Leading indicators of readiness among the general Army and Special Operations Forces: Predictive and psychometric analysis of the Global Assessment Tool

Self-assessments are commonly used to track Army readiness in specialized communities, but they are rarely analyzed for reliability and predictive validity. Before introducing new assessments, existing ones should be reevaluated. We examined the Global Assessment Tool (GAT), an annual Army-required self-assessment with multiple psychosocial and health behavior short scales. Psychometric analyses on nine scales included item response theory (IRT) and measurement invariance models across total Army (n = 743,057) and special operations forces (SOF; n = 3,478) cohorts. Predictive analyses examined demographic-adjusted associations between GAT scales and one-year incident medical non-readiness (MNR). Most scales had adequate reliability, although some exhibited highly skewed distributions, which likely increased measurement error. Most scales exhibited metric and scalar measurement equivalence across total Army and SOF groups. Scores from scales measuring positive characteristics were associated with lower odds of MNR (good coping, flexibility, optimism, positive affect, work engagement, friendship, organization trust; adjusted odds ratios ≤ 0.75); scores from scales measuring negative characteristics were associated with increased odds of MNR (poor sleep, depression, negative affect, loneliness; adjusted odds ratios ≥ 1.4). Associations were similar across Army and SOF cohorts. In conclusion, self-report data can potentially contribute to command surveillance, but iterative quality-checks are necessary after deployment.

Postpartum long-acting reversible contraceptive use among active-duty, female US Army soldiers

BACKGROUND

Postpartum use of long-acting reversible contraception has been found to be effective at increasing interpregnancy intervals, reducing unintended pregnancies, and optimizing health outcomes for mothers and babies. Among female active-duty military service members, reproductive planning may be particularly important, yet little is known about postpartum long-acting reversible contraceptive use among active-duty soldiers.

OBJECTIVE

This study aimed to (1) quantify postpartum uptake of long-acting reversible contraception among active-duty female US Army soldiers and (2) identify demographic and military-specific characteristics associated with use.

STUDY DESIGN

This retrospective cohort study used longitudinal data of all digitally recorded health encounters for active-duty US Army soldiers from 2014 to 2017. The servicewomen included in our analysis were aged 18 to 44 years with at least one delivery and a minimum of 4 months of total observed time postdelivery within the study period. We defined postpartum long-acting reversible contraception use as initiation of use within the delivery month or in the 3 calendar months following delivery and identified likely immediate postpartum initiation via the proxy of placement recorded during the same month as delivery. We then evaluated predictors of postpartum long-acting reversible contraception use with multivariable logistic regression.

RESULTS

The inclusion criteria were met by 15,843 soldiers. Of those, 3162 (19.96%) initiated the use of long-acting reversible contraception in the month of or within the 3 months following delivery. Fewer than 5% of these women used immediate postpartum long-acting reversible contraception. Among women who initiated postpartum long-acting reversible contraceptive use, 1803 (57.0%) received an intrauterine device, 1328 (42.0%) received an etonogestrel implant, and 31 received both (0.98%). Soldiers of younger age, self-reported White race, and those who were married or previously married were more likely to initiate long-acting reversible contraception in the postpartum period. Race-stratified analyses showed that self-reported White women had the highest use rates overall. When compared with these women, the adjusted odds of postpartum use among self-reported Black and Asian or Pacific Islander women were 18% and 30% lower, respectively (both P<.001). There was also a trend of decreasing postpartum use with increasing age within each race group. Differences observed between age groups and race identities could partially be attributed to differential use of permanent contraception (sterilization), which was found to be significantly more prevalent among both women aged 30 years or older and among women who identified as Black.

CONCLUSION

Among active-duty US Army servicewomen, 1 in 5 used postpartum long-acting reversible contraception, and fewer than 5% of these women used an immediate postpartum method. Within this population with universal healthcare coverage, we observed relatively low rates of use and significant differences in the uptake of effective postpartum long-acting contraceptive methods across self-reported race categories.

The combined effects of coping and pain interference on army readiness

Introduction

Chronic pain and associated interference with daily activities are common in the military and impact Force readiness. Chronic pain affects one-third of service members and is a leading cause of medical non-readiness (MNR) in the military. Research suggests that underlying psychological mechanisms related to trait coping styles and pain interference (PI) affect functional outcomes, but little research exists examining this relationship within an Army population. The purpose of this study was to examine the combined effects of PI and coping on U.S. Army soldier readiness by using annual well-being data from the Global Assessment Tool (GAT) and medical non-readiness (MNR) based on duty restriction records.

Methods

The sample comprised 866,379 soldiers who completed the GAT between 2014 and 2017 with no duty restrictions at the time of baseline GAT completion; subjects were observed through 2018 for duty restrictions. Parametric survival regression models with a Weibull distribution predicted demographic-adjusted hazards of MNR by dichotomized PI (no PI/PI) and beneficial/non-beneficial use of GAT coping components (good coping, bad coping, catastrophizing-flexibility, and catastrophizing-hopelessness). Incident MNR was evaluated for all duty restrictions, and stratified by selected body systems (upper extremity, lower extremity, psychiatric).

Results

Among soldiers with PI, hazards were higher in those reporting non-beneficial coping styles (bad coping, hopelessness) and lower in those reporting beneficial coping styles (good coping, flexibility). Across all coping styles, PI/coping interactions were particularly strong for catastrophizing-hopelessness and when examining MNR from psychiatric conditions.

Discussion

These findings suggest some synergistic associations between pain and coping that may impact pain-related occupational disability. Coping skills may be an effective interventional target for chronic pain reduction/prevention within military programs, such as the Master Resilience Training Course offered to soldiers in the Army. Further research should assess whether early coping style interventions can reduce pain-related outcomes.

Risk factors for musculoskeletal-related occupational disability among US Army soldiers

INTRODUCTION

Minimising temporary and permanent disability associated with musculoskeletal conditions (MSK-D) is critical to the mission of the US Army. Prior research has identified potentially actionable risk factors for overall military disability and its MSK-D subset, including elevated body mass index, tobacco use and physical fitness. However, prior work does not appear to have addressed the impact of these factors on MSK-D when controlling for a full range of factors that may affect health behaviours, including aptitude scores that may serve as a proxy for health literacy. Identifying risk factors for MSK-D when providing control for all such factors may inform efforts to improve military readiness.

METHODS

We studied 494 757 enlisted Army soldiers from 2014 to 2017 using a combined medical and administrative database. Leveraging data from the Army's digital 'eProfile' system of duty restriction records, we defined MSK-D as the first restriction associated with musculoskeletal conditions and resulting in the inability to deploy or train. We used multivariable Cox proportional hazards regression to assess the associations between incident MSK-D and selected risk factors including aptitude scores, physical fitness test scores, body mass index and tobacco use.

RESULTS

Among the subjects, 281 278 (45.14%) experienced MSK-D. In the MSK-D hazards model, the highest effect size was for failing the physical fitness test (adjusted HR=1.63, 95% CI 1.58 to 1.67, p<0.001) compared with scoring ≥290 points.

CONCLUSIONS

The analysis revealed the strongest associations between physical fitness and MSK-D. Additional efforts are warranted to determine potential mechanisms for the observed associations between selected factors and MSK-D.

