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Biomedical subjects

Michael R Peterson

Publications and source records attributed to Michael R Peterson.

16 recordsLinked to original sources
PubMed2006

Strong correlations produce the Curie-Weiss phase of NaxCoO2.

Within the t-J model we study several experimentally accessible properties of the 2D-triangular lattice system NaxCoO2, using a numerically exact canonical ensemble study of 12 to 18 site triangular toroidal clusters as well as the icosahedron. Focusing on the doping regime of x approximately 0.7, we study the temperature dependent specific heat, magnetic susceptibility, and the dynamic Hall coefficient R_{H}(T,omega) as well as the magnetic field dependent thermopower. We find a crossover between two phases near x approximately 0.75 in susceptibility and field suppression of the thermopower arising from strong correlations. An interesting connection is found between the temperature dependence of the diamagnetic susceptibility and the Hall coefficient. We predict a large thermopower enhancement, arising from transport corrections to the Heikes-Mott formula, in a model situation where the sign of hopping is reversed from that applicable to NaxCoO2.

Journal Article↗
PubMed2006

Association between obesity and depressive symptoms among U.S. Military active duty service personnel, 2002.

PURPOSE: The association between obesity and depression remains equivocal. The purpose of this study was to describe the prevalence and association of obesity and depressive symptoms among military personnel. METHODS: A cross-sectional analysis was performed using data (N=10,040) from the U.S. Department of Defense (DoD) Survey of Health-Related Behaviors. Prevalence odds ratios were calculated to describe the association between obesity and depressive symptoms. RESULTS: Approximately 10% of active duty men and 4% of active duty women were obese. The prevalence of depressive symptoms ranged from approximately 16% of overweight men to 49% of obese women. Obese men and women and underweight men had increased odds of depressive symptoms as compared with normal-weight individuals. CONCLUSIONS: The DoD should emphasize prevention and regular screening for obesity and depressive symptoms to improve readiness and reduce health care costs and disease burden in this cohort.

Adult↗
PubMed2006

Strong PDGFRA positivity is seen in GISTs but not in other intra-abdominal mesenchymal tumors: Immunohistochemical and mutational analyses.

Mutation of the platelet-derived growth factor receptor-alpha (PDGFRA) gene has been well documented as an alternative oncogenic mechanism in a subset of gastrointestinal stromal tumors (GISTs) lacking c-kit mutations. However, the role of PDGFRA immunohistochemistry in the diagnosis of GISTs has not been well studied. We investigated PDGFRA immunoreactivity in GISTs and in other intra-abdominal mesenchymal tumors, and correlated PDGFRA expression with CD117 positivity and with the mutational status of PDGFRA and c-kit genes. In addition, expression of phosphorylated AKT, an activated downstream molecule in the PDGFRA and c-kit signaling pathways, was correlated with PDGFRA and CD117 status. A total of 39 GISTs and 20 other mesenchymal tumors in the abdomen were included in this study. Thirty-five of 39 GIST cases (89.7%) were positive for PDGFRA and 19 of these 35 positive cases were strongly positive. Five of 20 non-GIST lesions (25%) were positive for PDGFRA, but none of these cases were strongly positive. With one exception, PDGFRA-positive cases were also positive for CD117. Phosphorylated AKT positivity was not associated with the immunoreactivity or mutation of PDGFRA and c-kit, suggesting that the activation of AKT is probably independent of the activation of PDGFRA and c-kit in GISTs. Of 14 GISTs assayed, 4 had mutations in c-kit at exons 11 or 17, and 4 had mutations in PDGFRA at exons 12 or 18. Three of 4 GIST cases with PDGFRA mutations show epithelioid morphology and strong PDGFRA immunoreactivity with prominent perinuclear dotlike accentuation (so-called Golgi pattern). In conclusion, strong PDGFRA positivity with Golgi pattern is a useful adjunct in the diagnosis of GISTs with PDGFRA mutation.

Abdominal Neoplasms↗
PubMed2006

Epstein-Barr virus-associated posttransplantation lymphoproliferative disorder following lung transplantation is more commonly of host origin.

