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Biomedical subjects

W S Clark

Publications and source records attributed to W S Clark.

At least 55 records · Page 3Linked to original sources
PubMed1995

Localization of an obstructing esophageal lesion. Is the patient accurate?

There are many options as to the accuracy of a patient's subjective localization of an obstructing esophageal lesion. However, there are few studies specifically examining this issue. Over a 35-month period, all patients evaluated by our gastroenterology service undergoing endoscopy for dysphagia were prospectively identified. The patient's subjective localization for the level of obstruction was evaluated by an investigator blinded to the results of prior barium esophagography and recorded on a schematic of the bony skeleton. At the time of endoscopy, the most proximal level of the obstructing lesion was documented. In all, 139 patients with dysphagia and an esophageal stricture were evaluated. Barium esophagograms were performed prior to endoscopy in all but nine patients (6.5%). The most common lesions causing dysphagia were carcinoma (34.5%), gastroesophageal reflux disease (22.3%), and a Schatzki's ring (15.8%). The level of obstruction was localized exactly in 30 patients (21.6%), within +/- 2 cm in 72 (52%), and within +/- 4 cm in 31 additional patients (74%). Eight patients (15%) with a distal esophageal lesion localized the obstruction to the proximal esophagus, whereas only two patients (5%) with a lesion in the proximal esophagus localized the level of obstruction to the distal esophagus. Overall, patients with distal obstructing lesions were more likely to have referral > 6 cm proximally than proximal lesions with referral to the distal esophagus (P = 0.003). There were no significant differences in accuracy based on the cause of dysphagia. In conclusion, a patient's subjective localization of the level of an esophageal stricture is highly accurate. Patients appear to be most accurate in localizing proximal rather than distal lesions.

Aged↗
PubMed1995

Diabetic ketoacidosis in obese African-Americans.

Our preliminary data indicate that 15% of African-American patients presenting with diabetic ketoacidosis (DKA) are obese. To determine underlying mechanisms, we analyzed the clinical characteristics and indexes of insulin secretion and insulin sensitivity in 35 obese patients with DKA, 22 obese patients with hyperglycemia, 10 lean patients with DKA, and 10 obese nondiabetic subjects. Studies were performed 1 day after resolution of DKA and after 12 weeks of follow-up. At presentation, both obese DKA and obese hyperglycemic patients had no detectable insulin response to intravenous glucose, but they did respond to glucagon administration. The acute insulin response (AIR) to glucagon in obese DKA patients (0.9 +/- 0.1 ng/ml, P < 0.01), but significantly greater than in lean patients with DKA (0.1 +/- 0.1 ng/ml, P < 0.01). After 12 weeks of follow-up, the AIR to glucose improved in both groups of obese diabetic patients but remained significantly lower than in nondiabetic control subjects (both P < 0.01). In contrast, the AIR to glucagon was not significantly different from that in obese control subjects. Insulin sensitivity was decreased in both groups of obese diabetic patients at presentation and improved after follow-up to levels similar to those in obese nondiabetic control subjects. Reactivity with islet cell antibodies was not detected in any of the patients. During follow-up, 25 of 35 obese DKA and 16 of 22 hyperglycemic patients were able to discontinue insulin therapy, with continued good metabolic control. Our results indicate that in African-Americans, obese patients with DKA represent a subset of type II diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Prospective evaluation of oropharyngeal findings in human immunodeficiency virus-infected patients with esophageal ulceration.

OBJECTIVE: Although the presence of oropharyngeal (OP) candidiasis plays an important role in the evaluation of human immunodeficiency virus (HIV)-infected patients with esophageal symptoms, there is little information on the utility of OP findings in patients with esophageal ulceration. METHODS: Over a 54-month period, all HIV-infected patients with esophageal ulceration had careful inspection of the oropharynx at the time of presentation with esophageal complaints and at endoscopy. HIV-infected patients without esophageal ulceration undergoing endoscopy during the last 30 months had OP findings similarly documented. OP ulceration ulceration was determined based on clinical, endoscopic, and histopathological findings. RESULTS: Of the 124 patients identified with esophageal ulcer, 14 (11%) had coexistent OP ulceration: herpes simplex virus, four; idiopathic esophageal ulcer, four; cytomegalovirus, three; herpes simplex virus and cytomegalovirus, two; idiopathic and cytomegalovirus, one. Four patients had OP ulcer without esophageal ulcer; only one of these patients had esophageal symptoms. All OP lesions healed with therapy for the esophageal ulcer. Twenty-eight patients with esophageal ulcer had OP candidiasis (23%); 21 of these patients (75%) also had Candida esophagitis. The sensitivity and specificity of OP ulcer for esophageal ulcer were 11% and 97%, respectively. The positive and negative predictive values of OP candidiasis for esophageal candidiasis were 90% and 82%, respectively. CONCLUSIONS: OP ulceration is uncommon in patients with esophageal ulceration, with the exception of herpes simplex virus esophagitis. OP candidiasis is common in patients with underlying esophageal ulcer, potentially resulting in diagnostic confusion. OP candidiasis appears to be a moderately useful diagnostic marker for Candida esophagitis.

