Bicycle helmet use among Maryland children: effect of legislation and education.

Although bicycle helmets are effective in preventing head injuries, use of helmets among children remains infrequent. In response to the bicycling deaths of two children, Howard County, Maryland, became the first US jurisdiction to mandate use of bicycle helmets for children. Schoolchildren were lectured by police about the law before its enactment. Prelaw and postlaw helmet use was observed in Howard County and two control counties: Montgomery (which sponsored a community education program) and Baltimore County (no helmet activities). Prelaw crude helmet use rates for children were 4% (95% confidence interval [CI] 0% to 10%) for Howard, 8% (95% CI 3% to 13%) for Montgomery, and 19% (95% CI 5% to 33%) for Baltimore. Postlaw rates were 47% (95% CI 32% to 62%), 19% (95% CI 11% to 27%), and 4% (95% CI 0 to 11%), respectively. The rate of bicycle helmet use by Howard County children is now the highest documented for US children. A similar increase in helmet use among children younger than 16 years nationwide could prevent about 100 deaths and 56,000 emergency-department-treated head injuries annually. Physicians and other health professionals should consider proposing and supporting the Howard County approach in their communities.

Does acute hyperglycemia alter rat aortic depressor nerve function?

Because it is not known where in the reflex arch, i.e., afference, central nervous system or efferences, hyperglycemia affects baroreflex function, the present study examined the effect of short-term (30 min) hyperglycemia on aortic depressor nerve function measured by a mean arterial pressure vs aortic depressor nerve activity curve, fitted by sigmoidal regression, or by cross-spectral analysis between mean arterial pressure and aortic depressor nerve activity. Anesthetized male Wistar rats received an intravenous bolus (0.25 mL) injection, followed by 30 min of infusion (1 mL/h) of 30% glucose (N = 14). Control groups received a bolus injection and infusion of 0.9% saline (N = 14), or 30% mannitol (N = 14). Glucose significantly increased both blood glucose and plasma osmolarity (P < 0.05). Mean arterial pressure did not change after glucose, saline or mannitol infusion. Mean arterial pressure vs nerve activity curves were identical before and 10 and 30 min after the beginning of glucose, saline or mannitol infusion. Slow (0.3 Hz) oscillations of arterial pressure were induced by controlled bleeding, and cross-spectral analysis was applied to arterial pressure and aortic nerve activity. Transfer function magnitude (aortic depressor nerve activity/mean arterial pressure ratio in the frequency domain) was calculated as an index of gain of the aortic depressor nerve. Transfer function magnitude was similar in all groups during induced or spontaneous oscillations of arterial pressure. In conclusion, the present study demonstrates, by means of two different approaches for assessing baroreceptor function, that aortic depressor nerve activity was not altered by short-term (30 min) hyperglycemia.

Age-age and trait-trait correlations for Eucalyptus grandis Hill ex Maiden and their implications for optimal selection age and design of clonal trials.

Previous results from seven locations of Eucalyptus grandis clonal trials in Colombia supported the a priori contention of sub-dividing them into three different environmental zones for testing and deployment. Within these zones, the determination of age-age genetic correlations for both height and mean annual increment (MAI) showed that strong age-age correlations are present for a rotation age of 6 years starting at 3 years age and, thereafter, suggesting this age as appropriate for selection. This biological selection age coincides with an "economical" age for selection based on discounted selection efficiency in perpetuity, considering a range of interest rates between 10% and 20%. High genetic correlations between wood density at 3 years and 6 years as well as the lack of genetic correlation between this trait and growth traits, also favors selection at age 3 and facilitates breeding strategies that consider the utilization of both traits for improvement. A simulation of optimal clonal test designs indicated that by using six locations and six blocks per location in a single-tree plot design, between 80% and 90% of the maximum selection efficiency could be obtained. This type of design allows testing of a large number of genotypes across a reasonable number of locations in a cost-effective manner.

Variance component estimation techniques compared for two mating designs with forest genetic architecture through computer simulation.

