Bio

Academic Appointments


Administrative Appointments


  • Co-Director, TL-1 Program, Stanford Center for Clinical and Translational Research and Education (SPECTRUM) (2013 - Present)

Honors & Awards


  • The Kaiser Foundation Award for Excellence in Preclinical Teaching, Stanford University School of Medicine (2010)
  • Honorary Cap and Gown membership, Women’s honor society at Stanford (2009)
  • Teaching Award, Division of Epidemiology (HRP) (2006, 2008, 2010, 2011, 2012)
  • Marjorie K. Ionta Award for Outstanding Graduate Student in Physical Therapy, MGH - Inst of Health Professions (1990)

Professional Education


  • PhD, Stanford University, Epidemiology (2003)
  • MS, U Mass (Amherst), Biostatistics (1998)
  • MS, MGH Inst of Health Professions, Physical Therapy (1991)

Research & Scholarship

Current Research and Scholarly Interests


My research interest focuses on the epidemiology of Parkinson’s disease and amyotrophic lateral sclerosis, specifically evaluating the genetic and environmental contributions to these neurodegenerative disorders. I am also interested in studying the relation of cognition, estradiol exposure (endogenous and exogenous), and genetic factors.

Teaching

2013-14 Courses


Graduate and Fellowship Programs


Publications

Journal Articles


  • Changes in health status among aging survivors of pediatric upper and lower extremity sarcoma: a report from the childhood cancer survivor study. Archives of physical medicine and rehabilitation Marina, N., Hudson, M. M., Jones, K. E., Mulrooney, D. A., Avedian, R., Donaldson, S. S., Popat, R., West, D. W., Fisher, P., Leisenring, W., Stovall, M., Robison, L. L., Ness, K. K. 2013; 94 (6): 1062-1073

    Abstract

    To evaluate health status and participation restrictions in survivors of childhood extremity sarcomas.Members of the Childhood Cancer Survivor Study cohort with extremity sarcomas who completed questionnaires in 1995, 2003, or 2007 were included.Cohort study of survivors of extremity sarcomas.Childhood extremity sarcoma survivors (N=1094; median age at diagnosis, 13y (range, 0-20y); current age, 33y (range, 10-53y); 49% male; 87.5% white; 75% had lower extremity tumors) who received their diagnosis and treatment between 1970 and 1986.Not applicable.Prevalence rates for poor health status in 6 domains and 5 suboptimal social participation categories were compared by tumor location and treatment exposure with generalized estimating equations adjusted for demographic/personal factors and time/age.In adjusted models, when compared with upper extremity survivors, lower extremity survivors had an increased risk of activity limitations but a lower risk of not completing college. Compared with those who did not have surgery, those with limb-sparing (LS) and upper extremity amputations (UEAs) were 1.6 times more likely to report functional impairment, while those with an above-the-knee amputation (AKA) were 1.9 times more likely to report functional impairment. Survivors treated with LS were 1.5 times more likely to report activity limitations. Survivors undergoing LS were more likely to report inactivity, incomes <$20,000, unemployment, and no college degree. Those with UEAs more likely reported inactivity, unmarried status, and no college degree. Those with AKA more likely reported no college degree. Treatment with abdominal irradiation was associated with an increased risk of poor mental health, functional impairment, and activity limitation.Treatment of lower extremity sarcomas is associated with a 50% increased risk for activity limitations; upper extremity survivors are at a 10% higher risk for not completing college. The type of local control influences health status and participation restrictions. Both of these outcomes decline with age.

