The relationship between indoor and outdoor temperature, apparent temperature, relative humidity, and absolute humidity.

Many studies report an association between outdoor ambient weather and health. Outdoor conditions may be a poor indicator of personal exposure because people spend most of their time indoors. Few studies have examined how indoor conditions relate to outdoor ambient weather. The average indoor temperature, apparent temperature, relative humidity (RH), and absolute humidity (AH) measured in 16 homes in Greater Boston, Massachusetts, from May 2011 to April 2012 was compared to measurements taken at Boston Logan airport. The relationship between indoor and outdoor temperatures is nonlinear. At warmer outdoor temperatures, there is a strong correlation between indoor and outdoor temperature (Pearson correlation coefficient, r = 0.91, slope, ß = 0.41), but at cooler temperatures, the association is weak (r = 0.40, ß = 0.04). Results were similar for outdoor apparent temperature. The relationships were linear for RH and AH. The correlation for RH was modest (r = 0.55, ß = 0.39). Absolute humidity exhibited the strongest indoor-to-outdoor correlation (r = 0.96, ß = 0.69). Indoor and outdoor temperatures correlate well only at warmer outdoor temperatures. Outdoor RH is a poor indicator of indoor RH, while indoor AH has a strong correlation with outdoor AH year-round.

War-related stressors are associated with asthma risk among older Kuwaitis following the 1990 Iraqi invasion and occupation.

BACKGROUND: Contemporary warfare involving civilian populations is a growing public health concern. In addition to the psychological impact, war-related trauma may result in physiological alterations and even broader health effects. Associations were examined between war-related stressors and incident asthma in elderly Kuwaiti civilians following the Iraqi invasion. METHODS: A random sample of all Kuwaiti nationals aged 50-69 years on the day prior to the invasion were identified. Among the 7873 meeting eligibility criteria, 5567 (71%) agreed to participate and 5028 completed the questionnaire (91% of those eligible). Of these, 3759 were in Kuwait during the invasion, of whom 2294 were alive at follow-up. After exclusions for prevalent asthma or missingness on covariates, 2066 were available for analysis. War-related experiences were summarised into a continuous score using Rasch modelling. Relative Cox proportional hazard rates (HR) were calculated for asthma adjusting for covariates. RESULTS: Over 13 years of follow-up, physician-diagnosed asthma was reported by 66/996 (6.6%) men and 104/1070 (9.7%) women. In models adjusted for gender, socioeconomic status, smoking, BMI, and air pollution related to burning oil fires, those reporting highest stress exposure were more than twice as likely to report asthma (HR 2.3, 95% CI 1.3, 3.9) compared to civilians reporting no stressors. Experiences were more salient when anchored to fear for loss of life. CONCLUSIONS: War-related trauma is associated with increased asthma risk in these elderly civilians. Although prior research has documented the significant and persistent psychological toll of war, these findings implicate even broader health effects.

Association of ventricular arrhythmias detected by implantable cardioverter defibrillator and ambient air pollutants in the St Louis, Missouri metropolitan area.

BACKGROUND: It has previously been reported that the risk of ventricular arrhythmias is positively associated with ambient air pollution among patients with implantable cardioverter defibrillators (ICD) in Boston. AIMS: To assess the association of community exposures to air pollution with ventricular arrhythmias in a cohort of ICD patients in metropolitan St Louis, Missouri. METHODS: ICD detected episodes reported during clinical follow up were abstracted and reviewed by an electrophysiologist to identify ventricular arrhythmias. A total of 139 ventricular arrhythmias were identified among 56 patients. A case-crossover design was used with control periods matched on weekday and hour of the day within the same calendar month. Conditional logistic regression models were adjusted for temperature, barometric pressure, and relative humidity in the 24 hours preceding the event. RESULTS: There was a significant (24%, 95% CI 7% to 44%) increase in risk of ventricular arrhythmias associated with each 5 ppb increase in mean sulphur dioxide and non-significantly increased risk (22%, 95% CI -6% to 60%; and 18%, 95% CI -7% to 50%) associated with increases in nitrogen dioxide (6 ppb) and elemental carbon (0.5 microg/m3), respectively in the 24 hours before the arrhythmia. CONCLUSIONS: These results provide evidence of an association between ventricular arrhythmias and ambient air pollutants in St Louis. This is consistent with previous results from Boston, although the pollutants responsible for the increased risk are different.

Effect of trihalomethane exposure on fetal development.

