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Biomedical subjects

A L Stewart

Publications and source records attributed to A L Stewart.

At least 55 records · Page 3Linked to original sources
PubMed1999

Representing contrast detection as an eigenvalue problem.

Contrast detection can be formulated as an eigenvalue problem. One of the simplest resulting models has only two parameters. The model is space variant and employs the Hermite functions as eigenfunctions. Computing the response to a sinusoidal acuity grating yields the observer's contrast response. The model itself, however, is developed within an abstract mathematical framework which is general enough to include Fourier analysis as a special case. Consequently, the methods of Fourier analysis are generalized to those of eigenfunction expansion and the spectral theory of linear operators.

Contrast Sensitivity↗
PubMed1998

Aetiology and prevention of emesis induced by radiotherapy.

The introduction of new antiemetics has resulted in renewed interest in the aetiology and control of radiation induced emesis. Studies both with fractionated treatment and with high-dose single exposures have clearly demonstrated the value of the 5HT3 receptor antagonist antiemetics. This paper reviews the selection of optimal antiemetics.

Adult↗
PubMed1998

A word-superiority effect in the presence of foveal load.

Foveal stimuli have been shown to disrupt visual information processing in the parafovea and periphery by their mere presence. In the present study, 6 subjects were presented letter triads 3.58 degrees to the right or left of the point of fixation. At the same time, a single letter was presented at the point of fixation that was either the same as the middle letter in the triad or different from any of the triad letters. On other trials, no letter was presented at the point of fixation. Analysis indicated a word superiority effect when a foveal letter was presented that was the same as the letter in the triad. Performance between words and nonwords did not differ significantly when the foveal letter was different or absent. It was concluded that the mere presence of foveal load alone is not disruptive to performance. Depending on the visual context of the target to be reported, the presence of a foveal stimulus may improve performance.

Discrimination, Psychological↗
PubMed1997

Relationships of quality-of-life measures to long-term lifestyle and drug treatment in the Treatment of Mild Hypertension Study.

OBJECTIVES: To compare 5 antihypertensive drugs and placebo for changes in quality of life (QL). To assess the relationship of lifestyle factors and change in lifestyle factors to QL in participants with stage I diastolic hypertension. METHODS: The Treatment of Mild Hypertension Study (TOMHS) was a randomized, double-blind, placebo-controlled clinical trial with minimum participant follow-up of 4 years. It was conducted at 4 hypertension screening and treatment academic centers in the United States. The cohort consisted of 902 men and women with hypertension, aged 45 to 69 years, with diastolic blood pressures less than 100 mm Hg. Informed consent was obtained from each participant after the nature of the procedures had been fully explained. Sustained nutritional-hygienic intervention was administered to all participants to reduce weight, to reduce dietary sodium and alcohol intake, and to increase physical activity. Participants were randomized to take (1) acebutolol (n = 132); (2) amlodipine maleate (n = 131); (3) chlorthalidone (n = 126); (4) doxazosin mesylate (n = 134); (5) enalapril maleate (n = 135); or placebo (n = 234). Changes in 7 QL indexes were assessed based on a 35-item questionnaire: (1) general health; (2) energy or fatigue; (3) mental health; (4) general functioning; (5) satisfaction with physical abilities; (6) social functioning; and (7) social contacts. RESULTS: At baseline, higher QL was associated with older age, more physical activity, lower obesity level, male gender, non-African American race, and higher educational level. Improvements in QL were observed in all randomized groups, including the placebo group during follow-up; greater improvements were observed in the acebutolol and chlorthalidone groups and were evident throughout follow-up. The amount of weight loss, increase in physical activity, and level of attained blood pressure control during follow-up were related to greater improvements in QL. CONCLUSIONS: In patients with stage I hypertension, antihypertensive treatment with any of 5 agents used in TOMHS does not impair QL. The diuretic chlorthali-done and the cardioselective beta-blocker acebutolol appear to improve QL the most. Success with lifestyle changes affecting weight loss and increase in physical activity relate to greater improvements in QL and show that these interventions, in addition to contributing to blood pressure control, have positive effects on the general well-being of the individual.

