PubMed Health⌕ Search

Biomedical subjects

C S Davis

Publications and source records attributed to C S Davis.

At least 19 recordsLinked to original sources
PubMed2001

Effects of covariance model assumptions on hypothesis tests for repeated measurements: analysis of ovarian hormone data and pituitary-pteryomaxillary distance data.

In the analysis of repeated measurements, multivariate methods which account for the correlations among the observations from the same experimental unit are widely used. Two commonly-used multivariate methods are the unstructured multivariate approach and the mixed model approach. The unstructured multivariate approach uses MANOVA types of models and does not require assumptions on the covariance structure. The mixed model approach uses multivariate linear models with random effects and requires covariance structure assumptions. In this paper, we describe the characteristics of tests based on these two methods of analysis and investigate the performance of these tests. We focus particularly on tests for group effects and parallelism of response profiles.

Adolescent↗
PubMed2001

Patterns of fluoride intake from birth to 36 months.

OBJECTIVES: Dental fluorosis prevalence has increased in the United States, Canada, and other nations due to the widespread availability of fluoride in many forms, with fluoride ingestion during the first three years of life appearing most critical in fluorosis etiology. With few contemporary studies of fluoride ingestion in this age group, the purpose of this paper is to describe patterns of estimated fluoride ingestion from birth to 36 months of age from water, dentifrice, and dietary fluoride supplements and combined. METHODS: Repeated responses to separate series of questions about water intake, use of fluoride dentifrice, and use of fluoride supplements were collected by questionnaire as part of the longitudinal Iowa Fluoride Study and used to estimate fluoride intake. Estimated intake is reported by source and combined at different ages. Effects of subject age and other covariates on fluoride intake were assessed using regression methods appropriate for the analysis of correlated data. RESULTS: For most children, water fluoride intake was the predominant source, especially through age 12 months. Combined daily fluoride intake increased through 9 months, was lower at 12 and 16 months, and increased again thereafter. Mean intake per unit body weight (bw) was about 0.075 mg F/kg bw through 3 months of age, 0.06 mg F/kg bw at 6 and 9 months, 0.035 mg F/kg bw at 12 and 16 months, and 0.043 mg F/kg bw from 20-36 months. Depending on the threshold chosen (e.g., 0.05 or 0.07 mg F/kg bw), variable percentages of the children exceeded the levels, with percentages greatest during the first 9 months. Regression analyses showed fluoride intake (mg F/kg bw) from 1.5-9 months to decrease with increasing child's age, mother's age, and mother's education, with a complex three-way interaction among these factors. From 12-20 months, fluoride intake increased with increasing child age and decreased with increasing mother's age. No statistically significant relationships were found for fluoride intake from 24-36 months. CONCLUSIONS: There is considerable variation in fluoride intake across ages and among individuals. Longitudinal studies may be necessary to fully understand the relationships between fluoride ingestion over time and development of fluorosis.

Adult↗
PubMed2001

The role of the tubulointerstitium in radiation-induced renal fibrosis.

The functional and morphological response of the remaining hypertrophied kidney in unilaterally nephrectomized rats to single doses of 0-20 Gy X rays was investigated. Functional and histological end points were assessed serially 4-24 weeks postirradiation. Renal irradiation led to time- and dose-dependent reductions in renal function, seen in terms of a decreased glomerular filtration rate, increased blood urea nitrogen, and reduced hematocrit. These changes were accompanied by morphological changes in the glomerular, tubular and interstitial portions of the kidney. However, dose-dependent changes were observed only in terms of tubulointerstitial lesions. Significant increases in the degree of interstitial staining for collagen type III and fibronectin were observed 24 weeks postirradiation. These increases in extracellular matrix components were accompanied by a significant increase in interstitial alpha smooth muscle actin, suggesting activation of interstitial fibroblasts into myofibroblasts. There was no evidence of glomerular Tgfb after renal irradiation. A significant increase in tubular Tgfb staining was only seen 8 weeks postirradiation. In contrast, there was a shift of staining to the interstitium such that by 24 weeks postirradiation interstitial Tgfb staining was significantly greater than that seen in controls. These findings suggest that the tubule epithelial cell and the interstitial fibroblast are both active participants in the development and/or progression of radiation-induced renal fibrosis.

