Including multiple imputation in a sensitivity analysis for clinical trials with treatment failures

When treatment failures occur during the course of a clinical trial, the treatment regimen following failure may be changed. This change in therapy complicates comparisons among the original treatment arms. As in some clinical trials with dropouts, intent-to-treat analysis can yield a large bias. We examine the use of multiple imputation to replace observations after treatment failure has occurred. As a sensitivity analysis, this approach is compared to existing methods for handling treatment failures - removing treatment failure subjects, removing data after the onset of treatment failure, and imputation the last observation prior to treatment failure for all subsequent observations - in addition to an analysis of all collected data based on randomized treatment assignment. A data set from the Asthma Clinical Research Network is used to demonstrate the methods.

Long-term inhaled corticosteroids in preschool children at high risk for asthma

BACKGROUND

It is unknown whether inhaled corticosteroids can modify the subsequent development of asthma in preschool children at high risk for asthma.

METHODS

We randomly assigned 285 participants two or three years of age with a positive asthma predictive index to treatment with fluticasone propionate (at a dose of 88 mug twice daily) or masked placebo for two years, followed by a one-year period without study medication. The primary outcome was the proportion of episode-free days during the observation year.

RESULTS

During the observation year, no significant differences were seen between the two groups in the proportion of episode-free days, the number of exacerbations, or lung function. During the treatment period, as compared with placebo use, use of the inhaled corticosteroid was associated with a greater proportion of episode-free days (P=0.006) and a lower rate of exacerbations (P<0.001) and of supplementary use of controller medication (P<0.001). In the inhaled-corticosteroid group, as compared with the placebo group, the mean increase in height was 1.1 cm less at 24 months (P<0.001), but by the end of the trial, the height increase was 0.7 cm less (P=0.008). During treatment, the inhaled corticosteroid reduced symptoms and exacerbations but slowed growth, albeit temporarily and not progressively.

CONCLUSIONS

In preschool children at high risk for asthma, two years of inhaled-corticosteroid therapy did not change the development of asthma symptoms or lung function during a third, treatment-free year. These findings do not provide support for a subsequent disease-modifying effect of inhaled corticosteroids after the treatment is discontinued. (ClinicalTrials.gov number, NCT00272441.).

Orthopaedic in-training examination scores: a correlation with USMLE results

BACKGROUND

Both the United States Medical Licensing Examination and the Orthopaedic In-Training Examination measure factual recall as well as interpretative and problem-solving skills. The former examination is used to a variable degree by postgraduate programs in resident selection. Orthopaedic In-Training Examination scores are one measure of the medical knowledge of residents and are used by all American orthopaedic residency programs on a yearly basis. This investigation was performed to retrospectively review Orthopaedic In-Training Examination scores of orthopaedic residents who took the examination in our program. In addition, we sought to determine whether a relationship existed between performance on the Orthopaedic In-Training Examination and the United States Medical Licensing Examinations taken while in medical school.

METHODS

The records of each orthopaedic resident who took the examination from November 1993 through November 2000 were reviewed. Correlation coefficients and 95% confidence intervals were calculated to assess the relationship, if any, between the Orthopaedic In-Training Examination percentiles and the three-digit scores on the Step-1 and Step-2 United States Medical Licensing Examination. In addition, examination scores were evaluated longitudinally from year-in-training 1 through 4.

RESULTS

A significant moderate-sized correlation was found between United States Medical Licensing Examination Step-2 scores and Orthopaedic In-Training Examination score percentiles (p < 0.05); however, with the numbers available, no correlation was seen between United States Medical Licensing Examination Step-1 scores and Orthopaedic In-Training Examination scores. The mean Orthopaedic In-Training Examination scores were in the 66th percentile for year-in-training 1, the 53rd percentile for year 2, the 57th percentile for year 3, and the 50th percentile for year 4. Residents in the laboratory for one year scored in the 88th percentile while in the laboratory (year 0), in the 86th percentile in year 1, and in the 48th percentile in year 4.

CONCLUSION

Although Step-1 United States Medical Licensing Examination scores have been used by our department as a major factor in resident selection historically, our data failed to reveal a significant correlation with performance on the Orthopaedic In-Training Examination. The decrease in Orthopaedic In-Training Examination scores over time for our residents who worked in the laboratory is most likely attributable to multiple factors, including clinical workload hours.