    View details for DOI 10.1016/j.apmr.2013.01.013

    View details for PubMedID 23380347

  • EFFECTS OF ENDOGENOUS AND EXOGENOUS ESTROGEN EXPOSURES IN MIDLIFE AND LATE-LIFE WOMEN ON EPISODIC MEMORY AND EXECUTIVE FUNCTIONS NEUROSCIENCE Henderson, V. W., Popat, R. A. 2011; 191: 129-138

    Abstract

    Cognitive aging affects episodic memory and executive functions, and these vulnerable domains are postulated to be modulated by endogenous and exogenous estrogen exposures. In midlife and late-life women without dementia, estrogen effects on cognition can be examined through associations with concentrations of serum estrone and estradiol and through clinical trials of estrogen-containing hormone therapy. To this end, we reviewed published studies including at least 100 women (larger studies are less prone to publication bias) addressing associations between estrogen levels and performance on neuropsychological tests of episodic memory or executive functions (including working memory; seven studies), or that reported results of placebo-controlled clinical trials of hormone therapy with objective measures within these cognitive domains (eight studies). Results were considered separately for midlife and late-life (age?65 years) women. There were no consistent associations between endogenous serum estrogen concentrations and episodic memory or executive functions in naturally menopausal midlife women or in older postmenopausal women. Clinical trial findings suggested no substantial impact of exogenous estrogens on episodic memory or executive functions over time frames of up to several years. A quantitative synthesis of clinical trial results supported the inference of absence of effect. This overall conclusion of no substantial effect on episodic memory or executive functions might reassure women concerned by potential adverse cognitive consequences of menopause or of relatively short-term midlife hormone therapy. There was no apparent window of opportunity during which exogenous hormones might benefit near-term cognition, but included studies provided limited power to identify such a window. Conclusions are tempered by small numbers of studies, imprecise estimates of long-term estrogen exposures, and narrow range of neuropsychological tests. Long-term (late-life) cognitive consequence of midlife estrogen exposures are poorly addressed by current data, as are cognitive consequences of surgical menopause and cognitive consequences of exogenous estrogens during the menopause transition. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

    View details for DOI 10.1016/j.neuroscience.2011.05.059

    View details for Web of Science ID 000295749300013

    View details for PubMedID 21664950

  • Association of DRD2 and DRD3 polymorphisms with Parkinson's disease in a multiethnic consortium JOURNAL OF THE NEUROLOGICAL SCIENCES McGuire, V., Van Den Eeden, S. K., Tanner, C. M., Kamel, F., Umbach, D. M., Marder, K., Mayeux, R., Ritz, B., Ross, G. W., Petrovitch, H., Topol, B., Popat, R. A., Costello, S., Manthripragada, A. D., Southwick, A., Myers, R. M., Nelson, L. M. 2011; 307 (1-2): 22-29

    Abstract

    To examine genetic associations of polymorphisms in the dopamine receptor D2 (DRD2) and D3 (DRD3) genes with risk of Parkinson's disease (PD).The study included 1325 newly diagnosed patients with PD and 1735 controls from a consortium of five North American case-control studies. We collected risk factor information by in-person or telephone interview. Six DRD2 and two DRD3 polymorphisms were genotyped using a common laboratory. Odds ratios were estimated using logistic regression.Among non-Hispanic whites, homozygous carriers of Taq1A DRD2 (rs1800497) polymorphism had an increased risk of PD compared to homozygous wildtype carriers (OR=1.5, 95% CI 1.0-2.3). In contrast, the direction of association for Taq1A polymorphism was opposite for African-Americans, showing an inverse association with PD risk (OR=0.10, 95% CI 0.2-0.7). Among white Hispanics who carried two alleles, the Ser9Gly DRD3 (rs6280) polymorphism was associated with a decreased risk of PD (OR=0.4, 95% CI 0.2-0.8). The inverse association of smoking with PD risk was not modified by any of the DRD2 or DRD3 polymorphisms.DRD2 polymorphisms are unlikely to be true disease-causing variants; however, three DRD2 polymorphisms (including Taq1A) may be in linkage disequilibrium with possible disease associated variants in the DRD2-ANKK1-NCAM1-TTC12 gene cluster.