Physical Fitness in Relationship to Depression and Post-Traumatic Stress Disorder During Pregnancy Among U.S. Army Soldiers

Background: Depression and post-traumatic stress disorder (PTSD) are prevalent in pregnancy, especially among military members. These conditions can lead to adverse birth outcomes, yet, there's a paucity of evidence for prevention strategies. Optimizing physical fitness is one understudied potential intervention. We explored associations between prepregnancy physical fitness and antenatal depression and PTSD in soldiers. Materials and Methods: This was a retrospective cohort study of active-duty U.S. Army soldiers with live births between 2011 and 2014, identified with diagnosis codes from inpatient and outpatient care. The exposure was each individual's mean Army physical fitness score from 10 to 24 months before childbirth. The primary outcome was a composite of active depression or PTSD during pregnancy, defined using the presence of a code within 10 months before childbirth. Demographic variables were compared across four quartiles of fitness scores. Multivariable logistic regression models were conducted adjusting for potential confounders selected a priori. A stratified analysis was conducted for depression and PTSD separately. Results: Among 4,583 eligible live births, 352 (7.7%) had active depression or PTSD during pregnancy. Soldiers with the highest fitness scores (Quartile 4) were less likely to have active depression or PTSD in pregnancy (Quartile 4 vs. Quartile 1 adjusted odds ratio 0.55, 95% confidence interval 0.39-0.79). Findings were similar in stratified analyses. Conclusion: In this cohort, the odds of active depression or PTSD during pregnancy were significantly reduced among soldiers with higher prepregnancy fitness scores. Optimizing physical fitness may be a useful tool to reduce mental health burden on pregnancy.

Financial Impact of Embedded Injury-Prevention Experts in US Army Initial Entry Training

CONTEXT

The US Army embedded injury-prevention experts (IPEs), specifically athletic trainers and strength and conditioning coaches, into initial entry training (IET) to limit musculoskeletal (MSK) conditions and their negative consequences. However, little is known about the financial impact of IPEs.

OBJECTIVE

To assess whether IPEs were associated with fewer sunk training costs due to MSK-related early discharges from service.

DESIGN

Retrospective cohort study.

SETTING

Database of US Army soldiers' administrative, medical, and readiness records.

PATIENTS OR OTHER PARTICIPANTS

A total of 198 166 soldiers (age = 20.7 ± 3.2 years, body mass index = 24.4 ± 3.5 kg/m2) who began IET during 2014 to 2017.

MAIN OUTCOME MEASURE(S)

Early discharge from service was defined as occurring within 6 months of beginning IET. All IET sites employed IPEs from 2011 to 2017, except for 2 sites during April to November 2015. Soldiers who began IET at these 2 sites during these times were categorized as not having IPE exposure. All others were categorized as having IPE exposure. The unadjusted association between IPE access and MSK-related early discharge from service was assessed using logistic regression. Financial impact was assessed by quantifying differences in yearly sunk costs between groups with and those without IPE exposure and subtracting IPE hiring costs.

RESULTS

Among 14 094 soldiers without IPE exposure, 2.77% were discharged early for MSK-related reasons. Among 184 072 soldiers with IPE exposure, 1.01% were discharged. Exposure to IPEs was associated with reduced odds of MSK-related early discharge (odds ratio = 0.36, 95% CI = 0.32, 0.40, P < .001) and a decrease in yearly sunk training costs of $11.19 to $20.00 million.

CONCLUSIONS

Employing IPEs was associated with reduced sunk costs because of fewer soldiers being discharged from service early for MSK-related reasons. Evidence-based recommendations should be developed for guiding policy on the roles and responsibilities of IPEs in the military to reduce negative outcomes from MSK conditions and generate a positive return on investment.

Rates of Lapidus Procedures in the US Military Before and After the Advent of and Advocacy for Tri-Plane Lapidus Corrective Surgery

Tri-plane corrective Lapidus surgery has been described as advantageous with respect to its anatomic basis and outcomes. Because the procedure has been broadly publicized, changes in overall Lapidus procedure rates due to increased numbers of patients opting for the tri-plane approach could have occurred. Data supporting this possibility appears lacking. We employed official personnel and health records of the total active-duty US military to conduct a retrospective cohort study of Lapidus surgery rates before and after the advent of the tri-plane corrective Lapidus procedure. Least-squares and locally-weighted scatterplot smoother regression functions were used to confirm time trends. Sociodemographic and occupational traits of Lapidus patients were compared using 2-sided t tests and chi square tests. Lapidus surgery rates among hallux valgus patients decreased during 2014 to 2016 and increased during 2017 to 2021. While multiple factors might explain these trends, they coincide with the advent of and advocacy for tri-plane Lapidus surgery. The results support the possibility that its rise influenced overall Lapidus rates in this population. As these findings represent limited evidence of such an influence, further research is required to confirm a causal link. If such a link is found, and if the ongoing research suggests that superior outcomes are associated with tri-plane Lapidus surgery, substantial implications could exist for this population. Benefits might include enhanced medical readiness due to the importance of lower extremity function during military duties. Additional research is needed to confirm the impact of the procedure and to determine whether Lapidus surgery rate patterns in civilian populations mirror these findings.

Incidence of Ankylosing Spondylitis Among Male and Female United States Army Personnel

OBJECTIVE

Incidence rates of ankylosing spondylitis (AS) among males versus females are poorly understood. Results of prior research have been mixed, including findings of a 3:1 incidence ratio for males versus females, but with increasing AS rates among females. The objective was to estimate the incidence of AS among members of the US military.

METHODS

We estimated the incidence of AS in a retrospective cohort study of diverse, working-age US military service members during March 2014 to June 2017 (n = 728,556) who underwent clinical practice guideline-directed screening for chronic back pain. Incident AS cases were identified using diagnostic codes from electronic medical and administrative records.

RESULTS

In contrast to some prior studies, AS incidence was similar among males and females (incidence rate ratio 1.16, P = 0.23; adjusted odds ratio [OR] 0.79 [95% confidence interval (95% CI) 0.61-1.02]; P = 0.072). AS rates increased approximately monotonically with age. Consistent with prior research, the AS incidence rate was greater in the White population than in the Black population (adjusted OR 1.39 [95% CI 1.01-1.66]; P = 0.04).

CONCLUSION

In this study population, the incidence of AS was similar for the sexes. Previous observations of male predominance have typically been derived from clinic populations that are less representative of the US race/ethnicity distribution and based on disease ascertainment tools that may have identified subjects later in their disease course. Our study population also differed in being subject to organized screenings for musculoskeletal symptoms. Our findings suggest that sex may not predict AS incidence in the US population.

Service discharges among US Army personnel with selected musculoskeletal and skin conditions: a retrospective cohort study

OBJECTIVES

To determine the probability of discharge from military service among soldiers following an incident diagnosis of ankylosing spondylitis (AS), rheumatoid arthritis (RA), psoriasis or systemic lupus erythematous.

METHODS

All soldiers on active duty in the US Army between January 2014 and June 2017 were included in a retrospective cohort analysis. Termination from service was ascertained using personnel records. Diagnostic codes were used to identify incident cases of the four musculoskeletal and skin diseases and, for comparison, diabetes mellitus (DM). Time to discharge was modelled using sex stratified multivariate survival analysis.

RESULTS

The analysis included 657 417 individuals with a total of 1.2 million person-years of observation. An elevated risk of discharge was observed in association with each of the five chronic conditions studied. The increase in adjusted risk of discharge was highest among soldiers with AS (men, HR=2.5, 95% CI 2.1 to 3.0; women, HR=2.1, 95% CI 1.4 to 3.2) and with DM (men, HR=2.4, 95% CI 2.2 to 2.7; women, HR=2.2, 95% CI 1.8 to 2.5), followed by those with RA (men, HR=1.8, 95% CI 1.5 to 2.2; women, HR=1.8, 95% CI 1.4 to 2.4).