AIMS: To examine the effect of trimester specific and pregnancy average total trihalomethane (TTHM) exposure on infant birth weight, low birth weight, and intrauterine growth retardation in term births, as well as gestational age and preterm delivery in all births. METHODS: Cross sectional analysis of 56 513 singleton infants born to residents of Massachusetts during 1990. City specific aggregate data were used to estimate maternal exposure to TTHM concentration; individual maternal information was used to adjust for confounding. RESULTS: Increased pregnancy average and second trimester TTHM exposure were associated with small for gestational age and reductions in birth weight after adjusting for potential confounding variables. Compared to

Increased asthma medication use in association with ambient fine and ultrafine particles.

The association between particulate air pollution and asthma medication use and symptoms was assessed in a panel study of 53 adult asthmatics in Erfurt, Germany in winter 1996/1997. Number concentrations of ultrafine particles, 0.01-0.1 microm in diameter (NC(0.01-0.1), mean 17,300 x cm(-3), and mass concentrations of fine particles 0.01-2.5 microm in diameter (MC(0.01-2.5)), mean 30.3 microg x m(-3), were measured concurrently. They were not highly correlated (r=0.45). The associations between ambient particle concentrations and the prevalence of inhaled beta2-agonist, corticosteroid use and asthma symptoms, were analysed separately with logistic regression models, adjusting for trend, temperature, weekend, holidays, and first order autocorrelation of the error. Cumulative exposures over 14 days of ultrafine and fine particles were associated with corticosteroid use. Beta2-agonist use was associated with 5-day mean NC(0.01-0.1) and MC(0.01-2.5). The prevalence of asthma symptoms was associated with ambient particle concentrations. The results suggest that reported asthma medication use and symptoms increase in association with particulate air pollution and gaseous pollutants such as nitrogen dioxide.

The effect of air pollution on inner-city children with asthma.

The effect of daily ambient air pollution was examined within a cohort of 846 asthmatic children residing in eight urban areas of the USA, using data from the National Cooperative Inner-City Asthma Study. Daily air pollution concentrations were extracted from the Aerometric Information Retrieval System database from the Environment Protection Agency in the USA. Mixed linear models and generalized estimating equation models were used to evaluate the effects of several air pollutants (ozone, sulphur dioxide (SO2), nitrogen dioxide (NO2) and particles with a 50% cut-off aerodynamic diameter of 10 microm (PM10) on peak expiratory flow rate (PEFR) and symptoms in 846 children with a history of asthma (ages 4-9 yrs). None of the pollutants were associated with evening PEFR or symptom reports. Only ozone was associated with declines in morning % PEFR (0.59% decline (95% confidence interval (CI) 0.13-1.05%) per interquartile range (IQR) increase in 5-day average ozone). In single pollutant models, each pollutant was associated with an increased incidence of morning symptoms: (odds ratio (OR)=1.16 (95% CI 1.02-1.30) per IQR increase in 4-day average ozone, OR=1.32 (95% CI 1.03-1.70) per IQR increase in 2-day average SO2, OR=1.48 (95% CI 1.02-2.16) per IQR increase in 6-day average NO2 and OR=1.26 (95% CI 1.0-1.59) per IQR increase in 2-day average PM10. This longitudinal analysis supports previous time-series findings that at levels below current USA air-quality standards, summer-air pollution is significantly related to symptoms and decreased pulmonary function among children with asthma.

Epidemiologic evidence of cardiovascular effects of particulate air pollution.

In the past decade researchers have developed a body of epidemiologic evidence showing increased daily cardiovascular mortality and morbidity associated with acute exposures to particulate air pollution. Associations have been found not only with cardiovascular deaths reported on death certificates but also with myocardial infarctions and ventricular fibrillation. Particulate air pollution exposure has been associated with indicators of autonomic function of the heart including increased heart rate, decreased heart rate variability, and increased cardiac arrhythmias. Several markers of increased risk for sudden cardiac death have also been associated with such exposures. These epidemiologic studies provide early guidance to possible pathways of particulate air pollution health effects, which can only be addressed fully in toxicologic and physiologic studies.

Increased particulate air pollution and the triggering of myocardial infarction.

