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Biomedical subjects

R S Thompson

Publications and source records attributed to R S Thompson.

At least 73 records · Page 4Linked to original sources
PubMed1996

Effectiveness of bicycle safety helmets in preventing head injuries. A case-control study.

OBJECTIVES: To examine the protective effectiveness of bicycle helmets in 4 different age groups of bicyclists, in crashes involving motor vehicles, and by helmet type and certification standards. RESEARCH DESIGN: Prospective case-control study SETTING: Emergency departments (EDs) in 7 Seattle, Wash, area hospitals between March 1, 1992, and August 31, 1994. PARTICIPANTS: Case subjects were all bicyclists treated in EDs for head injuries, all who were hospitalized, and all who died at the scene. Control subjects were bicyclists treated for nonhead injuries. MAIN RESULTS: There were 3390 injured bicyclists in the study; 29% of cases and 56% of controls were helmeted. Risk of head injury in helmeted vs unhelmeted cyclists adjusted for age and motor vehicle involvement indicate a protective effect of 69% to 74% for helmets for 3 different categories of head injury: any head injury (odds ratio [OR], 0.31; 95% confidence interval [CI], 0.26-0.37), brain injury (OR, 0.35; 95% CI, 0.25-0.48), or severe brain injury (OR, 0.26; 95% CI, 0.14-0.48). Adjusted ORs for each of 4 age groups (<6 y, 6-12 y, 13-19 y, and > or = 20 years) indicate similar levels of helmet protection by age (OR range, 0.27-0.40). Helmets were equally effective in crashes involving motor vehicles (OR, 0.31; 95% CI, 0.20-0.48) and those not involving motor vehicles (OR, 0.32; 95% CI, 0.20-0.39). There was no effect modification by age or motor vehicle involvement (P=.7 and P=.3). No significant differences were found for the protective effect of hard-shell, thin-shell, or no-shell helmets (P=.5). CONCLUSIONS: Bicycle helmets, regardless of type, provide substantial protection against head injuries for cyclists of all ages involved in crashes, including crashes involving motor vehicles.

Accidents, Traffic↗
PubMed1996

Effectiveness of bicycle safety helmets in preventing serious facial injury.

OBJECTIVE: To assess the effectiveness of helmets in preventing facial injuries. DESIGN: Case-control study between March 1, 1992, and August 31, 1994. SETTING: Seven Seattle, Wash, area hospitals including the regional trauma center and a large staff-model health maintenance organization. PATIENTS: Cases were patients with serious facial injury, ie, fractures or lacerations; controls were patients who had injuries other than facial. Minor facial injuries were excluded to avoid ascertainment bias in those seeking care for serious injuries to other areas. RESULTS: Serious facial injuries occurred to 700 (20.7%) patients. Helmets were used by 47% of cases and 57% of controls. After adjusting for age, sex, speed, and surface, we found that helmets reduced the risk of injury to the upper face (odds ratio [OR], 0.36; 95% confidence interval [CI], 0.26-0.49) and middle face (OR, 0.35; 95% CI, 0.24-0.50) but had no significant effect on serious injury to the lower face (OR, 0.88; 95% CI, 0.72-1.07). CONCLUSIONS: Bicycle helmets offer substantial protection for the upper and mid face in addition to their known protection against head injuries. Helmets do not appear to offer any protection for the lower face.

Adolescent↗
PubMed1996

The effect of variations in transducer position and sound speed in intravascular ultrasound: a theoretical study.