Response profiles to fluticasone and montelukast in mild-to-moderate persistent childhood asthma

BACKGROUND

Outcome data are needed to base recommendations for controller asthma medication use in school-aged children.

OBJECTIVE

We sought to determine intraindividual and interindividual response profiles and predictors of response to an inhaled corticosteroid (ICS) and a leukotriene receptor antagonist (LTRA).

METHODS

An ICS, fluticasone propionate (100 mug twice daily), and an LTRA, montelukast (5-10 mg nightly, age dependent), were administered to children ages 6 to 17 years with mild-to-moderate persistent asthma using only as-needed bronchodilators in a multicenter, double-masked, 2-sequence, 16-week crossover trial. Clinical, pulmonary, and inflammatory responses to these controllers were evaluated.

RESULTS

Improvements in most clinical asthma control measures occurred with both controllers. However, clinical outcomes (asthma control days [ACDs], the validated Asthma Control Questionnaire, and albuterol use), pulmonary responses (FEV(1)/forced vital capacity, peak expiratory flow variability, morning peak expiratory flow, and measures of impedance), and inflammatory biomarkers (exhaled nitric oxide [eNO]) improved significantly more with fluticasone than with montelukast treatment. eNO was both a predictor of ACDs (P = .011) and a response indicator (P = .003) in discriminating the difference in ACD response between fluticasone and montelukast.

CONCLUSIONS

The more favorable clinical, pulmonary, and inflammatory responses to an ICS than to an LTRA provide pediatric-based group evidence to support ICSs as the preferred first-line therapy for mild-to-moderate persistent asthma in children. eNO, as a predictor of response, might help to identify individual children not receiving controller medication who achieve a greater improvement in ACDs with an ICS compared with an LTRA.

A general class of correlation coefficients for the 2 x 2 crossover design

The Pearson correlation coefficient and the Kendall correlation coefficient are two popular statistics for assessing the correlation between two variables in a bivariate sample. We indicate how both of these statistics are special cases of a general class of correlation statistics that is parameterized by gamma element of [0, 1]. The Pearson correlation coefficient is characterized by gamma = 1 and the Kendall correlation coefficient by gamma = 0, so they yield the upper and lower extremes of the class, respectively. The correlation coefficient characterized by gamma = 0.5 is of special interest because it only requires that first-order moments exist for the underlying bivariate distribution, whereas the Pearson correlation coefficient requires that second-order moments exist. We derive the asymptotic theory for the general class of sample correlation coefficients and then describe the use of this class of correlation statistics within the 2 x 2 crossover design. We illustrate the methodology using data from the CLIC trial of the Childhood Asthma Research and Education (CARE) Network.

beta-Adrenergic receptor polymorphisms and response to salmeterol

RATIONALE

Several studies suggest that patients with asthma who are homozygous for arginine at the 16th position of the beta2-adrenergic receptor may not benefit from short-acting beta-agonists.

OBJECTIVES

We investigated whether such genotype-specific effects occur when patients are treated with long-acting beta-agonists and whether such effects are modified by concurrent inhaled corticosteroid (ICS) use.

METHODS

We compared salmeterol response in patients with asthma homozygous for arginine at B16 (B16Arg/Arg) with those homozygous for glycine at B16 (B16Gly/Gly) in two separate cohorts. In the first, subjects were randomized to regular therapy with salmeterol while simultaneously discontinuing ICS therapy. In the second, subjects were randomized to regular therapy with salmeterol while continuing concomitant ICS.

RESULTS

In both trials, B16Arg/Arg subjects did not benefit compared with B16Gly/Gly subjects after salmeterol was initiated. In the first cohort, compared with placebo, the addition of salmeterol was associated with a 51.4 L/min lower A.M. peak expiratory flow (PEF; p = 0.005) in B16Arg/Arg subjects(salmeterol, n = 12; placebo, n = 5) as compared with B16Gly/Gly subjects (salmeterol, n = 13; placebo, n = 13). In the second cohort, B16Arg/Arg subjects treated with salmeterol and ICS concurrently (n = 8) had a lower A.M. PEF (36.8 L/min difference, p = 0.048) than B16Gly/Gly subjects (n = 22) treated with the same regimen. In addition, B16 Arg/Arg subjects in the second cohort had lower FEV1 (0.42 L, p = 0.003), increased symptom scores (0.2 units, p = 0.034), and increased albuterol rescue use (0.95 puffs/d, p = 0.004) compared with B16Gly/Gly subjects.