CONCLUSIONS

Military discharges are consequential for the service and the service member. The doubling in risk of discharge for those with AS or RA was comparable to that for personnel with DM. Conditions that affect the spine and peripheral joints may often be incompatible with military readiness. Nevertheless, a substantial fraction of service members with these diagnoses continued in service.

Post-Traumatic Stress Disorder Among U.S. Army Drone Operators

INTRODUCTION: Exposure to traumatic events could increase post-traumatic stress disorder (PTSD) risk among enlisted U.S. Army drone operators. Published research on PTSD risk in this population is unavailable.METHODS: We used a combined medical and administrative longitudinal dataset to examine adjusted associations between drone operator service among U.S. Army enlisted members and three PTSD indicators: whether screened via the PTSD Checklist – Civilian (PCL-C); PCL-C scores; and incident PTSD diagnoses. We compiled summary statistics for and conducted tests of differences in independent variable distributions when comparing drone operators and others. Two multivariable survival regression models and an ordinary least squares model were used to estimate adjusted associations.RESULTS: There were 1.68 million person-years of observed time in the study population (N = 678,548; drone operator N = 2856). Compared to other servicemembers, the adjusted likelihood of undergoing PTSD screening was 35% lower [95% confidence interval (CI) for the adjusted hazard ratio (aHR): 0.56–0.76]. Among subjects who took the PCL-C, scores did not differ significantly on the basis of drone operator service (adjusted change: −1.26 points; CI: −3.41–0.89). The adjusted hazard of receiving a PTSD diagnosis was 34% lower among drone operators (CI: 0.54–0.80).DISCUSSION: These findings provide reassurance that enlisted U.S. Army drone operators are not at increased risk of PTSD. Further research is needed in order to identify the mechanisms of the decreased PTSD risk observed, and whether other or longer-term mental health risks are present among those in this occupation.Nelson DA, Wilson M, Kurina LM. Post-traumatic stress disorder among U.S. Army drone operators. Aerosp Med Hum Perform. 2022; 93(7):562–570.

An investigation of sickle cell trait, body mass index, and fitness in relation to venous thromboembolism among African American adults

BACKGROUND

The relationships of sickle cell trait (SCT), body mass index (BMI), and physical fitness to venous thromboembolism (VTE) in young adults have received little attention.

OBJECTIVES

To test for associations among SCT, BMI, fitness, and VTE.

PATIENTS/METHODS

We conducted a retrospective cohort study of 48,316 SCT-tested, African American individuals in the US Army during 2011-14. We used Cox proportional hazards models to compute adjusted hazards of deep vein thrombosis (DVT) and pulmonary embolism (PE) associated with selected factors.

RESULTS

Incidence rates of DVT and PE were 1.09 and 0.91 cases per 1000 person-years, respectively. Adjusted hazard ratios (aHRs) for DVT for men and women with SCT were 0.9 (95% confidence interval [CI]: 0.4-2.0; P = .711) and 1.51 (CI: 0.7-3.2; P = .274), respectively. aHRs for PE for SCT+ men and women were 1.1 (CI: 0.5-2.4; P = .773) and 1.2 (CI: 0.5-3.1; P = .650), respectively. Low physical fitness was associated with DVT and PE in women (DVT aHR =3.1; CI: 1.4-6.5; P = .004; PE aHR =4.6; CI: 2.1-9.9; P < .001) and DVT in men (aHR =2.2; CI: 1.0-4.6; P = .048). Recent weight gain of 1 or more BMI points was associated with DVT in men (aHR =1.8; CI: 1.1-2.8; P = .017).

CONCLUSIONS

We found no evidence of increased VTE risk associated with SCT in this population. However, lower fitness levels and BMI increases were so associated.

Summit on Exercise Collapse Associated with Sickle Cell Trait: Finding the "Way Ahead"

ABSTRACT

Although largely benign, sickle cell trait (SCT) has been associated with exertion-related events, to include sudden death. In 2011, a summit on SCT introduced the term exercise collapse associated with SCT (ECAST). A series of ECAST deaths in military personnel in 2019 prompted reevaluation of current efforts and led to a second summit in October 2019 hosted by the Consortium for Health and Military Performance of the Uniformed Services University in Bethesda, MD. The goals were to (1) review current service policies on SCT screening, (2) develop draft procedural instructions for executing current policy on SCT within the Department of Defense, (3) develop draft clinical practice guidelines for management of ECAST, (4) establish a framework for education on SCT and ECAST, and (5) prepare a research agenda to address identified gaps.

Military Occupational Disability Risk Surveillance: A Retrospective Cohort Study of Modifiable Risk Factors

INTRODUCTION

Occupational disability among military service members is an important target for preventive screening. The specific aim of this study was to quantify disability risk levels among soldiers with selected risk factors (body mass index extremes, poor or absent physical fitness scores, and tobacco and opioid use) and combinations thereof, suggesting priorities for preventive actions.

MATERIALS AND METHODS

This was a retrospective cohort study of 607,006 active-duty soldiers who served in the U.S. Army during 2011-2014. Official medical and administrative data were combined to produce a person-month-based panel dataset with identifiers removed. The subjects were observed longitudinally for incident disability (termed medical nonreadiness) during 1,305,618 person-years at risk. We employed Weibull parametric survival regression models to determine the adjusted medical nonreadiness hazard for selected variables. We then computed individual adjusted risk scores and the population proportions affected by risk factors and combinations thereof in postregression analyses. The project was approved by the Stanford University's Institutional Review Board and underwent secondary review by the Human Research Protections Office of the Defense Health Agency.

RESULTS

During the observed time, 81,571 (13.4%) of subjects were found medically not ready. High or low body mass index, low or missing physical fitness test scores, tobacco use, and the highest levels of opioid use were each associated with increased adjusted hazards of medical nonreadiness. The hazards increased substantially when multiple risk factors were present, albeit while affecting reduced population proportions.

CONCLUSIONS

We identified marked disability hazard increases, especially in association with opioid use and high body mass index. These factors, in addition to tobacco use and low physical fitness, are potential early prevention targets for clinicians who screen military service members.

Incidence of Pelvic Floor Disorders in US Army Female Soldiers

OBJECTIVE

To determine the incidence of pelvic floor disorders (PFD) among active-duty US Army female soldiers.

MATERIALS AND METHODS

We studied 102,015 women for incident PFD using the Stanford Military Data Repository, which comprises medical, demographic and service-related information on all soldiers on active duty in the US Army during 2011-2014. Cox proportional hazards estimated adjusted associations with PFD diagnoses. In the adjusted models, military-specific characteristics and fitness were evaluated alongside known PFD predictors.

RESULTS

Among 102,015 subjects at risk there was a cumulative incidence of 6.4% over a mean of 27 months (median 29, range 1-42). In adjusted models, obese soldiers were more likely to have a PFD compared to those of normal weight (hazard ratio [HR] 1.23, confidence interval [CI] 1.14-1.34, P <0.001) and those with recent weight gain were more likely to have a PFD compared to those without (HR 1.32, CI 1.24-1.40, P <0.05). Women with the lowest physical fitness scores were more likely to have a PFD (HR 1.14, CI 1.04-1.25) compared to those with the highest scores.