CONTEXT: Posttransplantation lymphoproliferative disorder (PTLD) in patients who have undergone solid organ transplantation is thought to be mostly of host (ie, transplant recipient) origin, as opposed to being predominantly of donor origin, which is observed in patients who have undergone bone marrow transplantation. Donor-origin PTLDs reportedly follow a more indolent course than host-origin PTLDs. OBJECTIVE: To determine the origin of PTLD and its clinical implications in patients who have undergone lung transplantation. DESIGN: Patients' medical records were reviewed for clinical data. We performed a molecular study to determine the origin of abnormal lymphoid cells in 4 PTLD cases identified from our autopsy files. Each case underwent restriction fragment length polymorphism analysis using polymerase chain reaction-based genotyping for CYP2D6. Epstein-Barr virus (latent membrane protein 1) immunostaining and polymerase chain reaction analysis were performed on PTLD-involved tissues. RESULTS: Three of 4 PTLD cases were of host origin, and the remaining case was of donor origin. Epstein-Barr virus was detected by immunohistochemical and polymerase chain reaction methods in all PTLD-involved tissues that were examined. There was no apparent difference in clinical manifestations between host-origin and donor-origin PTLD cases in our study. CONCLUSIONS: The PTLDs in our patients who had undergone lung transplantation were Epstein-Barr virus-positive and mostly of host origin, without any notable clinical difference from donor-origin PTLD.

Aged↗
PubMed2005

Reconstructing the electron in a fractionalized quantum fluid.

The low-energy physics of the fractional Hall liquid is described in terms of quasiparticles that are qualitatively distinct from electrons. We show, however, that a long-lived electronlike quasiparticle also exists in the excitation spectrum: the state obtained by the application of an electron creation operator to a fractional quantum Hall ground state has a nonzero overlap with a complex, high energy bound state containing an odd number of composite-fermion quasiparticles. The electron annihilation operator similarly couples to a bound complex of composite-fermion holes. We predict that these bound states can be observed through a conductance resonance in experiments involving a tunneling of an external electron into the fractional quantum Hall liquid. A comment is made on the origin of the breakdown of the Fermi liquid paradigm in the fractional Hall liquid.

Journal Article↗
PubMed2005

Clinical case mix adjustment of cesarean delivery rates in U.S. military hospitals, 2002.

OBJECTIVE: To assess whether significant variations in observed cesarean rates in U.S. military hospitals may be attributed to differences in clinical case mix. METHODS: Hospital discharge records for births in U.S. military hospitals in 2002 were grouped into mutually exclusive clinical strata to calculate predicted cesarean rates for subgroups defined by maternal race, health plan, hospital location, delivery volume, teaching status, and neonatal intensive care unit (NICU) status. The 95% confidence interval (CI) around each standardized ratio (SR) of the observed-to-predicted cesarean rate was used to assess statistical significance. RESULTS: Observed cesarean rates were significantly higher than predicted rates for small hospitals (23.1% and 20.4%, respectively, SR 1.13, 95% CI 1.08-1.19), teaching hospitals (23.7% and 22.5%, respectively, SR 1.05, 95% CI 1.02-1.08), black women (25.1% and 22.8%, respectively, SR 1.10, 95% CI 1.05-1.14), and other minorities (22.7%, and 21.6%, respectively, SR 1.05, 95% CI 1.01-1.09). No significant differences between observed and predicted cesarean rates were found across hospital locations or NICU status. Significant differences found for non-managed care beneficiaries were attributed to teaching status of the hospitals in which they delivered. CONCLUSION: Clinical case mix does not adequately account for the relatively high rates of cesarean delivery observed for small hospitals and teaching hospitals and among black women in the study population. Further study is recommended to identify additional clinical and nonclinical factors that should be considered when comparing performance across institutions, health plans, or individual providers.

Adult↗
PubMed2005

Childbearing in U.S. military hospitals: dimensions of care affecting women's perceptions of quality and satisfaction.

