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Biomedical subjects

L Ryan

Publications and source records attributed to L Ryan.

At least 91 records · Page 5Linked to original sources
PubMed1994

False positive MRI in the diagnosis of small intracanalicular vestibular schwannomas.

The current gold standard for diagnosing vestibular schwannomas is MRI with gadolinium-DTPA enhancement. This imaging modality is particularly useful in the detection of small intracanalicular tumours which can be missed by CT scanning. We present a case where MRI with enhancement suggested the presence of a 4 mm intracanalicular vestibular schwannoma. Surgical exploration of the internal auditory canal via a retrosigmoid approach, revealed no tumour, but inflammatory arachnoid matter around the vestibular nerve was found. A review of the audiological test results uncovered some results which did not correlate with the interpretation of the MRI scan. We would therefore caution against immediate surgical intervention in patients where the diagnosis of a small intracanalicular vestibular schwannoma is not totally supported by the audiological findings. In such cases rescanning with gadolinium enhancement after a suitable interval is recommended.

Cranial Nerve Neoplasms↗
PubMed1994

Mood dependent memory for events of the personal past.

Previous research on mood dependent memory (MDM) suggests that the more one must rely on internal resources, rather than on external aids, to generate both the target events and the cues required for their retrieval, the more likely is one's memory for these events to be mood dependent. To instantiate this "do-it-yourself" principle, three experiments were conducted in which Ss experiencing either a pleasant or an unpleasant mood generated autobiographical events in response to neutral nouns. Subsequently, Ss were tested for event free recall while in the same or the alternative mood state. All three studies showed MDM, such that the likelihood of recalling an event generated 2 or 3 days ago was higher when generation and recall moods matched than when they mismatched. Prospects for future research aimed at elucidating and extending these results are discussed.

Adult↗
PubMed1994

Modeling fetal death and malformation in developmental toxicity studies.

We review approaches to dose-response modeling and risk assessment for binary data from developmental toxicity studies. In particular, we focus on jointly modeling fetal death and malformation and use a continuation ratio formulation of the multinomial distribution to provide a model for risk. Generalized estimating equations are used to account for clustering of animals within litters. The fitted model is then used to calculate doses corresponding to a specified level of excess risk. Two methods of arriving at a lower confidence limit or Benchmark dose are illustrated and compared. We also discuss models based on single binary end points and compare our approach to a binary analysis of whether or not the animal was 'affected' (either dead or malformed). The models are illustrated using data from four developmental toxicity studies in EG, DEHP, TGDM, and DYME conducted through the National Toxicology Program.

Abnormalities, Drug-Induced↗
PubMed1993

Relation of female infertility to consumption of caffeinated beverages.

Several studies have reported an association between caffeine intake and delay to conception. To study this relation further, the authors examined caffeine use in 1,050 women with primary infertility and 3,833 women who had recently given birth during the period 1981-1983 in the United States and Canada. The cases were separated by the cause of their infertility: ovulatory factor, tubal disease, cervical factor, endometriosis, or idiopathic infertility. The relative risks of each type of infertility associated with caffeine were calculated using separate logistic regression models and controlling for relevant confounding factors, such as age, center, cigarette smoking, lifetime number of sexual partners, alcohol consumption, contraception, body mass index, and exercise. A significant increase in the risk of infertility due to tubal disease or endometriosis was observed for the upper levels of caffeine intake, indicating a threshold effect. For tubal infertility, a relative risk of 1.5 (95% confidence interval (CI) 1.1-2.0) was found in women who consumed more than 7 g of caffeine per month as compared with those who consumed 3 g or less per month. For endometriosis, the relative risk was 1.9 (95% CI 1.2-2.9) in women who consumed 5.1-7 g/month and 1.6 (95% CI 1.1-2.4) in those with an intake of more than 7 g/month. These data suggest that caffeine deserves further study with regard to its effects on the female reproductive system.

Adult↗
PubMed1993

Prognostic factors in metastatic melanoma.