AIDS-Related Opportunistic Infections↗
PubMed1993

Effect of routine use of therapy in slowing the clinical course of human immunodeficiency virus (HIV) infection in a population-based cohort.

Clinical trials have shown that the prophylactic use of zidovudine and aerosolized pentamidine (or other antibiotics used as prophylaxis against Pneumocystis carinii pneumonia) in acquired immunodeficiency syndrome (AIDS)-free human immunodeficiency virus (HIV)-infected persons delays the development of AIDS, but the effectiveness of such therapy in general use in the population still remains largely undocumented. To help answer this question, the authors estimate the effectiveness of this therapy in a population-based cohort of HIV-infected homosexual and bisexual men in San Francisco. The authors use a continuous-time Markov process to model the decline of CD4+ T-lymphocytes (T4-cells) measured in cells/microliter in HIV-infected persons. The model partitions the HIV (type 1) infection period into six progressive T4-cell count intervals (stages), followed by a seventh stage: AIDS diagnosis. The authors use maximum likelihood methods to fit the model to the observed transitions for 428 HIV-infected men during June 1984 to March 1991, from the San Francisco Men's Health Study. Since zidovudine was not widely used before 1988, the model has a component that controls for calendar time-related biases. The fitted model provides statistical estimates and confidence intervals for measuring therapy effectiveness. The authors estimate that prophylactic therapy reduces the progression rate from stage 4 (T4-cell count, 350-499) to stage 5 (T4-cell count, 200-349) by a factor of 0.26 (95% confidence interval (CI) -0.22 to 0.55); from stage 5 to stage 6 (T4-cell count < 200) by a factor of 0.33 (95% CI 0.04-0.54); and from stage 6 to 7 (AIDS) by a factor of 0.62 (95% CI 0.47-0.73). In addition, therapy started by an HIV-infected person in stage 4 is estimated to reduce the risk of developing AIDS by a factor of 0.83 (95% CI 0.46-0.94) at 6 months and 0.68 (95% CI 0.35-0.89) at 24 months after entering stage 4. Therapy started by HIV-infected persons in more advanced stages is estimated to reduce the risk of developing AIDS by factors ranging from 0.70 (95% CI 0.39-0.90), early in stage 5, to 0.28 (95% CI 0.14-0.45), late in stage 6. Thus, the prophylactic use of zidovudine and pentamidine in routine medical care has a strong, consistent, and significant effect in slowing the clinical course of HIV infection in a population-based cohort.

AIDS-Related Opportunistic Infections↗
PubMed1992

Treatment trial of oxiracetam in Alzheimer's disease.

Twenty-four carefully assessed patients with probable Alzheimer's disease were enrolled in a double-blind, placebo-controlled treatment study of oxiracetam, a nootropic agent reported to improve memory performance in patients with dementia. A broad battery of neuropsychological tests failed to reveal any improvement in the treated group or in any treated patient when individual test scores were analyzed. These findings indicate that oxiracetam is ineffective in reducing cognitive impairment due to Alzheimer's disease.

Aged↗
PubMed1991

Adenocarcinomas of the colon and rectum in persons under 40 years old. A population-based study.

Data collected by nine population-based tumor registries participating in the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute were analyzed to characterize the epidemiology of noncarcinoid adenocarcinomas of the colon and rectum in young adults. Tumors diagnosed in persons under 40 years old between 1973 and 1984 (n = 1736) were compared with those in persons 40 years and older (n = 106,760). This first large U.S. population-based study of colorectal adenocarcinomas in the young shows a higher incidence in blacks than whites and later detection in black males. It also shows a higher proportion of tumors of mucinous and signet ring histological type than in older age groups. Among the younger group, the average annual age-adjusted incidence rate was 34% higher in black males than in white males (12.6 vs. 9.4 per million persons) and 46% higher in black females than in white females (13.0 vs 8.9 per million persons). The proportion of tumors that were right-sided varied by age: 0-29 years, 30%; 30-39 years, 26%; 40-49 years, 22%; 50-59 years, 21%; 60-69 years, 24%; 70-79 years, 30%; and 80+ years, 35%. Males under age 40 were less likely to present with localized disease (whites, 27%; blacks, 21%) than were those aged 40 and older (whites, 39%; blacks, 36%). The proportion of tumors classified as mucinous decreased with age, from 28% among those aged 0-19 years to 5% among those 40 years and older. A similar trend was observed for signet ring tumors. Although this latter type accounted for 10% of large-bowel tumors among subjects aged 0-19 years, this proportion decreased with age to 0.2% in those 40 years and older.