    View details for DOI 10.1016/j.jns.2011.05.031

    View details for Web of Science ID 000293049500005

    View details for PubMedID 21663922

  • Understanding Study Design PM&R Sainani, K. L., Popat, R. A. 2011; 3 (6): 573-577

    View details for DOI 10.1016/j.pmrj.2011.04.001

    View details for Web of Science ID 000305437700010

    View details for PubMedID 21665169

  • Coffee, ADORA2A, and CYP1A2: the caffeine connection in Parkinson's disease EUROPEAN JOURNAL OF NEUROLOGY Popat, R. A., Van Den Eeden, S. K., Tanner, C. M., Kamel, F., Umbach, D. M., Marder, K., Mayeux, R., Ritz, B., Ross, G. W., Petrovitch, H., Topol, B., McGuire, V., Costello, S., Manthripragada, A. D., Southwick, A., Myers, R. M., Nelson, L. M. 2011; 18 (5): 756-765

    Abstract

    In 1-methyl-4-phenyl 1,2,3,6-tetrahydropyridine animal models of Parkinson's disease (PD), caffeine protects neurons by blocking the adenosine receptor A2A (ADORA2A). Caffeine is primarily metabolized by cytochrome P450 1A2 (CYP1A2). Our objective was to examine whether ADORA2A and CYP1A2 polymorphisms are associated with PD risk or modify the caffeine-PD association.Parkinson's Epidemiology and Genetic Associations Studies in the United States (PEGASUS) included five population-based case-control studies. One laboratory genotyped four ADORA2A and three CYP1A2 polymorphisms in 1325 PD cases and 1735 age- and sex-matched controls. Information regarding caffeine (coffee) consumption and other lifestyle factors came from structured in-person or telephone interviews. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using logistic regression.Two ADORA2A polymorphisms were inversely associated with PD risk - rs71651683, a 5' variant (adjusted allelic OR = 0.51, 95% CI 0.33-0.80, permutation-adjusted P = 0.015) and rs5996696, a promoter region variant (adjusted OR for AC and CC genotypes compared with the AA wild-type genotype were 0.76 (95% CI 0.57-1.02) and 0.37 (95% CI 0.13-1.01), respectively (permutation-adjusted P for trend = 0.04). CYP1A2 polymorphisms were not associated with PD risk; however, the coffee-PD association was strongest among subjects homozygous for either variant allele rs762551 (P(interaction) = 0.05) or rs2470890 (P(interaction) = 0.04).In this consortium study, two ADORA2A polymorphisms were inversely associated with PD risk, but there was weak evidence of interaction with coffee consumption. In contrast, the coffee-PD association was strongest among slow metabolizers of caffeine who were homozygous carriers of the CYP1A2 polymorphisms.

    View details for DOI 10.1111/j.1468-1331.2011.03353.x

    View details for Web of Science ID 000289627000017

    View details for PubMedID 21281405

  • Common Iliac Vein Stenosis and Risk of Symptomatic Pulmonary Embolism: An Inverse Correlation JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY Chan, K. T., Popat, R. A., Sze, D. Y., Kuo, W. T., Kothary, N., Louie, J. D., Hovsepian, D. M., Hwang, G. L., Hofmann, L. V. 2011; 22 (2): 133-141

    Abstract

    To test the hypothesis that a common iliac vein (CIV) stenosis may impair embolization of a large deep venous thrombosis (DVT) to the lungs, decreasing the incidence of a symptomatic pulmonary embolism (PE).Between January 2002 and August 2007, 75 patients diagnosed with unilateral DVT were included in a single-institution case-control study. Minimum CIV diameters were measured 1 cm below the inferior vena cava (IVC) bifurcation on computed tomography (CT) images. A significant stenosis in the CIV ipsilateral to the DVT was defined as having either a diameter 4 mm or less or a greater than 70% reduction in lumen diameter. A symptomatic PE was defined as having symptoms and imaging findings consistent with a PE. The odds of symptomatic PE versus CIV stenosis were assessed using logistic regression models. The associations between thrombus location, stenosis, and symptomatic PE were assessed using a stratified analysis.Of 75 subjects, 49 (65%) presented with symptomatic PE. There were 17 (23%) subjects with a venous lumen 4 mm or less and 12 (16%) subjects with a greater than 70% stenosis. CIV stenosis of 4 mm or less resulted in a decreased odds of a symptomatic PE compared with a lumen greater than 4 mm (odds ratio [OR] 0.17, P = .011), whereas a greater than 70% stenosis increased the odds of DVT involving the CIV (OR 7.1, P = .047).Among patients with unilateral DVT, those with an ipsilateral CIV lumen of 4 mm or less have an 83% lower risk of developing symptomatic PE compared with patients with a CIV lumen greater than 4 mm.