CONCLUSION

Over a median follow-up time of 29 months, 1 in 15 women in this active-duty cohort was diagnosed with a PFD. Optimizing risk factors including body mass index and physical fitness may benefit the pelvic health of female soldiers, independent of age, children, and years of service.

Stressful Life Changes and Their Relationship to Nutrition-Related Health Outcomes Among US Army Soldiers

Stressful life changes may tax people's adaptive capacity. We sought to determine if and when experiences of stressful life changes were associated with increased odds of adverse nutrition-related health outcomes among US Army soldiers relative to those who did not experience the same stressful life change. An additional aim was to determine which stressful life changes had the greatest association with these outcomes and if there were gender differences in the magnitude of the associations. Stressful life changes studied included: changes in marital status, combat deployment or return from deployment, relocation, adding a child, change in rank, change in occupation, and development of a physical limitation to duty. Using longitudinal data from the Stanford Military Data Repository, which represents all active-duty soldiers aged 17-62 between 2011 and 2014 (n = 827,126), we employed an event history analysis to examine associations between stressful life changes and a subsequent diagnosis of hyperlipidemia, substantial weight gain, and weight-related separation from the Army. Marriage was associated with an increase in the odds of substantial weight gain 3 months later for both men and women. Developing a physical duty limitation was associated with an increase in the odds of a hyperlipidemia diagnosis 2 months later for both men and women, as was substantial weight gain 2 months later. Stressful life changes were also associated with increased odds of nutrition-related health outcomes, although we found gender differences in the magnitude of the associations. Findings could be used to mitigate the effects of stress on health by health professionals.

The Value of Shorter Initial Opioid Prescriptions: A Simulation Evaluation

BACKGROUND

During the period from 1999 to 2016, more than 350,000 Americans died from overdoses related to the use of prescription opioids. To the extent that supply is directly related to overprescribing, policy interventions aimed at changing prescriber behavior, such as the recent Centers for Disease Control and Prevention guideline, are clearly warranted. Although these could plausibly reduce the prevalence of opioid overuse and dependency, little is known about their economic and health-related impacts.

OBJECTIVE

The aim of this study was to quantify the efficacy of a policy intervention aimed at reducing the length of initial opioid prescriptions.

STUDY DESIGN AND METHODS

A Markov decision process model was fitted on a retrospective cohort of 827,265 patients, and patient cost and health trajectories were simulated over a 24-month period. The model's parameters were based on patients who received short (≤ 3 days) or long (> 7 days) initial opioid prescriptions, matched using propensity score methods.

STUDY POPULATION

All active-duty US Army soldiers from 2011 to 2014; the data contained detailed medical and administrative information on over 11 million soldier-months corresponding to 827,265 individual soldiers.

MAIN OUTCOME MEASURE

Overall costs of a policy change, quality-adjusted life-years (QALYs) gained, and $/QALY gained.

RESULTS

Over a 2-year horizon, a reassignment of 10,000 patients to short initial duration would generate a cost saving in the vicinity of $3.1 million (excluding program costs), and would also lead to an estimated 4451 additional opioid-free months, i.e. months without any opioid prescriptions.

CONCLUSION

The analysis found that efforts to change prescriber behavior can be cost effective, and further studies into the implementation of such policies are warranted.

Regional Differences following Partial Salivary Gland Resection

Regenerative medicine aims to repair, replace, or restore function to tissues damaged by aging, disease, or injury. Partial organ resection is not only a common clinical approach in cancer therapy but also an experimental injury model used to examine mechanisms of regeneration and repair in organs. We performed a partial resection, or partial sialoadenectomy, in the female murine submandibular salivary gland (SMG) to establish a model for investigation of repair mechanisms in salivary glands (SGs). After partial sialoadenectomy, we performed whole-gland measurements over a period of 56 d and found that the gland increased slightly in size. We used microarray analysis and immunohistochemistry (IHC) to examine messenger RNA and protein changes in glands over time. Microarray analysis identified dynamic changes in the transcriptome 3 d after injury that were largely resolved by day 14. At the 3-d time point, we detected gene signatures for cell cycle regulation, inflammatory/repair response, and extracellular matrix (ECM) remodeling in the partially resected glands. Using quantitative IHC, we identified a transient proliferative response throughout the gland. Both secretory epithelial and stromal cells expressed Ki67 that was detectable at day 3 and largely resolved by day 14. IHC also revealed that while most of the gland underwent a wound-healing response that resolved by day 14, a small region of the gland showed an aberrant sustained fibrotic response characterized by increased levels of ECM deposition, sustained Ki67 levels in stromal cells, and a persistent M2 macrophage response through day 56. The partial submandibular salivary gland resection model provides an opportunity to examine a normal healing response and an aberrant fibrotic response within the same gland to uncover mechanisms that prevent wound healing and regeneration in mammals. Understanding regional differences in the wound-healing responses may ultimately affect regenerative therapies for patients.

Stated Pain Levels, Opioid Prescription Volume, and Chronic Opioid Use Among United States Army Soldiers

INTRODUCTION

The use of opioids has increased drastically over the past few years and decades. As a result, concerns have mounted over serious outcomes associated with chronic opioid use (COU), including dependency and death. A greater understanding of the factors that are associated with COU will be critical if prescribers are to navigate potentially competing objectives to provide compassionate care, while reducing the overall opioid use problem. In this study, we study pain levels and opioid prescription volumes and their effects on the risk of COU.This study leveraged passive data sources that support automated decision support systems (DSSs) currently employed in a large military population. The models presented compute monthly, person-specific, adjusted probability of subsequent COT and could potentially provide critical decision support for clinicians engaged in pain management.

MATERIALS AND METHODS

The study population included all outpatient presentations at military medical facilities worldwide among active duty United States Army soldiers during July 2011 to September 2014 (17,664,006 encounters; population N = 552,193). We conducted a retrospective cohort study of this population and employed longitudinal data and a discrete time multivariable logistic regression model to compute COT probability scores. The contribution of pain scores and opioid prescription quantities to the probability of COT represented analytic foci.

RESULTS

There were 13,891 subjects (2.5%) who experienced incident COT during the observed time period. Statistically significant interactions between pain scores and prescription quantity were present, in addition to effects of multiple other control variables. Counts of monthly opioid prescriptions and maximum stated pain scores per month were each positively associated with COT. A wide range in individual COT risk scores was evident. The effect of prescription volume on the COT risk was larger than the effect of the pain score, and the combined effect of larger pain scores and increased prescription quantity was moderated by the interaction term.

CONCLUSIONS

The results verified that passive data on the US Army can support a robust COT risk computation in this population. The individual, adjusted risk level requires statistical analyses to be fully understood. Because the same data sources drive current military DSSs, this work provides the potential basis for new, evidence-based decision support resources for military clinicians. The strong, independent impact of increasing opioid prescription counts on the COT risk reinforces the importance of exploring alternatives to opioids in pain management planning. It suggests that changing provider behavior through enhanced decision support could help reduce COT rates.

Stressful Life Changes Affect Nutrition-Related Health Outcomes Among US Army Soldiers (P18-070-19)

Objectives

This prospective cohort study aimed to determine if experiencing stressful life changes were associated with an earlier onset of adverse nutrition-related health outcomes among US Army Soldiers. An additional aim was to determine which stressful life changes were most associated with these outcomes and if there were gender differences in the magnitude of the associations.