CONCLUSIONS

Relative to B16Gly/Gly patients with asthma, B16Arg/Arg patients with asthma may have an impaired therapeutic response to salmeterol in either the absence or presence of concurrent ICS use. Investigation of alternate treatment strategies may benefit this group.

Association of criteria pollutants with plasma hemostatic/inflammatory markers: a population-based study

To elucidate the health effects of air pollution, the short-term association of criteria pollutants (particles <10 microm in diameter [PM(10)], O(3), CO, NO(2), and SO(2)) with hemostatic and inflammatory markers were examined using a population-based sample of 10,208 middle-age males and females of the biracial cohort of Atherosclerosis Risk in Communities (ARIC) study. For each participant, we calculated the following pollutant exposures 1-3 days prior to the randomly allocated cohort examination date: PM(10), CO, NO(2), and SO(2) as 24-h averages, and O(3) as an 8-h average of the hourly measures. The hemostatic/inflammatory factors included fibrinogen, factor VIII-C, von Willebrand factor (vWF), albumin, and white blood cell count (WBC). Linear regression models were used to adjust for cardiovascular disease (CVD) risk factors, demographic and socioeconomic variables, and relevant meteorological variables. One standard deviation (SD) increment of PM(10) (12.8 microg/m(3)) was significantly (P < 0.05) associated with 3.93% higher of vWF among diabetics and 0.006 g/dl lower of serum albumin among persons with a history of CVD. One SD increment of CO (0.60 p.p.m.) was significantly (P < 0.01) associated with 0.018 g/dl lower of serum albumin. Significant curvilinear associations, indicative of threshold effects, for PM(10) with factor VIII-C, O(3) with fibrinogen and vWF, and SO(2) with factor VIII-C, WBC, and serum albumin were found. This population-based study suggest that the hemostasis/inmflammation markers analyzed, which are linked to higher risk of CHD, are associated adversely with environmentally relevant ambient pollutants, with the strongest associations in the upper range of the pollutant distributions, and in persons with a positive history of diabetes and CHD.

Daily versus as-needed corticosteroids for mild persistent asthma

BACKGROUND

Although guidelines recommend daily therapy for patients with mild persistent asthma, prescription patterns suggest that most such patients use these so-called controller therapies intermittently. In patients with mild persistent asthma, we evaluated the efficacy of intermittent short-course corticosteroid treatment guided by a symptom-based action plan alone or in addition to daily treatment with either inhaled budesonide or oral zafirlukast over a one-year period.

METHODS

In a double-blind trial, 225 adults underwent randomization. The primary outcome was morning peak expiratory flow (PEF). Other outcomes included the forced expiratory volume in one second (FEV1) before and after bronchodilator treatment, the frequency of exacerbations, the degree of asthma control, the number of symptom-free days, and the quality of life.

RESULTS

The three treatments produced similar increases in morning PEF (7.1 to 8.3 percent; approximately 32 liters per minute; P=0.90) and similar rates of asthma exacerbations (P=0.24), even though the intermittent-treatment group took budesonide, on average, for only 0.5 week of the year. As compared with intermittent therapy or daily zafirlukast therapy, daily budesonide therapy produced greater improvements in pre-bronchodilator FEV1 (P=0.005), bronchial reactivity (P<0.001), the percentage of eosinophils in sputum (P=0.007), exhaled nitric oxide levels (P=0.006), scores for asthma control (P<0.001), and the number of symptom-free days (P=0.03), but not in post-bronchodilator FEV1 (P=0.29) or in the quality of life (P=0.18). Daily zafirlukast therapy did not differ significantly from intermittent treatment in any outcome measured.

CONCLUSIONS

It may be possible to treat mild persistent asthma with short, intermittent courses of inhaled or oral corticosteroids taken when symptoms worsen. Further studies are required to determine whether this novel approach to treatment should be recommended.

Sputum eosinophil counts predict asthma control after discontinuation of inhaled corticosteroids

BACKGROUND

Although inhaled corticosteroids (ICSs) are effective in preventing deterioration in asthma control, at least half of subjects with mild-to-moderate asthma will remain stable when these agents are discontinued.