    View details for DOI 10.1016/j.jvir.2010.10.009

    View details for Web of Science ID 000287166600004

    View details for PubMedID 21276911

  • Familial Aggregation of Parkinson's Disease in a Multiethnic Community-Based Case-Control Study MOVEMENT DISORDERS Shino, M. Y., McGuire, V., Van Den Eeden, S. K., Tanner, C. M., Popat, R., Leimpeter, A., Bernstein, A. L., Nelson, L. M. 2010; 25 (15): 2587-2594

    Abstract

    To assess the familial aggregation of Parkinson's disease (PD), we compared the cumulative incidence of PD among first-degree relatives of PD cases and controls. We identified newly diagnosed patients with PD (n = 573) during 1994 to 1995 within Kaiser Permanente Medical Care Program of Northern California and recruited 496 cases (87%) for the case-control study. Of 720 eligible controls matched by birth year and sex to cases, 541 (75%) agreed to participate. Information on family history of PD and other neurodegenerative diseases was obtained by in-person structured interview. We used the reconstructed cohort approach that provides a better estimate of the risk. The cumulative incidence of PD was significantly higher among relatives of PD patients compared with relatives of controls (2.0 vs. 0.7%; relative risk (RR) = 3.4, 95% confidence interval (CI) 1.9-5.9; P = 0.0001). The degree of familial aggregation was higher among first-degree relatives of Hispanic PD cases compared with Hispanic controls (3.7% vs. 0.4%; RR = 8.5, 95% CI 1.0-68.9) than it was among non-Hispanic Caucasian cases and controls (2.0% vs. 0.8%; RR = 2.7, 95% CI 1.5-5.1; P = 0.02). The familial aggregation of PD was stronger among the siblings of PD cases (RR = 5.4, 95% CI 1.8-16.0) than among parents (RR = 2.7, 95% CI 1.3-5.2). The incidence and familial aggregation of PD is highest among Hispanics, warranting further studies of genetic and environmental risk factors in the Hispanic population.

    View details for DOI 10.1002/mds.23361

    View details for Web of Science ID 000284060600016

    View details for PubMedID 20842689

  • Reliability and validity of two self-administered questionnaires for screening restless legs syndrome in population-based studies SLEEP MEDICINE Popat, R. A., Van Den Eeden, S. K., Tanner, C. M., Kushida, C. A., Rama, A. N., Black, J. E., Bernstein, A., Kasten, M., Chade, A., Leimpeter, A., Cassidy, J., McGuire, V., Nelson, L. M. 2010; 11 (2): 154-160

    Abstract

    A reliable and valid questionnaire for screening restless legs syndrome (RLS) is essential for determining accurate estimates of disease frequency. In a 2002 NIH-sponsored workshop, experts suggested three mandatory questions for identifying RLS in epidemiologic studies. We evaluated the reliability and validity of this RLS-NIH questionnaire in a community-based sample and concurrently developed and evaluated the utility of an expanded screening questionnaire, the RLS-EXP.The study was conducted at Kaiser Permanente of Northern California and the Stanford University Sleep Clinic. We evaluated test-retest reliability in a random sample of subjects with prior physician-assigned RLS (n=87), subjects with conditions frequently misclassified as RLS (n=31), and healthy subjects (n=9). Validity of both instruments was evaluated in a random sample of 32 subjects, and in-person examination by two RLS specialists was used as the gold standard.For the first three RLS-NIH questions, the kappa statistic for test-retest reliability ranged from 0.5 to 1.0, and sensitivity and specificity was 86% and 45%, respectively. For the subset of five questions on RLS-EXP that encompassed cardinal features for diagnosing RLS, kappas were 0.4-0.8, and sensitivity and specificity were 81% and 73%, respectively.Sensitivity of RLS-NIH is good; however, the specificity of the instrument is poor when examined in a sample that over-represents subjects with conditions that are commonly misclassified as RLS. Specificity can be improved by including separate questions on cardinal features, as used in the RLS-EXP, and by including a few questions that identify RLS mimics, thereby reducing false positives.

