Biomedical subjects

S Suissa

Publications and source records attributed to S Suissa.

At least 109 records · Page 6Linked to original sources

PubMed1991

Predictors of one year outcome in lupus nephritis: the importance of renal biopsy.

The short-term prognosis of lupus nephritis was evaluated by assessing serum creatinine 12 months after renal biopsy in 87 patients with lupus nephritis. On univariate analysis, significant clinical and laboratory predictors of this outcome included clinical signs of renal injury (serum creatinine, 24-hour urinary protein, prolonged renal disease, nephrotic syndrome, serum albumin), as well as thrombocytopenia, older age, and coexisting illness or hypertension at the time of biopsy. On renal biopsy, diffuse proliferative nephritis, higher activity, chronicity, or tubulointerstitial scores, or subendothelial or subepithelial electron dense deposits predicted a higher serum creatinine 12 months after biopsy. A clinical predictive model was developed which included as independent predictors serum creatinine, age, platelet count and 24-hour urinary protein. Any one of three biopsy variables added information to the clinical prediction model: a marked quantity of subendothelial deposits (p = 0.02), a higher activity index score (p = 0.02), or the presence of diffuse proliferative lupus nephritis (p = 0.05). However, the relative predictive accuracy of the clinical model did not improve with the addition of any of the biopsy variables. The value of renal biopsy in lupus nephritis is discussed based on the ability of biopsy information to confirm the prognosis, to add new predictive information for a group of subjects, and to improve predictive accuracy for individual patients.

Adolescent↗

PubMed1991

The 2 x 2 matched-pairs trial: exact unconditional design and analysis.

An exact unconditional method for the design and analysis of the 2 x 2 matched-pairs trial is presented. Unlike the exact conditional method, which is based on only the number of discordant pairs, the exact unconditional method uses the total number N of sampled pairs. This unconditional test, based on a simple Z statistic, yields sample sizes that are generally smaller than those produced by the exact conditional test for the cases tabulated herein, namely one-sided alpha = .01, .025, and .05 along with 80% and 90% power. Moreover, it is found to be uniformly more powerful than the latter for all the combinations of parameters considered in this paper, namely alpha = .01, .025, and .05, and N = 10(1)200. The method is illustrated by assessing various design options of an in vitro study of the effectiveness of antimicrobial agents. Some numerical examples of matching efficiency are also given.

Biometry↗

PubMed1990

Predicting arterial oxygenation during one-lung ventilation with continuous positive airway pressure to the nonventilated lung.

Forty patients undergoing elective thoracotomy were studied to assess the possibility of predicting PaO2 during one-lung ventilation (OLV) when continuous positive airway pressure (CPAP) was applied to the nondependent lung. The first 20 patients were studied retrospectively and the three most significant independent variables that correlated with PaO2 during OLV with CPAP were: side of operation (P = 0.04), FEV1/FVC ratio (P = 0.01), and the intraoperative PaO2 during two-lung ventilation (P = 0.0002). By the method of multiple linear regression, these three variables were used to construct a predictive equation for PaO2 during OLV with CPAP. The second 20 patients were studied prospectively and the predicted PaO2 correlated significantly with the observed PaO2 during OLV with CPAP (r = 0.86, P less than 0.001). Therefore, it is concluded that the PaO2 during OLV with CPAP can be predicted using routinely available data.

Aged↗

PubMed1989

Chronic exposure to sour gas emissions: meeting a community concern with epidemiologic evidence.

For 25 years residents of a rural area in southwestern Alberta have complained of health problems attributed to sour gas emissions from nearby natural gas refineries. We undertook a large epidemiologic study of the current health status and the selected morbidity rates among 2152 people in the exposed area. We established two comparison groups: one was a demographically similar unexposed population and the other a demographically different group also exposed to sour gas emissions in another region. The methods included a cross-sectional survey of current residents and separate historical cohort studies involving registry linkage to investigate cancer incidence and all-cause mortality. The cross-sectional survey involved a comprehensive health questionnaire, standardized clinical examinations by physicians blinded to the subjects' symptoms and concerns, and several laboratory tests. We were able to contact just under 60% of the people who we knew had moved from each area since 1958 and found no evidence of selective migration for health reasons. Although the residents of the exposed area reported an excess number of symptoms and health problems there were no significant differences in the mortality rate, incidence of cancer, reproductive problems, major ailments, hair levels of arsenic and certain metals or respiratory function between the groups.

