Power calculation for cohort studies with improved estimation of expected numbers of deaths

Summary This paper focuses on improving the accuracy of sample size calculations for cohort studies by careful calculation of the expected number of deaths in the population, taking into account either prior information or realistic assumptions about variables which may affect the mortality or incidence. Sometimes small changes in the assumptions can dramatically alter the expected numbers and may necessitate modifications in the design of the study. Possible modification include extension of the follow-up time, and recognition that the real strength of the study may lie in the potential for pooling several similar studies. The problem will be discussed with reference to two examples of occupational cohort studies where differing prior information was available.

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Zusammenfassung Diese Arbeit beschäftigt sich mit der Genauigkeit der Berechnung des Stichprobenumfangs in Kohortenstudien, wenn detaillierte Berechnungen für die erwartete Zahl der Verstorbenen berücksichtigt werden. Dies kann entweder durch die Ausnutzung vorhandener Informationen oder durch realistische Annahmen über die Faktoren, die Mortalität oder Inzidenz beeinflussen, geschehen. Schon kleine Unterschiede in diesen Annahmen kann die erwartete Zahl der Verstorbenen erheblich verändern und es notwendig machen, das Design einer Studie zu verändern. Solche Modifikationen bestehen z.B. in der Verlängerung der Follow-up Zeit der Studie oder in der Einsicht, dass es nötig ist, Daten aus mehreren Studien zusammenzufassen. Die Probleme werden anhand von zwei Beispielen aus dem Bereich der Berufsepidemiologie diskutiert.

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Résumé Cet article concerne la précision des estimations de taille d'échantillons pour les études de cohortes. Le calcul précis du nombre de décès attendus dans la population prend en compte les variables susceptibles d'affecter la mortalité ou l'incidence, provenant soit d'une connaissance préalable, soit d'hypothèses réalistes. De modestes changements d'hypothèses peuvent parfois altérer de façon substantielle les nombres attendus et nécessiter des modifications dans le protocole de l'étude. Parmi les modifications possibles, il faut citer la prolongation du temps de suivi de l'étude ainsi que le constat que la valeur réelle de l'étude pourrait reposer sur la possibilité de mise en commun de plusieurs études similaires. Le problème est discuté à l'aide de deux exemples d'études de cohortes professionnelles pour lesquelles différentes informations préalables sont disponibles.

     

RESPONSIVENESS AND SENSITIVITY TO CHOLINERGIC AGONISTS AND ANTAGONISTS IN BOVINE ISOLATED BRONCHIAL MUSCLE

1. Airways derived from different levels of the lung exhibit a difference in the reactivity and sensitivity to agonists. We have evaluated the effect of acetylcholine and cholinergic selective (pirenzepine, gallamine and 4-dipherylacetoxymethyl piperidine [4-DAMP]) and non-selective (atropine) antagonists on bovine proximal and distal smooth muscle preparations. 2. The distal preparations are more sensitive to acetylcholine than proximal bronchi. The relaxant effect of three selective antagonists on the distal and proximal tissues was the same when the results for each drug were compared. 3. Atropine and 4-DAMP were more potent than pirenzepine and gallamine in relaxing both proximal and distal bovine smooth muscle preparations. 4. These data suggest that the muscarinic sites on the smooth muscle of bovine airways are of the M3 subtype.     

Ultrastructural aspects ofTrypanosoma (Megatrypanum) freitasi in co-cultivation with mammalian cells

Cultures ofTrypanosoma (Megatrypanum) freitasi with L929 mouse fibroblasts at 27.5°C were examined by scanning and transmission electron microscopy in an attempt to clarify the processes of colony formation by the epimastigotes and of their attachment to substrata. It was seen that the flagellates occupy intercellular spaces and do not associate with intact fibroblasts. As the trypanosome population increases, ever larger portions of the substratum are cleared of fibroblasts and occupied by conglomerates of epimastigote colonies consisting of about a dozen organisms that attach to the substratum by their anterior extremities and form pyramidal clusters. Attachment of the epimastigotes involves the flagellar membrane, which becomes extraordinarily enlarged and assumes various aspects of broad sheets, filaments and loops over the substratum or along the flagellum, which exhibits a shortened axoneme. Desmosome or hemidesmosome plaques are present when the attachment takes place between membranes or between the membrane and the substratum.Supported by grants from CNPq and FINEP     

