Greater LA Research Articles

The accuracy of predicting maladaptation to new environments with genomic data.

Rapid environmental change poses unprecedented challenges to species persistence. To understand the extent that continued change could have, genomic offset methods have been used to forecast maladaptation of natural populations to future environmental change. However, while their use has become increasingly common, little is known regarding their predictive performance across a wide array of realistic and challenging scenarios. Here, we evaluate the performance of currently available offset methods (gradientForest, the Risk-Of-Non-Adaptedness, redundancy analysis with and without structure correction and LFMM2) using an extensive set of simulated data sets that vary demography, adaptive architecture and the number and spatial patterns of adaptive environments. For each data set, we train models using either all, adaptive or neutral marker sets and evaluate performance using in silico common gardens by correlating known fitness with projected offset. Using over 4,849,600 of such evaluations, we find that (1) method performance is largely due to the degree of local adaptation across the metapopulation (LA), (2) adaptive marker sets provide minimal performance advantages, (3) performance within the species range is variable across gardens and declines when offset models are trained using additional non-adaptive environments and (4) despite (1) performance declines more rapidly in globally novel climates (i.e. a climate without an analogue within the species range) for metapopulations with greater LA than lesser LA. We discuss the implications of these results for management, assisted gene flow and assisted migration.

A radiographic analysis of Mandibular Symphysis dimension in black South African adult patients with differing skeletal patterns

Orthodontic treatment often involves planned tooth movement within the confined spaces of the alveolar bone trough. Tooth movement within the alveolar trough may be limited by thin labial and lingual cortical plates. Moving lower incisors beyond the mandibular symphysis dimensions may result in damage to roots and alveolar bone.4 Aim and objective The aim of the study was to evaluate limitation of treatment in different skeletal patterns due to mandibular symphysis dimension in order to evaluate limitations of tooth movement within the confines of the mandibular alveolar trough.The objective was to determine the mandibular symphysis dimensions in subjects with differing skeletal patterns Design The design was a retrospective, cross-sectional study. Methods A sample of 180 pre-treatment lateral cephalometric radiographs of black South African subjects were stratified into three groups based on their skeletal classification. Each Class was further divided into equal numbers of males and females. Descriptive statistics, Student’s t-test, ANOVA test and Pearson correlation coefficient were used to analyse the data and p-values of <0.05 were considered statistically significant. Results Subjects with skeletal Class I pattern had a greater LA compared to subjects with skeletal Class II pattern. Subjects with skeletal Class I pattern had a greater LH and LA in females than in males. Subjects with skeletal Class III pattern had greater LH in males than in females.

Transit Blues in the Golden State: Regional transit ridership trends in California

Public investment in transit increased following the Great Recession, yet transit use nationally mostly fell, even prior to the 2020 pandemic. We investigate this troubling disjuncture by comparing transit ridership trends during the 2010s in two of America’s largest regions: Greater Los Angeles and the San Francisco Bay Area. While both California regions lost transit riders, we see substantial differences in the scale, timing, geography, and modes of these declines. In the LA area, ridership fell longer and further, spread more across routes, times, and sub-regions and concentrated on the region’s dominant operator. In both regions, increasing auto access appears to have played a central role, albeit in different ways. Greater LA saw increased automobile ownership, particularly among high-propensity transit riders. In the Bay Area, as jobs and housing have dispersed, ridehail services like Lyft and Uber may have eroded non-commute transit use.