BACKGROUND: The U.S. Department of Defense provides medical services for approximately 9.1 million beneficiaries, one-half of whom are women. Information is lacking about how well the military health system has adopted patient-centered approaches for promoting individual choice and preference in a bureaucratically structured military hospital. The purpose of this study was to examine women's evaluations of maternity care with respect to decision-making, confidence, trust in health care providers, and treatment within the military hospital. METHODS: The Department of Defense Inpatient Childbirth Survey was mailed to a simple stratified random sample of beneficiaries who received maternity care at a military hospital between July 1 and September 30, 2001. Data for 11 dimensions of women's care and experiences were examined from self-reported assessments of 2,124 respondents who gave birth at one of 44 military hospitals. A multiple logistic regression model was estimated to determine which dimensions of care predicted beneficiaries' likelihood to recommend the military hospital to family and friends. RESULT: Less than 50 percent of respondents would recommend the military hospital to family and friends. Significantly associated with women's willingness to recommend their specific military hospital to others were courtesy and availability of staff, confidence and trust in provider, treatment with respect and dignity, information and education, physical comfort, involvement of friends and family, continuity and transition, and involvement in decision-making. CONCLUSIONS: In a military population, obstetric patients who are treated with respect, courtesy, and dignity, are involved in decisions about their care, and have established trusting relationships with their practitioners are significantly more likely to recommend the military hospital to others. It is important for military health care leaders to establish a proactive program of patient-centered maternity care. Continuous care, education, support services, and a multidisciplinary approach should be integrated to retain and recapture obstetric patients who are served in military hospitals in the United States.

Adolescent↗
PubMed2004

Burden of disease associated with overweight and obesity among U.S. military retirees and their dependents, aged 38-64, 2003.

PURPOSE: The prevalence of overweight and obesity is increasing in the general US population and in beneficiaries of the Department of Defense (DoD) Military Healthcare System. The purpose of this study was to describe the prevalence and correlation of overweight, obesity and associated co-morbidities in the DoD beneficiary population. METHODS: A cross-sectional analysis was preformed on data from the DoD's 2003 Population Health Survey. Prevalence odds ratios (POR) were used to describe the association between overweight and obesity categories and prevalence of co-morbidities. RESULTS: Eighty percent of men and 60% of women were overweight or obese and 33% of men and 29% of women were obese. The PORs increased in magnitude corresponding to increasing BMI categories for all co-morbidities. The percent of individuals reporting between 2 and 4 co-morbidities also increased with increasing weight class. CONCLUSIONS: Overweight, obesity and associated co-morbidities are prevalent among DoD beneficiaries. Overweight and obese individuals have an increased prevalence of co-morbidities compared to normal weight individuals. Twenty plus years of active duty in the military does not confer any long-term protection against overweight, obesity or the associated co-morbidities. The DoD should emphasize prevention in order to reduce healthcare costs and the disease burden in this cohort.

Adult↗
PubMed2004

Flavor altering excitations of composite fermions.

Past theoretical studies have considered excitations of a given flavor of composite fermions across composite-fermion quasi-Landau levels. We show that in addition there exists a ladder of flavor changing excitations in which composite fermions are partially dissociated by a removal of some or all of their vortices, and suggest that these are relevant to the intriguing experimental discovery of Hirjibehedin et al. [Phys. Rev. Lett. 91, 186802 (2003)] of coexisting excitation modes of composite fermions of different flavors in the filling factor range 1/3 > nu > or = 1/5.

Journal Article↗
PubMed2004

Effect of preexisting chronic disease on primary cesarean delivery rates by race for births in U.S. military hospitals, 1999-2002.

BACKGROUND: A previous study of the United States Department of Defense healthcare beneficiaries reported elevated cesarean delivery rates for black and Asian women relative to white women that were independent of maternal socioeconomic status. This finding suggests that other maternal factors may explain the elevated rates. The purpose of this study was to examine the prevalence of specific chronic diseases identified as risk factors for complications during pregnancy, labor, and delivery, and to explore the strength of each disease to predict a cesarean outcome. METHODS: United States military hospital discharge records from 1999 to 2002 for singleton births to women without a previous cesarean were used to calculate primary cesarean and chronic disease rates for diabetes, hypertension, cardiovascular disease, renal disease, anemia, asthma, sexually transmitted diseases, and substance abuse. Stepwise logistic regression was used to calculate adjusted odds ratios for dichotomized race and chronic disease indicators for five maternal age groups using the chi2 difference (p < 0.05) to identify significant variables for inclusion in the model. Primary cesarean delivery rates were then adjusted for the presence of chronic diseases that were significantly associated with a cesarean outcome. RESULTS: Diabetes, genital herpes, and hypertension were significant predictors of cesarean use among all maternal age groups. Cardiovascular disease, renal disease, asthma, and anemia were predictors in some age groups. The remaining disease conditions were not significant predictors for cesarean delivery. Adjustment of cesarean rates for these chronic diseases did not significantly alter the differences in primary cesarean rates for black and Asian mothers relative to white mothers. CONCLUSIONS: The presence of certain chronic conditions before pregnancy may increase the likelihood that a woman will deliver by cesarean section. Adjustment of cesarean rates for the presence of these chronic diseases, however, does not account for the difference in cesarean rates observed for white and minority mothers in the study population. The potential for underreporting of chronic diseases complicates a true assessment of the impact of chronic disease on cesarean delivery rate variations between white and minority women.

