Search PubMed⌕ Search

Biomedical subjects

S D Walter

Publications and source records attributed to S D Walter.

At least 127 records · Page 7Linked to original sources
PubMed1984

An epidemiologic study of lifting and twisting on the job and risk for acute prolapsed lumbar intervertebral disc.

An epidemiologic case-control study undertaken in Connecticut during 1979-1981 indicated that persons with jobs requiring lifting objects of more than 11.3 kg (25 lb) an average of more than 25 times per day had over three times the risk for acute prolapsed lumbar intervertebral disc as people whose jobs did not involve lifting objects of this weight. If the body was usually twisted while the lifting was done, this elevation in risk was apparent with less frequent lifting. An especially high risk for prolapsed lumbar disc was associated with jobs involving lifting objects of more than 11.3 kg with the body usually twisted and the knees not bent while the lifting was done. Neither lifting objects of less than 11.3 kg nor twisting without lifting was associated with an increase in risk.

Adult↗
PubMed1984

Can a calcaneal morphologic index determine the degree of osteoporosis?

The proposal that a scoring system of the radiographic trabecular patterns of the os calcis could be related to degree of osteoporosis was tested. The technique fails as it showed no correlation with actual bone density determined by a Compton scatter technique and because of a low level of observer concordance. Possible reasons for the poor performance of the index developed in India when applied to North Americans are discussed.

Age Factors↗
PubMed1984

The impact of a psychosocial support program on survival with breast cancer: the importance of selection bias in program evaluation.

A retrospective follow-up study was conducted to assess the impact of a psychosocial support program on survival with breast cancer. One-hundred and two nonparticipants were individually matched to 34 participants on several prognostic factors, and both groups were followed from date of cancer diagnosis (1971-1980) until December, 1981. Preliminary findings suggest a strong beneficial effect of the program on survival, which is statistically significant. However, this observed effect is due largely to a selection bias caused by the failure to match on the duration of the lag period between cancer diagnosis and program entry. Correcting for this bias in the analysis results in a small, nonsignificant program effect. We are not able to rule out a possible effect, however, because of the relative lack of statistical power and because of a modest, though nonsignificant benefit observed for women who entered the program shortly after diagnosis. Furthermore, the program might have other beneficial effects on the quality of life.

Adult↗
PubMed1984

Acute prolapsed lumbar intervertebral disc. An epidemiologic study with special reference to driving automobiles and cigarette smoking.

An epidemiologic case-control study to identify risk factors for acute prolapsed lumbar intervertebral disc was undertaken in Connecticut during 1979-1981. This paper focuses on nonoccupational factors of possible etiologic significance. Persons in their 30s were affected most frequently. Among surgical cases, the ratio of men to women was 1.5 to 1, while among probable and possible cases not undergoing surgery, the male to female ratio was about 1 to 1. Cigarette smoking in the past year was associated with an increased risk for prolapsed disc. The greater the number of hours spent in a motor vehicle, the higher the risk. Use of Swedish and Japanese cars was associated with a lower-than-average risk, while use of other cars was associated with a higher-than-average risk. For each type of car, older cars were associated with higher risks than newer cars. Variables that did not affect the risk for prolapsed lumbar disc in this study included height, weight, number of pregnancies, number of children, frequency of wearing shoes with high heels, smoking cigars or pipes, and participation in baseball or softball, golf, bowling, swimming, diving from a board, tennis, bicycling or jogging.

Acute Disease↗
PubMed1984

The usefulness of the Denver Developmental Screening Test to predict kindergarten problems in a general community population.

The Denver Developmental Screening Test (DDST) was administered to 2,569 children five to seven months prior to starting kindergarten in September 1980 in a geographically well-defined community. The test was administered by trained public health nurses. At the end of the 1980-1981 school year, all 163 kindergarten teachers in the area completed a rating form for each child in their class. The rating form determined global ratings of: 1) learning abilities; 2) classroom behavior; 3) amount of special attention required; and 4) referrals to special education services outside the classroom. The specificity of the DDST in predicting kindergarten teacher ratings was 99 per cent for all areas. Test sensitivity varied from 5 per cent to 10 per cent in detecting problems in the four areas. The predictive values of an positive test varied from 31 per cent for behavior problems to 62 per cent for extra attention required in the classroom. Negative test predictive values varied from 79 per cent to 93 per cent. These results based on kindergarten teacher ratings suggest that, because of the low sensitivity and modest predictive value, the DDST may be relatively inefficient to use in a school entry screening program in a general community population of children.