Abstract 16395: Soluble ST2 and Its Association With Echocardiographic Measures of Cardiac Structure

Background: Soluble ST2 (sST2) has emerged as a powerful prognostic marker in chronic systolic heart failure with reduced ejection fraction (HFrEF). Elevated levels of sST2 are associated with adverse cardiac remodeling and fibrosis. We have previously described the prognostic value of sST2 collected from stable patients in the ambulatory setting and correlated it with long term clinical outcomes. However, few studies have demonstrated the association between sST2 levels and echocardiographic measures of cardiac structure and function as well as outcomes. Hypothesis: Baseline circulating levels of sST2, using the partition value of 35 ng/ml, will correlate with echocardiographic measures of cardiac chamber size and function in stable stage C patients in the ambulatory setting. Methods: Single-center, retrospective observational study of subjects presenting to an ambulatory heart failure (HF) clinic from July 2014 to December 2016. There were 156 subjects with stage C heart failure and a baseline sST2 level. For purposes of this analysis in HFrEF, we excluded patients with EF > 40% resulting in a study cohort of 103 subjects. The mean follow-up was 2.20 years ± 1.53 years. Analysis was performed with IBM SPSS Statistics 26. Discrete variables were expressed as counts (percentage) and were compared using the Chi-squared test. Mean differences of continuous variables were expressed as a mean ± standard deviation and compared using the unpaired Student’s t- test. Results: Patients who had baseline sST2 ≥ 35 ng/ml had a greater LA volume index (p=0.05) and RA area (p=0.01) compared to patients with sST2 < 35 ng/ml. Patients with sST2 ≥ 35 ng/ml had a mean LA volume index of 62.72 ± 30.28 ml/m 2 and RA area of 24.59 ± 7.87 ml/m 2 . We also found that sST2 ≥ 35 ng/ml was associated with increased risk for atrial arrhythmias (39.0% vs. 20.5%), a higher New York Heart Association classification (2.73 vs. 2.18), lower hemoglobin (11.5 vs 13.0), and lower systolic blood pressure (109.6 vs 124.8). Conclusion: In our study, subjects with sST2 levels ≥ 35 ng/ml was associated with increased atrial size by echocardiography, increased risk for atrial arrhythmia and higher NYHA class. These findings support the utility of sST2 for risk stratification in ambulatory patients with HFrEF.

Abstract 15216: Longitudinal Changes in Peak Aortic Valve Velocity in Late Life: Atherosclerosis Risk in Communities (ARIC) Study

Background: Aortic stenosis (AS) is a growing health problem within the aging population. We aimed to quantify longitudinal changes in aortic valve hemodynamics in late life. Methods: We studied 2,512 community-based elderly participants in the Atherosclerosis Risk in Communities (ARIC) study who underwent uniform echocardiographic imaging at study visits 5 (2011-2013) and 7 (2018-2019). Peak aortic valve (AV) velocity was assessed by continuous wave spectral Doppler from the apical 5 chamber view. Participants with heart failure or in atrial fibrillation at either echocardiographic examination were excluded. Results: Mean age at Visit 5 was 74 ± 4 years, 41% were male, 24% black, and the mean AV velocity at Visit 5 was 1.27 ± 0.28 m/s. Over median 6.6 [IQR: 6.1-7.0] years, AV velocity increased by 0.15 ± 0.32 m/s and the mean velocity at Visit 7 was 1.43 ± 0.43 m/s. Of 2,454 participants with peak AV velocity < 2.0 m/s at Visit 5, 123 (5%) developed a peak AV velocity > 2.0 m/s at Visit 7 (mean 2.45 ± 0.46 m/s). In models accounting for blood pressure and heart rate at both study visits, Visit 5 predictors of transitioning to a peak AV velocity > 2.0 m/s included age, male sex, white race, BMI, higher NT-proBNP and hs-troponin T, and greater LA volume index and E/e’ ratio ( Table ). Conclusions: Peak AV velocity increases over 6 years in late life, with ~5% developing a peak velocity > 2.0 m/s. Demographics, higher cardiac biomarkers, and worse diastolic function predict increases in peak AV velocity in late life. These data have important implications for the development of age-related aortic stenosis.

