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Biomedical subjects

S D Simon

Publications and source records attributed to S D Simon.

At least 55 records · Page 3Linked to original sources
PubMedDate not supplied

Is the randomized clinical trial the gold standard of research?

All research has flaws. Some flaws are so trivial that the research can still stand as the definitive study. Other flaws prevent a study from being definitive, but the study still provides useful guidance in the context of other research. Some flaws are so serious that the research provides no useful information at all. The tricky part is not finding flaws in the research but in deciding to what extent the flaws erode the credibility of the research. In general, the use of RCTs can add substantial credibility to a research study. There are calls for greater use of RCTs in many areas, such as surgery (Baum, 1999) and psychiatry (Andrews, 1999). Of course, nonrandomized trials are an important complement to RCTs when the latter are ethically inappropriate or logistically impossible (Black, 1996). Failure to use randomization or blinding, however, is not a fatal flaw. Furthermore, the artificial nature of RCTs will often restrict their applicability to overly simple interventions. When RCTs focus on narrow patient groups or exclude important segments of the population, there may be difficulty in generalizing their results. So it would be a mistake to label the RCT as a gold standard for all research. A silver standard may be a more appropriate label.

Humans↗
PubMedDate not supplied

Semen analysis of military personnel associated with military duty assignments.

A collaborative study between the U.S. Army Biomedical Research and Development Laboratory (USABRDL) and the National Institute for Occupational Safety and Health (NIOSH) was designed to assess fecundity of male artillery soldiers with potential exposures to airborne lead aerosols. Potential exposure assessment was based upon information provided in an interactive questionnaire. It became apparent from extensive questionnaire data that many soldiers in the initial control population had potentially experienced microwave exposure as radar equipment operators. As a result, a third group of soldiers without potential for lead or microwave exposures, but with similar environmental conditions, was selected as a comparison population. Blood hormone levels and semen analyses were conducted on artillerymen (n = 30), radar equipment operators (n = 20), and the comparison group (n = 31). Analysis of the questionnaire information revealed that concern about fertility problems motivated participation of some soldiers with potential artillery or microwave exposures. Although small study population size and the confounding variable of perceived infertility limit the reliability of the study, several statistically significant findings were identified. Artillerymen who perceived a possible fertility concern demonstrated lower sperm counts/ejaculate (P = 0.067) and lower sperm/mL (P = 0.014) than the comparison group. The group of men with potential microwave exposures demonstrated lower sperm counts/mL (P = 0.009) and sperm/ejaculate (P = 0.027) than the comparison group. Variables used to assess endocrine, accessory sex gland, and sperm cell function were not different than the comparison group. Additional studies, incorporating larger numbers of individuals, should be performed in order to more optimally characterize potential lead and microwave exposure effects on male fecundity.

Adult↗
PubMedDate not supplied

Male reproductive effects of lead, including species extrapolation for the rabbit model.

The effects of elevated blood lead on semen quality were evaluated in the rabbit model and compared to published effects in humans. Mature, male rabbits were given lead acetate by subcutaneous injection in the dose range of 0 to 3.85 mg/kg on a Monday-Wednesday-Friday basis. In each of eight treatment groups, a dosing regimen was developed to produce blood lead levels of 0, 20, 40, 50, 70, 80, 90, and 110 microg/dL. A 5-week pre-exposure period was followed by a 15-week exposure testing period allowing for response through six cycles of the seminiferous epithelium. Semen analyses revealed that increased blood lead levels were associated with adverse changes in the sperm count, ejaculate volume, percent motile sperm, swimming velocities, and morphology. Hormonal responses were minimal. Testicular pathology revealed a dose-dependent inhibition of spermiation. For six measures of semen quality, threshold estimates ranged from 16 to 24 microg/dL. Using the species extrapolation factor derived in this study, a rabbit dose would have to be divided by 1.56 to obtain the equivalent human dose for an equal percentage decrease in sperm concentration; however, rabbits are 3.75 more sensitive in terms of absolute decrease in sperm count for a given blood lead level.

Animals↗
PubMedDate not supplied

Reproductive function in relation to duty assignments among military personnel.

As a follow-up to the pilot study of semen quality of soldiers with various military assignments a larger, more complete study was conducted. Soldiers were recruited at Fort Hood, Texas. Thirty-three men were exposed to radar as part of their duty assignment in the Signal Corps, 57 men were involved with firing the 155 mm howitzer (potential lead exposure), and 103 soldiers had neither lead nor radar exposure and served as the comparison control group. Both serum and urinary follicle-stimulating hormone and luteinizing hormone and serum, salivary, and urine testosterone levels were determined in all men. A complete semen analysis was conducted on each soldier. For statistical analysis, the primary study variables were: sperm concentration, sperm/ejaculate, semen volume, percent normal morphology, percent motile, percent viable (both vital stain and hypoosmotic swelling), curvilinear velocity, straight-line velocity, linearity, sperm head length, width, area, and perimeter. Variables were adjusted for significant confounders (e.g., abstinence, sample age, race). No statistical differences (P < 0.05) were observed in any measurement. While these results are in agreement with two previous studies assessing soldiers firing the 155-mm howitzer, they contradict our previous report indicating that radar exposure caused a significant decrease in sperm numbers. A possible explanation is that the radar exposure in this study was that used in Signal Corps operations while the men in the previous study were using different radar as part of military intelligence operations. The data presented here in men firing the 155-mm howitzer combined with the results from the previous studies confirms that there are no deficits in semen quality in these men. The contradiction between the results of the radar exposure studies indicates that more data are needed to evaluate the relationship of military radar and male reproductive health.