Child, Preschool↗
PubMed1984

An epidemiological study of acute prolapsed cervical intervertebral disc.

In this epidemiological study of acute prolapsed cervical intervertebral disc, we found that people in the fourth decade of life were affected somewhat more frequently than individuals in other age groups, and men with a prolapsed cervical disc outnumbered women by a ratio of 1.4 to one. Factors that were associated relatively strongly with this diagnosis were frequent lifting of heavy objects on the job that was held around the time of the onset of symptoms, cigarette-smoking, and frequent diving from a board. Positive associations that were of borderline statistical significance or were not statistically significant were found with operating or driving vibrating equipment and time spent in motor vehicles. Variables that did not appear to affect the risk for a prolapsed cervical disc included participation in certain sports other than diving, frequent wearing of shoes with high heels, the number of pregnancies or live births, frequent twisting of the neck on the job, time spent sitting on the job, and smoking cigars or a pipe.

Acute Disease↗
PubMed1984

Measuring the reliability of clinical data: the case for using three observers.

Misclassification of clinical data occurs commonly, because of measurement or judgmental errors, or because of bias in the observational method. The sensitivity and specificity of a given observer (or method) may sometimes be estimated by comparison with an independent "definitive" diagnosis; this is not routinely practical, however, if the "definitive" method involves additional risk or cost. A second possibility is to compare two independent, fallible observers, using an index of agreement such as the kappa statistic; the misclassification probabilities are not then estimable, and the agreement indices have the disadvantage of being dependent on the population prevalence. In contrast, if three or more independent observers are used, their reliability may be assessed by the direct estimation of sensitivity and specificity. An example is given of a series of patients who were independently evaluated by three radiologists.

Data Collection↗
PubMed1984

Simplified models of screening for chronic disease: estimation procedures from mass screening programmes.

The performance of a screening programme depends on a number of parameters, which may need different types of information for their estimation. In this paper, two characteristics of interest, the sojourn-time distribution and the sensitivity, are considered, and estimation procedures, based on data which should be available from a mass screening programme, are proposed. The methods are applied to published data from the HIP breast cancer screening project, to which a negative exponential distribution for the sojourn-time distribution fitted better than the other families of distribution considered.

Breast Neoplasms↗
PubMed1983

Effect of pressurization on methylmethacrylate-bone interdigitation: an in vitro study of canine femora.

Aseptic mechanical loosening of the femoral and acetabular components is a major long term complication of total hip arthroplasty. Pressurized injection of bone cement (polymethylmethacrylate) has been advocated for increasing cement-bone interlock. To determine the relationship between cement intrusion pressure and its penetration into cancellous bone, an in-vitro study of paired, fresh frozen canine femora was conducted. Methacrylate cement was injected at predefined constant pressures from 0.11 to 1.23 MPa (16-175 psi). The penetration was quantified for each injection pressure. The results showed a positive logarithmic relationship between the relative penetration and the intrusion pressure, the former reaching a near asymptotic value at approximately 0.70 MPa (100 psi). Unequal radial distribution of cement within the metaphysis was demonstrated. Greater penetration was observed into the proximal postero-lateral cancellous bone bed as compared to other regions. The relationship between cement penetration and bone size was explored at a single-constant pressure of 0.35 MPa (50 psi). Although absolute cement penetration was found to be linearly related to the bone size, the relative penetration remained nearly constant with bone size.

Animals↗
PubMed1983

Coffee drinking and bladder cancer in Connecticut.