Clinically relevant genomic alterations identified by targeted exome sequencing in U.S. veterans with prostate cancer.

e17599 Background: Amongst male United States Veterans, prostate cancer accounts for one third of cancer diagnoses and is the second leading cause of cancer death. Prostate cancers in the Veteran population may have differing frequencies of clinically relevant genomic alterations than the general population owing to chemical exposures, military service, or other unknown factors. Veterans, however, have been underrepresented in large-scale prostate cancer sequencing cohorts to date. Methods: Archival or fresh prostate cancer tissue from Veterans cared for by our team within the VA Greater Los Angeles Healthcare System (a VA Prostate Cancer Center of Excellence) undergo targeted sequencing as part of routine clinical care through the VA Precision Oncology Program. Sequencing covers over 181 genes frequently mutated in cancers. Prostate cancers from 81 Veterans (76 primary tumors, 5 metastases) have been sequenced through the Personalis ACE CancerPlus platform. Results: 43% of Veterans had primary tumors with clinically relevant genomic alterations, including 6.2% with activating mutations in MAPK pathway members (KRAS, ERBB2, or BRAF), 3.7% with somatic mutations in DDR genes (BRCA2 or ATR), 7.3% with mutations in TP53 or RB1, 4.9% in APC, 1.2% in the WNT pathway (CTNNB1), 3.7% with mutations in the PI3K/AKT pathway (PIK3R1 or AKT1), 3.7% with PTEN deletions, and 22.2% had alterations involving an AR regulated gene (SLC45A3 or TMPRSS). Of the five metastatic tumors sequenced, one had a mutation in TP53 and another had an ETS gene fusion detected. Half of the Veterans who underwent tumor sequencing consented for screening for, or enrollment on, active clinical trials at VA Greater LA. Conclusions: Large-scale sequencing of prostate cancers within VA is feasible and may facilitate enrollment in precision oncology trials specifically designed for Veterans. These data suggest that clinically relevant genomic alterations within the primary tumors may differ between Veterans and the general population; larger data sets along with more robust sequencing platforms are required for clarification.

Alta California: From San Diego to San Francisco, A Journey on Foot to Rediscover the Golden State by Nick Neely

Reviewed by: Alta California: From San Diego to San Francisco, A Journey on Foot to Rediscover the Golden State by Nick Neely O. Alan Weltzien Nick Neely, Alta California: From San Diego to San Francisco, A Journey on Foot to Rediscover the Golden State. Berkeley, CA: Counterpoint P, 2019. 411 pp. Cloth, $26. Nick Neely proved himself one talented naturalist with his debut collection Coastal Range (2016). His new book is nothing if not ambitious, the title scrolling us back into pre-nineteenth-century California history we either don't know or would prefer to ignore. Alta proves a nature ramble on an enormous scale as well as a version of historical pilgrimage. Neely has closely studied the 1769 Gaspar de Portola Expedition, which became the basis for El Camino Real, the chain of iconic California missions, and the accelerated quasi genocide of many of the tribal peoples of the region. Neely decided to retrace the expedition's route 247 years later, [End Page 206] beginning in downtown San Diego and culminating in his hometown near the southwest edge of San Francisco Bay. He follows its timeline, beginning in mid-July and ending 650 miles later in early November. Alta represents a considerable act of historical imagination as Neely trudges through 2016's summer and autumn, pursuing many intriguing angles. A gifted naturalist, Neely never sees or hears a bird he doesn't know and seems equally at home with plants and trees, whether native species or well-known exotics such as eucalyptus. Through his daily walks north/northwest, he investigates and incorporates fascinating local history. The focus upon this Spanish "Corps of Discovery" also includes well-handled stories of nineteenth-century rancheros and agricultural history, as he folds considerable research and vignette into the account of his trek. Along his dusty way, we're treated to quotidian detail as well as healthy doses of self-mockery. Neely "eats out" early in his trip, parking his backpack against the walls of the fast-food nation. He thanks himself for buying a one-man inconspicuous gray tent, which helps avoid detection. Sometimes he doesn't pitch it: too visible, too hot. Neely uses a practiced eye as he steers toward stands of foliage, sleeps near the homeless and coyotes, but is, surprisingly, never hassled. And his sense of trespassing relaxes as he traverses the central California coast. Unsurprisingly, Neely's path opens him to casual encounters, and Alta features quick character sketches and bits of conversation with myriad folks, most of them friendly even if incredulous about his undertaking. He occasionally joins tourists and steps out of his lone trek, at the Getty Museum, for example, and San Simeon. His detour around and through Camp Pendleton anticipates more harrowing moments, including his illegal, nocturnal transit across railroad property near Point Conception. Imagine walking across greater LA, the ultimate highway city. Faithful to the 1769 route, Neely sometimes veers away from the coast, traversing steep coastal mountains and drainages, the ocean's crash pounding his ears. In Big Sur country and then in the Salinas River valley, he nods, as expected, at Robinson Jeffers and John Steinbeck. How do Neely's historical strands, or the felt textures of his walk [End Page 207] distant from interstates and US routes, help us understand what California has become? If this place poses an extreme example of American historical amnesia, how does Neely's comparative lesson instruct us about what should be remembered? The invaluable histories of Kevin Starr teach us California's recent past and its impacts on California now and tomorrow. Neely gives some attention along his way, as he must, to the fates of local tribes hard upon the establishment of El Camino and the string of missions: sites of slave labor, disease, and death. We learn tribal names and occasional words, just as we learn about the Mexican class system upended by the John C. Frémonts and gold-hungry Anglos. I wish this California native had used his journey to speculate more overtly about what his huge state has become in light of his research and sweat. I wish there were more explicit application of his historical walk to contemporary...