Methods

Stressful life changes were changes in marital status, combat deployment or returning from deployment, relocation, adding a child, change in rank, change in occupation, or development of a physical limitation to duty. Nutrition-related health outcomes were hyperlipidemia diagnosis, substantial weight gain, or weight-related separation from the Army. Using longitudinal data from the Stanford Military Data Repository representing all active-duty Soldiers who were age 17–62 between 2011 and 2014 (n = 827,126), event history analysis was used to model the association of stressful life changes with nutrition-related outcomes.

Results

Marriage was found to raise the odds of substantial weight gain three months later by 1.24 times (95% CI: 1.16, 1.32) for men and 1.68 times (95% CI: 1.51, 1.89) for women. Developing a physical duty limitation raised the odds of hyperlipidemia two months later by 1.42 times (95% CI: 1.15, 0.75) for men and 1.83 times (95% CI: 1.01, 3.32) for women and the odds of substantial weight gain two months later by 3.16 times (95% CI: 2.89, 3.44) in men and 1.69 times (95% CI: 1.36, 2.08) in women.

Conclusions

Differences in the magnitude of associations show stressful life changes affect male and female Soldiers differently. Identifying times after stressful life changes when the risk of developing an undesirable health outcome is highest offers new possibilities for proactively addressing health. Findings could guide the timing of interventions to mitigate the effects of stress on health in military and civilian populations.

Funding Sources

None. Disclaimer: Authors’ views do not reflect official DoD or Army policy.

Sickle cell trait and renal disease among African American U.S. Army soldiers

Sickle cell trait and certain renal disorders are disproportionately prevalent among African American individuals, so a clear understanding of their association is important. We conducted a longitudinal study using the Stanford Military Data Repository to examine sickle cell trait in relation to the incidence of acute kidney injury (AKI) and chronic kidney disease (CKD). Our study population consisted of African American U.S. Army soldiers on active duty between January 2011 and December 2014. The cumulative incidence was 0·51% for AKI (236 cases out of 45 901 soldiers) and 0·56% for CKD (255 cases out of 45 882 soldiers). Discrete time logistic regression models adjusting for demographic-, military- and healthcare-related covariates showed that sickle cell trait was associated with significantly higher adjusted odds of both AKI [odds ratio (OR): 1·74; 95% confidence interval (CI): 1·17-2·59] and CKD (OR: 2·00; 95% CI: 1·39-2·88). Elevated odds of AKI and CKD were also observed in association with prior CKD and AKI, respectively, and with obesity and prior hypertension. Individuals with sickle cell trait and their providers should be aware of the possibility of increased risk of AKI and CKD to allow for timely intervention and possible prevention.

Trajectories of body mass index among active-duty U.S. Army soldiers, 2011-2014

Establishing the shape and determinants of trajectories of body mass index (BMI) among Soldiers is critical given the importance of weight management to military service requirements. To establish the shape and determinants of BMI trajectories among Soldiers, we aimed to (1) model the overall BMI trajectory of Soldiers, (2) find the most common trajectory groups among Soldiers, (3) investigate the relationship between BMI trajectories and sociodemographic and military-specific characteristics, and (4) determine if there were Soldiers with large fluctuations in BMI. The study population included all US Army Soldiers on active-duty between 2011 and 2014 who were age 17–62 (n = 827,126). With longitudinal data from the Stanford Military Data Repository, we used group-based trajectory modeling to identify the BMI trajectories of Soldiers and multinomial logistic regression to estimate associations between Soldier characteristics and trajectory membership. Four distinct BMI trajectory groups were found: increasing, decreasing, constant, and inconstant. The constant, increasing, and decreasing trajectories were similar in shape and percentage between men and women. The constant trajectory had the fewest Soldiers who exceeded weight standards or had duty limitations. The increasing trajectory was associated with marriage and fewer service years. The decreasing trajectory was associated with more service years and higher educational attainment. The inconstant trajectory differed in shape between men and women. Over 6% of men and 12% of women had fluctuations in BMI indicative of weight cycling. Understanding the characteristics associated with BMI trends may assist the Army in targeting resources aimed to improve Soldier health and combat readiness.

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Four BMI trajectory groups were found: increasing, decreasing, constant, inconstant.

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The constant trajectory had the fewest Soldiers who exceeded weight standards.

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The increasing trajectory was associated with marriage and fewer service years.

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The decreasing trajectory was associated with more service years and education.

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6% of men and 12% of women had fluctuations in BMI indicative of weight cycling.

Association of Nonsteroidal Anti-inflammatory Drug Prescriptions With Kidney Disease Among Active Young and Middle-aged Adults

IMPORTANCE

Concern about the renal effects of nonsteroidand al anti-inflammatory drugs (NSAIDs) among young, healthy adults has been limited, but more attention may be warranted given the prevalent use of these agents.

OBJECTIVE

To test for associations between dispensed NSAIDs and incident acute kidney injury and chronic kidney disease while controlling for other risk factors.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective, longitudinal cohort study used deidentified medical and administrative data on 764 228 active-duty US Army soldiers serving between January 1, 2011, and December 31, 2014. Analysis was conducted from August 1 to November 30, 2018. All individuals new to Army service were included in the analysis. Persons already serving in January 2011 were required to have at least 7 months of observable time to eliminate those with kidney disease histories.

EXPOSURES

Mean total defined daily doses of prescribed NSAIDs dispensed per month in the prior 6 months.

MAIN OUTCOMES AND MEASURES

Incident outcomes were defined by diagnoses documented in health records and a military-specific digital system.

RESULTS

Among the 764 228 participants (655 392 [85.8%] men; mean [SD] age, 28.6 [7.9] years; median age, 27.0 years [interquartile range, 22.0-33.0 years]), 502 527 (65.8%) were not dispensed prescription NSAIDs in the prior 6 months, 137 108 (17.9%) were dispensed 1 to 7 mean total defined daily doses per month, and 124 594 (16.3%) received more than 7 defined daily doses per month. There were 2356 acute kidney injury outcomes (0.3% of participants) and 1634 chronic kidney disease outcomes (0.2%) observed. Compared with participants who received no medication, the highest exposure level was associated with significantly higher adjusted hazard ratios (aHRs) for acute kidney injury (aHR, 1.2; 95% CI, 1.1-1.4) and chronic kidney disease (aHR, 1.2; 95% CI, 1.0-1.3), with annual outcome excesses per 100 000 exposed individuals totaling 17.6 cases for acute kidney injury and 30.0 cases for chronic kidney disease.

CONCLUSIONS AND RELEVANCE

Modest but statistically significant associations were noted between the highest observed doses of NSAID exposure and incident kidney problems among active young and middle-aged adults.

Gender differences in limited duty time for lower limb injury

Background

Among active-duty military personnel, lower limb musculoskeletal injuries and related conditions (injuries) frequently arise as unintended consequences of physical training. These injuries are particularly common among women. The practical impact of such injuries on temporary military occupational disability has not been estimated with precision on a large scale.

Aims

To determine the proportion of service time compromised by limited duty days attributable to lower limb injuries, characterize the time affected by these limitations in terms of specific lower limb region and compare the limited duty time between male and female soldiers.

Methods

Administrative data and individual limited duty assignments (profiles) were obtained for active-duty US Army personnel who served in 2014. Lower limb injury-related profiles were used to calculate the percent of person-time requiring duty limitations by gender and body region.

Results

The study group was 568 753 soldiers of whom 14% were women. Nearly 13% of service days for active-duty US Army soldiers required limited duty for lower limb injuries during 2014. Knee injuries were responsible for 45% of those days. Within integrated military occupations, female soldiers experienced 27-57% more time on limited duty for lower limb injuries compared with men.