    View details for DOI 10.1016/j.sleep.2009.01.012

    View details for Web of Science ID 000275584500009

    View details for PubMedID 20089446

  • Short- and Long-Term Outcomes of Necrotizing Enterocolitis in Infants With Congenital Heart Disease PEDIATRICS Pickard, S. S., Feinstein, J. A., Popat, R. A., Huang, L., Dutta, S. 2009; 123 (5): E901-E906

    Abstract

    Congenital heart disease is a significant risk factor for necrotizing enterocolitis in the term infant. We compared the short- and long-term necrotizing enterocolitis-specific outcomes of infants with congenital heart disease with those of neonates without congenital heart disease.A retrospective study of 202 patients with necrotizing enterocolitis treated at our center from May 1999 to August 2007 was conducted. Infants with necrotizing enterocolitis were grouped according to the presence (n = 76) or absence (n = 126) of congenital heart disease. Demographic and necrotizing enterocolitis-specific outcomes were recorded. The groups were compared by nonparametric and chi(2) analyses. Univariate and multivariate odds ratios were determined for each outcome.The average birth weight and gestational age of the 2 groups were not significantly different. The initial necrotizing enterocolitis severity, as determined by Bell stage, was less for necrotizing enterocolitis subjects with congenital heart disease compared with those without congenital heart disease. When controlling for birth weight and gestational age, the congenital heart disease group had decreased risk of perforation, need for a bowel operation, strictures, need for a stoma, sepsis, and short bowel syndrome compared with the non-congenital heart disease group. Although not statistically significant, subjects with congenital heart disease had a trend toward decreased risk of death from necrotizing enterocolitis, recurrent necrotizing enterocolitis, and need for peritoneal drainage.Infants with congenital heart disease and necrotizing enterocolitis have decreased risk of major short- and long-term negative outcomes associated with necrotizing enterocolitis compared with neonates without congenital heart disease. Differences in initial severity, range of age at diagnosis, and prognoses between subjects with necrotizing enterocolitis with and without cardiac disease suggest that necrotizing enterocolitis in the cardiac patient is a distinct disease process and should be labeled cardiogenic necrotizing enterocolitis.

    View details for DOI 10.1542/peds.2008-3216

    View details for Web of Science ID 000265528900048

    View details for PubMedID 19403484

  • Effect of non-steroidal anti-inflammatory medications on the risk of amyotrophic lateral sclerosis AMYOTROPHIC LATERAL SCLEROSIS Popat, R. A., Tanner, C. M., Van Den Eeden, S. K., Bernstein, A. L., Bloch, D. A., Leimpeter, A., McGuire, V., Nelson, L. M. 2007; 8 (3): 157-163

