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Biomedical subjects

R S Thompson

Publications and source records attributed to R S Thompson.

At least 109 records · Page 6Linked to original sources
PubMed1989

Mathematical model for interpretation of Doppler velocity waveform indices.

Various empirical indices such as the pulsatility index (PI) are widely used for quantitative analysis of Doppler ultrasound velocity waveforms. The physical interpretation of these indices was studied using a mathematical model. Although the method has more general applicability, this particular study was concerned with the umbilical-placental circulation. A lumped element electrical circuit equivalent was used, with each arterial branch represented by a resistor and a capacitor. The placental villous bed was modelled by a two-step parallel branching structure. Placental vascular disease was modelled either as obliteration of a fraction of the terminal branches, or as a fractional decrease in the radius of the vessels. The main features of both normal and abnormal umbilical artery waveforms can be reproduced by this simple model. Theoretical relationships between the velocity waveform indices and the lumped resistances and capacitance of the system were obtained for different input pressure functions. Over a wide range of physically reasonable conditions, the umbilical artery PI is approximately proportional to the ratio of the placental resistance to the umbilical artery resistance. The PI also depends on the pulsatility of the input pressure waveform. The Fourier pulsatility index was evaluated for an arbitrary pressure function, and shown to behave like (PI)2 for the umbilical artery waveform.

Biomedical Engineering↗
PubMed1989

1,1,1-Trichloroethane: medium-term toxicity to carp, daphnids, and higher plants.

The toxicity of 1,1,1-trichloroethane to carp (Cyprinus carpio) and daphnids (Daphnia magna) and the effects of gaseous-phase exposure on the growth of higher plants (Sorghum bicolor and Brassica napus) were investigated. The test systems were designed to minimize loss of the volatile material during the exposure period. During an exposure period of 14 days, there were no mortalities or other symptoms of toxicity in carp exposed to a mean measured 1,1,1-trichloroethane concentration of 7.7 mg/liter. The survival and reproduction of daphnids over a test period of 17 days were not affected at a measured concentration of 1.3 mg/liter. Growth of emergent seedlings was not inhibited at measured gaseous-phase concentrations of 18 mg/liter for S. bicolor and 6.9 mg/liter for B. napus. The simple modifications made to standard techniques proved sufficient to maintain the exposure concentrations of this volatile chemical. Mean measured concentrations were generally greater than 60% of the nominal values.

Animals↗
PubMed1989

Population-based study of unintentional injury incidence and impact during childhood.

We report a prospective study of medically treated unintentional injuries ascertained in an HMO population of children and adolescents 19 years of age and younger over a one-year period. The overall rate of medically treated injuries was 247 per 1,000, 147/1,000 for those treated in the clinic, and 100/1,000 for those treated in the emergency room (ER). Overall, 2.5 percent of patients were hospitalized. The highest rates of injury were for falls (60 per 1,000), recreational activities (57 per 1,000) and competitive sports (49 per 1,000). The site of care varied little by injury diagnosis or etiology, with the exception that sprains/strains, fractures, and injuries due to play and sports were more commonly treated in the clinic. The impact of trauma on activity was considerable, with 55.9 percent of injuries resulting in restricted activity, 10.6 percent in greater than or equal to 2 days of school missed, and 6.7 percent in greater than or equal to 2 days spent in bed.

Accidental Falls↗
PubMed1989

Risk of injury to children less than 5 years of age in day care versus home care settings.

Recent studies have suggested that day care may be a relatively unsafe environment. In this population-based study, the incidence of injuries in day care and home care were evaluated based on the number of hours children were exposed to each environment. In this population, 43.6% of children less than 5 years of age spent part of the year in day care. The rate of injuries in day care was 2.50 per 100,000 child-hours of exposure compared with a rate of 4.88 per 100,000 child-hours of exposure in the home environment. There were no differences in overall severity of injuries in the two groups. It was concluded that children are at no greater risk of injury in day-care settings than in the home environment.