Adolescent↗

PubMed1989

Body size and breast cancer prognosis: a statistical explanation of the discrepancies.

A historical cohort of 68 female breast cancer patients from one institution who were enrolled in a multicenter randomized controlled trial between 1971 and 1973 were followed up to the beginning of 1986. Weight and height at the time of mastectomy were transformed into two indices of body size, namely the Quetelet Index and a weight to "ideal weight" ratio. These two indices were analyzed for their relation with overall and disease-free survival, while controlling for the effect of several potential confounding variables. While neither index was linearly related to the hazard of death or recurrence, a significant quadratic (curvilinear) relation was found for both indices and both hazards. In all cases the hazard function was concave up, indicating that not only overweight but also underweight status is predictive of an unfavorable prognosis of breast cancer. This finding offers a possible explanation for the discrepancies among previous studies on this topic.

Adult↗

PubMed1989

Case-control study of hydrocarbon exposures in patients with renal cell carcinoma.

A retrospective case-control study tested the hypothesis that exposure to hydrocarbon combustion products is associated with the development of renal cell carcinoma. One control per case, matched for sex, date of birth (within 5 years) and urologist, was chosen. Controls were patients who presented with hematuria and were shown not to have a urinary tract tumour. A total of 164 cases and 161 controls responded to mailed questionnaires and telephone interviews. Smoking more than 20 cigarettes per day was associated with the presence of metastatic renal cell carcinoma (p less than 0.001). Exposure to burning coal was associated with an increased relative risk of the disease but only when the exposure occurred between the ages of 10 and 24 years (p less than 0.05). Dose-response relations were demonstrated for intensity of exposure (p less than 0.025) and duration of occupational exposure (p less than 0.05). The distribution of latent periods from first exposure to diagnosis was bimodal, with one mode at 21 to 30 years and another at 41 to 50 years. Occupational exposure to tar or pitch or both was also associated with an increased relative risk of renal cell carcinoma (p less than 0.05).

Adolescent↗

PubMed1989

Unidirectional multiple comparisons of Poisson rates.

This paper presents an exact significance test procedure for unidirectional multiple comparisons of Poisson variables. It is sufficiently general for application to situations where the 'denominator', which might be the amount of follow-up time in cohort studies or the expected number of events in studies that use standardized rates, differs from one group to the other, and where a group-specific alternative hypothesis is of interest. We use unidirectional Z statistics, of the form proposed by Dunnett, along with the conditional distribution needed in computing the exact attained significance levels, to address three distinct unidirectional hypotheses. In one case, we compare one exposed with several reference groups, while in the other two cases, we compare several exposed groups with one reference group. We also provide a multiple stage testing approach. Data from studies in cancer and trauma epidemiology illustrate the procedures.

Cohort Studies↗

PubMed1989

Modeling percentage change: a potential linear mirage.

The percentage change over time in a variable such as serum creatinine or blood pressure is a potentially appealing outcome measure for longitudinal studies of prognosis or therapy. We demonstrate that when the baseline value of the variable used in the calculation of the percentage change outcome is included in a linear regression model as an independent predictor, a quadratic relationship between the baseline level and the predicted outcome level of this same variable is inevitably masked by the linear regression model. Misinterpretation of the percentage change model has resulted in conflicting results regarding the value of serum creatinine as a prognostic marker in lupus nephritis. We illustrate the problem and resolve the conflict using data on 87 patients with lupus nephritis. A straightforward alternative approach to the use of percentage change as an outcome is proposed: it is not subject to the problems of interpretation noted in the percentage change model.