P4138Clinical differences between methamphetamine and non-methamphetamine associated non-ischemic dilated cardiomyopathy

Abstract Background Methamphetamine associated cardiomyopathy (MACM) is an increasingly recognized form of dilated cardiomyopathy around the globe which remains poorly characterized. Purpose To compare the clinical characteristics of MACM to those of non-MA associated dilated CM (NMACM). Methods Consecutive patients with MACM presenting to our institution between Jun 2018 and Jan 2019 were prospectively studied and compared to an age and gender-matched cohort of dilated non-ischemic CM cases. Results Seventy patients were studied (35 MACM and 35 NMACM). Mean age was similar between groups (49±9 vs. 48±10 years, p=0.465) and 97% of patients were male. Median duration of MA use prior to cardiomyopathy diagnosis was 5 years (range 0–30). Patients were predominantly Hispanic in both groups (48% vs. 62%, p=0.229), but with a greater proportion of Caucasians in the MACM group compared to NMACM (26% vs 6%, p=0.045).MACM was characterized by lower left ventricular ejection fraction (LVEF) and greater left ventricular end diastolic volume (LVEDV) compared to NMACM. RV dilation was present more often in MACM cases (Table). Years of MA use was associated with greater LA volumes (R2= 0.13, p=0.048). Association with larger LVEDV and incidence of RV dilation were borderline significant (R2= 0.11, p=0.054 and p=0.058 respectively). The amount of MA used per week correlated with higher RVSP (R2=0.317, p=0.004). Polysubstance abuse was associated with greater LVEF (p=0.028), lower LVEDV (p=0.037) and lower LV mass (p=0.004). Echocardiographic parameters MACM Non-MACM p-value LVEDV (ml) 215 (62) 181 (40) 0.009* LVESV (ml) 166 (63) 133 (41) 0.017* LVEF (%) 20 (8) 26 (10) 0.006* LV Mass (g) 311 (109) 285 (81) 0.286 LA Volume (ml) 88 (26) 85 (29) 0.670 RV Dilation (no.) 23 (65.7%) 14 (40.0%) 0.027* Reduced RV Function (no.) 21 (60.0%) 21 (60.0%) 0.596 RVSP (mmHg) 40 (14) 44 (12) 0.671 RAP (mmHg) 9 (5) 10 (5) 0.682 Intracardiac Thrombus (no.) 3 (8.6%) 2 (5.7%) 0.500 Mean values are reported with standard deviation. *p<0.05. Conclusion MACM is associated with higher degree of LV and RV dilatation as well as LV systolic dysfunction when compared to matched NMACM cases. Years of MA use and amount of MA consumed appear to influence severity of disease. Acknowledgement/Funding None