Accidents, Home↗
PubMed1988

Low-dose aspirin therapy improves fetal weight in umbilical placental insufficiency.

A randomized, placebo-controlled, double-blind trial was carried out to evaluate the fetal benefits of low-dose aspirin (150 mg/day) as a treatment of placental insufficiency during the last trimester of pregnancy. Forty-six women referred for study because there was concern about fetal welfare were found to have an elevated umbilical artery wave form systolic/diastolic ratio. Mothers with severe hypertension were excluded because fetal condition would not necessarily be the dominant determinant of obstetric decision making. A distinction was made between a high systolic/diastolic ratio (greater than 95th but less than 99.95th percentile) and an extreme systolic/diastolic ratio (greater than 99.95th percentile). There were 34 patients in the high ratio group and 12 in the extreme group. Aspirin therapy was associated with an increase in birth weight (mean difference 526 gm [p less than 0.02]), head circumference (1.7 cm [p less than 0.025]), and placental weight (136 gm [p less than 0.02]) in those patients with a high initial umbilical artery systolic/diastolic ratio. For the 12 women with an extreme initial systolic/diastolic ratio, aspirin therapy did not result in a significantly different pregnancy outcome.

Adult↗
PubMed1988

Effectiveness of smoking cessation interventions integrated into primary care practice.

Using a complete factorial design, we tested three interventions for smoking cessation in routine primary care practice. The interventions tested were 1) physician counseling, 2) mailed letters and educational materials designed by the National Cancer Institute (NCI), and 3) referral to smoking cessation classes. Thirty-seven family practice physicians at three of Group Health's outpatient facilities participated. Patient participation rates were 95%, and follow-up was complete for 92% of those participating. None of the interventions had any effect on point prevalence of quitting as determined 8-9 months later by self-report. However, the combination of physician counseling and NCI materials doubled the odds of occurrence of significant antismoking behavior (quit, quit and relapse, or cut down) during the ensuing 8-9 months in those individuals receiving that combination. Referral to smoking cessation classes was strikingly ineffective in this setting. Of 369 individuals designated by study design for referral, only 14% even investigated the classes. This compares with a 10% self-referral rate for those persons not designated for referral by our study design. Our results and other recent work suggest that more intensive interventions on multiple occasions based on relapse prevention strategies hold promise for future success in smoking cessation efforts in primary care.

Counseling↗
PubMed1988

Cost-justification analysis of prenatal maternal serum alpha-feto protein screening.

The costs to an insurer of a 10-year maternal serum alpha-feto protein (MSAFP) screening program were subtracted from future medical care costs avoided by the insurer (benefits) to examine whether such a program would be cost-justified from the perspective of a managed health care system (i.e., result in net costs greater than or equal to 0). The analysis considered MSAFP screening for neural tube defects (NTDs) alone and then was repeated to consider screening for both NTDs and Down's syndrome. Using a 5% discount rate for future dollars, the costs to the insurer of a screening program for NTDs alone over 10 years exceeded costs avoided by $10.00 per person screened. Adding screening for Down's syndrome using the same MSAFP test increased the net cost by $22.00 to a total of--$32.00 per screenee. The estimate of the cost to the insurer was sensitive to assumptions regarding the costs of medical care avoided, the expense of MSAFP, the proportion of screened women requiring a genetic amniocentesis, and the cost of that procedure. The conclusion that screening would not result in a cost savings to the insurer was not changed by reasonable assumptions regarding 1) the appropriate discount rate; 2) the costs of MSAFP; 3) the costs of genetic amniocentesis; 4) the sensitivity of MSAFP; 5) the proportion of the population requiring genetic amniocentesis; and 6) the costs of 10 years of medical care for someone affected by Down's syndrome or an NTD. Other analyses suggested that screening for NTDs or Down's syndrome would be cost-justified when viewed from the perspective of society. The present work suggests this conclusion does not hold when the perspective of the insurer is taken because avoided costs of care realized by society exceed those realized by the insurer.