Conclusions

The substantial amount of limited duty for lower limb musculoskeletal injuries among soldiers highlights the need for improvement in training-related injury screening, prevention and timely treatment with particular attention to knee injuries. The excessive impact of lower limb injuries on female soldiers' occupational functions should be a surveillance priority in the current environment of expanding gender-integrated training.

Timing and Predictors of Mild and Severe Heat Illness among New Military Enlistees

PURPOSE

Heat illnesses are important and potentially fatal conditions among physically active individuals. We determined predictors of heat illness among enlistees in a large military population experiencing common physical activity patterns.

METHODS

We estimated the adjusted odds of mild (MHI) and severe (SHI) heat illness associated with demographic, health-related, and geographic factors among active-duty, US Army soldiers enlisting between January 2011 and December 2014 (N = 238,168) using discrete-time multivariable logistic regression analyses.

RESULTS

We observed 2612 incident cases of MHI and 732 incident cases of SHI during 427,922 person-years of follow-up, with a mean and median of 21.6 and 21 months per subject. During the first 6 duty months, 71.3% of the MHIs and 60.2% of the SHIs occurred, peaking at month 2. The odds of MHI quadrupled among those with prior SHI (odds ratio [OR], 4.02; 95% confidence interval [CI], 2.67-6.03). Body mass index (BMI) extremes increased the odds substantially (OR at BMI ≥30 kg·m: for MHI, 1.41 (CI, 1.19-1.67); for SHI, 1.94 (CI, 1.47-2.56); OR at BMI <18.5 kg·m: for MHI, 1.50 (CI, 1.01-2.21); for SHI, 2.26 (CI, 1.16-4.39)). Tobacco use was associated with a 55% increase (CI, 1.37-1.77) in MHI odds. The odds of MHI increased if taking nonsteroidal anti-inflammatory drugs, opioids, or methylphenidate stimulants. Lower age and lower entry aptitude scores were associated with progressively increased MHI odds.

CONCLUSIONS

Most heat illnesses occurred at the outset of service, indicating the need for focused prevention methods at the initiation of military duty. Prior heat illness, BMI extremes, medications, and tobacco use represent potentially actionable risk factors to address by education, policy, and/or clinician intervention.

Deployment and Preterm Birth Among US Army Soldiers

With increasing integration of women into combat roles in the US military, it is critical to determine whether deployment, which entails unique stressors and exposures, is associated with adverse reproductive outcomes. Few studies have examined whether deployment increases the risk of preterm birth; no studies (to our knowledge) have examined a recent cohort of servicewomen. We therefore used linked medical and administrative data from the Stanford Military Data Repository for all US Army soldiers with deliveries between 2011 and 2014 to estimate the associations of prior deployment, recency of deployment, and posttraumatic stress disorder with spontaneous preterm birth (SPB), adjusting for sociodemographic, military-service, and health-related factors. Of 12,877 deliveries, 6.1% were SPBs. The prevalence was doubled (11.7%) among soldiers who delivered within 6 months of their return from deployment. Multivariable discrete-time logistic regression models indicated that delivering within 6 months of return from deployment was strongly associated with SPB (adjusted odds ratio = 2.1, 95% confidence interval: 1.5, 2.9). Neither multiple past deployments nor posttraumatic stress disorder was significantly associated with SPB. Within this cohort, timing of pregnancy in relation to deployment was identified as a novel risk factor for SPB. Increased focus on servicewomen's pregnancy timing and predeployment access to reproductive counseling and effective contraception is warranted.

Gender differences in the associations of body mass index, physical fitness and tobacco use with lower extremity musculoskeletal injuries among new US Army soldiers

BACKGROUND

Musculoskeletal (MSK) injuries are a leading cause of morbidity among US Army soldiers, especially among women and the newly enlisted. While extremes of body mass index (BMI), low physical fitness and tobacco use have been identified as risk factors, no prior studies have determined the combined effects of these risk factors or tested for gender differences in the associations.

METHODS

We conducted a retrospective cohort study utilising the Stanford Military Data Repository to study all enlisted soldier accessions to the US Army between January 2011 and January 2014, with follow-up through December 2014 (n=238 772). We used discrete-time logistic regression to test for associations between demographic, socioeconomic and health behaviour-related predictors and incident lower extremity injuries. We included interaction terms to test for gender differences.

RESULTS

Among men, there were greater adjusted odds of injury among underweight (OR 1.27), overweight (OR 1.14) and obese soldiers (OR 1.54) (all p<0.001) relative to normal-weight soldiers. No statistically significant differences in the odds of injury on the basis of BMI were observed for female soldiers. Physical fitness was a significantly stronger predictor of injury for female as compared with male soldiers, while the association between tobacco use and injury was stronger for men (OR 1.47) than for women (OR 1.30) (p<0.001 for both).

CONCLUSION

This is the largest known study to simultaneously assess important, modifiable musculoskeletal injury risk factors and to test for gender differences in these associations. These findings provide critical gender-related nuances for clinicians and leaders seeking to reduce the risk of these problems.

Sickle Cell Trait and Heat Injury Among US Army Soldiers

There is concern that sickle cell trait (SCT) increases risk of exertional collapse, a primary cause of which is heat injury. However, to our knowledge, no population-based studies among active individuals have addressed this, representing a critical evidence gap. We conducted a retrospective cohort study of SCT-tested African-American soldiers who were on active duty in the US Army anytime between January 2011 and December 2014. Using Cox proportional hazards models and adjusting for demographic and medical factors, we observed no significant associations between SCT and either mild heat injury (hazard ratio (HR) = 1.15, 95% confidence interval (CI): 0.84, 1.56; n = 45,999) or heat stroke (HR = 1.11, 95% CI: 0.44, 2.79; n = 46,183). Risk of mild heat injury was substantially higher among soldiers with recent prescriptions for antipsychotic agents (HR = 3.25, 95% CI: 1.33, 7.90). Risk of heat stroke was elevated among those with a prior mild heat injury (HR = 17.7, 95% CI: 8.50, 36.7) and among overweight and obese individuals (HR = 2.91 (95% CI: 1.38, 6.17) and HR = 4.04 (95% CI: 1.72, 9.45), respectively). In a setting where universal precautions are utilized to mitigate risk of exertion-related illnesses, SCT is not associated with either mild heat injury or heat stroke.

Is Provider Secure Messaging Associated With Patient Messaging Behavior? Evidence From the US Army

Background

Secure messaging with health care providers offers the promise of improved patient-provider relationships, potentially facilitating outcome improvements. But, will patients use messaging technology in the manner envisioned by policy-makers if their providers do not actively use it?

Objective

We hypothesized that the level and type of secure messaging usage by providers might be associated with messaging initiation by their patients.

Methods

The study employed a dataset of health care and secure messaging records of more than 81,000 US Army soldiers and nearly 3000 clinicians with access to a patient portal system. We used a negative binomial regression model on over 25 million observations to determine the adjusted association between provider-initiated and provider-response messaging and subsequent messaging by their patients in this population over a 4-year period.

Results

Prior provider-initiated and response messaging levels were associated with new patient messaging when controlling for the patient’s health care utilization and diagnoses, with the strongest association for high provider-response messaging level. Patients whose providers were highly responsive to the messages of other patients initiated 334% more secure messages (P<.001) than patients with providers who did not personally respond to other patients’ messages.