Adenocarcinoma↗
PubMed1991

The relation of socioeconomic status to oral and pharyngeal cancer.

We assessed the relation between socioeconomic status and risk of oropharyngeal cancer in a population-based interview study of 762 male cases and 837 male controls in four areas of the United States. Three primary indicators of socioeconomic status were evaluated: education, occupational status, and percentage of potential working life spent in employment. With adjustment for the effects of established risk factors, such as use of tobacco products, alcohol consumption, and poor dentition, a relatively low percentage of years worked was also a risk factor. Educational attainment and occupational status were not independently related to risk of oropharyngeal cancer. These results are consistent with the hypothesis that behaviors that lead to social instability, and/or social instability itself, are linked to an increased risk of oral and pharyngeal cancers.

Adult↗
PubMed1991

The dynamics of CD4+ T-lymphocyte decline in HIV-infected individuals: a Markov modeling approach.

We modeled the decline of CD4+ T-lymphocytes (T4 cells) in HIV-infected individuals with a continuous-time Markov process. The model partitions the HIV infection period into six progressive T4-cell count intervals (states), followed by a seventh state: a definitive HIV-infection end point, i.e., AIDS diagnosis or Walter Reed stage 6 (opportunistic infections). The Markov model was used to estimate the state-specific progression rates from data as functions of important progression cofactors. We applied the model to data on 1,796 HIV-positive individuals in the U.S. Army. The estimated mean waiting time from seroconversion to when the T4-cell count persistently drops below 500/mm3, but is greater than 349/mm3, is 4.1 years, and the waiting time to a T4-cell count of less than 200/mm3 is estimated at 8.0 years. The estimated rate of T4-cell decline was higher for HIV-infected individuals with initially high numbers of T4 cells, but the estimated rate of decline remains relatively uniform when the T4-cell count dropped persistently below 500/mm3. The opportunistic infection incubation period, i.e., the time from seroconversion to opportunistic infection diagnosis, is estimated at 9.6 years. Age is found to be an important cofactor. The estimated mean opportunistic infection incubation periods are 11.1, 10.0, and 8.9 years for the youngest (less than or equal to 25 years old), the middle (26-30 years old), and the oldest (greater than 30 years old) age groups, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMed1990

Race, nutritional status, and survival from breast cancer.

The effects of nutritional status on differences in the survival of black and white women with breast cancer were studied in a cohort of 1,960 Georgia women diagnosed during 1975-1979. After data were adjusted for stage of disease, socioeconomic status, and other prognostic factors, poorer survival rates were shown in black women. Within each stage classification, lower levels of serum albumin and hemoglobin and higher relative body weight were more common among blacks and were independently associated with poorer survival. Among women with stage 3 disease, adjustment for these variables substantially reduced the excess mortality rate among blacks, suggesting that racial differences in survival may be partly explained by differences in nutritional status or extent of disease within stage.

Aged↗
PubMed1989

Statistical analysis of the stages of HIV infection using a Markov model.

We use a staged Markov model to estimate the distribution and mean length of the incubation period for acquired immunodeficiency syndrome (AIDS) from a cohort of 603 human immunodeficiency virus (HIV) infected individuals who have been followed through various stages of infection. The model partitions the infected period into four progressive stages: (1) infected but antibody-negative; (2) antibody-positive but asymptomatic; (3) pre-AIDS symptoms and/or abnormal haematologic indicator; and (4) clinical AIDS. We also model a fifth stage: death due to AIDS. The estimated mean (median) waiting times in each stage of infection are stage 1, 2.2 (1.5) months; stage 2, 52.6 (36.5) months; stage 3, 62.9 (43.6) months; and stage 4, 23.6(16.3) months. We estimate the mean AIDS incubation period (from infection to development of clinical AIDS) as 9.8 years with a 95 per cent confidence interval of [8.4, 11.2] years. The paper also considers the estimated density function of the AIDS incubation period and the estimated survival functions for individuals in each stage of infection. This work represents one of the most complete statistical descriptions to date of the natural history of HIV infection.

Acquired Immunodeficiency Syndrome↗
PubMed1989

In vivo binding of circulating immune complexes by C3b receptors (CR1) of transfused erythrocytes.