The intravascular insonation of a blood vessel in the presence of an impedance interface between blood and the inner vessel wall is studied theoretically. The model, which uses a ray approximation, is three dimensional and allows consideration of arbitrary noncircular lumen shapes. Model results are presented for the image geometry, and the insonating intensity over the vessel wall. It is shown that the inner lumen can be imaged accurately with the transducer at any position within the lumen, and at any forward viewing angle, provided the point of origin of the beam is stationary. If it is not stationary but rotating with the same angular velocity as the beam itself, the inner vessel wall is not mapped accurately. A particular geometric distortion which has been observed in practice is predicted if the transducer is near vessel wall. Acoustic impedance interfaces will be encountered in vascular disease because the speed of sound in fatty plaque is less than in blood, whereas the speed of sound in fibrous and calcified plaque is greater than in blood. A simplified model representation of an atherosclerotic lumen in developed using a cardioid-like curve and a single impedance interface. Model results show that refraction at this interface leads to an intensity distribution which is not uniform around the lumen, and which depends on lumen shape and transducer position. The exception is the special case of a circular lumen with a centrally positioned transducer. Noncircular impedance interfaces encountered in vivo in vascular disease may cause considerable intensity distortion, particularly if the transducer is close to the wall in an irregularly shaped lumen.

Arteriosclerosis↗
PubMed1996

Effect of a cylindrical refracting interface on ultrasound intensity and the CW Doppler spectrum.

The insonation of axisymmetric flow in a tube by an ultrasound beam which is refracted at the tube surface is considered. A three-dimensional (3-D) model for refraction at a cylindrical interface is developed. The incident beam, which is planar but otherwise arbitrary, is refracted at a single acoustic impedance interface between the medium within the tube and the surrounding medium. A ray approximation is used as the ultrasonic wavelength is small compared to the radius of curvature of the tube. A parametric form for the ray paths is obtained and used to derive an expression for the intensity. The intensity depends on the specific position within the tube, as well as the ratio of sound speeds, N, and the Doppler angle thetaD. A diverging (N = 1.2, thetaD = 45 degrees) and a converging (N = 0.8, thetaD = 45 degrees) case are presented in detail. The converging interface results in more extreme intensity distortion. The regions of maximum and minimum intensity over a tube slice are immediately adjacent in both diverging and converging cases. Once the intensity distribution across a tube slice is known, the previously reported volume integral method for the calculation of continuous wave (CW) Doppler spectral power density (spd) functions may be used. The effect of refraction of the incident beam on the spd function is shown for both an infinite beam and a circular beam with radius equal to the tube radius. A curved acoustic impedance interface, as may be encountered in vitro in flow phantoms or in vivo in vascular disease, leads to nonuniform insonation and spectral distortion which depends on transducer orientation.

Animals↗
PubMed1996

Addressing a neglected coronary heart disease risk factor in an HMO: exercise counseling and fitness testing at group health cooperative.

Group Health Cooperative, following the lead of the American Heart Association (AHA), the Centers for Disease Control (CDC), and the US Preventive Services Task Force (USPSTF), has identified inactivity as one of the most significant risk factors for the prevention of coronary heart disease (CHD). This paper reports on the programs being developed at Group Health Cooperative to address inactivity. A clinical tool designed to make fitness testing and comprehensive exercise counseling practical in routine primary care was designed and piloted. The fitness test was based on the One-Mile Walk Test, with computerization of the results analysis and reporting. The test helped the physician assess the patient's current exercise habits and physical fitness in terms of Vo2max (maximal oxygen consumption). The computer program showed the patient and the physician how the individual's Vo2max compared to norms for the patient's age and gender. The program provided comprehensive written exercise counseling and individualized advice about activity and fitness based on the patient's current exercise habits. The test cost little to administer, and helped reduce the time and effort of the primary physician in providing exercise counseling, while making optimal use of the physician's power to motivate. Exercise counseling is a very cost-effective preventive intervention. We believe that an organized and systematic exercise counseling program, together with a program for measuring fitness, would be the most effective intervention. Evidence indicates that effective exercise counseling should result in substantial reduction in disease in our population.

Adult↗
PubMed1996

What have HMOs learned about clinical prevention services? An examination of the experience at Group Health Cooperative of Puget Sound.

Over the last 20 years, HMOs have begun to develop population- and evidence-based systems for their clinical prevention services. Because of their integrated information systems and staff communications, HMOs are uniquely positioned to help physicians to identify systematically the primary risk factors or secondary prevention needs of individuals and to provide specific referral or screening services and off-site telephone counseling services to effect seamless, organized intervention. A review of the relevant published literature was combined with the empirical experience of the Group Health Cooperative of Puget Sound in Seattle to illustrate the approach of one large staff-model HMO. Challenges for the future include creating clinical information systems, establishing adequate funding, instituting practitioner incentives, training practitioners for behavioral change, and developing and integrating patient self-care.