Abstract 17170: Sarcomere Gene Mutation Hypertrophic Cardiomyopathy Exhibits Distinct Age-Dependent Adverse Remodeling

Introduction: Hypertrophic cardiomyopathy (HCM) due to mutations in sarcomere genes (G+HCM) has been associated with greater risk of adverse outcomes compared to genetic-test negative HCM (G-HCM). HCM morphologic progression across the age spectrum has not been well-defined in the presence or absence of sarcomere mutations. Hypothesis: We hypothesized that G+ HCM is associated with greater adverse remodeling than G- HCM across the age spectrum of adult HCM. Methods: In a prospectively collected HCM cohort, we studied adult HCM probands who had preserved systolic function (EF >50%). To ascertain morphologic differences with age, we compared the continuous variables of left atrial size/body surface area (LA/BSA) and maximum wall thickness (MWT) by echocardiogram, analyzed by age subgroup and by linear regression. Results: Of 500 HCM probands, 241 were G+ and 259 were G-. MWT was larger for all G+ compared to all G- (19.2mm +/- 6.4mm vs. 16.8mm +/- 4.7mm, p<0.001). By age subgroup, MWT was larger for G+ for ages 20-40 (20.1mm vs 15.7mm, p<0.001) and ages 40-60 (19.4mm vs 16.3mm, p<0.001) but not different for 60+ (17.8mm vs 18.1mm, p=0.8). In linear regression by age, there was no significant change in extent of MWT with age among G+ (p=0.7). In contrast, G- patients exhibited a positive correlation of greater MWT with age (p<0.001), which was significantly different than the age relationship for G+ (p=0.008). LA/BSA was larger for all G+ compared to all G- (21.9mm/m 2 +/- 3.9mm/m 2 versus 20.9mm/m 2 +/- 3.8mm/m 2 , p<0.006). By age subgroup, LA/BSA was not significantly different for G+ compared to G- ages 20-40 (20.9mm/m 2 vs 19.9mm/m 2 , p=0.193) but significantly larger for ages 40-60 (21.6mm/m 2 vs 20.0mm/m 2 , p<0.01) and age 60+ (24.5mm/m 2 vs 22.6mm/m 2 , p=0.02). The regression slopes were similar for G+ vs G- (0.07 mm/m 2 /yr versus 0.09mm/m 2 /yr, p=0.36) but the elevations were significantly larger for G+ (p<0.0001), indicating persistently larger LA size in G+ across the age spectrum. Conclusion: LV hypertrophy extent is similar across adult age groups in G+ HCM, while hypertrophy in G- HCM is milder in age groups <60 and similar to G+ HCM only at age >60. Although LA dilation is progressive with age in all HCM, G+ HCM exhibits greater LA dilation across the adult age spectrum.

Combination of on-demand sedation, water exchange, cap-assisted colonoscopy and underwater polypectomy - a novel approach of minimally invasive colonoscopy and polypectomy associated with plausible increased value for screening

Objective: In a performance improvement project, the novel approach of combining water exchange, cap-assisted colonoscopy and on demand sedation (minimizing complications of invasive sedation) and underwater polypectomy (obviating sideeffects of invasive sub-mucosal injection) was assessed. Subjects/methods: Veterans undergoing screening and surveillance at VA Greater lA Healthcare System began colonoscopy with the novel approach. Air insufflation was used during withdrawal for inspection, biopsy and polypectomy of small ( 1 cm) polyps. Results: Fifty-five males were offered the option of on demand sedation by the author. Six (3 sedated, 3 unsedated) were excluded due to poor bowel preparation. Of the 49 evaluable Veterans, 15 (31%) declined the option, 34 (69%) accepted. Final cecal intubation was 100% (49/49). Of the 34 who started without medication, 5 (15%) required sedation during colonoscopy, 29 (85%) completed without. Success of unsedated colonoscopy with the novel approach was 97% (28/29) [one changed to air insufflation]. 55% (16/29) of the unsedated patients completed with no pain. Compared with historical on demand sedation cohorts worldwide, the novel approach achieved the highest completion rate without sedation, and without pain. Amongst the unsedated, overall (57%) and proximal (50%) colon adenoma detection rates (A dR)