Adult↗
PubMed1988

Doppler ultrasound waveform indices: A/B ratio, pulsatility index and Pourcelot ratio.

Three different indices, the A/B ratio, the pulsatility index (PI) and the Pourcelot ratio (PR), are in common use for quantitative analysis of umbilical artery Doppler ultrasound waveforms. A detailed examination of the similarities and differences between these indices, together with the expected errors for each, was undertaken to enable informed comparisons and choices to be made. The indices were calculated from 133 last trimester recordings using an objective and very reliable computer analysis technique. The PI is more difficult to calculate than the other two quantities and the extra computation does not provide any extra information. The A/B ratio appears the simplest index to use but the values are not normally distributed. With the PR a normal distribution of values can be assumed. A theoretical consideration of errors showed that none of the indices is intrinsically less error prone for last trimester waveforms overall. The errors in the A/B ratio increase as the value of the index increase, whereas the converse holds for the PI and PR.

Blood Flow Velocity↗
PubMed1988

Umbilical artery velocity waveforms: normal reference values for A/B ratio and Pourcelot ratio.

Normal reference values for the umbilical artery Pourcelot ratio and A/B ratio are reported. Thirty-five normal patients were studied serially from 20 weeks to term. The A/B ratio centiles were corrected for non-normality of the underlying distribution by transforming from the Pourcelot ratio values. The correction needed was small during the last trimester, but larger for second trimester data. Of the 35 patients 24 were nulliparous and there was a slight tendency for the waveform indices to be higher in the nulliparae, but the numbers in this study were too small to be conclusive about the effect of parity.

Blood Flow Velocity↗
PubMed1988

Neurologic events following diphtheria-tetanus-pertussis immunization.

The frequency of serious neurologic events following the administration of 106,000 doses of diphtheria-tetanus-pertussis vaccine at Group Health Cooperative of Puget Sound was determined using a population-based case-control study with disease ascertainment through pharmacy and hospitalization records. There were no cases of acute unexplained encephalopathies in close temporal relation to vaccination. There was the new onset of one serious seizure disorder in the three days following immunization, with 1.13 expected on the basis of chance alone.

Brain Diseases↗
PubMed1987

Umbilical artery flow velocity waveforms in high-risk pregnancy. Randomised controlled trial.

300 patients at high fetal risk (mean gestational age 34 wk) were randomised to a group for antenatal doppler umbilical artery waveform studies and a control group. The timing of delivery was similar in the control and doppler-report-available groups overall. However, in the report group obstetricians allowed the pregnancies of those not selected for elective delivery to continue longer. There was no difference in the rates for elective delivery (induction of labour or caesarean section) in the two groups, whereas among those who went into labour (induced or spontaneous) emergency caesarean section was more frequent in the control group (23%) than in the report group (13%). Fetal distress in labour was also more common in the control group. Babies from the control group spent longer in neonatal intensive care (level 3) and needed more respiratory support than did those in the report group. The findings indicate that the availability of doppler studies leads to better obstetrical decision making.

Blood Flow Velocity↗
PubMed1987

A clinically effective breast cancer screening program can be cost-effective, too.

The logistics of complying with current American Cancer Society breast cancer screening recommendations in a large health maintenance organization, serving more than 50,000 women age 40 or older, are described. An alternative screening approach estimated to be at least as health-effective as the American Cancer Society recommendations has been developed and appears to solve the problem and is financially feasible. Cost-effectiveness depends on optimal use of mammography and health-care personnel resources. The authors show how the start-up and maintenance costs of an organized program can be offset by future cost savings resulting from reduced long-term disability in patients diagnosed at Stages 0-1 as opposed to Stages 2 and later. Careful selection of the delivery model before implementation can make a breast cancer screening program cost-effective as well as health-effective.

Adult↗
PubMed1987

Smokers and drinkers in a health maintenance organization population: lifestyles and health status.