OBJECTIVE

We sought to determine whether noninvasive markers of inflammation predict which individuals maintain asthma control after discontinuation of ICSs.

METHODS

We analyzed data obtained from 164 subjects with mild-to-moderate asthma who participated in a 16-week trial comparing the effects of continued ICS use with the effects of a switch to salmeterol or placebo.

RESULTS

In comparison with continued ICS use, a switch to salmeterol or placebo was associated with increased rates of asthma deterioration over 16 weeks (9.3% vs 24.1% and 37.5%, respectively; P = .04 and P < .001, respectively). We found that neither exhaled nitric oxide nor methacholine PC 20 , when measured at randomization or 2 weeks after randomization, were significant predictors of subsequent asthma control in subjects who discontinued ICSs. However, both induced sputum eosinophil counts measured 2 weeks after a switch from ICS to placebo and changes in sputum eosinophil counts from before cessation of ICSs to after a switch to placebo predicted subsequent asthma deterioration (area under the receiver-operating characteristic curve, 0.771 [ P < .001] and 0.825 [ P < .001], respectively).

CONCLUSION

On the basis of a model treatment strategy, we estimate that allocating subjects to ICS therapy on the basis of changes in sputum eosinophil counts after a trial discontinuation could allow 48% of subjects with mild-to-moderate asthma to discontinue ICS therapy without an increased risk of asthma deterioration over a period of at least 14 weeks.

Characterization of within-subject responses to fluticasone and montelukast in childhood asthma

BACKGROUND

Responses to inhaled corticosteroids (ICSs) and leukotriene receptor antagonists (LTRAs) vary among asthmatic patients.

OBJECTIVE

We sought to determine whether responses to ICSs and LTRAs are concordant for individuals or whether asthmatic patients who do not respond to one medication respond to the other.

METHODS

Children 6 to 17 years of age with mild-to-moderate persistent asthma were randomized to one of 2 crossover sequences, including 8 weeks of an ICS, fluticasone propionate (100 microg twice daily), and 8 weeks of an LTRA, montelukast (5-10 mg nightly depending on age), in a multicenter, double-masked, 18-week trial. Response was assessed on the basis of improvement in FEV 1 and assessed for relationships to baseline asthma phenotype-associated biomarkers.

RESULTS

Defining response as improvement in FEV 1 of 7.5% or greater, 17% of 126 participants responded to both medications, 23% responded to fluticasone alone, 5% responded to montelukast alone, and 55% responded to neither medication. Compared with those who responded to neither medication, favorable response to fluticasone alone was associated with higher levels of exhaled nitric oxide, total eosinophil counts, levels of serum IgE, and levels of serum eosinophil cationic protein and lower levels of methacholine PC(20) and pulmonary function; favorable response to montelukast alone was associated with younger age and shorter disease duration. Greater differential response to fluticasone over montelukast was associated with higher bronchodilator use, bronchodilator response, exhaled nitric oxide levels, and eosinophil cationic protein levels and lower methacholine PC(20) and pulmonary function values.

CONCLUSIONS

Response to fluticasone and montelukast vary considerably. Children with low pulmonary function or high levels of markers associated with allergic inflammation should receive ICS therapy. Other children could receive either ICSs or LTRAs.

Statistical issues in clinical trials that involve the double-blind, placebo-controlled food challenge

The double-blind, placebo-controlled food challenge is a rigorous tool that has become popular for evaluating adverse reactions to foods. The standard use of the double-blind, placebo-controlled food challenge has been to document food allergies for individual patients, but it recently has been gaining acceptance as a procedure for investigating the effectiveness of therapies to prevent/minimize food-induced anaphylaxis. The purpose of this study was to describe the statistical design and analysis issues for clinical trials that use the double-blind, placebo-controlled food challenge in measuring sensitivity to food allergens. Nonparametric tests for within-group and between-group comparisons are described, as well as a discrete-time survival analysis. The statistical methods are applied to simulated data from a clinical trial that compares control therapy and experimental therapy groups. The results indicate that the experimental therapy is significantly better than control in improving the tolerance to peanut flour in patients with peanut allergy. Although simple nonparametric tests for within-group and between-group comparisons are easy to apply, a discrete-time survival analysis provides the best approach because of its flexibility in accounting for important independent variables (regressors) and longitudinal data. Statistical software packages can be adapted to perform such analyses.

