidence of increasing with difference in cover between successive images. Nonparametric and parametric methods for testing for carryover are presented. The need for development of psychological models to explain the proposed statistical models is discussed.

Adolescent↗
PubMed1995

Effects of interstate migration on the geographic distribution of stroke mortality in the United States.

BACKGROUND AND PURPOSE: This study examines the effects of lifetime net interstate migration on the geographic distribution of stroke mortality in the United States. METHODS: National Center for Health Statistics and Bureau of the Census data were used to map the geographic distribution of age-adjusted, race-, and race/sex-specific stroke mortality rates by interstate migration status for natives, outmigrants, nonmigrants, inmigrants, and residents in the United States for 1979 to 1981. RESULTS: High age-adjusted stroke mortality rates were significantly clustered in the southeastern United States for both whites and blacks; in addition, for whites, low-rate states were concentrated in some Mountain and northeastern states. Migrant status did not change this large-scale pattern, but individual states showed significant migration effects, which varied in magnitude and direction. Among whites, states that benefited from migration, with markedly lower stroke mortality rates among residents than natives, included Arizona, Colorado, District of Columbia, and Florida, whereas states that suffered from migration included California, Idaho, Montana, North Dakota, Nevada, and Oklahoma. Among blacks, only Colorado showed an apparent large benefit from migration, whereas 21 states suffered from migration. CONCLUSIONS: Although the overall large-scale spatial distribution of resident stroke mortality rates cannot be explained by migration effects, some individual states had rates that were strongly influenced by migration. Patterns of mortality among migrant groups in Sun Belt retirement destination states probably result from differential selection effects for retirement migration in older adults. Patterns of mortality for black migrants to the North are probably influenced by "carryover" effects from their origin states.

Adult↗
PubMed1994

Interaction in crossover studies: a modified analysis with more sensitivity.

The crossover trial has an intuitive appeal to clinicians because each patient is used as his own control. Thus, between-subject variability of symptoms is eliminated. However, this study design suffers from the bias of treatment-by-period interaction. If, for example, the effect of the first treatment period carries on into the next one, then it influences the response to the latter period (carryover effect). A second problem is, that the standard approach (Hills-Armitage analysis) for interaction has a low sensitivity. An alternative method that looks at the performance of the separate treatment groups and not, as the standard approach, at the means of the groups is presented. This alternative approach does have more sensitivity than the standard in the common clinical situation where there is interaction in just one of the treatment groups. This study shows that this is so. However, the standard approach is more sensitive in the case of two-group interaction. One approach supplements the other.

Clinical Trials as Topic↗
PubMed1996

Clinical Trials: Design Flaws Associated with Use of a Placebo.

BACKGROUND: The placebo arm of a trial, although it controls for psychological placebo effects and natural history of a disease and facilitates effective blinding, is susceptible to bias just like the true treatment arm is. The placebo arm of a trial may even be particularly vulnerable to specific types of bias. The present article focuses on design flaws associated with the use of a placebo. RESULTS: (1) Placebo-controlled trials using mortality rather than morbidity as the end point may have both ethical and statistical problems. (2) Bias may affect placebo data to a larger extent than active treatment data. (3) Trials may provide an atmosphere of exaggerated placebo effects and, consequently, inadequate power to determine differences between placebo and active treatment groups. (4) A biased placebo period due to carryover effect is a common problem of controlled trials with a crossover or self-controlled design. (5) Adjustment for asymmetries between placebo and treatment group in a parallel-group trial is inappropriate if such asymmetries are not completely independent on the main variables of the study. (6) Samples may not be representative when a large number of patients inappreciative of a possible treatment with placebo refuse randomization. CONCLUSIONS: It is emphasized that routinely accounting for design flaws associated with use of placebo may further improve the powerful method of controlled clinical trials.

Journal Article↗
PubMed1989

The performance of the two-stage analysis of two-treatment, two-period crossover trials.

In the two-treatment, two-period crossover trial, patients are randomly allocated either to one group that receives treatment A followed by treatment B, or to another group that receives the treatments in the reverse order. Grizzle first proposed a two-stage procedure for analysing the data from such a trial. This paper examines the long-run sampling properties of this procedure, in terms of mean square error of point estimates, coverage probability of confidence intervals and actual significance level of hypothesis tests for the differences between the effects of the two treatments. The advantages of incorporating baseline observations into the analysis are also explored. Because the preliminary test for carryover is highly correlated with the analysis of data from the first period only, actual significance levels are higher than nominal levels even when there is no differential carryover. When carryover is present, the nominal level very seriously understates the actual level, and this becomes even worse when baseline observations are ignored. Increasing sample size only exacerbates the problem since this adverse behaviour then occurs at smaller values of the carryover effect. It is concluded that the two-stage analysis is too potentially misleading to be of practical use.