This study examines, among a large health maintenance organization population, the prevalence of two high-risk lifestyle practices (smoking and problem drinking), their interrelationships, and their relationships with other lifestyle practices, sociodemographic characteristics, and health status measures. Results, based on a random sample of 1,133 adults, showed that smoking and problem drinking are strongly correlated. Individuals with no drinking problems had an age-, sex-, and education-adjusted smoking prevalence of approximately 20%, while problem drinkers smoked at about twice that rate. In addition, reporting one type of problem drinking behavior (binge, chronic, or drinking and driving) at least doubled, and in one instance increased by sixfold, the likelihood of reporting another type of problem drinking behavior. Smokers and problem drinkers were more likely to be younger than age 65, to be irregular seat belt users (smokers and binge drinkers only), and not to belong to voluntary organizations. Results of the analysis suggest that detection, prevention, and treatment of drug use, in general, might prove more beneficial than only focusing on smoking and problem drinking. In addition, because binge drinking and drinking and driving were so widespread among younger age groups, it might prove more beneficial to consider preventive strategies that change the sale and distribution of alcohol and make the environment safer in which to drink, such as providing transportation to get drinkers back home.

Adult↗
PubMed1987

Umbilical artery flow velocity waveforms and placental resistance: the effects of embolization of the umbilical circulation.

Embolization of the umbilical placental circulation in fetal lambs was carried out to occlude the small vessels of the placental vascular bed and to observe the effect on the umbilical artery flow and flow velocity waveforms. Thirteen singleton fetuses were studied from day 120 of pregnancy. Embolization was achieved by injecting approximately 9 X 10(6) microspheres of 15 micron diameter into the fetal placental cotyledons along the umbilical arteries over 9 days. Umbilical and uterine flows were measured by radioactive microsphere counting. The umbilical placental resistance was increased (0.25 to 0.35 mm Hg.ml.min-1) by embolization, and there was an increase in the umbilical artery systolic/diastolic ratio. Embolization produced a significant fall in umbilical flow expressed either as total flow (312 to 237 ml.min-1) or when normalized by reference against splanchnic flow (3.36 to 1.53). We conclude that the umbilical artery flow velocity waveform systolic/diastolic ratio measures the reflection coefficient at the peripheral vascular bed (the "resistance vessels") of the placenta.

Animals↗
PubMed1987

Diphtheria-tetanus-pertussis immunization and sudden infant death syndrome.

We compared the recency of diphtheria-tetanus-pertussis (DTP) immunization in healthy children with birthweights greater than 2500 gms who died of sudden infant death syndrome (SIDS) to that of age-matched reference children, using a modified case-control analysis. Focusing on very narrow time intervals following immunization, we found the SIDS mortality rate in the period zero to three days following DTP to be 7.3 times that in the period beginning 30 days after immunization (95 per cent confidence interval, 1.7 to 31). The mortality rate of non-immunized infants was 6.5 times that of immunized infants of the same age (95 per cent CI, 2.2 to 19). The latter result and to some extent the former appear to be ascribable to known risk factors for SIDS. Although the mortality ratios for SIDS following DTP, as estimated from this study, are high the period of apparently elevated risk was very short, so that only a small proportion of SIDS cases in infants with birthweights greater than 2500 gms could be associated with DTP.

Birth Weight↗
PubMed1987

Osteoporosis prevention: strategies applicable for general population groups.

Osteoporosis is a common condition of the elderly population that entails considerable morbidity and mortality. Although prevention recommendations often focus on perimenopausal women, the condition begins well before the age of menopause and also affects men. Prevention techniques include hormonal replacement therapy, optimization of calcium intake and absorption, weight-bearing exercise, cessation of tobacco and alcohol abuse, fall prevention, and management of predisposing medical conditions. All of these techniques are analyzed by commonly accepted criteria. Recommendations for osteoporosis prevention that are applicable to general population groups are presented.

Aged↗