Adult↗
PubMedDate not supplied

Transitioning preterm infants with nasogastric tube supplementation: increased likelihood of breastfeeding.

OBJECTIVE: To compare nasogastric tube and bottle supplementation as two means of transitioning preterm infants to breastfeeding within an established breastfeeding support program. DESIGN: Prospective, randomized controlled trial; mothers and health care providers, who were not blinded. SETTING: Metropolitan private regional perinatal center; 40-bed intensive-care nursery. PARTICIPANTS: Eighty-four preterm breastfed infants whose birth weight was 1,000-2,500 g. MAIN OUTCOME MEASURES: Rates of exclusive and partial breastfeeding at discharge from the intensive-care nursery, and at 3 days, 3 months, and 6 months after discharge. RESULTS: Compared with infants receiving bottle supplements, infants receiving nasogastric tube supplements were more likely to be breastfeeding at discharge and at 3 days, 3 months and 6 months, after adjusting for confounding variables. Odds ratios (confidence intervals = 95%) showed that the group receiving nasogastric supplements was 4.5 times (1.4 to 15) more likely to be breastfed at discharge and 9.4 times more likely to be fully breastfed (3.1 to 28.4). There were significantly fewer apnea and bradycardia episodes in the group receiving nasogastric supplements, although they had more episodes that required stimulation for resolution. Groups were not different with respect to length of hospitalization and infant weight at discharge. CONCLUSIONS: Using nasogastric tube supplementation during transition to oral feedings increases the likelihood of breastfeeding at discharge, 3 days, 3 months, and 6 months. This intervention requires a program with skilled personnel and an environment that allows the mother and infant to be in close physical proximity. Further study should investigate differences in the effects on maternal confidence, imprinting, and suck mechanism when preterm infants are bottle fed and breastfed.

Adolescent↗
PubMedDate not supplied

Interpreting positive studies.

When examining the results of a positive research study, one needs to consider two issues of clinical relevance. First, is the outcome measure of direct interest to patients, or is it clearly linked to a measure of direct interest to patients? Second, is the difference large enough to lie outside the range of clinical indifference? Don't accept the findings of a positive research study without a careful consideration of clinical relevance.

Biomarkers↗
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Understanding the odds ratio and the relative risk.

Both the odds ratio and the relative risk compare the relative likelihood of an event occurring between two groups. The relative risk is easier to interpret and is consistent with general intuition. Some designs, however, allow only for the calculation of the odds ration. Covariate adjustment is easier for an odds ratio. Finally, the odds ratio avoids ambiguity by being invariant to lthe labeling of the outcome measure. The Table summarizes the advantages and disadvantages of the odds ratio and relative risk. Whe reading research that summarizes data using odds ratios, or relative risks, be aware of the limitations of booth of these measures.

Odds Ratio↗
PubMedDate not supplied

Longitudinal study of semen quality of unexposed workers. Sperm motility characteristics.

As part of a longitudinal study of human semen characteristics of unexposed workers, sperm motility measurements were made using computer-assisted sperm analysis. Motility analyses were conducted on monthly samples from 46 men for 9 months. Measurements of curvilinear velocity, straight-line velocity (VSL), linearity, amplitude of lateral head displacement (ALH), and beat-cross frequency were collected in eight microscope fields for each semen sample. The variability within a sample, between samples from the same individual (between monthly samples), and between individuals were calculated using a nested analysis of variance. For all sperm motility measurements, at least 90% of the variation was observed between cells within a semen sample. For all variables, the component of variation between subjects was the smallest percentage (ranging from 1.3% for ALH to 4.0% for VSL). When sample means were used in the nested analysis of variation, at least 75% of the variation was observed between samples from the same individual. These results will be useful in power calculations for future studies.

Adult↗
PubMedDate not supplied

Longitudinal study of semen quality of unexposed workers: sperm head morphometry.

As part of a longitudinal study of human semen characteristics of unexposed workers, sperm head measurements were made using image analysis (Image Technologies Corp., Deer Park, NY). Morphometry was conducted on monthly samples from 45 men for 9 months. Measurements of area, perimeter, length, width, the width-length ratio, and the oval factor (4 [pi] area/perimeter) of 100 sperm heads per sample were obtained. The variability within a sample, between monthly samples from the same individual, and between individuals were calculated for each parameter. Tolerance intervals for each parameter were calculated, and are expected to contain 75% of all individual measurements. Similar intervals were calculated for the means and coefficients of variation of a semen sample. The largest source of variability was attributed to individual cell variation within a semen sample.

Adult↗