Blood Pressure↗

PubMed1989

Respiratory health of a population living downwind from natural gas refineries.

Since 1958 there has been a perception of excess illness in a rural Canadian population living downwind from two natural gas refineries, the emissions of which contain mostly sulfur dioxide but also hydrogen sulfide. To determine if there was an excess of adverse health outcomes in the population exposed (defined by place of residence), a health survey was undertaken in 1985 in this area and in one unexposed to emissions but demographically similar. Participation was 92% from both the exposed population (n = 2,157) and a representative sample (n = 839) of the main reference population. More respiratory symptoms were reported in the exposed group than in the non-exposed group among those 5 to 13 yrs of age (28% versus 18%) and among never-smokers greater than or equal to 14 yrs of age (35% versus 24%). FEV1, FVC, and FEV1/FVC were similar in both areas. Dichotomizing the level of exposure (high, low) within the exposed area revealed a trend in the high exposure area toward increased respiratory symptoms in the younger age group (39% versus 24%), but decreased symptoms in the older age group (33% versus 36% among never-smokers). FEV1 was similar between the two areas. The excess of respiratory symptoms in the exposed area unassociated with impaired spirometric values would be compatible with increased awareness of health or a small biologic environmental effect.

Child↗

PubMed1989

The influence of psychological status on respiratory symptom reporting.

The American Thoracic Society respiratory symptom questionnaire (ATS-Q) is widely used and has provided valuable information in epidemiologic studies. To determine the influence of psychological status on respiratory symptoms, we compared subjects' ATS-Q responses to their Ilfeld Psychiatric Symptom Index (PSI) scores. To minimize the potential confounding effect of respiratory disease on the association between respiratory and psychological status, from a population-based survey of 3,628 subjects, we studied only the 600 "healthy" subjects, defined by the following characteristics: between 14 and 55 yr of age; never-smokers; no diagnoses of respiratory, heart, kidney, thyroid disease, or anemia; and normal spirometry (defined as an FEV1 and FVC greater than 80% of predicted). Associations were found between respiratory symptoms (cough, phlegm, wheeze, dyspnea) and PSI subscales (anxiety, anger, depression, and cognitive disturbance). Adjusted odds ratios for respiratory symptoms ranged from 1.13 to 2.15 for every 10% increase in PSI score. Psychological status is an important determinant of respiratory symptoms and therefore must be taken into consideration when interpreting results of epidemiologic studies using questionnaire information.

Adolescent↗

PubMed1989

Evaluation of the efficacy of simulation games in traffic safety education of kindergarten children.

Using a simulation game designed to teach children to obey certain traffic safety rules, an experimental study was conducted with 136 five-year-old children in four Quebec schools. Within each classroom, subjects were randomly divided into four groups: three intervention groups and one control group. Each of the experimental groups was subjected to a different intervention with outcome measured using three instruments related to attitudes, behavior, and transfer of learning of pedestrian traffic safety. Results suggest that simulation games including role-playing/group dynamics and modeling/training can change attitudes and modify behavior in the area of pedestrian traffic safety in children of this age.

Accident Prevention↗

PubMed1989

Severe hypoglycemia in IDDM children.

The incidence of severe hypoglycemia was determined in a 1-yr prospective study of 350 insulin-dependent diabetic (IDDM) children. There were no significant differences in mean glycosylated hemoglobin, age, and duration of disease between the patients who had severe hypoglycemia and those who did not. There were 25 episodes in 24 patients (6.8%). Their insulin doses at the time of the episode (U.kg-1.day-1) were significantly higher than those of the nonhypoglycemic group (mean +/- SD 1.01 +/- 0.30 vs. 0.89 +/- 0.29; P = .04). The hypoglycemic group had a significantly higher mean number of previous episodes of severe hypoglycemia than the nonhypoglycemic group (0.92 +/- 1.18 vs. 0.25 +/- 0.68; P = .01). In only 64% of the episodes, an unusual circumstance such as strenuous physical activity or missed or delayed meals preceded the event. Multivariate analysis of the data by logistic regression showed risks of developing hypoglycemia of 2.5 per 0.5 U/day insulin and of 2.0 per previous episode of severe hypoglycemia. We conclude that severe hypoglycemia may be a recurrent problem in some diabetic children, but it does not appear to be related to age or blood glucose control. The presence of previous episodes may be a guide to identify patients at greater risk of developing severe hypoglycemia. Adherence to regular testing, strict spacing and consistency of meals, and extra food for extra activity may reduce this serious complication.