Analysis of Variance↗
PubMed1988

Comprehensive evaluation of a model alcohol education curriculum.

A comprehensive evaluation was conducted of a representative alcohol education program designed to enhance knowledge and self-esteem, instill appropriate attitudes and teach the decision-making skills necessary for youth to make responsible decisions about the use of alcohol. The curriculum was implemented approximately as intended. The immediate, cumulative and longer-term effects of curriculum exposure on the variables thought to mediate alcohol use were modest or unsystematic. There was no consistent evidence of carryover effects from curriculum exposure on subsequent use of alcohol, cigarettes or other drugs. The curriculum was ineffective in attaining its goals.

Adolescent↗
PubMed2003

Milk yield and mammary growth effects due to increased milking frequency during early lactation.

Increased milking frequency (IMF) at the beginning of lactation has been shown to increase milk yield not only during IMF but also after its cessation. The objectives of this experiment evaluated the effects of increased milking frequency initiated during early lactation on mammary growth and effects on milk yield (MY). Thirty-one cows were divided into treatment groups: 1) 2X: cows milked twice daily (2X) beginning at parturition (d 1), 2) IMF1: cows milked four times daily (4X) from d 1 to 21 postpartum (PP) and 3) IMF4: cows milked 2X d 1 to 3 and 4X d 4 to 21 PP. The 4X cows were milked immediately before 2X cows and again approximately 3 h later, at the end of the normal milking routine. All cows were milked 2X from d 21 to 305 postpartum. Milk yields were 34.5, 37.8 and 37.6 kg/d during wk 1 to 44 for 2X, IMF1 and IMF4, respectively. Mammary biopsies from four cows per treatment were obtained on d 7 and 14 PP to evaluate mammary cell proliferation. Tritiated-thymidine incorporation tended to increase on d 7 in IMF1 cows, and arithmetic means of the percentage of cells expressing Ki-67 proliferation antigen were consistent with a proliferative response to IMF though not significant. Blood was sampled three times per wk during the first 2 wk and then once per wk during wk 3, 4, 5, 6, 8, and 10. Plasma insulin-like growth factor-1 (IGF-1) averaged 20.1 ng/ml in IMF cows vs. 24.2 in 2X but was not accompanied by a change in bST. Prolactin was also not affected by treatment. Neither milk yield nor potential effects on mammary cell proliferation were correlated with systemic IGF-1. Implementing an IMF routine increases MY during treatment and elicits a carryover effect on the remainder of lactation. Milk yield responses after an IMF routine may be the result of increased mammary cell proliferation.

Animals↗
PubMed1994

Multi-period crossover trials.

This paper presents a review of crossover designs for use in medical applications which have three or more treatment periods. Only outcomes which can be analysed as continuous variables are considered. Designs which purport to allow for carryover effects are reviewed in detail, as are methods for analysing data collected in such trials. In practice, it is often possible to eliminate carryover by interposing sufficiently long 'washout' periods between successive treatments, and suitable designs for this case are also mentioned. Much current practice revolves around a model which has been widely criticized: the shortcomings of this model and the implications of possible remedies, for design as well as analysis, are discussed.

Cross-Over Studies↗
PubMed1993

Vitamin E in tardive dyskinesia: time course of effect after placebo substitution.

Alpha-tocopherol (vitamin E) has been found to be effective in the treatment of tardive dyskinesia (TD). Studies to date have been short in duration and have not found long-term carryover effects of vitamin E. The present study examined the persistence of the effects of vitamin E after longer term (36-week) treatment was discontinued. Vitamin E significantly improved TD over this period. However, the effects of vitamin E persisted so that TD scores approached baseline only after 12 weeks of placebo substitution.

Adult↗
PubMed2003

The effects of traditional and computer-aided instruction on promoting independent skin care in adults with paraplegia.