Conclusions

Our results indicate that provider messaging usage levels and types thereof predict their patients’ subsequent communication behavior. The findings suggest the need for more study into the factors associated with provider messaging to fully understand the mechanisms of this relationship.

Sickle Cell Trait, Rhabdomyolysis, and Mortality among U.S. Army Soldiers

BACKGROUND

Studies have suggested that sickle cell trait elevates the risks of exertional rhabdomyolysis and death. We conducted a study of sickle cell trait in relation to these outcomes, controlling for known risk factors for exertional rhabdomyolysis, in a large population of active persons who had undergone laboratory tests for hemoglobin AS (HbAS) and who were subject to exertional-injury precautions.

METHODS

We used Cox proportional-hazards models to test whether the risks of exertional rhabdomyolysis and death varied according to sickle cell trait status among 47,944 black soldiers who had undergone testing for HbAS and who were on active duty in the U.S. Army between January 2011 and December 2014. We used the Stanford Military Data Repository, which contains comprehensive medical and administrative data on all active-duty soldiers.

RESULTS

There was no significant difference in the risk of death among soldiers with sickle cell trait, as compared with those without the trait (hazard ratio, 0.99; 95% confidence interval [CI], 0.46 to 2.13; P=0.97), but the trait was associated with a significantly higher adjusted risk of exertional rhabdomyolysis (hazard ratio, 1.54; 95% CI, 1.12 to 2.12; P=0.008). This effect was similar in magnitude to that associated with tobacco use, as compared with no use (hazard ratio, 1.54; 95% CI, 1.23 to 1.94; P<0.001), and to that associated with having a body-mass index (BMI; the weight in kilograms divided by the square of the height in meters) of 30.0 or more, as compared with a BMI of less than 25.0 (hazard ratio, 1.39; 95% CI, 1.04 to 1.86; P=0.03). The effect was less than that associated with recent use of a statin, as compared with no use (hazard ratio, 2.89; 95% CI, 1.51 to 5.55; P=0.001), or an antipsychotic agent (hazard ratio, 3.02; 95% CI, 1.34 to 6.82; P=0.008).

CONCLUSIONS

Sickle cell trait was not associated with a higher risk of death than absence of the trait, but it was associated with a significantly higher risk of exertional rhabdomyolysis. (Funded by the National Heart, Lung, and Blood Institute and the Uniformed Services University of the Health Sciences.).

PEA-15 potentiates H-Ras-mediated epithelial cell transformation through phospholipase D

The small GTPase H-Ras is a proto-oncogene that activates a variety of different pathways including the extracellular-signal-regulated kinase mitogen-activated protein kinase (ERK/MAPK) pathway. H-Ras is mutated in many human malignancies and these mutations cause the protein to be constitutively active. PEA-15 blocks ERK-dependent gene transcription and inhibits proliferation by sequestering ERK in the cytoplasm. We therefore investigated whether PEA-15 influences H-Ras mediated transformation. We found that PEA-15 does not block H-Ras activated proliferation when H-Ras is constitutively active. We show instead that in H-Ras transformed mouse kidney epithelial cells, co-expression of PEA-15 resulted in enhanced soft agar colony growth and increased tumor growth in vivo. Overexpression of both H-Ras and PEA-15 resulted in accelerated G1/S cell cycle transition and increased activation of the ERK signaling pathway. PEA-15 mediated these effects through activation of its binding partner phospholipase D1 (PLD1). Inhibition of PLD1 or interference with PEA-15/PLD1 binding blocked PEA-15’s ability to increase ERK activation. Our findings reveal a novel mechanism by which PEA-15 positively regulates Ras/ERK signaling and increases the proliferation of H-Ras transformed epithelial cells through enhanced PLD1 expression and activation. Thus, our work provides a surprising mechanism by which PEA-15 augments H-Ras driven transformation. These data reveal that PEA-15 not only suppresses ERK signaling and tumorigenesis but can alternatively enhance tumorigenesis in the context of active Ras.

Ethnic differences in femur geometry in the women's health initiative observational study

SUMMARY

Participants in the observational study of the Women's Health Initiative (WHI) were studied to determine if ethnic differences in femur geometry can help to explain differences in hip fracture rates. Structural differences in femurs of African and Mexican-American women appear to be consistent with lower rates of hip fractures vs. whites.

INTRODUCTION

Ethnic origin has a major influence on hip fractures, but the underlying etiology is unknown. We evaluated ethnic differences in hip fracture rates among 159,579 postmenopausal participants in the WHI then compared femur bone mineral density (BMD) and geometry among a subset with dual X-ray absorptiometry (DXA) scans of the hip and total body.

METHODS

The subset included 8,206 non-Hispanic whites, 1,476 African-American (AA), 704 Mexican-American (MA), and 130 Native Americans (NA). Femur geometry derived from hip DXA using hip-structure analysis (HSA) in whites was compared to minority groups after adjustment for age, height, weight, percent lean mass, neck-shaft angle and neck length, hormone use, chronic disease (e.g., diabetes, rheumatoid arthritis, cancer), bone active medications (e.g., corticosteroids, osteoporosis therapies), and clinical center.

RESULTS

Both AA and MA women suffered hip fractures at half the rate of whites while NA appeared to be similar to whites. The structural advantage among AA appears to be due to a slightly narrower femur that requires more bone tissue to achieve similar or lower section moduli (SM) vs. whites. This also underlies their higher BMD (reduces region area) and lower buckling ratios (buckling susceptibility). Both MA and NA women had similar advantages vs. whites at the intertrochanter region where cross-sectional area and SM were higher but with no differences at the neck. NA and MA had smaller bending moments vs. whites acting in a fall on the hip (not significant in small NA sample). Buckling ratios of MA did not differ from whites at any region although NA had 4% lower values at the IT region.

CONCLUSION

Differences in the geometry at the proximal femur are consistent with the lower hip fracture rates among AA and MA women compared to whites.

Determining localized garment insulation values from manikin studies: computational method and results

The localized thermal insulation value expresses a garment's thermal resistance over the region which is covered by the garment, rather than over the entire surface of a subject or manikin. The determination of localized garment insulation values is critical to the development of high-resolution models of sensible heat exchange. A method is presented for determining and validating localized garment insulation values, based on whole-body insulation values (clo units) and using computer-aided design and thermal analysis software. Localized insulation values are presented for a catalog consisting of 106 garments and verified using computer-generated models. The values presented are suitable for use on volume element-based or surface element-based models of heat transfer involving clothed subjects.

Radial bone density and breast cancer risk in white and African-American women

A number of different models for assessing individual risk of breast cancer use known risk factors such as age, age at menarche, age at first live birth, previous breast biopsies, and family history. High bone mass in white women is also associated with an increased breast cancer risk; however, bone mass as a risk factor has not been studied in African-American women. We conducted a case-control study to evaluate bone mineral density as a risk factor for breast cancer in white and African-American women. We recruited 221 women with newly diagnosed breast cancer from a comprehensive breast cancer center at a large university hospital, and 197 control women who were frequency matched for ethnicity and age. Odds ratios were based on proximal and distal radial bone density measured by peripheral bone densitometry (Norland pDEXA) and expressed as a standardized "Z-score" (age and ethnicity specific). Logistic regression models were fitted controlling for body mass index, menopausal status, age, and HRT use (ever/never and duration). With proximal bone density Z-score included in the model as a continuous variable, a one-unit increase in radial shaft bone density increased the risk of breast cancer by 25% (p=0.02). When proximal bone density Z-score was analyzed as a dichotomous variable (< or = 0, > 0) the odds ratio was 1.98 (95% CI, 1.32 to 2.97); that is, having an above average proximal bone density (age-specific) doubles the risk of breast cancer. There were no significant interactions with, and no appreciable confounding effects by, other covariates. An above-average radial shaft Z-score is a significant risk factor for breast cancer in both white and African-American women. The present study extends the association between bone mass and breast cancer risk to African-Americans, and suggests another potential application for bone density testing.