The association between coffee consumption and bladder cancer is investigated in a population-based case-control study carried out in Connecticut during 1978-1979. Measures of coffee consumption employed include total weekly cups, years of consumption, and more than seven cups per week, in addition to use frequencies of specific coffee types. After adjustment for age and cigarette smoking, a significant elevation in risk for consuming more than seven cups weekly was found for males (odds ratio = 1.5) but not for females (odds ratio = 1.0); there was also some evidence of a dose-response relationship in males. Among nonsmokers of both sexes combined, the odds ratio for more than seven cups per week was 1.9. Male smokers showed age- and smoking-adjusted odds ratios for coffee similar to those of male nonsmokers. Female smokers had a decreased risk for bladder cancer associated with increased coffee consumption which reflects the substantially lowered risk among older (65 years and over) smoking women who may constitute a selected resistant group; odds ratios among younger female smokers were close to 1.0. Males also showed elevated risks associated with consumption of regular (non-decaffeinated) and ground (noninstant) coffees. No relationship with duration of consumption was found.

Adult↗
PubMed1983

Effects of interaction, confounding and observational error on attributable risk estimation.

The properties of attributable risk are discussed for situations in which there are several risk factors that are possibly interacting or confounded. Conditions are identified when the attributable risk among the exposed is constant, when the marginal attributable risk estimate is valid, and when the public health effects of separate risks are additive. Such conditions reflect, in various ways, the interaction and confounding of the different risk factors involved. For diseases with more than two risk factors, these conditions are sufficient but not necessary; thus it is possible to have additive public health effects of two risk factors even though they are confounded and interactive. In contrast, when there are exactly two binary risk factors, the conditions are sufficient and necessary. It is shown that bias in attributable risk through misclassification of exposure arises primarily through insensitivity errors. Particularly with zero false negative rates and equal false positive rates for cases and controls, the attributable risk estimate is unbiased; however, a larger standard error pertains to the estimate based on misclassified data.

Environmental Exposure↗
PubMed1983

Estimation of the duration of a pre-clinical disease state using screening data.

In this paper, the authors show how data on the observed prevalence of disease at a screen and on the incidence of disease during intervals between screens may be used to estimate jointly the distribution of the length of time during which individuals remain in the pre-clinical state and the sensitivity of the screen. Apart from being of biologic interest, such estimates may be used to evaluate the length of time by which the date of diagnosis could be advanced by screening (the lead time) as well as to predict the relative effectiveness of various alternative screening strategies. The methodology uses only information which should be routinely available in the course of a typical screening program, and makes only rather mild statistical assumptions. The authors illustrate the methods with breast cancer screening data from the Health Insurance Plan of Greater New York (HIP). Although these data have been analyzed by several other authors, the present approach is the first which simultaneously gives estimates of the pre-clinical state duration, the sensitivity of the screening method, and the underlying incidence rate in the screened group, while also taking into account the problem of length-biased sampling.

Adult↗
PubMed1983

Plasma fibronectin level and clinical status in cardiac surgery patients.

To determine whether changes in plasma fibronectin concentration were related to the development of postoperative complications, we studied both plasma fibronectin concentration and the postoperative clinical course for 41 patients undergoing elective cardiopulmonary bypass surgery. Patients were divided retrospectively into three groups based on their hospital course. Group I (n = 21) had mild complications, group II (n = 15) had moderate complications, and group III (n = 5) had severe complications. Fibronectin was monitored preoperatively, intraoperatively, and postoperatively until discharge. Although fibronectin levels were unaffected by induction of anesthesia, a decrease in fibronectin concentration was seen after bypass in all patients. This decline was transient, however, and fibronectin concentration rose within 4 to 5 hr after the end of surgery. A subsequent fall to a level below the lower limit of normal (less than 180 micrograms/ml) was consistently seen only in critically ill (group III) patients and coincided with adverse changes in their clinical status.

Aged↗
PubMed1982

Errors in kinematic parameters of a planar joint: guidelines for optimal experimental design.

Kinematic characteristics of a body joint performing planar motion are precisely defined by the centers and angles of rotation as the joint undergoes its full range of physiological movement. These potentially (clinically) useful non-invasive kinematic parameters are, however, highly sensitive to input coordinate measurement errors and the experimental design. This paper compares results of an experimental study and a statistically based mathematical model of the errors in the centers and angles of rotation. Guidelines are provided to design optimal kinematic experiments so that, for given measurement equipment, the highest possible precision may be achieved in the results.

Biomechanical Phenomena↗