BACKGROUND: Elevated concentrations of ambient particulate air pollution have been associated with increased hospital admissions for cardiovascular disease. Whether high concentrations of ambient particles can trigger the onset of acute myocardial infarction (MI), however, remains unknown. METHODS AND RESULTS: We interviewed 772 patients with MI in the greater Boston area between January 1995 and May 1996 as part of the Determinants of Myocardial Infarction Onset Study. Hourly concentrations of particle mass <2.5 microm (PM(2.5)), carbon black, and gaseous air pollutants were measured. A case-crossover approach was used to analyze the data for evidence of triggering. The risk of MI onset increased in association with elevated concentrations of fine particles in the previous 2-hour period. In addition, a delayed response associated with 24-hour average exposure 1 day before the onset of symptoms was observed. Multivariate analyses considering both time windows jointly revealed an estimated odds ratio of 1.48 associated with an increase of 25 microg/m(3) PM(2.5) during a 2-hour period before the onset and an odds ratio of 1.69 for an increase of 20 microg/m(3) PM(2.5) in the 24-hour period 1 day before the onset (95% CIs 1.09, 2.02 and 1.13, 2.34, respectively). CONCLUSIONS: The present study suggests that elevated concentrations of fine particles in the air may transiently elevate the risk of MIs within a few hours and 1 day after exposure. Further studies in other locations are needed to clarify the importance of this potentially preventable trigger of MI.

The effect of chelation therapy with succimer on neuropsychological development in children exposed to lead.

BACKGROUND: Thousands of children, especially poor children living in deteriorated urban housing, are exposed to enough lead to produce cognitive impairment. It is not known whether treatment to reduce blood lead levels prevents or reduces such impairment. METHODS: We enrolled 780 children with blood lead levels of 20 to 44 microg per deciliter (1.0 to 2.1 micromol per liter) in a randomized, placebo-controlled, double-blind trial of up to three 26-day courses of treatment with succimer, a lead chelator that is administered orally. The children lived in deteriorating inner-city housing and were 12 to 33 months of age at enrollment; 77 percent were black, and 5 percent were Hispanic. Follow-up included tests of cognitive, motor, behavioral, and neuropsychological function over a period of 36 months. RESULTS: During the first six months of the trial, the mean blood lead level in the children given succimer was 4.5 microg per deciliter (0.2 micromol per liter) lower than the mean level in the children given placebo (95 percent confidence interval, 3.7 to 5.3 microg per deciliter [0.2 to 0.3 micromol per liter]). At 36 months of follow-up, the mean IQ score of children given succimer was 1 point lower than that of children given placebo, and the behavior of children given succimer was slightly worse as rated by a parent. However, the children given succimer scored slightly better on the Developmental Neuropsychological Assessment, a battery of tests designed to measure neuropsychological deficits thought to interfere with learning. All these differences were small, and none were statistically significant. CONCLUSIONS: Treatment with succimer lowered blood lead levels but did not improve scores on tests of cognition, behavior, or neuropsychological function in children with blood lead levels below 45 microg per deciliter. Since succimer is as effective as any lead chelator currently available, chelation therapy is not indicated for children with these blood lead levels.

Health effects of air pollution exposure on children and adolescents in São Paulo, Brazil.

Children and adolescents have been considered more susceptible to the effects of air pollution than adults. In order to investigate the responses of children of different ages to air pollution exposure, daily records of hospital admissions for children in five age groups (equal or less than 2 years of age, 3-5, 6-13, 14-19, and all ages together, i.e., from 0-19 years of age) were obtained from January 1993 to November 1997 in São Paulo, Brazil, and were compared to daily records of PM10, O3, SO2, CO and NO2 concentrations in ambient air. For each age group a generalized additive Poisson regression was fitted controlling for smooth functions of time, temperature, humidity, and days of the week, with an additional indicator for holidays. Polynomial distributed lag models were used to estimate the 7-day cumulative effect of each pollutant. Children 2 years or less were the most susceptible to the effects of all five pollutants with an increase of 9.4% (95% CI: 7.9,10.9) in respiratory admissions associated with each interquartile range increase in PM10. The oldest group was the second most susceptible to air pollutants, with each interquartile range increase in PM10 associated with a 5.1% (95% CI: 0.3,9.8) increase in respiratory admissions. An interquartile range increase in CO was associated with an 11.3% (95% CI: 5.9,16.8) increase in respiratory hospitalizations. When a multipollutant model was used, the effect of PM10 on respiratory admissions for all ages together was unchanged, while the SO2 and the other pollutants effect was substantially reduced. This study showed that daily respiratory hospital admissions for children and adolescents in São Paulo increased with air pollution, and that the largest effects were found for the youngest (2 years or less) and oldest (14-19 years) age groups.

FEV(1) is associated with risk of asthma attacks in a pediatric population.