Empirical bayes gene screening tool for time-course or dose-response microarray data

An efficient method to reduce the dimensionality of microarray gene expression data from thousands or tens of thousands of cDNA clones down to a subset of the most differentially expressed cDNA clones is essential in order to simplify the massive amount of data generated from microarray experiments. An extension to the methods of Efron et al. [Efron, B., Tibshirani, R., Storey, J., Tusher, V. (2001). Empirical Bayes analysis of a microarray experiment. J. Am. Statist. Assoc. 96:1151-1160] is applied to a differential time-course experiment to determine a subset of cDNAs that have the largest probability of being differentially expressed with respect to treatment conditions across a set of unequally spaced time points. The proposed extension, which is advocated to be a screening tool, allows for inference across a continuous variable in addition to incorporating a more complex experimental design and allowing for multiple design replications. With the current data the focus is on a time-course experiment; however, the proposed methods can easily be implemented on a dose-response experiment, or any other microarray experiment that contains a continuous variable of interest. The proposed empirical Bayes gene-screening tool is compared with the Efron et al. (2001) method in addition to an adjusted model-based t-value using a time-course data set where the toxicological effect of a specific mixture of chemicals is being studied.

Alternatives for measuring endogenous adrenocortical activity in asthmatics treated with inhaled corticosteroids

We compared a 12-hour, hourly integrated plasma cortisol profile in asthmatics treated with a corticosteroids with a variety of modified methods based on less frequent blood sampling. Excellent agreement with the reference was observed for sampling at 10 p.m. and 8 a.m. (correlation coefficient of 0.97; 95 % confidence interval 0.97, 0.98); at 9 p.m. and 7 a.m. (r = 0. 95; 0. 94, 0.96); at 11 p.m. and 7 a.m. (r = 0.94; 0.93, 0.95); every 2 hours (r = 0. 96; 0.96, 0.97); and every 3 hours (r = 0. 91, 0.91, 0.93). The two-sample alternatives (10 p.m/8 a.m. and 9 p.m/7 a.m.) are accurate, as well as more convenient, economical, and practical.

Use of regularly scheduled albuterol treatment in asthma: genotype-stratified, randomised, placebo-controlled cross-over trial

BACKGROUND

The issue of whether regular use of an inhaled beta2-adrenergic agonist worsens airflow and clinical outcomes in asthma is controversial. Retrospective studies have suggested that adverse effects occur in patients with a genetic polymorphism that results in homozygosity for arginine (Arg/Arg), rather than glycine (Gly/Gly), at aminoacid residue 16 of the beta2-adrenergic receptor. However, the existence of any genotype-dependent difference has not been tested in a prospective clinical trial.

METHODS

Patients with mild asthma, not using a controller medication, were enrolled in pairs matched for forced expiratory volume in 1 s (FEV1) according to whether they had the Arg/Arg (n=37; four of 41 matches withdrew before randomisation) or Gly/Gly (n=41) genotype. Regularly scheduled treatment with albuterol or placebo was given in a masked, cross-over design, for 16-week periods. During the study, as-needed albuterol use was discontinued and ipratropium bromide was used as needed. Morning peak expiratory flow rate (PEFR) was the primary outcome variable. The primary comparisons were between treatment period for each genotype; the secondary outcome was a treatment by genotype effect. Analyses were by intention to treat.

FINDINGS

During the run-in period, when albuterol use was kept to a minimum, patients with the Arg/Arg genotype had an increase in morning PEFR of 23 L/min (p=0.0162); the change in patients with the Gly/Gly genotype was not significant (2 L/min; p=0.8399). During randomised treatment, patients with the Gly/Gly genotype had an increase in morning PEFR during treatment with regularly scheduled albuterol compared with placebo (14 L/min [95% CI 3 to 25]; p=0.0175). By contrast, patients with the Arg/Arg genotype had lower morning PEFR during treatment with albuterol than during the placebo period, when albuterol use was limited (-10 L/min [-19 to -2]; p=0.0209). The genotype-attributable treatment difference was therefore -24 L/min (-37 to -12; p=0.0003). There were similar genotype-specific effects in FEV1, symptoms, and use of supplementary reliever medication.

INTERPRETATION

Genotype at the 16th aminoacid residue of the beta2-adrenergic receptor affects the long-term response to albuterol use. Bronchodilator treatments avoiding albuterol may be appropriate for patients with the Arg/Arg genotype.