This study aimed to explore the viability of using computer-aided instruction (CAI) as an educational tool for promoting independent skin care in adults with paraplegia. There is a need to identify effective intervention strategies that provide health education for skin care management and the prevention of pressure ulcers for individuals with spinal cord injuries (SCI). There continues to be tremendous financial and personal costs associated with the treatment of pressure ulcers and the prevalence of skin breakdown among the SCI population, despite traditional educational methods. The methodology used in this study evaluated to what degree CAI assisted individuals with paraplegia to acquire knowledge and demonstrate skills necessary for optimal skin care. Results were obtained using a multiple baseline across subjects approach including an ABC (for two subjects) and an AC (for one subject) single case experimental design. Results indicated that CAI was more effective than traditional educational methods in increasing the initiation and performance of pressure-relieving techniques. Limitations in this study include the possibility of carryover effects, relatively short time periods for baseline and treatment conditions, and extraneous variables that were difficult to control such as the participants' level of motivation and cooperation. Further study using a larger group design with a control group is recommended to explore the effects CAI has on promoting optimal skin care among adults with paraplegia.

Adult↗
PubMed1998

Daytime vigilance after morning bright light exposure in volunteers subjected to sleep restriction.

This study was designed to test the hypothesis that bright light (BL) can have a stimulating effect on vigilance even in the absence of suppression of melatonin secretion and that this effect can be detected when measured in subjects with low vigilance levels. Seven normal subjects were exposed to bright-white light (BL group) and seven to dim-red light (DL group) on 2 consecutive days, each following a night of 4-h sleep restriction. The light treatment was administered in the late morning, between 0900 and 1330 hours. Salivary melatonin measurements indicated that BL did not suppress melatonin secretion or induce circadian phase shifts. The effects of the two treatments were compared on validated measures of daytime vigilance: immediate effects were evaluated on subjective alertness during the light treatment, whereas short-term (0.5-10.5 h) and long-term (20.5-34.5 h) carryover effects were measured on subjective alertness, daytime sleep latencies (DSL), and psychomotor performance. After two nights of sleep restriction, subjective alertness and daytime sleep latencies decreased significantly, but there was no effect of the light treatment. BL treatment did not affect global performance, but there was an effect on the strategy used by the subjects, as shown by faster reaction times and increased percentage of errors in the BL group. It was concluded that daytime BL exposure did not have a stimulating effect on our measures of vigilance even in sleep-deprived subjects but that it may increase physiological arousal and affect the subjects' behavior in some specific performance tasks.

Adult↗
PubMed1986

Comparison of short and long half-life benzodiazepine hypnotics: triazolam and quazepam.

Two benzodiazepine hypnotics, triazolam, 0.25 mg, with a short elimination t1/2, and quazepam, 15 mg, with a long t1/2, were evaluated in 22-night sleep laboratory studies. Quazepam improved sleep significantly during both short- and intermediate-term use. Daytime sleepiness, which decreased with continued use, was the side effect most often associated with quazepam dosing. In contrast, triazolam dosing did not significantly improve any of the major sleep efficiency parameters, and there was a rapid development of tolerance for the drug's slight initial effectiveness. In addition, there were a number of behavioral side effects including amnesia, confusion, and disinhibition. Withdrawal of triazolam was associated with sleep and mood disturbances (rebound insomnia and rebound anxiety), whereas quazepam exerted carryover effectiveness. Thus the data in this study show that the 0.25 mg dose of triazolam, which is being prescribed increasingly, has a profile of side effects that is similar to that of the 0.5 mg dose.

Adult↗
PubMed1998

The case-time-control design: further assumptions and conditions.

The case-time-control design is a strategy that was developed to tackle the problem of confounding by indication in the nonexperimental assessment of intended or known effects of drugs. By using subjects as their own controls, the case-time-control design, under an explicitly defined model, eliminates the biasing effect of unmeasured confounding factors in the situation where exposure varies over time. The correct application of this design is based on a specific model that contains inherent assumptions and imposes certain conditions for the approach to be valid. In a recent article, Greenland questioned the validity of the case-time-control design by presenting several "counterexamples." In this paper, we review the assumptions inherent to the validity of the case-time-control model. We show that the presumed counterexamples are not what they are claimed to be, simply because they do not conform to the logistic model explicitly underlying the case-time-control approach. These examples are shown to arise from an alternative model that includes a confounder by period interaction, a term expressly avoided in the case-time-control model. When the data from these examples are modified to satisfy the correct model, the resulting case-time-control estimates of the treatment odds ratio are exactly 2, the true treatment effect. We clarify the necessity of this assumption in the context of matching in epidemiology. We also discuss briefly the assumptions of conditional independence and carryover effects.