Aged↗
PubMed1997

Evaluation of CHAMPS, a physical activity promotion program for older adults.

We evaluated physical activity changes resulting from a six-month public health model intervention that encouraged seniors (N = 89) 62-91 years of age (mean = 76) living in two low-income congregate housing facilities to increase their physical activity by participating in existing community-based physical activity classes and programs of their choice. The program was offered to everyone regardless of their health problems. Enrollees were encouraged to adopt activities tailored to their preferences, physical abilities, health status, income, and transportation resources. Using a comparison-group design, the intervention group was more active for all comparison months of the intervention period (p values < .05). The intervention also was associated with improvements in self-esteem (p < .05), though not with an array of other measures of health-related quality-of-life. Those who adopted and maintained a new physical activity over the six-month intervention period experienced improvements in anxiety, depression, and overall psychological well-being relative to those who did not. The intervention was subsequently replicated through a senior center (N = 22). A much larger proportion of the senior center sample adopted and maintained a new activity for six months (68%) compared to the congregate facilities sample (35%), which may have been due to differences in recruitment methods and sample characteristics in the two settings. An intervention promoting increased physical activity through the use of existing community resources may help increase physical activity in older adults.

Adaptation, Psychological↗
PubMed1997

Ondansetron versus a chlorpromazine and dexamethasone combination for the prevention of nausea and vomiting: a prospective, randomised study to assess efficacy, cost effectiveness and quality of life following single-fraction radiotherapy.

Lower hemibody radiotherapy is an effective palliative treatment for patients with wide-spread bone metastases, but is frequently associated with the unpleasant side effects of nausea and vomiting. Patients often require admission to hospital for at least an overnight stay, with its inevitable costs. This study has investigated the clinical efficacy and safety profile of ondansetron, a 5HT3 receptor antagonist, and compared it to a standard antiemetic combination, chlorpromazine and dexamethasone. Sixty-six patients were randomised to receive antiemetic prophylaxis with either oral ondansetron or a combination of chlorpromazine and dexamethasone (33 patients in each arm): 60 were treated with lower abdominal radiotherapy (8 Gy mid-plane dose) and 6 with radiotherapy to the upper lumbar spine (12.5 Gy incident dose). Patients were assessed for severity of nausea and vomiting and for whether they would use the same antiemetic again. Quality of life was assessed using the Functional Living Index Cancer (FLIC) and Functional Living Index Emesis (FLIE) quality-of-life questionnaires. A detailed cost-benefit analysis was also performed. Ondansetron scored highly as an antiemetic, being significantly better at controlling emesis on all four study days (P < 0.001) and significantly better at controlling nausea on day 1 (P < 0.001) than the standard combination of chlorpromazine and dexamethasone. Quality of life was better in the ondansetron-treated group, and ondansetron was found to be safe with no significant adverse effects. As a result, 98% of patients and investigators would use ondansetron again. Cost-benefit analysis revealed that, when complete control of emesis is the aim, ondansetron is not unduly expensive compared to the standard antiemetic regimen. As ondansetron was clearly effective in patients receiving hemibody irradiation it seems it would be prudent to adopt it for use in such patients routinely. The use of ondansetron would allow them to be treated as outpatients, with the attendant financial and psychosocial benefits of such an approach.

Adult↗
PubMed1997

Relation of deranged neonatal cerebral oxidative metabolism with neurodevelopmental outcome and head circumference at 4 years.