The effects of packed erythrocyte transfusion with high CR1 activity on circulating immune complex concentrations were studied in 14 transfusion experiments involving 12 patients with immune complex related diseases. Before erythrocyte transfusion circulating immune complex concentrations ranged from 8 to 128 micrograms/ml. After transfusion (2-3 units) immune complex concentrations decreased depending on the levels of CH50 titres in the recipients. In 11 experiments, in which the patients' CH50 titres ranged from 21 to 44, immune complex concentrations decreased by 75-100% within five days. The CH50 titres were also decreased after erythrocyte transfusion but subsequently increased to initial ranges within 6-35 days. In three patients with low CH50 titres (1.0-10.0) decreases in immune complexes were not observed. Direct Coombs' tests for IgG and C3 were performed before and after erythrocyte transfusion to determine potential in vivo binding of circulating immune complexes. Thus in eight of 14 experiments, in which erythrocytes carried no IgG before packed erythrocyte transfusion, seven became Coombs' positive for IgG after the transfusion. In seven of 14 experiments, in which erythrocytes were negative for complement before transfusion, five became positive afterwards. Moreover, in 12 instances slight increases of CR1 activity of patients' erythrocytes were observed within eight days, which improved further within 35 days after erythrocyte transfusion. These studies suggest that transfusion of erythrocytes with high CR1 activity results in the removal of circulating immune complexes and that this process is dependent on complement consumption. These experiments support the hypothesis that erythrocyte-CR1 has a functional role in the removal of circulating immune complexes and may thereby inhibit the deposition of immune complexes within body tissue constituents.

Antigen-Antibody Complex↗
PubMed1988

Breast self-examination and survival from breast cancer.

The relationship between breast self-examination (BSE) and survival was evaluated in 2093 women with breast cancer newly diagnosed between June 1975 and February 1979. In this population self-examiners were younger, more educated, and more likely to be white, premenopausal, and married than nonexaminers. Self-examiners also tended to seek medical care more rapidly and to have earlier stages of disease at diagnosis. Five years after diagnosis, the cumulative observed survival rates from breast cancer were 76.7% among self-examiners and 60.9% among nonexaminers (P less than 0.0001). In a multivariate analysis known sociodemographic and treatment confounders accounted for 25% of the excess of breast cancer deaths among nonexaminers. Approximately half of the remaining survival differential was attributable to the more limited disease among selfexaminers. The residual association between BSE and survival may be related to uncontrolled effects of stage or other unrecognized confounders.

Age Factors↗
PubMed1988

Risk of genitourinary malignancies after cancer of the prostate.

The risk of second malignancies was evaluated in all men in metropolitan Atlanta who were initially diagnosed as having prostate cancer between January 1, 1975 and December 31, 1982. The cohort of 3675 men was observed through the end of calendar year 1984, yielding a total of 11,916 man-years of observation. Within this population 220 second cancers were diagnosed at sites other than the prostate as compared with 181.2 cancers expected based upon incidence rates for the local general population. Excesses of second malignancies were found in the urethra, kidney and bladder, as well as for melanoma of the skin. The increased risk of second neoplasms was generally greater in men younger than 70. The associated genitourinary malignancies tended to occur within 3 years of the prostatic cancer. Although increased clinical surveillance of this population could explain some of the observed excess of second cancers, these findings also are consistent with multiple cancers arising from shared etiologic factors.

Age Factors↗
PubMed1987

Prognostic factors for gastrointestinal and bronchopulmonary carcinoid tumors.

Data collected by population-based cancer registries in Iowa and metropolitan Atlanta were evaluated to determine prognostic factors for gastrointestinal (n = 270) and bronchopulmonary (n = 151) carcinoids. The predictors considered in univariate and multivariate analyses were: age, sex, race, marital status, anatomic subsite, stage, occurrence of other malignancies, and surgery. For surgically treated gastrointestinal tumors, the cumulative percentages of survivors at five years were: appendix, 85.6%; small intestine, 66.0%; and large intestine, 37.7%. The likelihood of death from gastrointestinal carcinoids was found to be related independently to increasing age (P = 0.001), advanced stage (P less than 0.0001), location within the large intestine (P less than 0.0001), and occurrence of another malignancy (P = 0.02). The overall five-year survival rate for bronchopulmonary carcinoids was 87.6%, and lack of surgical treatment (P less than 0.0001) and advanced stage (P = 0.006) were associated independently with unfavorable prognosis.

Carcinoid Tumor↗
PubMed1987

Oil contamination of raptors migrating along the Red Sea.

There are few accounts of oil contamination of raptors, and it has not been considered a threat for them. However, we and our colleagues found oil-based asphalt on 55 individuals of 9 species out of 1052 raptors (5.2%) captured and examined in the spring of 1985 and 1986 during our raptor migration study at Elat, Israel. Some were extensively contaminated and probably succumbed to the effects of ingested asphalt. The birds most likely picked up the contamination while drinking water from pools with surface oil. Examples of the contamination will be described. Over 1.2 million raptors were counted passing Elat during the spring of 1985. If 5% of these were contaminated, that would be over 60,000 birds, and this does not consider the raptors that migrate along the Red Sea and do not pass near Elat, nor those that pass Elat unseen by the counters. Thus asphalt contamination could be a major problem for raptors migrating along the Red Sea.

Journal Article↗