Computer simulation was used to compare minimum variance quadratic estimation (MIVQUE), minimum norm quadratic unbiased estimation (MINQUE), restricted maximum likelihood (REML), maximum likelihood (ML), and Henderson's Method 3 (HM3) on the basis of variance among estimates, mean square error (MSE), bias and probability of nearness for estimation of both individual variance components and three ratios of variance components. The investigation also compared three procedures for dealing with negative estimates and included the use of both individual observations and plot means as the experimental unit of the analysis. The structure of data simulated (field design, mating designs, genetic architecture and imbalance) represented typical analysis problems in quantitative forest genetics. Results of comparing the estimation techniques demonstrated that: estimates of probability of nearness did not discriminate among techniques; bias was discriminatory among procedures for dealing with negative estimates but not among estimation techniques (except ML); sampling variance among estimates was discriminatory among procedures for dealing with negative estimates, estimation techniques and unit of observation; and MSE provided no additional information to variance of the estimates. HM3 and REML were the closest competitors under these criteria; however, REML demonstrated greater robustness to imbalance. Of the three negative estimate procedures, two are of practical significance and guidelines for their application are presented. Estimates from individual observations were always preferable to those from plot means over the experimental levels of this study.

The incidence of fall injury events among the elderly in a defined population.

Falls are a leading cause of death from injury among older persons in the United States, and about one in three older persons falls each year. Yet, reliable estimates of the incidence of fall injury events in a population-based setting are not readily available. Therefore, the authors analyzed population-based surveillance data, between July 1985 and June 1987, from the Study to Assess Falls Among the Elderly, Miami Beach, Florida. The rate of fall injury events coming to acute medical attention increased exponentially with age for both elderly men and women (predominantly white), reaching a high for those aged 85 years or more of 138.5 per 1,000 for males and 158.8 per 1,000 for females. Compared with males, females had a higher incidence of fractures other than skull. Males were nearly twice as likely to die, however, following a fall injury event than were females. Of those fall injury events identified through the surveillance system, about 42% resulted in hospital admission. The mean length of hospital stay was 11.6 days overall and was 15.5 days for hip fracture, 9.8 days for skull fracture/intracranial injury, 11.2 days for all other fractures, and 9.1 days for all other injuries. About 50% of fall injury events that occurred at home and required hospital admission resulted in a person being discharged to a nursing home.

Does acute hyperglycemia alter rat aortic depressor nerve function?

Because it is not known where in the reflex arch, i.e., afference, central nervous system or efferences, hyperglycemia affects baroreflex function, the present study examined the effect of short-term (30 min) hyperglycemia on aortic depressor nerve function measured by a mean arterial pressure vs aortic depressor nerve activity curve, fitted by sigmoidal regression, or by cross-spectral analysis between mean arterial pressure and aortic depressor nerve activity. Anesthetized male Wistar rats received an intravenous bolus (0.25 mL) injection, followed by 30 min of infusion (1 mL/h) of 30 percent glucose (N = 14). Control groups received a bolus injection and infusion of 0.9 percent saline (N = 14), or 30 percent mannitol (N = 14). Glucose significantly increased both blood glucose and plasma osmolarity (P < 0.05). Mean arterial pressure did not change after glucose, saline or mannitol infusion. Mean arterial pressure vs nerve activity curves were identical before and 10 and 30 min after the beginning of glucose, saline or mannitol infusion. Slow (0.3 Hz) oscillations of arterial pressure were induced by controlled bleeding, and cross-spectral analysis was applied to arterial pressure and aortic nerve activity. Transfer function magnitude (aortic depressor nerve activity/mean arterial pressure ratio in the frequency domain) was calculated as an index of gain of the aortic depressor nerve. Transfer function magnitude was similar in all groups during induced or spontaneous oscillations of arterial pressure. In conclusion, the present study demonstrates, by means of two different approaches for assessing baroreceptor function, that aortic depressor nerve activity was not altered by short-term (30 min) hyperglycemia.