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Biomedical subjects

S Arndt

Publications and source records attributed to S Arndt.

At least 145 records · Page 8Linked to original sources
PubMed1983

Comparison of cardiovascular risk in maximal isometric and dynamic exercise.

With the hypothesis that isometric exercise testing offers important clinical information yet is neglected because of overemphasis on its risk, we compared it with dynamic testing for variables indicative of myocardial ischemia. In a medical office, 287 patients were each subjected once to both a one-minute maximal handgrip stress test and maximal treadmill test while monitored noninvasively for cardiovascular responses. Systolic blood pressures usually increased more with the treadmill test, diastolic more with the handgrip. The treadmill tests caused greater mean heart rate and rate-pressure products, as well as more ST segment displacements, arrhythmias, and symptoms and signs. However, there were some unpredictable individual differences in the isometric blood pressure responses. Isometric testing is easy and useful and, if properly monitored, causes less risk to the patient than dynamic testing.

Adult↗
PubMed1983

The construct and predictive validity of adaptive behavior.

The construct and predictive validity of adaptive behavior of mentally retarded persons was investigated using a multitrait multimethod analysis. The validity issues of concern were (a) how generalizable the adaptive behavior dimension is over a variety of measurement methods, (b) how adaptive behavior relates to mental age (MA), and (c) how well adaptive behavior assessment references placement in programs and situations. Adaptive behavior and MA were assessed by program participation, psychometric ratings, and overall staff ratings. Adaptive behavior had high convergent validity and low discriminant validity and predicted MA program placement better than did MA. We concluded that adaptive behavior scores could replace MA.

Adaptation, Psychological↗
PubMed1982

Life-span development of institutionalized and community-based mentally retarded residents.

Life-span development of mentally retarded residents in institution and community settings was examined. Results showed that significant growth in adaptive behavior occurred for all groups of residents regardless of their level of retardation. Furthermore, the shapes of these growth curves were parallel across the different levels of retardation over the age range studies (5 to 50 years). Measures of the quality of the environment were available for institutionalized residents and were found to be unrelated to adaptive behavior growth; however, environmental quality was associated with initial levels of adaptive behavior, suggesting that for institutionalized residents, adaptive behavior competence may determine the type of environment provided.

Adaptation, Psychological↗
PubMed1981

A general measure of adaptive behavior.

A factor analysis was used to determine the extent to which multiple domain scores offer a more detailed view of adaptive and maladaptive behavior than do two general scores defined as simple sums. The general indices of adaptive and maladaptive behavior accounted for an overwhelming majority of the multiple domain score variance. This held true even when the range of ability was restricted. Since multiple indices of adaptive behavior offer little specific variance and create statistical problems, I concluded that adaptive behavior should be measured using a single general score. The same conclusion was reached with regard to maladaptive behavior.

Adult↗
PubMed1978

Cognitive mode and asymmetry in cerebral functioning.

Male graduate students from the fields of sculpture, psychology, and law were used to test the assumption that an individual's cognitive mode (verbal-analytic vs. spatial-holistic) is related to actual laterality in cerebral functioning. A measure of asymmetry of cognitive mode for each student, based on relative performance on three verbal-analytic tests compared to three spatial-holistic tests, successfully discriminated occupational groups. Laterality in cerebral functioning was indexed by relative reaction times to discriminate visual stimuli presented unilaterally to the left or right hemisphere. Reaction times to discriminate faces were less for the right hemisphere, while letters were discriminated faster by the left hemisphere. However, measures of cerebral laterality were not related to occupational group membership nor to asymmetry of cognitive mode. Asymmetry in performance on tests of cognitive mode may reflect an individual's general approach to problem solving, but is not closely related to laterality in cerebral functioning.

Adult↗
PubMedDate not supplied

The reliability of "bizarre" delusions.

The concept of bizarre delusions figures prominently in the diagnosis of schizophrenia under DSM-III-R criteria. Yet this concept may be difficult to apply in the clinical world. The interrater reliability of distinguishing bizarre versus non-bizarre delusions was estimated by compiling a sample of 40 delusional ideas and asking a group of psychiatrists (ranging from experts in the field to residents) to identify them as bizarre or non-bizarre. The interrater reliability of the 45 respondents was consistently low as measured by kappa statistic (kappa less than 0.40) within and across groups of raters, and regardless of whether or not a structured definition was applied. Implications for DSM-IV are discussed.

Delusions↗
PubMedDate not supplied

Alogia, attentional impairment, and inappropriate affect: their status in the dimensions of schizophrenia.