    Abstract

    Inflammatory processes may be involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). We examined the association of non-steroidal anti-inflammatory drugs (NSAIDs) with the risk of ALS in case-control study of incident cases (n = 111) conducted within the Kaiser Permanente Medical Care Program of Northern California during the years 1996-2000. Controls (n = 258) randomly selected from the same population were frequency matched by age and gender to the ALS cases. Information regarding use of NSAIDs (non-aspirin and aspirin) and three classes of 'control' medications was collected by in-person structured interview. Subjects who used medication at least twice a week for at least a month were classified as 'ever users'. Multivariable logistic regression models were adjusted for age, gender, history of osteoarthritis/rheumatoid arthritis and pain, and other medication use. Overall, there was no association between NSAID use and ALS; however, some sex differences were noted for non-aspirin NSAID use. Among men, non-aspirin NSAID use was associated with a two-fold increased risk of ALS (adjusted odds ratio (OR) 2.0, 95% confidence interval (CI) 1.0-3.9), whereas among women, non-aspirin NSAID use was not associated with increased ALS risk (adjusted OR 0.5, 95% CI 0.2-1.2). ALS risk was not associated with aspirin use or with 'control' medications. This study did not find any evidence to suggest that NSAID use reduces the risk of ALS. The observed sex differences with non-aspirin NSAID use could be due to chance or an unmeasured confounder.

    View details for DOI 10.1080/17482960601179456

    View details for Web of Science ID 000246949600004

    View details for PubMedID 17538777

  • Clinical and demographic predictors of long-term disability in patients with relapsing-remitting multiple sclerosis - A systematic review ARCHIVES OF NEUROLOGY Langer-Gould, A., Popat, R. A., Huang, S. M., Cobb, K., Fontoura, P., Gould, M. K., Nelson, L. M. 2006; 63 (12): 1686-1691

    Abstract

    To identify clinical and demographic factors associated with long-term disability in patients with relapsing-remitting multiple sclerosis.We searched the MEDLINE (1966-May 2005), EMBASE, CINAHL, Cochrane, and PsycINFO computerized databases, and reviewed reference lists of retrieved articles.We included studies that examined predictors of long-term disability in patients with relapsing-remitting multiple sclerosis. We excluded studies that did not distinguish relapsing-remitting multiple sclerosis from primary progressive multiple sclerosis, enrolled fewer than 40 subjects, observed subjects for less than 5 years, or collected follow-up information in less than 80% of the inception cohort.Two reviewers assessed study quality in 4 domains: cohort assembly, definitions and assessments of prognostic factors and outcomes, and statistical methods. One reviewer extracted data on the direction, magnitude, precision, and statistical significance of the effect of each predictor on prognosis.Heterogeneity of study designs precluded us from pooling the results of 27 eligible studies. Study quality was limited by cross-sectional design, enrollment of prevalent cases from referral centers, and lack of multivariate adjustment. Sphincter symptoms at onset (hazard ratio, 1.1-3.1), incomplete recovery from the first attack (hazard ratio, 1.3-3.3), and a short interval between the first and second attack (hazard ratio, 1.6-1.9) were most strongly and consistently associated with poor prognosis. Other factors widely believed to be of prognostic importance, including sex and age at onset, demonstrated inconsistent or weak effects on prognosis.The most robust predictors of long-term physical disability in relapsing-remitting multiple sclerosis are sphincter symptoms at onset and early disease course outcomes. These factors can be used to guide treatment decisions for drugs with significant toxicities.

    View details for Web of Science ID 000242733000003

    View details for PubMedID 17172607

  • Effect of reproductive factors and postmenopausal hormone use on the risk of amyotrophic lateral sclerosis NEUROEPIDEMIOLOGY Popat, R. A., Van Den Eeden, S. K., Tanner, C. M., Bernstein, A. L., Bloch, D. A., Leimpeter, A., McGuire, V., Nelson, L. M. 2006; 27 (3): 117-121

    Abstract

    To examine the associations of reproductive factors and postmenopausal hormone use with the risk of amyotrophic lateral sclerosis (ALS) among women.This case-control study was conducted within the Kaiser Permanente Medical Care Program (KPMCP) of Northern California during the years 1996-2000. Among the 193 postmenopausal women, 62 were incident ALS cases and 131 were controls randomly selected from KPMCP members and frequency matched by age and respondent type (self versus proxy) to the cases. Statistical analyses were carried out using logistic regression.Reproductive factors such as age at menarche, age at final menstrual period, parity, oral contraceptive use, and type of menopause (natural vs. hysterectomy with or without oophorectomy) were not associated with risk of ALS. Postmenopausal hormone use was positively, but not significantly, associated with the risk of ALS (adjusted OR 1.9, 95% CI 0.9-3.8).Reproductive factors were not associated with ALS risk. There is no evidence that suggests a protective effect of postmenopausal hormone use against the development of ALS. However, due to insufficient power, we cannot rule out a possible increase in ALS risk associated with postmenopausal hormone use.