Child↗

PubMed1988

Bowel obstruction in patients with ovarian cancer: a search for prognostic factors.

Patients with concomitant ovarian cancer and bowel obstruction were studied in an effort to find objective prognostic factors predictive of patient outcome. A total of 62 patients were followed from 31 to 354 weeks, and a total of 20 variables were considered in the analyses. At the end of the study 49 patients were dead of their disease, and 13 were alive (six disease free and seven with persistent disease). Survival probabilities of the sample were 79% at 6 weeks, 48% at 20 weeks, and 24% at 104 weeks. Univariate analyses revealed no significant difference in the survival times of medically versus surgically treated patients; age greater than 60 years at diagnosis of cancer, presence of ascites, low serum albumin levels, elevated blood urea nitrogen levels, elevated alkaline phosphatase levels, lack of previous radiotherapy (p less than 0.002 for all), advanced tumor stage, normal/ileus x-ray results, and a short diagnosis to obstruction interval (p less than 0.04 for all) resulted in lower survival probabilities.

Adult↗

PubMed1988

Risk of recurrence of occupational back pain over three year follow up.

A random sample including 2342 cases representative of all occupational back injuries in Quebec (1981) was followed up prospectively over three years to assess the recurrence rate of back problems (lumbar, thoracic, and cervical). Each medical and accident report was reviewed to obtain the site of symptoms and occupation. Age, sex, industrial sector, and number of episodes of absence from work were abstracted from the computerised Quebec Compensation Board files. The recurrence rate was 20.0% at one year follow up and 36.3% at three years. A multivariate analysis using a Poisson regression, was performed to model the risk of recurrence over time. Men had a higher chance of recurrence (risk ratio = 1.85, 95% CI = 1.50-2.27) but among recurrent cases, the average total number of episodes was comparable between men and women. Age showed a protective effect on the probability of recurrence (10 years: RR = 0.93, 95% CI = 0.88-0.98) due to the lower recurrence rate in the 45-64 year old group (31.8%). Cervical and lumbar symptoms had identical recurrence profiles whereas thoracic symptoms had a significantly lower recurrence rate. Drivers had the highest recurrence rate (42.1%) and nurses had the highest average number of recurrences (2.03) among recurrent cases. Both occupations had statistically significant excesses after controlling for the other variables.

Adolescent↗

PubMed1988

Clinical interpretation of airway response to a bronchodilator. Epidemiologic considerations.

Airways responsiveness to a bronchodilator is frequently measured to assist in determining the cause of respiratory symptoms. Clinically, a greater than 15% improvement in the FEV1 is often used to define the "increased" response indicative of asthma. However, unlike other tests of lung function, reference standards derived from "healthy" members of a general population sample have never been reported. As part of a health survey carried out in Alberta, Canada, 2,609 subjects completed a standardized respiratory symptom questionnaire and had FEV1 measured before and 20 min after inhaling terbutaline sulfate via a 750-ml spacer device. Among asymptomatic never-smoking subjects with a FEV1 greater than 80% of predicted, the upper 95th percentile of bronchodilator response (BDR), when expressed as 100 x (FEV1 postBDR - FEV1 preBDR)/predicted baseline FEV1 averaged 9%. This value remained remarkably stable across gender, age (7 to 75 yr), and height groups, and deviated to 6% only when baseline FEV1 was greater than 120% of predicted. Consistent with other respiratory function variables, in which the upper limit of normal is often defined as the upper 95th percentile, our population-derived reference values provide a conceptual definition of BDR that can easily be applied to define "increased" response in the clinical setting.