Bayesian inference for randomized clinical trials with treatment failures

During the course of a clinical trial, subjects may experience treatment failure. For ethical reasons, it is necessary to administer emergency or rescue medications for such subjects. However, the rescue medications may bias the set of response measurements. This bias is of particular concern if a subject has been randomized to the control group, and the rescue medications improve the subject's condition. The standard approach to analysing data from a clinical trial is to perform an intent-to-treat (ITT) analysis, wherein the data are analysed according to treatment randomization. Supplementary analyses may be performed in addition to the ITT analysis to account for the effect of treatment failures and rescue medications. A Bayesian, counterfactual approach, which uses the data augmentation (DA) algorithm, is proposed for supplemental analysis. A simulation study is conducted to compare the operating characteristics of this procedure with a likelihood-based, counterfactual approach based on the EM algorithm. An example from the Asthma Clinical Research Network (ACRN) is used to illustrate the Bayesian procedure.

The Prevention of Early Asthma in Kids study: design, rationale and methods for the Childhood Asthma Research and Education network

Pediatric asthma remains an important public health concern as its prevalence and cost to the health care system is rising. In order to promote innovative research in asthma therapies, the National Heart, Lung and Blood Institute created the Childhood Asthma Research and Education Network in 1999. As its first study, the steering committee of the Childhood Asthma Research and Education Network designed a randomized clinical trial to determine if persistent asthma could be prevented in children at a high risk to develop the disease. This communication presents the design of its first clinical trial, the Prevention of Asthma in Kids (PEAK) trial and the organization of the Childhood Asthma Research and Education Network that developed and implemented this trial. Studies of the natural history of asthma have shown that, in persistent asthma, the initial asthma-like symptoms and loss of lung function occur predominately during the first years of life. Therefore, in the Prevention of Asthma in Kids study, children 2 and 3 years old with a positive asthma predictive index were randomized to twice daily treatment with fluticasone 88 microg or placebo via metered-dose inhaler and Aerochamber for 2 years. The double blind treatment period was followed by a 1-year observational period. Lung function was measured by spirometry and oscillometry technique at 4-month intervals throughout the study. Bronchodilator reversibility and exhaled nitric oxide (ENO) studies were performed at the end of the treatment and observation periods. The primary outcome measure was the number of asthma-free days. Other secondary outcomes included number of exacerbations, use of asthma medications and lung function. These measures were chosen to reflect the progression of the disease from intermittent wheezing to persistent asthma and measurement of the extent of airflow limitation and airway reactivity.

Acute Effects of Moderate Intensity Resistance Exercise on Bone Cell Activity

Resistance exercise has positive effects on bone mass, but little is known about the mechanisms by which this occurs. The purpose of this study was to determine if a single bout of moderate intensity resistance exercise alters biochemical markers of bone cell activity. Indices of bone turnover were measured in nine healthy, untrained men (21.9 +/- 1.2 yrs old), before and following a single 45 minute session of resistance exercise, and during a control trial. A cross-over design was used so that all participants performed both trials in random order. Blood samples were collected immediately before, immediately after, and at 1, 8, 24, and 48 hours post exercise and analyzed for bone-specific alkaline phosphatase (BAP), type I collagen propeptide (PICP), and type I collagen N-telopeptide (sNTX). Urine from the second morning void was collected over four days (day before, day of, and two days following exercise) and analyzed for type I collagen N-telopeptide (uNTX). Exercise resulted in a significant increase (p < 0.05) in the ratio of biochemical markers of bone formation to bone resorption eight hours post exercise, largely due to a decrease in sNTX. Markers return to baseline within 24 hrs. These data suggest that moderate intensity resistance training acutely reduces bone resorption, leading to a favorable change in overall bone turnover, for at least 8 hours post exercise in untrained young men. Further work is needed to determine if long-term benefits to bone strength follow with persistent training.