Adult↗
PubMed2004

Effect of managed care enrollment on primary and repeat cesarean rates among U.S. Department of Defense health care beneficiaries in military and civilian hospitals worldwide, 1999-2002.

BACKGROUND: In response to rising cesarean rates, it is reasonable for health care organizations to look to a managed care model as a means of controlling further rate increases. However, little conclusive evidence exists to support this solution. We undertook a study of the Department of Defense health care beneficiary population to assess the impact of enrollment in TRICARE Prime, the Department's managed care health plan, on cesarean delivery rates. METHODS: Pooled hospital discharge records from 1999-2002 for live, singleton births were analyzed to calculate primary and repeat cesarean rates for TRICARE Prime and non-Prime beneficiaries in the military and civilian hospitals that comprise the Department of Defense health care network. Stepwise logistic regression was used to calculate adjusted odds ratios for clinical indicators for each combination of health plan and hospital setting using the chi2 difference(p <0.05)to eliminate nonsignificant variables from the model. Total primary and repeat cesarean rates were compared with primary and repeat cesarean rates for women with no reported clinical complications to account for differences in case mix across subgroups. Statistical significance of the differences calculated for subgroups was assessed using chi2. RESULTS: Primary cesarean rates were significantly lower for TRICARE Prime enrollees relative to non-Prime beneficiaries for all race subgroups and three of five age subgroups in military hospitals and four of five age subgroups in civilian hospitals. No significant differences in repeat cesarean rates were observed between Prime and non-Prime beneficiaries within any race or age subgroup. Breech presentation followed by dystocia, fetal distress, and other complications were significant predictors for primary cesarean. Previous cesarean delivery was the leading predictor for repeat cesarean delivery. Primary and repeat cesarean rates observed for military hospitals were consistently lower than rates observed for civilian hospitals within each health plan type and age group. CONCLUSIONS: Enrollment in the managed care health plan was significantly associated with lower risk of primary cesarean delivery relative to membership in other health plans offered to Department of Defense health care beneficiaries. Repeat cesarean rates in this population varied independently of health plan type. Primary cesarean delivery was generally associated with clinical complications, whereas previous cesarean delivery was the strongest indicator for a repeat cesarean delivery. A clear explanation of reduced cesarean rates for Prime enrollees remains elusive, but it is likely that factors beyond individual practitioner decision-making were at work.

Adult↗
PubMed2004

Effects of maternal characteristics on cesarean delivery rates among U.S. Department of Defense healthcare beneficiaries, 1996-2002.