BACKGROUND: Each year, 6000 people die in the United States from metastatic melanoma. Further study of factors affecting the prognosis of patients with this disease is needed. METHODS: The authors analyzed response and survival data from 635 patients who had entered three Eastern Cooperative Oncology Group trials for metastatic melanoma. RESULTS: Factors associated with poorer survival after study entry included poor performance status and the presence of symptoms, such as reduced appetite, fever, or nausea/vomiting. Male patients had poor survival, as did patients entering the study less than 1 year after a documented recurrence to study entry. As expected, characteristics of the initial primary disease (treatment and symptoms) had little association with survival after entering the advanced disease protocol. Two summary measures of the extent of metastatic involvement had a strong influence on survival. These were the number of nonbone metastases and the clinician's assessment as to the most significant metastatic site. Patients with the liver as their clinically most significant metastatic site had a poorer prognosis than those otherwise classified, including those with central nervous system metastases. The prognosis also worsened with an increasing number of sites of nonbone metastases, including skin and soft tissue. Tumor response occurred in only 11% of the patients. Patients with poor performance status and those with lung involvement had a significantly lower response rate than did others. Although the frequency of response was low, patients with objective responses survived significantly longer than did the nonresponders (based on an analysis appropriately adjusted for the time of response using a time-dependent proportional-hazards model). CONCLUSIONS: These results provide useful guidelines for the design and analysis of clinical trials in metastatic melanoma.

Adult↗
PubMed1993

The involvement of CD14 in stimulation of cytokine production by uronic acid polymers.

In this study the molecular mechanisms behind the stimulatory activities of the uronic acid polymers poly mannuronic acid (poly M), high M alginate and oxidized cellulose (C60XY) were investigated and compared with lipopolysaccharide (LPS). The cytokine-inducing abilities of the uronic acid polymers and LPS were examined on CD14-positive human monocytes and CD14-negative U373 astrocytoma cells. It was found that LPS induced monocytes and U373 cells to produce tumor necrosis factor (TNF) and interleukin(IL)-6, respectively, by different mechanisms. The poly uronic acids induced monocytes to produce TNF, but with 100-1000 times less potency compared to LPS. On U373 cells, LPS at concentrations > or = 32 ng/ml resulted in a dose-related IL-6 production, whereas the poly uronic acids had negligible effects even at 1 mg/ml. The binding data demonstrate that only the CD14-positive monocytes in the peripheral blood mononuclear cells population bound poly M. Furthermore, poly M was found to bind to CD14 in the presence of serum. Antibodies against CD14 also inhibited the TNF-inducing activity of the three uronic acid polymers tested. In conclusion, these results demonstrate that uronic acid polymers induce TNF production through mechanisms which involve CD14.

Alginates↗
PubMed1993

Rate of speech effects in aphasia: voice onset time.

This study investigated the ability to produce appropriate voice onset time (VOT) contrasts under conditions of rate modulation in groups of nonfluent aphasic subjects, fluent aphasic subjects, and nonneurological controls. Acoustic analyses of the consonants [b d g p t k] produced in the context of the vowels [i e a o u] at two different rates of speech revealed that normal subjects' VOTs were significantly shorter at the fast rate of speech relative to the slow/normal rate, as expected. In addition, the rate change had a significantly greater effect on voiceless stops as compared to voiced and on velar consonants as compared to labials and alveolars. The nonfluent aphasic patients exhibited a similar pattern except that no differences in magnitude of rate-related changes were found across place of articulation. Further, similar to previous studies, the nonfluent aphasic patients produced voice and voiceless consonants with somewhat overlapping VOT distributions, indicating an impairment in temporal integration in these subjects. Finally, the fluent aphasic patients demonstrated a surprisingly aberrant pattern of results, with VOTs under th fast condition shorter than under the slow, but no differences in magnitude of change across place of articulation or voicing categories. The results are discussed in relation to the nature of speech production deficits in both nonfluent and fluent aphasic patients. Implications for remediation are considered.

Adult↗
PubMed1993

Models of cognitive deficit and statistical hypotheses: multiple sclerosis, an example.

The purpose of the current study was to describe four models of cognitive deficit and to outline the statistical hypotheses underlying each model. The four models of cognitive deficit were (a) specific deficit; (b) subgroup deficit; (c) a syndrome dissociation model; and (d) a global function dissociation model. Neuropsychological data are analyzed to examine each of these four models in a sample of mild Multiple Sclerosis (MS) patients. The results suggest that for these subjects and tests, the specific deficit model best fits the data. The results are reviewed initially in the context of MS. There follows a consideration of statistical caveats and finally, general applications of the proposed procedures.