Association of higher levels of ambient criteria pollutants with impaired cardiac autonomic control: a population-based study

An association between air pollution and increased cardiovascular disease (CVD) mortality has been reported, but underlying mechanisms are unknown. The authors examined short-term associations between ambient pollutants (particulate matter less than 10 microm in aerodynamic diameter (PM10), ozone, carbon monoxide, nitrogen dioxide, and sulfur dioxide) and cardiac autonomic control using data from the fourth cohort examination (1996-1998) of the population-based Atherosclerosis Risk in Communities Study. For each participant, the authors calculated PM10 and gaseous pollutant exposures as 24-hour averages and ozone exposure as an 8-hour average 1 day prior to the randomly allocated examination date. They calculated 5-minute heart rate variability indices and used logarithmically transformed data on high-frequency (0.15-0.40 Hz) and low-frequency (0.04-0.15 Hz) power, standard deviation of normal R-R intervals, and mean heart rate. Linear regression was used to adjust for CVD risk factors and demographic, socioeconomic, and meteorologic variables. Regression coefficients for a one-standard-deviation increase in PM10 (11.5 microg/m3) were -0.06 ms2 (standard error (SE), 0.018), -1.03 ms (SE, 0.31), and 0.32 beats/minute (SE, 0.158) for log-transformed high-frequency power, standard deviation of normal R-R intervals, and heart rate, respectively. Similar results were found for gaseous pollutants. These cross-sectional findings suggest that higher ambient pollutant concentrations are associated with lower cardiac autonomic control, especially among persons with existing CVD, and highlight a putative mechanism through which air pollution is associated with CVD.

Neutralizing Antibody against Interleukin-6 Attenuates Posthemorrhagic Vasospasm in the Rat Femoral Artery Model

OBJECTIVE

The degree to which inflammation contributes to the development of posthemorrhagic vasospasm is controversial. In the present study, we investigated the relationship between various inflammatory cytokines (tumor necrosis factor-alpha, interleukin [IL]-1alpha, IL-1beta, and IL-6) and the development of experimental vasospasm.

METHODS

Posthemorrhagic vasospasm was produced in the rat femoral artery model. A latex pouch was placed around each femoral artery, and one pouch was injected with autologous blood and the other with saline as an internal control. Animals were killed at various time points (1 h to 16 d) after surgery (blood exposure), and the degree of vasospasm was assessed by image analysis of artery cross sectional area. Levels of inflammatory cytokines were determined by enzyme-linked immunosorbent assay, and the ability of a polyclonal antibody against rat IL-6 to inhibit vasospasm was tested.

RESULTS

The rat femoral artery model produced a biphasic vasospasm response, with maximal chronic delayed vasospasm occurring at 8 days after hemorrhage. Enzyme-linked immunosorbent assay revealed a significant increase in IL-6 concentrations in blood-exposed arteries relative to saline-exposed arteries at multiple time points (6, 12, 24, and 48 h) after hemorrhage (P < 0.0001). A relative increase in IL-1alpha levels was noted at 24 hours (P < 0.01). IL-1beta levels were similarly elevated in both blood- and saline-exposed arteries, and tumor necrosis factor-alpha levels were not detectable. Administration of a neutralizing polyclonal antibody against rat IL-6 directly into the blood-exposed periarterial pouch at the time of initial surgery resulted in a dose-dependent reduction in the degree of vasospasm compared with vehicle-treated controls at 8 days after hemorrhage (P < 0.05).

CONCLUSIONS

These results indicate that cytokine-mediated inflammation is active in the setting of posthemorrhagic vasospasm produced by the rat femoral artery model. In particular, the profound increase in IL-6 levels after exposure to hemorrhage and the ability of a polyclonal antibody against IL-6 to reduce vasospasm suggest that IL-6 may play a prominent role in the development of vasospasm in this model.

Head Injury and Pulmonary Embolism: A Retrospective Report Based on the Pennsylvania Trauma Outcomes Study

OBJECTIVE

We retrospectively examined the database of the Pennsylvania Trauma Systems Foundation to determine the risk of pulmonary embolism in adult patients sustaining isolated head trauma or multiple injuries, including head trauma, to answer two questions: What is the incidence of symptomatic pulmonary embolism during hospitalization in a trauma center in patients who have sustained a head injury? Are patients with head injuries more at risk for pulmonary embolism than trauma patients without head injuries?

METHODS

We determined the total number of adult submissions per year to the Pennsylvania Trauma Outcomes Study from 1992 to 1996. Age, sex, Glasgow Coma Scale score, Abbreviated Injury Score for head injury, Injury Severity Score, intensive care unit days, hospital days, and the presence or absence of head injury, spinal injury, pelvic fractures, and/or femur fractures were recorded. Statistical techniques to evaluate their correlation with the incidence of pulmonary embolism included chi(2) testing, linear regression analysis, Kendall analysis, and logistic regression analysis.