Cerebral oxidative metabolism was studied using phosphorus magnetic resonance spectroscopy during the first week of life and neurodevelopmental outcome was assessed at 4 years in 62 infants who had clinical and/or biochemical evidence consistent with birth asphyxia (critically impaired intrapartum gas exchange). Twenty-one died and the neurodevelopmental status of the 41 who survived was assessed by a range of tests at age 4 years. The minimum recorded values for the cerebral phosphocreatine:inorganic phosphate concentration ratio (an index of oxidative metabolism) were related to outcome. The results showed significant relations between the extent of derangement of neonatal oxidative metabolism and a range of adverse outcomes, including death, and at 4 years reduced head growth and the presence and severity of neuromotor impairments, overall neurodevelopmental impairments, and cognitive functioning. Strong correlations between the extent of derangement of neonatal oxidative metabolism and outcome at 1 and 4 years were also shown. We conclude that the severities of adverse outcomes at 1 and 4 years of age were closely related to the extent of cerebral energy derangement in the first week of life, and we also conclude that primary intrapartum hypoxic-ischaemic cerebral injury was generally responsible for the events that led to death, microcephaly, and impaired

Asphyxia Neonatorum↗
PubMed1997

Primary care and patient perceptions of access to care.

BACKGROUND: Although much is known about how insurance affects access to care, it is unclear whether good primary care contributes to access. The purpose of this study was to determine how optimal primary care given by providers at a regular place of care, defined in terms of continuity, comprehensiveness, communication, and availability, contributed to perceptions of access to care in a large population-based probability sample of adults. METHODS: Data were from a cross-sectional survey of 6674 English- and Spanish-speaking adults 18 to 64 years of age, randomly sampled from 41 urban California communities with a range of levels of access to care. RESULTS: Following adjustment for sociodemographics and need for care, we found that having "optimal" primary care contributed independently to improved self-rated access, as did having health insurance, a regular place, and a regular provider. The largest difference n access was between having any health insurance and not having insurance. Once insurance was available, each additional element contributed in a cumulative manner to self-rated access. For those with insurance and a regular place, adding optimal primary care improved self-rated access to an extent similar to adding a regular provider. CONCLUSIONS: We conclude that although providing insurance to the uninsured is the most effective means of improving self-rated access, the other elements each improve access as well. Once insurance and a regular place are provided, good primary care at that place may be equivalent to having a regular provider in terms of perceived access. Results support promotion of primary care as a model of health care that encourages good access.

Adolescent↗
PubMed1996

Primary care and receipt of preventive services.

OBJECTIVE: To examine whether health insurance, a regular place of care, and optimal primary care are independently associated with receiving preventive care services. DESIGN: A cross-sectional telephone survey. SETTING: Population based. PARTICIPANTS: Probability sample of 3,846 English-speaking and Spanish-speaking women between the ages of 18 and 64 in urban California. INTERVENTIONS: Women were asked about their demographic characteristics, financial status, health insurance status, need for ongoing care, regular place of care, and receipt of blood pressure screening, clinical breast examinations, mammograms, and Pap smears. Women who reported a regular place of care were asked about four components of primary care: availability, continuity, comprehensiveness, and communication. MEASUREMENTS AND MAIN RESULTS: In multivariate analyses that controlled for differences in demographics, financial status, and need for ongoing care, having a regular place of care was the most important factor associated with receiving preventive care services (p < .0001). Having health insurance (p < .001) and receiving optimal primary care from the regular place of care (p < .01) further significantly increased the likelihood of receiving preventive care services. CONCLUSION: A regular source of care is the single most important factor associated with the receipt of preventive services, but optimal primary care from a regular place increases the likelihood that women will receive preventive care.

Adolescent↗
PubMed1996

The effects of foveal load and visual context on peripheral letter recognition.

Peripheral letter recognition was examined by presenting subjects with a letter triad centered 7.16 degrees to the right of fixation. At the same time, a single letter was presented at the point of fixation that was either the same as one of the letters in the triad or different from any of the triad letters. On other trials, no letter was presented at the point of fixation. Results supported and extended previous foveal load research. The disruptive effect of foveal load does not depend solely on the presence or absence of a foveal stimulus. Recognition of the first letter in non-words was disrupted when a foveal letter was presented that was different from the peripheral letter. Recognition of the middle letter for both words and non-words was disrupted when a foveal letter was presented that was the same as the middle letter. A significant interaction between foveal letter and triad type was also found. No evidence was found to suggest that recognition of a peripheral letter is significantly better when that same letter is also present at the point of fixation.