The telephone survey: a methodological strategy for obtaining information

Studies have shown that students and the general population have little knowledge about nursing schools and the nursing profession. This study investigates the extent to which a sample of the population of Brazil is aware of the existence of nursing schools, and how they have obtained this information. Data were collected by telephone interviews. The sample consisted of 326 subjects whose telephone numbers were taken from the telephone book. Analysis showed that 73% of the subjects were aware of the existence of two nursing schools in the city; however, 65.03% did not know the names of these schools. Direct communication with friends and family, as well as indirect communication by television and advertising, were the sources of information mentioned by those questioned.     

Crown of microfilaments in the extending cytoplasmic processes of medulloblastoma glial progenitors.

Microfilaments and microtubules play a part in the extension of neuronal processes but their roles in the formation of glial processes have not yet been determined. The objectives of this study were to determine the organization of microfilaments in differentiating glial progenitors (RB2 cells) and to study the effects of microfilament or microtubule disruption on process extension. Intense F-actin staining (crown of microfilaments) was observed at the leading edge of a small extending conical tip in differentiating RB2 cells, but was absent in process-bearing TE671 rhabdomyosarcoma cells. No significant difference was noted in the mean number of TE671 cells with processes treated with a microfilament disrupter from that of similarly treated controls. In contrast, a significant difference was noted in the mean number of RB2 cells with processes after microfilament disruption treatment from that of similarly treated controls. Microtubule disruption arrested extension and caused process retraction in both cell types. The results of this study demonstrate that microtubules play an equally important part in the extension and stabilization of the RB2 and TE671 processes. Moreover, the crown of microfilaments concentrated in the glial RB2 process (and not in the TE671 process) may be critical to its extension during differentiation.     

Prolactin,growth hormone and insulin-like growth factor-l in newborn children of smoking mothers*

OBJECTIVE Since maternal smoking causes fetal circulatory abnormalities, as well as disturbances of the maternal endocrine equilibrium, we measured the PRL, hGH and insulin-like growth factor-l (IGF-I) concentrations in the cord and venous blood of neonates of smoking mothers to determine whether or not the tobacco smoke affects the endocrine status of the neonate. DESIGN The above hormones were measured in the cord blood of the newborns of both smoking and non-smoking mothers. Also, PRL and hGH were determined at 24 and 72 hours after birth in newborns of both groups. PATIENTS Fifty-three newborns of smoking and 47 newborns of non-smoking mothers were investigated. Seventeen of the newborns of the smoking and 21 of the nonsmoking mothers were preterm. The remainder were full-term. MEASUREMENTS PRL was measured with a solid-phase immunoradiometric assay, hGH with a solid-phase two-site immunoradiometric assay and IGF-I with a solid-phase radioimmunoassay after extraction with acid-etha-nol. RESULTS The median value of PRL in the 17 preterm newborns of smoking mothers was 4941 mU/l (range 1322-7230), whereas in the 21 preterm newborns of nonsmoking mothers it was 2013 mU/l (range 243-4740) (P = 0 0002). The median hGH value in the above subjects was 1020 mU/l (range 35 2-208 4) and 59 8 mU/l (range 11 6-134-2), respectively (P = 0 0039). The median IGF-I was 580 7 U/l (range 253 2-4851 1) and 530 6 U/l (range 239 6-3591 5), respectively (P = 0 429). In the 36 full-term newborns of smoking mothers the median PRL value was 5171 mU/l (range 2074-7530), whereas in the 26 full-term newborns of non-smoking mothers it was 5081 (range 244-6540) (P = 0 048). The median hGH was 69 6 mU/l (range 42 3-280 0) and 32 2 mU/l (range 6 2-200 0), respectively (P = 0 0031). Also, the median IGF-I value was 926 3 U/l (range 348 5-5344 7) and 462 1 U/l (range 250 2-1578 7), respectively (P = 00024). On the 3rd day the PRL in the preterm neonates of both smoking and non-smoking mothers showed the same 16-5% drop, and thus the difference between the groups was maintained. A similar reduction in the hormone levels was observed in the full term neonates. CONCLUSIONS The findings indicate that the maternal tobacco-smoking causes disturbances of the endocrine status of the fetus, as shown by the increased levels of PRL, hGH and IGF-I, which are more pronounced between 30 and 37 weeks of gestation than at term.     