Abstract 16642: Distinctive Characteristics of Left Atrial Remodeling in Heart Failure With Preserved or Reduced Ejection Faction

Introduction: Left atrial structure and function (LA) is affected by the presence of heart failure (HF), but the specific impact of HF subtype is poorly characterized. Hypothesis: HF-induced LA remodeling differs between patients with preserved (pEF) or reduced ejection fraction (rEF). Methods: 198 consecutive HF patients referred to Mayo Clinic (51% HFpEF, NYHA 3.1±0.7, 66±13 years, 39% females) and 40 HF-free controls of similar age and gender underwent right heart catheterization (LA pressures), echocardiography (LA volumes) and follow-up. Results: Compared with controls, HF patients had larger atria and more impaired LA reservoir and contractile function (total and active LAEF, all p<0.001). At identical mean LA pressure (20 vs 20 mmHg, p=0.9), HFrEF patients had larger LA volumes (LAVI 50 vs 41 ml/m 2 p<0.001), but HFpEF patients had higher LA peak (V-wave) and lower LA minimal pressures, with higher LA stiffness (0.79 vs 0.48 mmHg.ml -1 , p<0.001, Fig-A) and LA pressure pulsatility (19 vs 13 mmHg, p<0.001). Despite smaller LA size, better LA function (total LAEF 39 vs 35 %, p=0.04, active LAEF 30 vs 22 %, p<0.001) and less mitral regurgitation (grade 1.8 vs 2.5, p<0.001), HFpEF patients had more atrial fibrillation (42 vs 26%, p=0.02). After a median follow-up 350 days, 31 HFpEF and 28 HFrEF patients died. LA function was associated with mortality in HFpEF, but not in HFrEF (Fig-B). Conclusions: HFrEF is characterized by greater eccentric LA remodeling, but HFpEF is associated with increased LA stiffening and greater LA pressure pulsatility which may contribute to greater burden of atrial fibrillation. The observation that LA function is more closely linked to outcome in HFpEF supports the goal to maintain or improve LA function in HFpEF.

Childhood Obesity Increases Left-Ventricular Mass Irrespective of Blood Pressure Status

Adults with a left-ventricular mass index (LVMI) in grams normalized to height in meters(2.7) (LVMI g/m(2.7))>51g/m(2.7) are more prone to cardiovascular and cerebrovascular events. We delineated the odds for cardiac structural sequelae amongst apparently normal white and African-American (AA) children with varying body mass indices (BMI) and office blood pressures. A total of 2,071 children with normal echocardiograms were categorizedinto risk groups based on BMI and systolic blood pressures (SBPs). Predictors of cardiac sequelae examined were age, sex, race, and z-scores (z) for BMI, SBP, and diastolic blood pressure. Cardiac sequelae measures included (LVMI g/m(2.7))>51g/m(2.7), (LVMI) (g/m(2.7)) z, left atrial size (LA(ht)) (mm) z, and relative wall thickness z. Mean age was 14±2years with 56% being male and 13% being AA. Children were divided into "controls" (n=1,059) and risk groups based on BMI and SBP. Odds ratio for LVMI (g/m(2.7))>51.0g/m(2.7), varied from 5.3 up to 8.5 in children with increased BMI. Both increased BMI and SBP z were associated with increased LVMI (g/m(2.7)) z; however, BMI z had a stronger association. Increased BMI z and AA race were associated with greater LA(ht) (mm) z. AA controls had a nonsignificantly increased LVMI z and a significantly increased LA(ht) (mm) and RWT z. Being overweight or obese is associated with cardiac sequelae in children to the extent known to be associated with adverse outcomes in adults. Healthy AA children have unique cardiac structural differences.