RESULTS

The average incidence of symptomatic pulmonary embolism in head-injured patients occurring during their acute hospital stay was 0.38%. This rate was not significantly greater than the 0.27% incidence of pulmonary embolism in patients without head injury. Factors that significantly increased this incidence were age greater than 45 years, Injury Severity Score greater than 15, male sex, and the presence of pelvic or femur fractures or of spinal cord injury.

CONCLUSION

We found no evidence that head injury is a significant independent risk factor for development of symptomatic pulmonary embolism during the acute hospitalization of the trauma patient.

Relationship of exhaled nitric oxide to clinical and inflammatory markers of persistent asthma in children

BACKGROUND

Exhaled nitric oxide (eNO) is a noninvasive test that measures airway inflammation. Insufficient information is available concerning correlations between eNO and biologic, physiologic, and clinical characteristics of asthma in children currently not taking controller medications.

OBJECTIVE

The aim of this study was to find correlations between eNO and other characteristics of children with mild to moderate asthma currently not taking medications.

METHODS

Children aged 6 to 17 years with mild to moderate persistent asthma, taking only albuterol as needed, were characterized during 2 visits 1 week apart before being randomly assigned into a clinical trial. At the screening visit, online measurements of eNO, spirometry before and after bronchodilator, and biomarkers of peripheral blood eosinophils, serum eosinophil cationic protein, total serum IgE, and urinary leukotriene E4 were obtained. During a week characterization period before randomization, symptoms were recorded on a diary and peak expiratory flows were measured twice daily using an electronic device. At the randomization visit, eNO was repeated followed by a methacholine challenge and aeroallergen skin testing. Correlations and rank regression analyses between eNO and clinical characteristics, pulmonary function, and biomarkers were evaluated.

RESULTS

eNO was significantly correlated with peripheral blood eosinophils (r =.51, P <.0001), IgE (r =.48, P <.0001), and serum eosinophil cationic protein (r =.31, P =.0003) but not with urinary leukotriene E4 (r =.16, P =.08). A moderate correlation was found between eNO and the number of positive aeroallergen skin tests (r =.45, P <.0001). eNO did not correlate with FEV1% predicted but was weakly correlated with FEV1/forced vital capacity (r = -.19, P =.032), bronchodilator response (r =.20, P =.023), and FEV1 PC20 methacholine (r = -.31, P =.0005). No significant correlations were found between eNO and clinical characteristics or morning or evening peak expiratory flow measurements. The rank regression analysis demonstrated that 5 variables accounted for an R square of.52 (eosinophils [P <.0001], IgE [P =.0023], age [P <.0001], months of inhaled corticosteroid use in the year before study entry [P =.01], and FEV1 PC20 [P =.0061]).

CONCLUSIONS

These findings suggest that eNO provides information about the asthmatic state consistent with information from other markers of inflammation. It is a noninvasive technique that could be used in decisional management of children with asthma.

A case-control study of menstrual factors in relation to breast cancer risk in African-American women

Menstrual characteristics may serve as surrogate measures of endogenous estrogen and may be related to breast cancer risk. No previous studies have systematically investigated menstrual factors in relation to the disease in African-American women. This case-control study is aimed to assess the relationship between menstrual factors and breast cancer in African-American women. Cases were 304 African-American women, aged 20-64 living in three Tennessee counties, diagnosed with breast cancer between 1995 and 1998. Controls were selected through random-digit dialing and frequency matched to cases (n=305). Phone interviews were conducted on menstrual factors--age at menarche, time to regularity, cycle length, flow length, age at menopause--and other risk factors. Logistic regression showed that compared to women with short cycle length (<28 days), women with average cycle length > or =28 had decreased risk of breast cancer (odds ratio (OR)=0.60, 95% confidence interval (CI), 0.38-0.94). Dose-response analyses showed decreasing risk with longer cycle length. Results by menopausal status revealed an inverse relationship was shown only in postmenopausal women. No significant associations were observed for other menstrual factors. Findings suggest that cycle length has an inverse association with breast cancer in African-American women that may primarily exist for post-menopausal tumors.