Animals↗
PubMed2000

Tape-recorded hypnosis instructions as adjuvant in the care of patients scheduled for third molar surgery.

UNLABELLED: As medical costs continue to escalate, there is willingness to consider the role played by nontraditional factors in health. We investigated the usefulness of tape-recorded hypnosis instruction on perioperative outcome in surgical patients in a prospective, randomized, and partially blinded study. Sixty patients scheduled for third molar surgery were studied. Patients were allocated to either an experimental group (E) or a control group (C). Group E received an audio tape to listen to daily for the immediate preoperative week, which guided the patients through a hypnotic induction and included suggestions on enhancement of perioperative well-being. Group C did not receive any tapes. The same surgeon administered local anesthesia and a standard regimen of sedation and performed the operation for all patients. The following variables were assessed 1 wk before surgery, immediately before and after surgery, and for 3 days after surgery by the indicated measurements: State anxiety by a Spielberger scale; nausea and pain by visual analog scales; number of tablets of the analgesics that were used; number of episodes of vomiting; and complications. In addition, the surgeon's assessment of ease of surgery was recorded. Two variables showed differences between the groups. First, Group C exhibited a mean increase of 11.7 points on the Spielberger scale from the screening to the presurgery period, while Group E showed only a mean increase of 5.5 points during the same period, P = 0.01. Second, the mean number of vomiting episodes was more in Group E, 1.3, than in Group C, 0.3, P = 0.02. In conclusion, anxiety was reduced before surgery by means of an audio tape containing hypnotic instructions; however, for no apparent reason, there was also an increase in the incidence of vomiting. IMPLICATIONS: We administered hypnosis instructions to patients before third molar surgery. Anxiety was reduced, but there was an increase in the incidence of vomiting. Although an easy and cost-effective method, the value of this approach remains to be established.

Adult↗
PubMed2000

Identification and quantification of hydroxamic acids in maize seedling root tissue and impact on western corn rootworm (Coleoptera: Chrysomelidae) larval development.

Hydroxamic acid content was analyzed in the root tissue of four maize, Zea mays L., lines using high-performance liquid chromatography (HPLC) and related to western corn rootworm, Diabrotica virgifera virgifera LeConte, larval development and survivorship. Maize lines evaluated included Mp710 (PI 596627), MpSWCB-4, (PI 550498), Sc213 (PI 548792), and Dk580 (DeKalb commercial hybrid). Maize plants from each line were grown in test tubes containing a transparent agarose gel medium in a growth chamber. After 8 d of growth, root tissue of each line was harvested and hydroxamic acid content analyzed using HPLC. Three hydroxamic acids, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), 6-methoxybenzoxazolinone (MBOA), and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), were identified in the maize roots tested. DIMBOA concentration was quantified and ranged from 246.37 +/- 70.53 micrograms to 91.84 +/- 49.82 micrograms DIMBOA per gram of root tissue. No significant difference was found among lines in D. v. virgifera larval development and survivorship.

Animals↗
PubMed2000

Cancer treatment-induced menopause: meaning for breast and gynecological cancer survivors.

Many cancer survivors are faced with irreversible changes resulting from cancer treatment. One such change some women face after cancer is treatment-induced menopause. Eight women (four with breast and four with gynecological cancers) were interviewed to explore the impact of treatment-induced menopause on their lives. Results indicated that participants' understanding and coping with menopause occurred within the larger context of the total cancer experience. For some of the women, menopause was not a significant problem; for others, the symptoms caused major distress and were a continuing reminder of the losses suffered due to cancer. Important concerns for all participants were: taking and keeping control, the desire to return to "normal" after cancer, and maintaining a coherent sense of self. Strong statements were also made about the power of knowing and the power of support in coping with treatment-induced menopause. Findings are discussed with implications for nursing practice.

Adaptation, Psychological↗
PubMed1999

Estimation of the average correlation coefficient for stratified bivariate data.