Adult↗
PubMed1993

Implications of statistical tests of variance and means.

The primary purpose of this paper is to illustrate that tests for the homogeneity of variance in the statistical analysis of clinical neuropsychological data may provide unique information. Specifically, tests of variance homogeneity are more sensitive to outliers than the more commonly used tests of group means. Moreover, when both a test of means and of variance are done and the results compared, the nature of the deficit within the sample can be interpreted with greater confidence.

Analysis of Variance↗
PubMed1993

Self-reported use of pharmaceuticals and primary ovulatory infertility.

Over 1.5 billion prescriptions were filled by pharmacies in 1990, but little information exists on the effect that pharmaceutical agents have on female reproductive capacity. As part of a case-control study of risk factors for primary ovulatory infertility, we examined self-reported use of several prescription and nonprescription medications in 597 women with ovulatory infertility and 3,833 controls admitted for delivery at seven hospitals. Only women reporting use of a drug for at least 6 months, beginning before the onset of infertility in cases and before conception in controls, were considered exposed. An elevated risk of ovulatory infertility was found for women who ever used thyroid preparations [relative risk (RR) = 2.3, 95% confidence interval (CI) = 1.5-3.5] or antidepressants (RR = 2.9, 95% CI = 0.9-8.3), although the latter estimate was based on only five cases who reported having taken antidepressants. Current users of tranquilizers and ever-users for more than 2 years were also at greater risk of infertility than never-users (RR = 3.2, 95% CI = 1.1-8.5 and RR = 2.9, 95% CI = 0.8-11, respectively). Women who used asthma medication before age 21 had more than a twofold increase in risk of ovulatory infertility (RR = 2.5, 95% CI = 1.0-5.9).

Adult↗
PubMed1993

Similar mechanisms of action of defined polysaccharides and lipopolysaccharides: characterization of binding and tumor necrosis factor alpha induction.

Little has been reported about the effects of different polysaccharides on cytokine production from human monocytes. In this study, we show that several well-defined polysaccharides, including polymers with different sizes of beta 1-4-linked D-mannuronic acid (poly-M, high-M alginate, and M-blocks) and cellulose oxidized in the C-6 position, induced human monocytes to produce tumor necrosis factor alpha (TNF-alpha). Poly-M was the most efficient polysaccharide tested and, on a weight basis, was approximately as efficient as lipopolysaccharide (LPS) from Escherichia coli. TNF-alpha production was shown to depend strongly on the molecular weights of poly-M and high-M alginate, with maximal TNF-alpha production occurring at molecular weights above 50,000 and 200,000, respectively. G-blocks, alpha 1-4-linked L-guluronic acid polymers that did not induce cytokine production from monocytes, reduced the cytokine production induced by the beta 1-4-linked polyuronic acids and LPS. Furthermore, both G-blocks and LPS were found to inhibit the binding of poly-M to monocytes, as measured by flow cytometry. In addition, we found that the binding of LPS to monocytes was inhibited by G-blocks, M-blocks, and poly-M. Our results indicate that beta 1-4-linked polyuronic acids and LPS may stimulate monocytes to produce TNF-alpha by similar mechanisms and may bind to a common receptor.

Biological Assay↗
PubMed1993

Using historical controls in the analysis of developmental toxicity data.

Historical control data can often aid in the interpretation of the results from laboratory dose-response experiments. For example, formal statistical methods for using historical data are well established for carcinogenicity studies. In that case, a score test derived from a beta-binomial model yields a simple modification of the standard Cochran-Armitage test for trend. However, this test cannot be used for developmental toxicity studies since it does not allow for the additional correlation structure induced by the presence of litter effects. In this paper, quasi-likelihood methods are used to incorporate historical control information into a trend test for the types of correlated binary outcomes that typically arise in developmental toxicity studies. The proposed test is asymptotically equivalent to the beta-binomial score test in the special case when all the litter sizes are equal to 1. Malformation data from a series of developmental toxicity studies illustrate the results.

Abnormalities, Drug-Induced↗
PubMed1993

Global tests for multiple binary outcomes.