Inter-species extrapolation of skin heating resulting from millimeter wave irradiation: modeling and experimental results

This study reports measurements of the skin surface temperature elevations during localized irradiation (94 GHz) of three species: rat (irradiated on lower abdomen), rhesus monkey (posterior forelimb), and human (posterior forearm). Two exposure conditions were examined: prolonged, low power density microwaves (LPM) and short-term, high power density microwaves (HPM). Temperature histories were compared with calculations from a bio-heat transfer model. The mean peak surface temperature increase was approximately 7.0 degrees C for the short-term HPM exposures for all three species/locations, and 8.5 degrees C (monkey, human) to 10.5 degrees C (rat) for the longer-duration LPM exposures. The HPM temperature histories are in close agreement with a one-dimensional conduction heat transfer model with negligible blood flow. The LPM temperature histories were compared with calculations from the bio-heat model, evaluated for various (constant) blood flow rates. Results suggest a variable blood flow model, reflecting a dynamic thermoregulatory response, may be more suited to describing skin surface temperature response under long-duration MMW irradiation.

Selective stationary phase for solid-phase microextraction analysis of sarin (GB)

A number of critical field applications require monitoring air samples for trace levels of chemical warfare agents. Solid-phase microextraction (SPME) is a convenient format to conduct these analyses. Measurements could be significantly improved if a SPME phase selective for nerve agents were substituted for non-selective polymers typically used (e.g., polydimethylsiloxane). This paper evaluates a novel stationary phase, previously developed for methylphosphonate sensor applications, for use with SPME sampling. The phenol-based polymer, BSP3, was found to offer far higher selectivity toward sarin (GB) than polydimethylsiloxane due to a pronounced affinity toward the target analyte and a lower affinity toward hydrocarbons.

Empirical validation of SAR values predicted by FDTD modeling

Rapid increase in the use of numerical techniques to predict current density or specific absorption rate (SAR) in sophisticated three dimensional anatomical computer models of man and animals has resulted in the need to understand how numerical solutions of the complex electrodynamics equations match with empirical measurements. This aspect is particularly important because different numerical codes and computer models are used in research settings as a guide in designing clinical devices, telecommunication systems, and safety standards. To ensure compliance with safety guidelines during equipment design, manufacturing and maintenance, realistic and accurate models could be used as a bridge between empirical data and actual exposure conditions. Before these tools are transitioned into the hands of health safety officers and system designers, their accuracy and limitations must be verified under a variety of exposure conditions using available analytical and empirical dosimetry techniques. In this paper, empirical validation of SAR values predicted by finite difference time domain (FDTD) numerical code on sphere and rat is presented. The results of this study show a good agreement between empirical and theoretical methods and, thus, offer a relatively high confidence in SAR predictions obtained from digital anatomical models based on the FDTD numerical code.

A new procedure for measuring peripheral compression in normal-hearing and hearing-impaired listeners

Forward-masking growth functions for on-frequency (6-kHz) and off-frequency (3-kHz) sinusoidal maskers were measured in quiet and in a high-pass noise just above the 6-kHz probe frequency. The data show that estimates of response-growth rates obtained from those functions in quiet, which have been used to infer cochlear compression, are strongly dependent on the spread of probe excitation toward higher frequency regions. Therefore, an alternative procedure for measuring response-growth rates was proposed, one that employs a fixed low-level probe and avoids level-dependent spread of probe excitation. Fixed-probe-level temporal masking curves (TMCs) were obtained from normal-hearing listeners at a test frequency of 1 kHz, where the short 1-kHz probe was fixed in level at about 10 dB SL. The level of the preceding forward masker was adjusted to obtain masked threshold as a function of the time delay between masker and probe. The TMCs were obtained for an on-frequency masker (1 kHz) and for other maskers with frequencies both below and above the probe frequency. From these measurements, input/output response-growth curves were derived for individual ears. Response-growth slopes varied from >1.0 at low masker levels to <0.2 at mid masker levels. In three subjects, response growth increased again at high masker levels (>80 dB SPL). For the fixed-level probe, the TMC slopes changed very little in the presence of a high-pass noise masking upward spread of probe excitation. A greater effect on the TMCs was observed when a high-frequency cueing tone was used with the masking tone. In both cases, however, the net effects on the estimated rate of response growth were minimal.

Psychophysical recovery from single-pulse forward masking in electric hearing

Psychophysical single-pulse forward-masking (SPFM) recovery functions were measured for three electrodes in each of eight subjects with the nucleus mini-22 cochlear implant. Masker and probe stimuli were single 200-micros/phase biphasic current pulses. Recovery functions were measured at several masker levels spanning the electric dynamic range of electrodes chosen from the apical, middle, and basal regions of each subject's electrode array. Recovery functions were described by an exponential process in which threshold shift (in microA) decreased exponentially with increasing time delay between the masker and probe pulses. Two recovery processes were observed: An initial, rapid-recovery process with an average time constant of 5.5 ms was complete by about 10 ms. A second, slow-recovery process involved less masking than the rapid-recovery process but encompassed much longer time delays, sometimes as long as several hundred milliseconds. Growth-of-masking slopes for the rapid process depended upon time delay, as expected in an exponential recovery process. Unity slopes were observed at a time delay of 0 ms, whereas progressively shallower slopes were observed at time delays of 2 ms and 5 ms. Many recovery functions demonstrated nonmonotonicities or "facilitation" at very short masker-probe delays (1-2 ms). Such nonmonotonicities were usually most pronounced at low masker levels. Time constants for the rapid-recovery process did not vary systematically with masker level or with electrode location along the implanted array. Most subjects demonstrated rapid-recovery time constants less than 7 ms; however, the subject with the longest duration of deafness prior to implantation exhibited clearly prolonged time constants (9-24 ms). Time constants obtained on basal electrodes were inversely related to word recognition scores.

The effect of basilar-membrane nonlinearity on the shapes of masking period patterns in normal and impaired hearing

Masking period patterns (MPPs) were measured in listeners with normal and impaired hearing using amplitude-modulated tonal maskers and short tonal probes. The frequency of the masker was either the same as the frequency of the probe (on-frequency masking) or was one octave below the frequency of the probe (off-frequency masking). In experiment 1, MPPs were measured for listeners with normal hearing using different masker levels. Carrier frequencies of 3 and 6 kHz were used for the masker. The probe had a frequency of 6 kHz. For all masker levels, the off-frequency MPPs exhibited deeper and longer valleys compared with the on-frequency MPPs. Hearing-impaired listeners were tested in experiment 2. For some hearing-impaired subjects, masker frequencies of 1.5 kHz and 3 kHz were paired with a probe frequency of 3 kHz. MPPs measured for listeners with hearing loss had similar shapes for on- and off-frequency maskers. It was hypothesized that the shapes of MPPs reflect nonlinear processing at the level of the basilar membrane in normal hearing and more linear processing in impaired hearing. A model assuming different cochlear gains for normal versus impaired hearing and similar parameters of the temporal integrator for both groups of listeners successfully predicted the MPPs.