Bias↗
PubMed2026

Development and validation of a liquid chromatography-tandem mass spectrometry method for the quantification of twenty-five steroids in equine serum.

Steroids are potential biomarkers for monitoring equine pregnancy. However, immunoassays currently used for their quantification suffer from cross-reactivity and limited specificity, thus requiring more accurate methods. This study reports the development and validation of a robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous quantification of 25 steroids covering the main biosynthetic pathways of progestogens, corticosteroids, androgens, and estrogens. Steroids were extracted by protein precipitation followed by evaporation, derivatization, and reconstitution before LC-MS/MS analysis. A surrogate matrix was used for calibration and validation to avoid endogenous interference. Validation was performed according to and partly adapted from Clinical and Laboratory Standards Institute guidelines (CLSI), including linearity, trueness, precision, limits of detection and quantification, measurement uncertainty, recovery, matrix effects, carryover, selectivity, and stability. Calibration curves were fitted using the best-performing weighted linear or quadratic regression model, yielding excellent linearity (R2&#xa0;>&#xa0;0.990), trueness between -9.0% and 2.3%, and intra- and inter-day precision <6.3%. Lower limits of quantification ranged from 2.07 to 2250&#xa0;pg/mL depending on physiological analytes concentration. Extraction recovery averaged 24.3-114.9%, matrix effects were acceptable, and accuracy ranged from 94.4% to 98.9%. No carryover or interferences were detected. Measurement uncertainty remained <15%. This study presents the first LC-MS/MS method partially validated per CLSI criteria for the quantification of 24 steroids in equine serum. The method offers a sensitive and specific alternative to immunoassays and provides a robust tool for equine steroid profiling with potential applications in pregnancy monitoring, placentitis diagnosis, and fetal sex determination.

Animals↗
PubMed2006

Comparison of electric stimulation methods for reduction of triceps surae spasticity in spinal cord injury.

OBJECTIVES: To compare the effect of 3 methods of electric stimulation to reduce spasticity of the triceps surae in patients with complete spinal cord injury (SCI) and to investigate the carryover effect. DESIGN: Placebo-controlled study with repeated measurements after the interventions. SETTING: Research department affiliated with a rehabilitation hospital in the Netherlands. PARTICIPANTS: Ten patients with a complete SCI were recruited from the outpatient population of the rehabilitation hospital. All subjects had American Spinal Injury Association grade A impairment scores, except for one, who had grade C. The patients had no voluntary triceps surae contractibility. INTERVENTIONS: Forty-five minutes of cyclic electric stimulation of the agonist, antagonist, or dermatome of the triceps surae or a placebo approach. MAIN OUTCOME MEASURES: Outcome measures were the Modified Ashworth Scale (MAS), clonus score, and the H-reflex and M wave (H/M) ratio. The electromyographic response to a stretch of the soleus over the whole range of motion was also determined. The magnitude and ankle angle at which the electromyographic response started were calculated. RESULTS: Stimulation of the agonist provided a significant reduction in the MAS compared with the placebo approach (P<.001). There was no significant change in the H/M ratio or the electromyographic response amplitude after any of the stimulation methods, whereas stimulation of the antagonist muscle resulted in a significant reduction in the ankle angle at which the electromyographic response started, compared with the placebo approach (P<.037). CONCLUSIONS: Triceps surae stimulation reduces the MAS for that specific muscle, whereas the angle at which the reflex starts changes after antagonist stimulation.

Adult↗
PubMed1994

Analysis of multiple-dose bioequivalence studies.

In multiple-dose bioequivalence studies, it is possible at steady state to take repeated measurements of pharmacokinetic variables, such as area under the curve (AUC) and the maximum concentration (CMAX) of the blood concentration-time profile, within each period of a crossover design. We develop a bivariate random effects model for such a situation in a 2 x 2 crossover design using the natural log scale for AUC and CMAX that assumes no differential carryover effects and includes components for inter- and intrasubject variability with respect to both formulations. We derive the uniformly minimum variance unbiased estimators, which also happen to be restricted maximum likelihood estimators, and we provide a sample size formula.

Cross-Over Studies↗