BACKGROUND: National rates of cesarean birth continue a three decade-long escalation, despite widespread recognition that a reduction in the use of the procedure is a continuing appropriate public health goal, as evidenced by the Healthy People 2010 reduction targets. Nonclinical factors associated with cesarean delivery include maternal age, race, socioeconomic status, and insurance coverage. This study compared cesarean delivery rates and trends for the U.S. Department of Defense healthcare beneficiary population from 1996 to 2002 with those observed nationally, and assessed the association of these nonclinical factors with cesarean rate variation in the U.S. Department of Defense healthcare beneficiary population. METHODS: Hospital discharge and claims records for babies born in the military and civilian hospitals that comprise the Department of Defense healthcare network were used to calculate total and primary cesarean delivery rates and vaginal birth after cesarean (VBAC) rates from 1996 to 2002. Annual cesarean rates for subgroups defined by maternal age, race, and socioeconomic status were calculated to examine rate variations and rate trends within the study population. Pooled data from 1999 to 2002 were used to compare rates across socioeconomic status, stratified by age and race. Statistical significance of the differences calculated for subgroups was assessed using chi-square. RESULTS: Total and primary cesarean delivery rates among the U.S. Department of Defense population were lower than those reported nationally for every year examined. Cesarean delivery and VBAC rate trends in the national and Department of Defense populations were similar. Within the Department of Defense population, total cesarean delivery increased with increasing maternal age and was more highly associated with racial minorities relative to white women. The higher socioeconomic subgroup (defined as active duty, retired, and warrant officers and their families in this study) was generally associated with reduced cesarean delivery rates. CONCLUSIONS: Cesarean deliveries are performed less frequently for the U.S. Department of Defense healthcare beneficiary population relative to the national population. Associations between socioeconomic factors and cesarean rates reported for the national population were not apparent in the study population. The consistent pattern of rate variation across racial subgroups in the Department of Defense population suggests that factors beyond those examined in this study are needed to explain the elevated cesarean rates for racial minorities.

Adult↗
PubMed2004

Effect of September 11th terrorist attacks on the self-reported health status of Department of Defense health care beneficiaries.

This study examined the changes in the self-reported health status of Department of Defense health care beneficiaries associated with the September 11th terrorist attacks. Responses to a single-item, general health measure from pre- and post-September 11 quarterly survey events for the calendar year 2001 were analyzed to compare the unfavorable health response rates before and after the attacks. Increases in rates of unfavorable health status following the terrorist attacks were reported by the total population and 39 of 44 subgroups examined. Statistically significant increases in unfavorable health were reported by active duty personnel and dependents of active duty personnel; beneficiaries under the age of 44 years; beneficiaries affiliated with the Army and Marines; and beneficiaries in the Mid-Atlantic, Mid-West/Central, and Pacific Rim regions. These findings suggest that stress associated with the likelihood of being deployed or having a family member deployed following the terrorist attacks significantly contributed to the increase in unfavorable health response reported on the post-September 11 survey.

Adult↗
PubMed2003

Two-dimensional electron system in high magnetic fields: Wigner crystal versus composite-fermion liquid.

The two-dimensional system of electrons in a high magnetic field offers an opportunity to investigate a phase transition from a quantum liquid into a Wigner solid. Recent experiments have revealed an incipient composite fermion liquid in a parameter range where theory and many experiments had previously suggested the Wigner crystal phase, thus calling into question our current understanding. This Letter shows how very small quantitative corrections (<1%) in the energy due to the weak interaction between composite fermions can cause a fundamental change in the nature of the ground state, thus providing insight into the puzzling experimental results.

Journal Article↗
PubMedDate not supplied

Status of U.S. military retirees and their spouses toward achieving Healthy People 2010 objectives.

PURPOSE: To assess the status of U.S. military retirees and their spouses 38 to 64 years of age relative to select Healthy People 2010 objectives and to identify sociodemographic characteristics associated with select health behaviors. DESIGN: Cross-sectional analyses with self-reported standardized measures from the U.S. Department of Defense Population Health Survey, 2003. SETTING: The continental United States. SUBJECTS: U.S. military retirees and their spouses 38 to 64 years of age. MEASURES: Data for this study were self-reported responses to the Population Health Survey. Dichotomous variables were created to indicate whether each Healthy People 2010 objective had been met. Each objective was measurable with the survey by using the definitions set forth in Healthy People 2010. These objectives included healthy weight and obesity based on body mass index (height and weight); daily fruit, vegetable, and grain-product consumption; physical inactivity, moderate physical activity, and vigorous physical activity; binge drinking; cigarette use; and smoking-cessation attempts. RESULTS: The study population did not meet any of the Healthy People 2010 objectives included in this study. Sociodemographic characteristics that were associated with this result included being male, not having a college degree, and a less-than-excellent self-reported general health status. CONCLUSION: Health-promotion interventions are needed to improve the health status of this population and to achieve the goals set forth in Healthy People 2010.

Adult↗