Improving spatial concentration estimates for nitrogen oxides using a hybrid meteorological dispersion/land use regression model in Los Angeles, CA and Seattle, WA

Predictions from a simple line source dispersion model, Caline3, were included as a covariate in a land use regression (LUR) model for NO X /NO 2 in Los Angeles, CA and Seattle, WA. The Caline3 model prediction assumed a unit emission factor for all roadway segments (1.0 g/vehicle-mile). The NO X and/or NO 2 measurements for LA and Seattle were obtained from a comprehensive measurement campaign that is part of the Multi-Ethnic Study of Atherosclerosis Air Pollution Study (MESA Air). The measurement campaigns in both cities were approximately 2 weeks in duration employing approximately 145 measurement sites in Greater LA and 26 sites in Seattle. The best “standard” LUR model (obtained without the inclusion of the Caline3 predictions) in LA had R 2 values of 0.53 for NO X and 0.74 for NO 2. The leave-one-out cross-validated R 2 values for NO X and NO 2 were 0.45 and 0.71, respectively. The equivalent “standard” NO 2 model for Seattle had an R 2 of 0.72 and a leave-one-out cross-validated R 2 of 0.63. When the Caline3 variable was included in the LA hybrid model, the R 2 values were 0.71 and 0.79 for NO X and NO 2, respectively. The corresponding cross-validated R 2 values were 0.66 and 0.77, for NOX and NO2, respectively. In Seattle, the inclusion of the Caline3 variable resulted in a NO 2 model with an R 2 of 0.81 and a corresponding cross-validated R 2 of 0.67. In LA, hybrid model performance was not affected by excluding roadways with annual average daily traffic volumes (AADT) < 100,000. When the Caline3 predictions for heavy-duty trucks and lighter-duty vehicles were modelled as separate terms, the estimated fleet average NO X emission factors were 8.9 (SE = 0.7) and 0.16 (SE = 0.12) grams NO X /vehicle mile for heavy-duty and lighter-duty vehicles, respectively. These values are consistent with fleet average emission factors computed for LA with EMFAC 2007.

Influence of Prediction Approach for Spatially-Dependent Air Pollution on Health Effects Estimation

ISEE-338 Objective: Air pollution studies increasingly estimate individual-level exposure from area-based measurements near participant residences. Common exposure prediction approaches either assign the measurement at the closest monitor or predict concentration at individual sites using kriging. Although many studies have adopted either prediction method, little is known about their validity for health effects estimation. Predicted exposure may produce bias and/or increase uncertainty of health effect estimates. This simulation study explores how prediction approaches for fine particulate matter (PM2.5) affect relative risk estimates for cardiovascular events in a single geographic area. Material and Methods: We used 2002 PM2.5 data (mean = 18.59 μg/m3) from the LA area to select parameters to define a correlation structure based on distance. In addition to 2 structures estimated from measured PM2.5, 3 artificial structures with different correlation features were selected to test sensitivity. Based on each of the 5 structures, annual average PM2.5 was generated at 22 existing monitoring sites in greater LA and 2000 preselected individual locations in urban LA. Five subjects were assumed to live at each individual location. Associated survival time until cardiovascular event (RR = 1.24 per 10 μg/m3 increase in PM2.5) was simulated for 10,000 subjects for 10 years. Using only generated PM2.5 at monitoring sites, we predicted PM2.5 concentrations at subject locations by nearest monitor and kriging interpolation. Finally, relative risks (RR) for time to cardiovascular event were estimated in the Cox proportional hazards model using predicted annual average PM2.5 exposures. Results: By comparing RR estimates for cardiovascular events using predicted exposure in each structure, nearest monitor prediction was more biased but less variable than kriging prediction. As variance-dominated bias, nearest monitor predictions gave RR estimates with lower mean square error; this was consistent in all sensitivity analyses. Conclusions: In our simulation study, nearest monitor prediction performed better than kriging prediction for health effects estimation.