Health Maintenance Organizations↗
PubMed1995

Primary and secondary prevention services in clinical practice. Twenty years' experience in development, implementation, and evaluation.

This article reviews lessons from 20 years of experience in development and provision of clinical preventive services at Group Health Cooperative of Puget Sound, a large health maintenance organization. Critical factors for enhancing service include the use of a population-based epidemiologic viewpoint coupled with specific evidence-based criteria to examine issues; involvement of practitioners in the process; a systems approach to implementation focused on predisposing factors of the practitioners and enabling factors in the practice, organizational, and community environments; feedback of program outcomes; and the use of automated clinical information systems. Outcome results from our clinical prevention efforts include a 32% decrease in late-stage breast cancer (1989 to 1990); 89% of 2-year-old children with complete immunizations (1994); decrease in adult smokers from 25% to 17% (1985 to 1994); and an increase in bicycle safety helmet use among children from 4% to 48% along with a 67% decrease in bicycle-related head injuries (1987 to 1992). Systematic population-based approaches to the development and provision of clinical preventive services targeting the one-to-one level of primary care and multiple infrastructure levels of care are forging a synthesis of clinical medicine and public health approaches. This approach will become pervasive as clinical information systems improve, risk information is captured routinely, and practitioners gain skills in the art of patient risk behavior change and population-based care.

Breast Neoplasms↗
PubMed1995

PSA screening: a public health dilemma.

Screening for prostate cancer with serum prostate specific antigen (PSA) is one of the most controversial practices in health care today and guidelines from professional and policy organizations are contradictory. Prostate cancer is unique because of a wide discrepancy between prevalent asymptomatic cancer and clinical disease and an uncertain natural history. Proponents and critics of mass screening agree that PSA can detect early cancer and that definitive data that PSA reduces prostat cancer mortality are not available. Differences in screening recommendations reflect distinct viewpoints regarding what constitutes screening benefit and what level of evidence is needed to endorse a screening practice. This review describes what is known about the areas most relevant to the conflicting perspectives: the epidemiology and natural history of prostate cancer, the ability of PSA to detect disease and operational characteristics of PSA as a screening test, and the efficacy of treatment of early disease.

Decision Making↗
PubMed1994

A population-based case-cohort evaluation of the efficacy of mammographic screening for breast cancer.

Screening efficacy may be evaluated in population-based, observational studies, provided one addresses biases that arise in nonrandomized screening evaluations. The authors evaluated the association of mammographic screening with breast cancer mortality among women without prevalent breast cancer. The cohort consisted of 94,656 women, aged > or = 40 years, enrolled in a large health maintenance organization in Washington State during the period 1982-1988. A case-cohort design limited chart abstraction of risk factor and screening information to 4% of the cohort. There were 1,144 incident breast cancer cases, including 126 who died of breast cancer during the study interval. An age-stratified proportional hazards analysis compared the screening experience of the breast cancer deaths with that of 2,237 controls. The family history of breast cancer, previous biopsy, and parity were included in the model to control for potential confounding effects of selection bias. With a mean follow-up of only 3.5 years postscreening, there was a small but statistically nonsignificant reduction in the risk of breast cancer mortality among women screened 1 year prior to diagnosis compared with unscreened women. The relative risk was 0.80 (95% confidence interval 0.34-1.85) for women aged > or = 40 years and 0.61 (95% confidence interval 0.23-1.62) for women aged > or = 50 years. This paper illustrates how case-cohort methodology can be used to perform efficient assessment of screening efficacy in large cohorts, while eliminating or controlling for sources of bias.

Adult↗
PubMed1994

Aortic Doppler velocity measurement and cardiac function in the fetal lamb.