BACKGROUND: FEV(1) is endorsed by the National Asthma Education and Prevention Program as a means for grading asthma severity. However, few data exist on the relationship between FEV(1) and asthma outcomes during long-term follow-up. OBJECTIVE: We explored the relationship between the percent predicted FEV(1) (FEV(1)%) and subsequent asthma attacks in a longitudinal study of pediatric lung health. METHODS: A retrospective cohort of 13,842 children (100,292 observations) seen annually over a 15-year interval was analyzed for measurement of pulmonary function, and a respiratory questionnaire was completed. Up to grade 9, a standard questionnaire was completed by a parent or guardian; thereafter it was completed by the patient. For each observation, the report of an attack during the past year was paired with FEV(1) recorded at the field survey 1 year earlier. RESULTS: A progressive decrease in the proportion of individuals reporting an attack was associated with increasing decile of FEV(1)%. Two categorization schemes for FEV(1)% were examined: a scheme based on the National Asthma Education and Prevention Program recommendations (<60%, 60%-80%, and >80%), and an alternative scheme (<80%, 80%-100%, and >100%). In multivariate models, FEV(1)% was an independent predictor of attacks: among the parental report group, the odds ratios were 2.1 (95% CI, 1.3-3.4) and 1.4 (95% CI, 1.2-1.6) for FEV(1)% < 60% and FEV(1)% of 60% to 80% compared with FEV(1)% > 80%, respectively; and among the self-report group, odds ratios were 5.3 (95% CI, 2.2-12.9) and 1.4 (95% CI, 1.2-1.7) for FEV(1)% < 60% and FEV(1)% of 60% to 80% compared with FEV(1)% > 80%, respectively. With the alternative classification scheme, the relationship was similar, but the difference in risk between categories of FEV(1)% decreased. CONCLUSION: The strong association between FEV(1)% and risk of asthma attack over the subsequent year supports an emphasis on objective measures of lung function in assessment of risk for adverse asthma outcomes.

Airborne particles are a risk factor for hospital admissions for heart and lung disease.

We examined the association between particulate matter [less than/equal to] 10 microm; (PM(10)) and hospital admission for heart and lung disease in ten U.S. cities. Our three goals were to determine whether there was an association, to estimate how the association was distributed across various lags between exposure and response, and to examine socioeconomic factors and copollutants as effect modifiers and confounders. We fit a Poisson regression model in each city to allow for city-specific differences and then combined the city-specific results. We examined potential confounding by a meta-regression of the city-specific results. Using a model that considered simultaneously the effects of PM(10) up to lags of 5 days, we found a 2.5% [95% confidence interval (CI), 1.8-3. 3] increase in chronic obstructive pulmonary disease, a 1.95% (CI, 1. 5-2.4) increase in pneumonia, and a 1.27% increase (CI, 1-1.5) in CVD for a 10 microg/m(3) increase in PM(10). We found similar effect estimates using the mean of PM(10) on the same and previous day, but lower estimates using only PM(10) for a single day. When using only days with PM(10) < 50 mg/m(3), the effect size increased by [greater/equal to] 20% for all three outcomes. These effects are not modified by poverty rates or minority status. The results were stable when controlling for confounding by sulfur dioxide, ozone, and carbon monoxide. These results are consistent with previous epidemiology and recent mechanistic studies in animals and humans.

The National Morbidity, Mortality, and Air Pollution Study. Part I: Methods and methodologic issues.

The Health Effects Institute, established in 1980, is an independent and unbiased source of information on the health effects of motor vehicle emissions. HEI supports research on all major pollutants, including regulated pollutants (such as carbon monoxide, ozone, nitrogen dioxide, and particulate matter) and unregulated pollutants (such as diesel engine exhaust, methanol, and aldehydes). To date, HEI has supported more than 200 projects at institutions in North America and Europe and has published over 100 research reports. Typically, HEI receives half its funds from the US Environmental Protection Agency and half from 28 manufacturers and marketers of motor vehicles and engines in the US. Occasionally, funds from other public and private organizations either support special projects or provide resources for a portion of an HEI study. Regardless of funding sources, HEI exercises complete autonomy in setting its research priorities and in reaching its conclusions. An independent Board of Directors governs HEI. The Institute's Research and Review Committees serve complementary scientific purposes and draw distinguished scientists as members. The results of HEI-funded studies are made available as Research Reports, which contain both the Investigators' Report and the Review Committee's evaluation of the work's scientific quality and regulatory relevance.

The effect of ozone on inner-city children with asthma: identification of susceptible subgroups.