The applied statistician often encounters the need to compare two or more groups with respect to more than one outcome or response. Several options are generally available, including reducing the dimension of the problem by averaging or summarizing the outcomes, using Bonferroni or other adjustments for multiple comparisons, or applying a global test based on a suitable multivariate model. For normally distributed data, it is well established that global tests tend to be significantly more sensitive than other procedures. While global tests have also been proposed for multiple binary outcomes, their properties have not been well studied nor have they been widely discussed in the context of clustered data. In this paper, we derive a class of quasi-likelihood score tests for multiple binary outcomes, and show that special cases of this class correspond to other tests that have been proposed. We discuss extensions to allow for clustered data, and compare the results to the simple approach of collapsing the data to a single binary outcome, indicating the presence or absence of at least one response. The asymptotic relative efficiencies of the tests are shown to depend not only on the correlation between the outcomes, but also on the response probabilities. Although global tests based on a multivariate model are generally recommended, our findings suggest that a test based on the collapsed data can maintain surprisingly high efficiency, especially when the outcomes of interest are rare. Data from several developmental toxicity studies illustrate our results.

Abnormalities, Drug-Induced↗
PubMed1993

Efficacy of ifosfamide in combination with doxorubicin for the treatment of metastatic soft-tissue sarcoma. The Eastern Cooperative Oncology Group.

On the basis of ifosfamide's demonstrated single-agent activity in adult soft-tissue sarcoma, the Eastern Cooperative Oncology Group (ECOG) tested whether ifosfamide would add to the efficacy of doxorubicin in a three-regimen, controlled phase III trial. Doxorubicin, ECOG's standard to which newer chemotherapeutic treatments are compared, was given at a dose of 80 mg/m2 every 3 weeks and was designated the control regimen. Ifosfamide was given at a dose of 3,750 mg/m2 on days 1 and 2 every 3 weeks in combination with 30 mg/m2 doxorubicin given each day for 2 days; additionally, mesna was given to counter the genitourinary toxicity associated with ifosfamide. A second experimental regimen consisted of doxorubicin (40 mg/m2), mitomycin (8 mg/m2), and cisplatin (60 mg/m2), all given intravenously on day 1, with repeated cycles being scheduled for day 21. Of the 279 adults with soft-tissue sarcoma who were entered in the study, 260 were analyzed. The overall response rate was 20% for doxorubicin, 34% for ifosfamide/doxorubicin, and 31% for doxorubicin/mitomycin/cisplatin, with the difference between the first two regimens being significant (P = 0.04). The median survival was 8.8, 11.5, and 9 months, respectively, for the three regimens. Myelosuppression, the predominant toxicity, occurred in 60%, 88%, and 58% of patients, respectively.

Adult↗
PubMed1992

Statistical properties of the NOAEL.

The use of the no observed adverse effect level (NOAEL) in setting allowable exposure levels for noncancer endpoints is a source of controversy. Based on computer simulations and empirical studies, several authors have criticized the use of the NOAEL in terms of its sensitivity to sample size and its high sampling variability from experiment to experiment. The purpose of this paper is to derive the statistical distribution of the NOAEL. Using Weibull models, we investigate the impact of the shape of the underlying dose-response curve on the distribution of the NOAEL. The results confirm previous criticisms of the NOAEL and show that average risk levels associated with the NOAEL may be substantial. These results provide additional motivation for developing alternative approaches to risk assessment.

Animals↗
PubMed1992

Phase II trials of interferons-alpha and -beta in advanced sarcomas.

Interferons (IFNs)-alpha and -beta were administered to patients with metastatic sarcomas in two different Eastern Cooperative Oncology Group studies. In one study, patients received IFN-alpha 2b, 20 million units/m2 i.v. 5 days/week x 4, then 10 million units s.c.t.i.w. In the second study, patients received IFN-beta ser 180 million units t.i.w. Of 87 patients evaluable for response, there were three responses in 64 patients (5%) treated with IFN-alpha-2b and no responses in 23 patients treated with IFN-beta ser. Severe or life-threatening fatigue with decline in performance status complicated treatment of 37% of patients receiving IFN-alpha 2b and 17% of patients receiving IFN-beta ser. Further investigation of IFNs in sarcomas should depend on evidence from preclinical studies demonstrating synergistic effects of IFNs combined with a cytoreductive modality which has proven activity in these malignancies.

Adult↗