Aortic haemodynamic parameters, and Doppler waveforms in particular, were investigated in acute experiments with fetal lambs. Cardiovascular changes were produced by central infusion of the drugs esmolol and dopamine. Pulsed Doppler waveforms were obtained from the descending thoracic aorta, simultaneous with recordings of pulsatile aortic volume flow rate, diameter and blood pressure. The relation between Doppler-derived velocities and the corresponding full vessel lumen velocities was shown to be fairly linear and consistent across different animals. The aortic volume flow per beat decreased with esmolol (p < 0.003, repeated measures ANOVA); the Doppler and vessel lumen mean velocities also decreased, whether measured only at peak systole or over the full cardiac cycle (at most p < 0.003). With dopamine the aortic flow per beat increased (p < 0.001), as did the Doppler and vessel lumen mean velocities (at most p < 0.02). An inverse relation between the aortic flow per beat and the peripheral resistance was observed. To identify inotropic changes in the presence of vascular effects, a theoretical model based on cardiac power output changes was implemented. The data were divided into three groups, according to whether the model did or did not identify a definite inotropic effect (positive or negative). The Doppler velocity changes for these three groups were different (p < 0.0001). The mean Doppler velocity increased by 7 cm s-1 in the positive inotropic effect group, and decreased by 4 cm s-1 in the negative group. The aortic flow parameters of the human fetus are very similar to those of the fetal lamb.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1994

Medical conditions and motor vehicle collision injuries in older adults.

OBJECTIVE: To determine whether medical conditions that can impair sensory, cognitive, or motor function increase the risk of injury due to motor vehicle collision in older drivers. DESIGN: Case-control study. SETTING: Group Health Cooperative of Puget Sound, a large prepaid health plan. PARTICIPANTS: Group Health members age 65 or older who were licensed drivers in 5 counties. Cases were injured while driving during 1987 or 1988. Controls were matched to cases on age, gender, and county of residence but experienced no such injury during the study years. MEASUREMENTS: The outcome was injury requiring medical care due to a police-investigated motor vehicle collision. Risk factors evaluated included selected medical conditions active within the previous 3 years, as determined from the medical record. MAIN RESULTS: Injury risk was 2.6-fold higher in older diabetic drivers (95% CI: 1.4-4.7), especially those treated with insulin (odds ratio [OR] = 5.8, 95% CI: 1.2-28.7) or oral hypoglycemic agents (OR = 3.1, 95% CI: 0.9-11.0), those with diabetes for over 5 years (OR = 3.9, 95% CI: 1.7-8.7), and those with both diabetes and coronary heart disease (OR = 8.0, 95% CI: 1.7-37.7). Increases were also found for older drivers with coronary artery disease (OR = 1.4), depression (OR = 1.7), alcohol abuse (OR = 2.1), or falls (OR = 1.4), but these associations could easily have arisen by chance. CONCLUSIONS: Counseling about driving risks may be warranted for certain elderly diabetic drivers. Further research is needed to determine whether transient hypoglycemia or long-term complications explain these effects.

Accidents, Traffic↗
PubMed1994

The Seattle children's bicycle helmet campaign: changes in helmet use and head injury admissions.

OBJECTIVE: To describe the impact of a community bicycle helmet campaign on helmet use and the incidence of bicycle-related head injuries. SETTING: Metropolitan community and a large health maintenance organization. INTERVENTIONS: Communitywide bicycle helmet campaign. OUTCOMES: Rate of observed bicycle helmet use in the community and incidence of bicycle-related injuries in an health maintenance organization population. RESULTS: Helmet use among school-aged children increased from 5.5% in 1987 to 40.2% in 1992. Bicycle-related head injuries decreased by 66.6% in 5- to 9-year-old and 67.6% in 10- to 14-year-old members of an health maintenance organization. CONCLUSIONS: Educational campaigns can increase helmet use and decrease the incidence of bicycle-related head injury.

Adolescent↗
PubMed1993

Phorbol ester sequentially downregulates cAMP-regulated basolateral and apical Cl- transport pathways in T84 cells.