Adult↗
PubMed1996

It takes a confounded face to pop out of a crowd.

It is widely reported that a picture of an angry face seems to figuratively pop out of an array of happy faces, although all of these reports are based on a single experiment by Hansen and Hansen. Pop out, when it occurs, indicates that an observer has located the target by means of a preattentive, parallel search. Hansen and Hansen concluded that it was the affect displayed by the face which caused it to pop out from its surrounding distracters. However, Hansen and Hansen's angry faces contained extraneous dark areas which were introduced when they transformed Ekman and Friesen's photographs of angry and happy faces into black-on-white sketches. When the original artifact-free gray-scaled versions of angry and happy faces were used no evidence for pop out was found. All target faces were found during a serial, self-terminating search regardless of their expression. The angry face in Hansen and Hansen's experiments may have popped out from a crowd of happy faces because of a contrast artifact inadvertently introduced when they created their stimuli.

Artifacts↗
PubMed1996

Factors associated with enrollment of older adults into a physical activity promotion program.

This article investigates the extent to which a proactive two-phased recruitment approach resulted in recruitment of a representative sample of older adults from two lower income congregate housing facilities into a physical activity promotion program. Enrollees were similar to nonenrollees with respect to education, gender, marital status, race/ethnicity, self-rated health, physical functioning, psychological distress, exercise frequency, level of social contact, having a confidant, use of alcohol, and smoking status. However, enrollees were younger, more likely to speak English as a primary language, less likely to be completely sedentary, and more likely to be overweight. Overall, 21% of the target population were recruited into the program. Recruitment strategies such as those used in this study appeared to enable enrollment of a reasonably representative sample of a small well-defined population.

Aged↗
PubMed1996

Measuring the need for medical care in an ethnically diverse population.

OBJECTIVE: To examine measures of need for health care and their relationship to utilization of health services in different racial and ethnic groups in California. DATA SOURCE: Telephone interviews obtained by random-digit dialing and conducted between April 1993 and July 1993 in California, with 7,264 adults (ages 18-64): 601 African Americans, 246 Asians, 917 Latinos interviewed in English; 1,045 Latinos interviewed in Spanish; and 4,437 non-Latino whites. STUDY DESIGN: A cross-sectional survey was conducted from a stratified, probability telephone sample. DATA COLLECTION: Interviews collected self-reported indicators of need for health care: self-rated health, activity limitation, major chronic conditions, need for ongoing treatment, bed days, and prescription medication. The outcome was self-reported number of physician visits in the previous three months. PRINCIPAL FINDINGS: Compared to whites, one or more of the other ethnic groups varied significantly (p < .05) on each of the six need-for-care measures after adjustment for health insurance, age, sex, and income. Latinos interviewed in Spanish reported lower percentages and means on five of the need measures but the highest percentage with fair or poor health (32 percent versus 7 percent in whites). Models regressing each need measure on the number of outpatient visits found significant interactions of ethnic group with need compared to whites. After adjustment for insurance and demographics, the estimated mean number of visits in those with the indicator of need was consistently lower in Latinos interviewed in Spanish, but the differences among the other ethnic groups varied depending on the measure used. CONCLUSION: No single valid estimate of the relationship between need for health care and outpatient visits was found for any of the six indicators across ethnic groups. Applying need adjustment to the use of health care services without regard for ethnic variability may lead to biased conclusions about utilization.

Adolescent↗
PubMed1995

Follow-up by questionnaire?