    View details for DOI 10.1159/000095550

    View details for Web of Science ID 000241773900001

    View details for PubMedID 16946622

  • Effect of reproductive factors and postmenopausal hormone use on the risk of Parkinson disease NEUROLOGY Popat, R. A., Van Den Eeden, S. K., Tanner, C. M., McGuire, V., Bernstein, A. L., Bloch, D. A., Leimpeter, A., Nelson, L. M. 2005; 65 (3): 383-390

    Abstract

    Parkinson disease (PD) is less common in women possibly because of hormonal or reproductive influences. The objective of this study was to evaluate the associations of reproductive factors and postmenopausal hormone use with the risk of PD among postmenopausal women.Incident cases (n = 178) and randomly selected age-matched controls (n = 189) who were members of the Kaiser Permanente Medical Care Program (KPMCP) of Northern California participated in the study conducted during the years 1994 to 1995. Statistical analyses were carried out using logistic regression.The association of postmenopausal hormone use with PD risk depended on the type of menopause. Among women with history of a hysterectomy with or without an oophorectomy, estrogen use alone was associated with a 2.6-fold increased risk (adjusted odds ratio (OR) 2.6, 95% CI: 1.1 to 6.1) and significant trends in the risk of PD were observed with increasing duration of estrogen use, but disease risk was not influenced by recency of use. In contrast, among women with natural menopause, no increased risk of PD was observed with hormone use (estrogen alone or a combined estrogen-progestin regimen). Early age at final menstrual period (44 years or younger) was associated with reduction in risk (adjusted OR 0.5, 95% CI: 0.3 to 1.0). Age at menarche and parity were not associated with the risk of PD.Postmenopausal use of estrogen alone may increase the risk of Parkinson disease (PD) among women with a hysterectomy. Among women with natural menopause for whom the usual treatment is combined estrogen-progestin therapy, no increased risk of PD was observed.

    View details for Web of Science ID 000231067200010

    View details for PubMedID 16087902

  • Biomechanical analysis of failed sit-to-stand. IEEE transactions on rehabilitation engineering Riley, P. O., Krebs, D. E., Popat, R. A. 1997; 5 (4): 353-359

    Abstract

    Background sit-to-stand (STS) failure is a transient loss of balance that can engender falls among elders. The purpose of this paper is to describe the mechanisms whereby failed STS differs from successful STS. The authors compared successful STS from 11 normal elders to 20 "sitback" and 20 "step" type failed STS's in 13 subjects. Kinematic and kinetic data were incorporated into our 11-segment whole body model to estimate the net joint forces and torques and body segment momenta. Significant between group differences in the magnitude and timing of momentum generation and dissipation, knee extensor torques and the magnitude of the vertical ground reaction force were identified. Both types of failed sit-to-stand maneuvers are less energetic than successful rises. STS failures might result from either weakness or balance control and coordination impairment, or both, resulting in an insufficiently energetic effort. Further research is required to differentiate between these two possible sources of impairment. Determining the root cause of functional limitations is necessary to develop effective interventions.