The effect of phorbol esters on adenosine 3',5'-cyclic monophosphate (cAMP)-regulated epithelial Cl- transport was studied in T84 cells, a human colonic cell line that serves as a model for electrogenic Cl- secretion. Preincubation of T84 cell monolayers with phorbol 12-myristate 13-acetate (PMA) caused a time- and dose-dependent inhibition of the net transepithelial secretory response to 10 microM forskolin (half-maximal inhibition at a concentration of approximately 10 nM PMA and a time of 45 min). Similar inhibition was observed with phorbol 12,13-dibutyrate but not the inactive phorbol ester phorbol 12,13-diacetate. Na(+)-K(+)-2Cl- cotransporter activity, assessed by bumetanide-sensitive 86Rb+ uptake, and K+ conductance, assessed by 86Rb+ efflux, were both found to be markedly reduced by PMA with a time course that paralleled the loss of the cAMP-regulated Cl- secretory response. One- and four-hour treatment of T84 cells with 100 nM PMA caused a sustained increase in the membrane-bound fraction of protein kinase C (PKC) but a decrease in total cellular PKC. Although, at these time points, the Na(+)-K(+)-2Cl- cotransporter and K+ efflux pathways were markedly inhibited (associated with inhibition of the forskolin-stimulated transepithelial Cl- secretory response), the activity of the cAMP-regulated Cl- efflux pathway, assessed by 125I-labeled efflux, remained unaffected. With prolonged exposure to PMA (up to 10), the cAMP-regulated Cl- efflux pathway was also eventually inhibited, and transepithelial electrical resistance progressively declined.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Transport↗
PubMed1993

Cost-effectiveness analysis of bicycle helmet subsidies in a defined population.

OBJECTIVE: To examine the potential effects of bicycle safety helmet cost subsidy on bicycle head injury rates and costs. DESIGN: Using empiric data on the incidence and costs of bicycle injuries to children, we examined the hypothetical effects of various bicycle helmet subsidies in a cost-effectiveness analysis. A hypothetical cohort of 100,000 5- through 9-year-olds was followed for 5 years after helmet cost subsidization. Sensitivity analyses were done of three different levels of safety helmet subsidy ($5, $10, $15), three discount rates (2%, 4%, 6%), 10 levels of safety helmet use ranging from 10% to 100%, and the occurrence or nonoccurrence of catastrophic head injuries. PATIENTS: Forty-three children 5 through 9 years of age and 27 children 10 through 14 years of age with head injuries due to bicycling were identified through emergency department surveillance of a population of 29,533. SETTING: Group Health Cooperative of Puget Sound, a large health maintenance organization. OUTCOME MEASURES: Bicycle head injuries prevented and the savings or costs associated with various subsidy, safety helmet use, and discount rates. RESULTS: Hypothetically, an increase in bicycle helmet use rates to 40% to 50% due to subsidies of $5 or $10 prevents 564 to 840 head injuries in a cohort of 100,000 5- through 9-year-olds over 5 years. Under these conditions and a 2% discount rate, cost savings ranging from $189,207 to $427,808 will result when catastrophic head injuries are included in the analysis. CONCLUSION: Subsidization of bicycle safety helmets to achieve a cost of $14 to $20 per helmet and use rates of 40% to 50% will likely prove cost-effective. Empirical evidence from a Seattle campaign suggests that such helmet use rates are achievable.

Adolescent↗
PubMed1992

Measurement of severity for nonhospitalized injuries in the pediatric age group.

To better classify minor injuries in the pediatric outpatient population, we empirically developed a scale to predict functional impairment, one week and one month postinjury, based on data available at the time of care. A sample of 857 injured children aged five to 19 years was randomly split into two subsamples. Using logistic regression techniques, predictive models were developed and confirmed on the subsamples and then applied to the full sample. Age, location of injury, and type of injury were predictive of impairment one week post-injury; however, type of injury was the only consistently significant predictor. Type of injury, specifically fracture, dislocation, and sprain, and location of injury (lower extremity) were significant predictors of functional impairment one month postinjury; however, once again, the type of injury was the only variable consistently significant across all models. Other than the type of injury, the variables available at the time of care were too uniform between disabled and nondisabled patients to be useful in developing a severity scale for minor injuries. We conclude that other outcome measurements or scale development techniques should be explored to develop a useful classification scheme for minor injuries.

Adolescent↗