Recently, proposals have been made to include larger numbers of infants and reduce the cost of obtaining follow-up information pertaining to modern perinatal management. These proposals have been made in response to requests from purchasers and providers of health care as well as the obstetricians and neonatologists actively engaged in delivery of the service. These initiatives are welcome, but care must be taken to provide objective, meaningful data. In addition to standardised recording including by questionnaire, standardised data collection designed to identify relevant impairments must be the primary objective; the nature and extent of disability at particular ages can then be assigned but it is misleading to regard disability as the principle outcome measure.

Developmental Disabilities↗
PubMed1995

Sleep problems and their correlates in a working population.

OBJECTIVE: To measure the prevalence of sleep problems in a working population and examine their association with health problems, health-related quality-of-life measures, work-related problems, and medical expenditures. Also, to explore the usefulness of a sleep-problems screen for mental health conditions and underlying sleep disorders. DESIGN: Cross-sectional survey administered via voice mail and telephone interview. SETTING: A San Francisco Bay Area telecommunications firm. PARTICIPANTS: Volunteer sample of 588 employees who worked for a minimum of six months at the company and were enrolled in its fee-for-service health plan. MEASUREMENTS AND MAIN RESULTS: Thirty percent of respondents reported currently experiencing sleep problems and were found to have worse functioning and well-being (general health, cognitive functioning, energy), more work-related problems (decreased job performance and lower satisfaction, increased absenteeism), and a greater likelihood of comorbid physical and mental health conditions than were the respondents who did not have sleep problems. They also demonstrated a trend toward higher medical expenditures. CONCLUSIONS: Self-perceived sleep problems were common among the respondents and were associated with poorer health and health-related quality of life. A single question about sleep problems may serve as an effective screen for identifying primary care patients with mental health problems, as well as underlying sleep disorders.

Absenteeism↗
PubMed1994

Space-variant models of visual acuity using self-adjoint integral operators.

The purpose of this paper is to outline a more general approach to visual acuity experiments than the classical methods borrowed from the optical sciences. A theory based on integral operators with symmetric kernels replaces the standard use of filters constructed from windowed sines and cosines. This more general approach allows greater latitude in the range of phenomena to be modelled. It also permits all the standard techniques used in Fourier expansion of a stimulus and response to be generalized to a space-variant system such as the human visual field.

Cybernetics↗
PubMed1994

The responses of neurons in the temporal cortex of primates, and face identification and detection.

The ability of a human observer to detect the presence of a briefly flashed picture of a face can depend on the picture's spatial configuration, that is on whether its features are rearranged (jumbled) or are in their normal configuration. The face-detection effect (FDE) is found under conditions of backward masking, when the presence of a face can be detected with shorter masking intervals when it is in the normal than when in the rear-ranged configuration. A similar effect is found when the subject is asked to classify the face as rearranged or not - the face-classification effect (FCE). Part of the interest of the FDE and the FCE is that they show how the configuration of a stimulus can be an important factor in the perceptual processing which leads to detection and classification of the stimulus. To analyse these effects we recorded from single neurons in the cortex in the superior temporal sulcus of macaques when they were shown (in a visual fixation task) normal and rearranged faces under backward masking conditions shown in experiments 2 and 3 to produce, with the same apparatus, the FCE, and also to produce comparable effects on the identification of which face was present (called hereafter the face-identification effect), and also of the clarity of the face. We found in experiment 1 that there are some face-selective neurons which respond to faces only, or better, when the features in the faces are in their normal configuration rather than rearranged. We also showed in this experiment that the difference in the response to the normal as compared to the rearranged faces became greater when the masking stimulus was delayed more. Thus, at intermediate delays, there are more neurons active for the normal than for the rearranged face. We therefore propose that the FDE, the FCE, and the face-identification effect arise because the total number of neurons activated by faces in their normal configuration is greater than that activated by rearranged faces, because of the sensitivity of some face-selective neurons to the spatial arrangement of the features. The experiments also show that backward visual masking does produce abrupt termination of the firing of neurons in the temporal cortical visual system, so that the duration of a neuronal response is very short when visual stimuli can just be perceived.

Analysis of Variance↗