If the relationship between two ordered categorical variables X and Y is influenced by a third categorical variable with K levels, the Cochran-Mantel-Haenszel (CMH) correlation statistic QC is a useful stratum-adjusted summary statistic for testing the null hypothesis of no association between X and Y. Although motivated by and developed for the case of K I x J contingency tables, the correlation statistic QC is also applicable when X and Y are continuous variables. In this paper we derive a corresponding estimator of the average correlation coefficient for K I x J tables. We also study two estimates of the variance of the average correlation coefficient. The first is a restricted variance based on the variances of the observed cell frequencies under the null hypothesis of no association. The second is an unrestricted variance based on an asymptotic variance derived by Brown and Benedetti. The estimator of the average correlation coefficient works well in tables with balanced and unbalanced margins, for equal and unequal stratum-specific sample sizes, when correlation coefficients are constant over strata, and when correlation coefficients vary across strata. When the correlation coefficients are zero, close to zero, or the cell frequencies are small, the confidence intervals based on the restricted variance are preferred. For larger correlations and larger cell frequencies, the unrestricted confidence intervals give superior performance. We also apply the CMH statistic and proposed estimators to continuous non-normal data sampled from bivariate gamma distributions. We compare our methods to statistics for data sampled from normal distributions. The size and power of the CMH and normal theory statistics are comparable. When the stratum-specific sample sizes are small and the distributions are skewed, the proposed estimator is superior to the normal theory estimator. When the correlation coefficient is zero or close to zero, the restricted confidence intervals provide the best performance. None of the confidence intervals studied provides acceptable performances across all correlation coefficients, sample sizes and non-normal distributions.

Aged↗
PubMed1998

Threats to the validity of clinical trials employing enrichment strategies for sample selection.

Subject selection and exclusion criteria employed in typical clinical effectiveness trials of investigational new drugs have two fundamental aims: (1) to ensure that patients entering a study are truly suffering from the condition the drug is intended to treat and (2) to maximize the likelihood that the study will detect an effect of the drug if, in fact, one exists. Typical protocol selection criteria not only specify exacting procedures for establishing and documenting the diagnosis of those recruited for a study but also seek to increase, relative to the prevalence in the general population, the proportion of individuals in the sample likely to respond to pharmacological treatment. Because it is ordinarily impossible to learn prior to extensive clinical experience with a new drug which, if any, patient characteristics reliably predict a consistent treatment response, strategies for sample "enrichment" typically operate by excluding patients (for example, those with very advanced and/or complicated illness, those with serious concomitant illness, those at the extremes of age, those with very mild illness, and so forth) in whom a dependable response to treatment seems unlikely on logical and/or generic grounds. Some studies use positive strategies for sample "enrichment." In studies evaluating drugs intended to treat recurrent episodes of psychiatric illnesses, many protocols recommend selective recruitment of patients with a history of meaningful positive responses to antipsychotic treatment during prior episodes. Sample selection procedures of these kinds impose limits on the generalizability of a study's results (i.e., external validity), but the use of nonrandom patient samples is ordinarily held to have no effect on the internal validity of the results. In short, studies employing highly selected patient samples are, despite their limited external validity, regularly accepted as valid sources of evidence bearing on a drug's effectiveness. There are exceptions, however; this paper describes one in which the use of a seemingly innocuous sample enrichment maneuver proved highly damaging to the ultimate credibility of an important multicenter trial. In particular, exposure to an experimental treatment during an open qualification phase may invalidate drug-placebo comparisons made during a later randomized, blinded, controlled phase. Our review of the trial also reveals that the enrichment maneuver employed probably failed to accomplish its intended aims, selecting patients whose improvements on the outcome variable may be as reasonably ascribed to chance as to drug effect. This is all the more surprising because the method of sample enrichment employed has much in common with those long recommended in the clinical trial literature.

Aged↗
PubMed1998

Gamma-linolenic acid (GLA) is cytotoxic to 36B10 malignant rat astrocytoma cells but not to 'normal' rat astrocytes.