Adolescent↗

PubMed1988

Prospective study of predictors of beta-cell survival in type I diabetes.

We conducted a prospective study to describe the course of the pancreatic beta-cell function from the time of clinical diagnosis of insulin-dependent (type I) diabetes to determine whether DR type, presence of islet cell antibodies (ICA), presence of insulin antibodies (IA), age at onset, and sex could help in the prediction of residual endogenous insulin secretion. A cohort of 68 children was followed for 18 mo after diagnosis of type I diabetes. The outcome variables selected for analysis were 1) serum C-peptide peak concentration after a Sustacal meal, 2) time of disappearance of the serum C-peptide response, and 3) time after diagnosis at which the maximal serum C-peptide response was observed. After institution of insulin therapy, serum C-peptide peak concentrations rose temporarily for 1-6 mo and declined thereafter. Multivariate analysis of the data showed that DR type (P = .2488) and presence of IA (P = .1604) had no effect on serum C-peptide over time, but sex (P = .0146), age at onset (P = .0002), and presence of ICA (P = .0147) significantly contributed to the variation of serum C-peptide over time. Furthermore, age at onset, presence of ICA, and sex were also the only significant predictors of the time of disappearance of the beta-cell function. The relative risks of beta-cell-function disappearance were 0.87 (P = .0015), 9.43 (P = .0181), and 2.25 (P = .0468), respectively. In conclusion, there are distinct variations in the natural course of the beta-cell function in type I diabetes. beta-Cell-function survival is significantly shortened the younger the subject is at disease onset, if ICA are present at diagnosis, and if the subject is male.

Adolescent↗

PubMed1988

Impact of SMBG on control of diabetes as measured by HbA1. 3-yr survey of a juvenile IDDM clinic.

Three hundred twelve diabetic children and adolescents were seen in our diabetic clinic and instructed to test their capillary blood glucose (CBG) twice daily and to use an algorithm to adjust their short-acting insulin. Of this group, 219 youngsters had a full 3-yr period of observation. At each clinic visit, blood was obtained for fasting blood glucose and HbA1 and, once a year, cholesterol and triglycerides were also measured. Patient and parent accuracy in measuring CBG was found to be adequate. The changes over time in HbA1 were nondifferential across age and sex, and there was no difference in the level of HbA1 between age and sex groups, the number of tests reported to have been done by the patients, the number of injections of insulin per day, or the serum cholesterol. There was a significant relationship between the HbA1 and the fasting blood glucose (P less than .001) measured by the laboratory as well as with the serum triglyceride (P less than .01). The failure to improve diabetic control, despite measures that would have been expected to do so, was believed to relate more to a lack of compliance than to a flaw in the therapeutic approach. It was interesting to note that the adolescent patients in the study were in no worse control than the younger children in the group. Although better technical skills are available today to manage diabetes, the psychosocial approach to patient motivation requires improvement.

Adolescent↗

PubMed1988

Application of an Euclidian distance measure to the selection of reference areas in epidemiologic research concerning environmental issues.

A procedure for selecting reference areas in epidemiologic research employing census data and squared Euclidian distance is described. The procedure was adapted from cluster analysis, a multivariate statistical technique that has been applied in many disciplines. With the use of 12 census variables as the basis for evaluating sociodemographic differentiation, squared Euclidian distances were calculated between a geographically delineated index area in southwest Alberta, where residents had complained for several years about the effects of exposure to sour gas emissions, and 119 provincial census tracts in the rest of nonmetropolitan southern Alberta. The Euclidian distances can be interpreted as social distance scores with values close to zero representing a high level of sociodemographic similarity between the index area and potential reference areas. The social distance scores, in association with environmental data, suggested a clear choice for the most comparable unexposed reference area and illustrated the difficulty of finding a suitable most comparable exposed reference area. Results from the demographic component of the subsequent health survey indicated that the index area and reference area were similar in most respects. Furthermore, tests with and without statistical adjustment for confounding variables produced negligible differences on most of the important target outcome variables.

Adolescent↗