Within a cohort of 846 inner-city asthmatic children aged 4 to 9 yr, we looked for subgroups that were more susceptible to the effects of summer ozone. Daily diaries were compared with ambient ozone levels to evaluate effect modification by demographic and environmental characteristics. Children born > 3 wk prematurely or weighing < 5.5 lb. had greater declines in morning % peak expiratory flow rate (PEFR) (1.8% versus 0.3% per 15 ppb ozone, p < 0.05) and a higher incidence of morning symptoms (odds ratio = 1.42 versus 1.09 per 15 ppb ozone, p < 0.05) than did children who had been full-term infants of normal birthweight. Among children who had been of low birthweight (LBW) or had been premature infants, greater declines were seen among those whose reported baseline medication category was "no medication" (3.2% decline) or "steroids" (2.7%) as opposed to beta agonists or xanthines (0.8%) or cromolyn without steroids (0. 1%). Among the children who had been normal birthweight and full-term infants, the cromolyn without steroids group had the greatest declines in %PEFR (1.3%, versus < 0.5% in each of the other three groups). Nonatopic children also had greater responses to ozone. We conclude that among an asthmatic cohort, children who had had an LBW or a premature birth showed the greatest responses to ozone.

Association of fine particulate matter from different sources with daily mortality in six U.S. cities.

Previously we reported that fine particle mass (particulate matter [less than and equal to] 2.5 microm; PM(2.5)), which is primarily from combustion sources, but not coarse particle mass, which is primarily from crustal sources, was associated with daily mortality in six eastern U.S. cities (1). In this study, we used the elemental composition of size-fractionated particles to identify several distinct source-related fractions of fine particles and examined the association of these fractions with daily mortality in each of the six cities. Using specific rotation factor analysis for each city, we identified a silicon factor classified as soil and crustal material, a lead factor classified as motor vehicle exhaust, a selenium factor representing coal combustion, and up to two additional factors. We extracted daily counts of deaths from National Center for Health Statistics records and estimated city-specific associations of mortality with each source factor by Poisson regression, adjusting for time trends, weather, and the other source factors. Combined effect estimates were calculated as the inverse variance weighted mean of the city-specific estimates. In the combined analysis, a 10 microg/m(3) increase in PM(2.5) from mobile sources accounted for a 3.4% increase in daily mortality [95% confidence interval (CI), 1.7-5.2%], and the equivalent increase in fine particles from coal combustion sources accounted for a 1.1% increase [CI, 0.3-2.0%). PM(2.5) crustal particles were not associated with daily mortality. These results indicate that combustion particles in the fine fraction from mobile and coal combustion sources, but not fine crustal particles, are associated with increased mortality.

Is daily mortality associated specifically with fine particles? Data reconstruction and replication of analyses.

In 1996, Schwartz, Dockery, and Neas reported that daily mortality was more strongly associated with concentrations of PM2.5 than with concentrations of larger particles (coarse mass [CM]) in six U.S. cities ("original paper"/"original analyses"). Because of the public policy implications of the findings and the uniqueness of the concentration data, we undertook a reanalysis of these results. This paper presents results of the reconstruction of these data and replication of the original analyses using the reconstructed data. The original investigators provided particulate air pollution data for this paper. Daily weather and daily counts of total and cause-specific deaths were reconstructed from original public records. The reconstructed particulate air pollution and weather data were consistent with the summaries presented in the original paper. Daily counts of deaths in the reconstructed data set were lower than in the original paper because of restrictions on residence and place of death. The reconstruction process identified an administrative change in county codes that led to higher numbers of deaths in St. Louis. Despite these differences in daily counts of deaths, the estimated effects of particulate air pollution from the reconstructed dataset, using analytic methods as described in the original paper, produced combined effect estimates essentially equivalent to the originally published results. For example, the estimated association of a 10 micrograms/m3 increase in 2-day mean particulate air pollution on total mortality was 1.3% (95% confidence interval [CI] 0.9-1.7%, t = 6.53) for PM2.5 based on the reconstructed dataset, compared to the originally reported association of 1.5% (95% CI 1.1-1.9%, t = 7.41). For coarse particles, the estimated association from the reconstructed dataset was 0.4% (95% CI -0.2-0.9%, t = 1.43) compared to the originally reported association of 0.4% (95% CI -0.1-1.0%, t = 1.48). These results from the reconstructed data suggest that the original results reported by Schwartz, Dockery, and Neas were essentially replicated.

Air pollution and incidence of cardiac arrhythmia.