Previous factor analyses have shown that at least three factors are needed to encompass the positive and negative symptoms of schizophrenia. Despite marked similarities across studies, it remains unclear whether certain symptoms such as alogia, attentional impairment, and inappropriate affect are more closely related to negative or positive symptoms. An exploratory analysis was undertaken of the separate items on the Scale for the Assessment of Positive Symptoms (SAPS) and Scale for the Assessment of Negative Symptoms (SANS) that constitute the global rating of alogia, as well as the global ratings of attentional impairment and inappropriate affect in 90 schizophrenic patients. Findings indicate that inappropriate affect loads significantly with bizarre behavior and positive formal thought disorder on a disorganization factor, whereas attentional impairment loads significantly on psychotic, disorganization, and negative symptom factors. The global rating of alogia appears to comprise both positive and negative symptoms, with the item poverty of content of speech loading on the disorganization factor, and other items such as poverty of speech, blocking, and increased latency loading on the negative symptom factor. It is concluded that three dimensions are needed to characterize the symptoms of schizophrenia as measured by the SAPS/SANS. The use of three dimensions may be a robust way to further explore the relationship between signs and symptoms and their underlying mechanisms in schizophrenia.

Adolescent↗
PubMedDate not supplied

Symptom dimensions and brain morphology in schizophrenia and related psychotic disorders.

The heterogeneity of symptoms in schizophrenia may reflect heterogeneity of underlying pathophysiological mechanisms. Factor analytic studies have consistently identified three symptom factors, psychotic, negative and disorganized, as independent dimensions of schizophrenic psychopathology. This study examined the relationship of these symptom dimensions with volumes of specific brain regions. One-hundred and sixty-six schizophrenia spectrum patients were clinically evaluated with the Comprehensive Assessment of Symptoms and History (CASH) and scanned with a 1.5 Tesla magnetic resonance imaging scanner. Regions of interest (ROIs) were manually traced on 5 mm and 3 mm coronal slices by a single technician, blind to all aspects of subject identity. Correlations between ROI volumes and indices of symptom severity were determined. Analyses of covariance were then used to test for specific relationships between each of the three symptom dimensions and ROI volumes. Tests were made of each dimension, controlling for all others. Overall symptom severity was significantly correlated with larger ventricle volumes (lateral, third and temporal horns) and smaller temporal lobe, hippocampal and superior temporal gyral volumes. Both psychotic and negative symptom severity predicted increased third ventricular volume. Psychotic symptom severity uniquely predicted decreased superior temporal gyral volume as well as increased temporal horn volume. Within the psychotic symptom dimension, hallucinations alone predicted left superior temporal gyral volume. No significant associations between disorganized symptoms and any ROIs were demonstrated. These results provide clues to the localization of specific brain regions underlying symptom clusters in schizophrenia, and provide further validating evidence for the construct of independent dimensions of psychopathology within schizophrenia and related psychotic disorders.

Adolescent↗
PubMedDate not supplied

Effects of errors in a multicenter medical study: preventing misinterpreted data.

Large research projects offer significant advantages for research, but they pose special data quality problems. Data gathered in such projects may contain a greater absolute number of mistakes because of the people collecting data, the complexity of data processing, and the collation required. We wanted to learn from the types and frequencies of errors encroaching on data in a multicenter field trial, and to assess the effects of these errors had they passed through. We used extensive error trapping while processing 688 forms from seven sites in the field trial. Snapshots of the dataset were taken at several points in the process, before and after checking and correcting. We discovered 2.4% of the received data to be mistaken. These errors would have affected the data's reliability, decisions based on the study, and possibly the choice of analysis. Almost all of the mistakes were made at the time of measurement and may be related to raters' perceived importance of the variables. We found that communication and education effectively reduced the number of mistakes and their impact on the study over the course of the field trial. While an estimate of the overall error rate is important, the number of mistakes, in general, is only imperfectly related to the errors' effects on the study's results. Our results also suggest that statistical models that treat mistakes as simple independent events can be misleading.

Bias↗
PubMedDate not supplied

fMRI of neuronal activation with symptom provocation in unmedicated patients with obsessive compulsive disorder.