Effect of intervention to improve breastfeeding technique on the frequency of exclusive breastfeeding and lactation-related problems.

This randomized clinical trial compared frequencies of exclusive breastfeeding and lactation-related problems during the first 30 days among 74 mothers who received a 30-minute counseling session on breastfeeding technique in the maternity ward, and 137 controls. The frequency of exclusive breastfeeding among mothers who had received intervention was similar to controls by 7 days (79.7% vs 82.5%, respectively) and 30 days (60.8% vs 53.3%). There was no difference between groups in the frequency of sore nipples at 7 and 30 days, in breast engorgement and mastitis, and in the quality of breastfeeding technique at 30 days. Therefore, a single intervention at maternity was not sufficient to improve breastfeeding technique, increase exclusive breastfeeding rates, and reduce the incidence of breastfeeding problems during the first month.     

Cholesterol-sensing receptors, liver X receptor alpha and beta, have novel and distinct roles in osteoclast differentiation and activation.

The liver X receptor (alpha,beta) is responsible for regulating cholesterol homeostasis in cells. However, our studies using the LXRalpha-/-, LXRbeta-/-, and LXRalpha-/-beta-/- mice show that both LXRalpha and beta are also important for bone turnover, mainly by regulating osteoclast differentiation/activity. Introduction: The liver X receptors (alpha,beta) are primarily responsible for regulating cholesterol homeostasis within cells and the whole body. However, as recent studies show that the role for this receptor is expanding, we studied whether the LXRs could be implicated in bone homeostasis and development. MATERIALS AND METHODS: pQCT was performed on both male and female LXRalpha-/-, LXRbeta-/-, LXRalpha-/-beta-/-, and WT mice at 4 months and 1 year of age. Four-month-old female mice were additionally analyzed with reference to qPCR, immunohistochemistry, histomorphometry, transmission electron microscopy, and serum bone turnover markers. RESULTS: At the mRNA level, LXRbeta was more highly expressed than LXRalpha in both whole long bones and differentiating osteoblast-like MC3T3-E1 and osteoclast-like RAW 264.7 cells. Four-month-old female LXRalpha-/- mice had a significant increase in BMD because of an increase in all cortical parameters. No difference was seen regarding trabecular BMD. Quantitative histomorphometry showed that these mice had significantly more endosteal osteoclasts in the cortical bone; however, these cells appeared less active than normal cells as suggested by a significant reduction in serum levels of cross-linked carboxyterminal telopeptides of type I collagen (CTX) and a reduction in bone TRACP activity. Conversely, the female LXRbeta-/- mice exhibited no change in BMD, presumably because a significant decline in the number of the trabecular osteoclasts was compensated for by an increase in the expression of the osteoclast markers cathepsin K and TRACP. These mice also had a significant decrease in serum CTX, suggesting decreased bone resorption; however, in addition presented with an increase in the expression of osteoblast associated genes, bone formation markers, and serum leptin levels. CONCLUSIONS: Our findings show that both LXRs influence cellular function within the bone, with LXRalpha having an impact on osteoclast activity, primarily in cortical bone, whereas LXRbeta modulates trabecular bone turnover.