Air pollution episodes have been associated with increased cardiovascular hospital admissions and mortality in time-series studies. We tested the hypothesis that patients with implanted cardioverter defibrillators experience potentially life-threatening arrhythmias after such air pollution episodes. We compared defibrillator discharge interventions among 100 patients with such devices in eastern Massachusetts, according to variations in concentrations of particulate matter, black carbon, and gaseous air pollutants that were measured daily for the years 1995 through 1997. A 26-ppb increase in nitrogen dioxide was associated with increased defibrillator interventions 2 days later (odds ratio = 1.8; 95% confidence interval = 1.1-2.9). Patients with ten or more interventions experienced increased arrhythmias in association with nitrogen dioxide, carbon monoxide, black carbon, and fine particle mass. These results suggest that elevated levels air pollutants are associated with potentially life-threatening arrhythmia leading to therapeutic interventions by an implanted cardioverter defibrillator.

The National Morbidity, Mortality, and Air Pollution Study. Part II: Morbidity and mortality from air pollution in the United States.

BACKGROUND: Epidemiologic time-series studies conducted in a number of cities have identified, in general, an association between daily changes in concentration of ambient particulate matter (PM) and daily number of deaths (mortality). Increased hospitalization (a measure of morbidity) among the elderly for specific causes has also been associated with PM. These studies have raised concerns about public health effects of particulate air pollution and have contributed to regulatory decisions in the United States. However, scientists have pointed out uncertainties that raise questions about the interpretation of these studies. One limitation to previous time-series studies of PM and adverse health effects is that the evidence for an association is derived from studies conducted in single locations using diverse analytic methods. Statistical procedures have been used to combine the results of these single location studies in order to produce a summary estimate of the health effects of PM. Difficulties with this approach include the process by which cities were selected to be studied, the different analytic methods applied to each single study, and the variety of methods used to measure or account for variables included in the analysis. These individual studies were also not able to account for the effects of gaseous air pollutants in a systematic manner.

Climate, traffic-related air pollutants, and asthma prevalence in middle-school children in taiwan.

This study compared the prevalence of asthma with climate and air pollutant data to determine the relationship between asthma prevalence and these factors. We conducted a nationwide survey of respiratory illness and symptoms in middle-school students in Taiwan. Lifetime prevalences of physician-diagnosed asthma and of typical symptoms of asthma were compared to air monitoring station data for temperature, relative humidity, sulfur dioxide, nitrogen oxides, ozone, carbon monoxide, and particulate matter with aerodynamic diameter [less than/equal to] 10 microm (PM(10)). A total of 331,686 nonsmoking children attended schools located within 2 km of 55 stations. Asthma prevalence rates adjusted for age, history of atopic eczema, and parental education were associated with nonsummer (June-August) temperature, winter (January-March) humidity, and traffic-related air pollution, especially carbon monoxide and nitrogen oxides, for both girls and boys. Nonsummer temperature, winter humidity, and traffic-related air pollution, especially carbon monoxide and nitrogen oxides, were positively associated with the prevalence of asthma in middle-school students in Taiwan.

Heart rate variability associated with particulate air pollution.

BACKGROUND: Epidemiologic studies have linked fine particulate air pollution with cardiopulmonary mortality, yet underlying biologic mechanisms remain unknown. Changes in heart rate variability (HRV) may reflect changes in cardiac autonomic function and risk of sudden cardiac death. This study evaluated changes in mean heart rate and HRV in human beings associated with changes in exposure to particulate air pollution. METHODS: Repeated ambulatory electrocardiographic monitoring was conducted on 7 subjects for a total of 29 person-days before, during, and after episodes of elevated pollution. Mean HR, the standard deviation of normal-to-normal (NN) intervals (SDNN), the standard deviation of the averages of NN intervals in all 5-minute segments of the recording (SDANN), and the square root of the mean of squared differences between adjacent NN intervals (r-MSSD) were calculated for 24-hour and 6-hour time segments. Associations of HRV with particulate pollution levels were evaluated with fixed-effects regression models. RESULTS: After controlling for differences across patients, elevated particulate levels were associated with (1) increased mean HR, (2) decreased SDNN, a measure of overall HRV, (3) decreased SDANN, a measure that corresponds to ultralow frequency variability, and (4) increased r-MSSD, a measure that corresponds to high-frequency variability. The associations between HRV and particulates were small but persisted even after controlling for mean HR. CONCLUSIONS: This study suggests that changes in cardiac autonomic function reflected by changes in mean HR and HRV may be part of the pathophysiologic mechanisms or pathways linking cardiovascular mortality and particulate air pollution.