BACKGROUND: Previous studies suggest that a neural circuit involving over-activation of cortical, paralimbic, limbic, and striatal structures may underlie OCD symptomatology, but results may have been limited by medication use in those studies. To address this, we examined the effects of symptom induction on fMRI neural activation in medication-free patients with OCD. METHODS: Seven outpatients with OCD were exposed to individually tailored provocative and innocuous stimuli during fMRI scans. Self-ratings of OCD symptoms were performed prior to each scan and after exposure to stimuli. Images were analyzed as composite data sets and individually. RESULTS: Stimulus presentation was associated with significant increases in OCD self-ratings. Significant activation was demonstrated in several regions of the frontal cortex (orbitofrontal, superior frontal, and the dorsolateral prefrontal); the anterior, medial and lateral temporal cortex; and the right anterior cingulate. Right superior frontal activation inversely correlated with baseline compulsion symptomatology and left orbitofrontal cortical activation was inversely associated with changes in OCD self-ratings following provocative stimuli. CONCLUSIONS: These results in unmedicated patients are consistent with those from previous studies with medicated patients and suggest that OCD symptomatology is mediated by multiple brain regions including the anterior cingulate as well as frontal and temporal brain regions.

Adult↗
PubMedDate not supplied

Adding subjects or adding measurements: Which increases the precision of longitudinal research?

When designing repeated measurement studies, researchers must strike a balance between increasing the number of subjects and increasing the number of measurement times for each subject. The question often becomes "Do I gain more statistical precision by adding subjects or by adding additional follow-up measurements?" This study presents a method for evaluating the relative benefit of adding subjects versus adding measurement times. We used the standard error of estimate (SE) for mean change as the criterion of precision. An existing dataset on post-stroke patients containing six follow-up assessments of six standard rating scales was used. SE values for two common change indices were found and compared for all possible two, three, four, five, and six repeated measurements. Sample sizes required to achieve the same benefit as adding an additional measurement are presented. These data suggest that collecting five or six repeated measurements may be sufficient for accurately assessing change and that attempts to further precision should be accomplished by increasing the sample size.

Adolescent↗
PubMedDate not supplied

Correlating and predicting psychiatric symptom ratings: Spearman's r versus Kendall's tau correlation.

Simple correlations play a large role in the analysis of psychiatric data. They are used to predict outcome, validate new instruments, establish treatment efficacy and find symptom patterns. Researchers and data analysts often face a question about which correlation coefficient to use in a study but are often unaware of the strengths and weaknesses of the alternative correlation measures. The presence of outliers, nonconstant variance, skewed distributions and unequal n are common in psychiatric data and this poses severe problems for many classic statistical methods. We compare Pearson, Spearman and Kendall's correlation coefficients using a large sample of subjects with schizophrenia spectrum disorders who were evaluated with 7 different psychiatric rating scales. Samples sizes ranging from 8 to 50 were evaluated using bootstrapping methods. The criteria for evaluation of the correlations were the type I error rates, power, bias and confidence interval width. Pearson's r did not always control for false positives at the nominal rate and was often unstable. Spearman's r performed better than Pearson's but provided a biased estimate of the true correlation. Spearman's r was also difficult to interpret. Our results suggest that Kendall's tau(b) has many advantages over Pearson's and Spearman's r; when applied to psychiatric data, tau(b) maintained adequate control of type I errors, was nearly as powerful as Pearson's r, provided much tighter confidence intervals and had a clear interpretation.

Adult↗
PubMedDate not supplied

Charting patients' course: a comparison of statistics used to summarize patient course in longitudinal and repeated measures studies.

Investigators conducting longitudinal studies of psychiatric illnesses often analyze data based on psychiatric symptom scales that were administered at multiple time points. This study examines the statistical properties of seven indices that summarize patient long-term course. These indices can be used to compare differences between two or more groups or to test for changes in symptoms over time. They may also be treated as outcome measures and correlated with other clinical variables.The performance of each of the seven indices was assessed using data from two large ongoing studies of psychiatric patients: a longitudinal study of affective disorders and a longitudinal study of first-episode psychosis. These two datasets were subjected to bootstrapping techniques in order to calculate both type I error rates and statistical power for each summary statistic. Of the seven indices, Kendall's tau performed the best as a measure of patients' symptom course. Kendall's tau appears to offer more statistical power to detect change in course, yet its average type I error rate was comparable to the other indices.

Adult↗
PubMedDate not supplied

High rate of Bartonella henselae infection in HIV-positive outpatients in Johannesburg, South Africa.

The emerging opportunistic pathogen Bartonella henselae has a wide range of clinical presentation, which includes, particularly, bacillary angiomatosis. This non-random pilot survey of outpatients attending HIV clinics in Johannesburg, South Africa, sampled 188 patients, in whom there was a 10% prevalence of Bartonella bacteraemia, as determined by nested polymerase chain reaction.

AIDS-Related Opportunistic Infections↗