    View details for PubMedID 9422460

  • Rehabilitation of balance in two patients with cerebellar dysfunction PHYSICAL THERAPY GILLBODY, K. M., Popat, R. A., Parker, S. W., Krebs, D. E. 1997; 77 (5): 534-552

    Abstract

    The treatment of two patients with cerebellar dysfunction is described. One patient was a 36-year-old woman with a 7-month history of dizziness and unsteadiness following surgical resection of a recurrent pilocystic astrocytoma located in the cerebellar vermis. The other patient was a 48-year-old man with cerebrotendinous xanthomatosis (CTX) and diffuse cerebellar atrophy, and a 10-year history of progressive gait and balance difficulties. Each patient was treated with a 6-week course of physical therapy that emphasized the practice of activities that challenged stability. The patient with the cerebellar tumor resection also performed eye-head coordination exercises. Each patient had weekly therapy and performed selected balance retraining exercises on a daily basis at home. Measurements taken before and after treatment for each patient included self-perception of symptoms, clinical balance tests, and stability during selected standing and gait activities; for the patient with the cerebellar tumor resection, vestibular function tests and posturography were also performed. Both patients reported improvements in symptoms and demonstrated similar improvements on several kinematic indicators of stability during gait. The patient with the cerebellar tumor resection improved on posturography following treatment, whereas the patient with CTX improved on clinical balance tests. This case report describes two individualized treatment programs and documents functional improvements in two patients with different etiologies, durations, and clinical presentations of cerebellar dysfunction. The outcomes suggest that patients with cerebellar lesions, acute or chronic, may be able to learn to improve their postural stability.

    View details for Web of Science ID A1997WY50200008

    View details for PubMedID 9149763

  • QUANTITATIVE ASSESSMENT OF 4 MEN USING ABOVE-ELBOW PROSTHETIC CONTROL ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION Popat, R. A., Krebs, D. E., MANSFIELD, J., Russell, D., Clancy, E., GILLBODY, K. M., Hogan, N. 1993; 74 (7): 720-729

    Abstract

    We studied the relationship between kinematically unconstrained activities of daily living (ADL) tasks and a kinematically constrained task in above-elbow (AE) amputee subjects using myoelectrically controlled prostheses. Four men, 24 to 49 years old, with unilateral AE amputation wore a prosthesis interfaced to a programmable controller to emulate two different elbow control schemes, conventional velocity and a new "natural" controller. Subjects were timed during three ADL tasks--cutting meat, donning socks, and rolling dough--with both controllers. The prosthesis emulator was then connected to a crank device with a handle, and the subjects turned the crank from bottom to top positions in a vertical plane using each controller. Synergistic shoulder-elbow joint coordination required for crank turning was quantified as the maximum slope of the change in elbow torque versus the change in crank-angle. Performance between the two controllers differed significantly for the crank test but not for ADL tasks. One subject did not complete all crank turning tests. Positive canonical correlation of 0.77 was found between time and crank domain measures. We conclude that biomechanical assessments should be integrated with time-based clinical tests to comprehensively evaluate performance of AE amputee subjects with a myoelectric device.

    View details for Web of Science ID A1993LM07900010

    View details for PubMedID 8328894

Conference Proceedings


  • Common iliac vein stenosis: a risk factor for oral contraceptive-induced deep vein thrombosis Chan, K. T., Tye, G. A., Popat, R. A., Kuo, W. T., Unver, K., Kothary, N., Sze, D. Y., Hofmann, L. V. MOSBY-ELSEVIER. 2011

    Abstract

    The objective of the study was to determine whether women with significant left common iliac vein stenosis who also use combined oral contraceptives (COCs) have a combined likelihood of deep vein thrombosis (DVT) greater than each independent risk.This was a case-control study comparing 35 women with DVT against 35 age-matched controls. Common iliac vein diameters were measured from computed tomography and magnetic resonance imaging. Logistic regression modeling was used with adjustment for risk factors.DVT was associated with COC use (P = .022) and with increasing degrees of common iliac vein stenosis (P = .004). Compared with women without venous stenosis or COC use, the odds of DVT in women with a 70% venous stenosis who also use COCs was associated with a 17-fold increase (P = .01).Venous stenosis and COC use are independent risk factors for DVT. Women concurrently exposed to both have a multiplicative effect resulting in an increased risk of DVT. We recommend further studies to investigate this effect and its potential clinical implications.

    View details for DOI 10.1016/j.ajog.2011.06.100

    View details for Web of Science ID 000297329200019

    View details for PubMedID 21893308

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