This study compares the effect of gamma-linolenic acid (GLA) and its precursor linoleic acid (LA) on survival of 36B10 malignant rat astrocytoma cells and 'normal' rat astrocytes. GLA was cytotoxic to 36B10 cells but not to astrocytes. By contrast, LA supplementation did not affect the survival of either cell types. There were minor differences in the uptake, distribution and use of radiolabelled GLA and LA by the 36B10 cells and astrocytes. GLA and LA supplementation increased the total polyunsaturated fatty acid (PUFA) content of the cells indicating increased oxidative potential. However, elevated levels of 8-isoprostane, an indicator of increased oxidative stress, were only observed in the GLA supplemented 36B10 cells. Addition of the antioxidant trolox to GLA-enriched 36B10 cells blocked the cytotoxic effect. Further, GLA enhanced the radiation sensitivity of the astrocytoma cells but not the astrocytes; trolox blocked the GLA-mediated increase in astrocytoma cell radiosensitivity. LA did not affect the radiation response of either cell type. While cyclo-oxygenase inhibitors did not affect GLA cytotoxicity, they blocked the enhanced radiation response of GLA-supplemented cells. The lipoxygenase inhibitor NDGA did not affect the toxicity produced by GLA. Thus, GLA is toxic to the neoplastic astrocytoma cells but not to normal astrocytes.

Animals↗
PubMed1998

Occupational injuries among older workers with visual, auditory, and other impairments. A validation study.

This study aims to validate a previously defined model of the risk of occupational injuries among older workers with visual, auditory, or other impairments. That model was based upon the Health and Retirement Study (HRS). The previous logistic regression model was recalculated using data from the 1994 National Health Interview Survey (NHIS). The parameter estimates for impaired hearing (.181 in NHIS, 1.55 in HRS), impaired vision (2.42 in NHIS, 1.48 in HRS), and self-employment (0.22 in NHIS, 0.49 in HRS) were in same direction and of roughly the same magnitude. The previously defined model was confirmed using NHIS data. The data suggest that as the workforce ages, more attention must be paid to the accommodation of disabilities in the workplace, especially sensory impairments-poor vision and hearing.

Accidents, Occupational↗
PubMed1998

Occupational injuries among older workers with disabilities: a prospective cohort study of the Health and Retirement Survey, 1992 to 1994.

OBJECTIVES: We tested the hypothesis that among older workers, disabilities in general, and hearing and visual impairments in particular, are risk factors for occupational injuries. METHODS: Using the first 2 interviews of the Health and Retirement Study, a nationally representative survey of Americans aged 51 to 61 years, we conducted a prospective cohort study of 5600 employed nonfarmers. RESULTS: Testing a logistic regression model developed in a previous cross-sectional study, we found that the following occupations and risk factors were associated with occupational injury as estimated by odds ratios: service personnel, odds ratio = 1.71 (95% confidence interval = 1.13, 2.57); mechanics and repairers, 3.47 (1.98, 6.10); operators and assemblers, 2.33 (1.51, 3.61); laborers, 3.16 (1.67, 5.98); jobs requiring heavy lifting, 2.05 (1.55, 2.70); self-employment, 0.50 (0.34, 0.73); and self-reported disability, 1.58 (1.14, 2.19). Replacing the general disability variable with specific hearing and visual impairment variables, we found that poor hearing (1.35 [0.95, 1.93]) and poor sight (1.45 [0.94, 2.22]) both had elevated odds ratios. CONCLUSIONS: Poor sight and poor hearing, as well as work disabilities in general, are associated with occupational injuries among older workers.

Accidents, Occupational↗
PubMed1997

The role of radionuclide angiocardiography in the treatment of patients receiving doxorubicin-based chemotherapy: a reassessment.

We attempted to evaluate the role of radionuclide angiography in the routine treatment of patients receiving doxorubicin-based therapy in a university hospital setting. We identified 222 cancer patients treated with doxorubicin or who underwent radionuclide angiography with the intent to receive doxorubicin at the University of Iowa in 1989. We examined the cumulative doses of doxorubicin, results of radionuclide angiograms, cardiac risk factors, and clinical outcomes and survival of patients. Of 222 patients, 168 (76%) underwent at least one radionuclide angiogram and received doxorubicin. Only a baseline study was performed in 136 (81%) of these 168 patients. Only 32 underwent follow-up study during therapy; six patients discontinued therapy for an 11-21% decrease in left ventricular function. The mean dose of doxorubicin received was 211 mg/m2, and 193 patients (96%) received a cumulative dose <450 mg/m2. Only two patients (1%) had heart failure. A questionnaire sent to medical oncologists in Iowa showed that use of radionuclide angiography in our institution reflected practice throughout the state. The majority of patients in our population who underwent radionuclide angiography had a single baseline study, which provides little clinically useful information. The majority of patients receiving doxorubicin as currently employed can be safely treated without radionuclide angiography.

Adolescent↗
PubMed1997

Randomized study of prophylactic platelet transfusion threshold during induction therapy for adult acute leukemia: 10,000/microL versus 20,000/microL.

PURPOSE: We designed and conducted a randomized single-institution trial comparing two common prophylactic platelet transfusion thresholds in patients undergoing induction therapy for acute leukemia. PATIENTS AND METHODS: Seventy-eight patients undergoing induction therapy for acute leukemia were randomized to receive prophylactic apheresis platelet concentrates when the platelet count was either < or = 10,000/microL or < or = 20,000/microL. RESULTS: There was no significant difference in the total number of bleeding episodes per patient with a median of four in the < or = 10,000/microL arm and two in the < or = 20,000/microL arm (25th to 75th percentiles of 2, 7 and 1, 5, respectively; P = .12). Patients randomized to the < or = 10,000/microL arm received more platelet transfusions for bleeding [one (0, 2) v zero (0, 0); P = .0003]. In contrast, patients on the < or = 20,000/microL arm received more platelet transfusions for prophylactic indications [10 (5, 14) v six (3, 8); P = 0.001], as would be expected, but less for bleeding. Nevertheless, the total number of platelet transfusions given to patients on the < or = 20,000/microL arm was higher and nearly significant [11 (6, 15) v seven (5, 11); P = .07]. There were no statistically significant differences between the groups with regard to RBC transfusion requirements, febrile days, days hospitalized, days thrombocytopenic, need for HLA-matched platelets, remission rate, or death during induction chemotherapy. No patient in either group died from hemorrhage or underwent major surgery for bleeding complications. CONCLUSION: Giving prophylactic platelets at a threshold of < or = 10,000/microL compared with < or = 20,000/microL can decrease the total utilization of platelets with only a small adverse effect on bleeding, and no statistically significant effect on morbidity.

Acute Disease↗
PubMed1997

A phase II trial of deferoxamine in patients with hormone-refractory metastatic prostate cancer.

The management of hormone-refractory metastatic prostate cancer remains a therapeutic dilemma. We report the results of a phase II trial with deferoxamine administrated at a dose of 50 mg/kg (maximum dose 5 g) administered intravenously over 8 hr daily, repeated for 5 days at 4-week intervals for 2 courses. Fourteen patients with advanced hormone-refractory prostate cancer were treated and 28 courses were delivered. Essentially no toxicity was observed. Using combined clinical and prostate-specific antigen (PSA) criteria. 13 of 14 patients had disease progression. However, 9 of 14 patients had stable measurable or evaluable disease and progressed solely based on PSA criteria. Deferoxamine in this dose and schedule has no activity in hormone-refractory prostate cancer. Further investigation of the effect of deferoxamine on PSA production/expression is warranted.

Adenocarcinoma↗
PubMed1997

Identifying the hospitalized patient at risk for nosocomial bloodstream infection: a population-based study.

Included in a 3-year population-based study were all patients (n = 64,281) admitted to a single tertiary care hospital (902 beds) using prospective hospital-wide surveillance for nosocomial infections. The objective of the study was to identify patients at risk for nosocomial bloodstream infection by using readily available hospital admission variables. After identifying potential risk factors for infection by univariate analyses, we derived multivariate models for predicting bloodstream infection by using logistical regression procedures. A total of 931 patients (1.45 per 100 admissions) developed a nosocomial bloodstream infection (2.2 episodes per 1000 patient-days) between 1 July 1987, and 30 June 1990. The crude mortality among infected patients was 34%, and the 319 deaths represented 22% of the total in-hospital mortality. Independent predictors of bloodstream infection were age, gender, primary diagnosis, and admission to a critical care unit. The sensitivity and specificity of the models for classifying patients as infected or noninfected were 81% and 81% for infants (1-11 months old) and 72% and 72% for adults, respectively. The negative predictive value of both models exceeded 99%. Applied to all patients on admission, the models we developed allowed us to survey only 28% of patients to identify more than 70% of those who will develop a nosocomial bloodstream infection.

Adolescent↗