Mark Raizenne

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.

It's about time: a comparison of Canadian and American time-activity patterns.

This study compares two North American time–activity data bases: the National Human Activity Pattern Survey (NHAPS) of 9386 interviewees in 1992–1994 in the continental USA with the Canadian Human Activity Pattern Survey (CHAPS) of 2381 interviewees in 1996–1997 in four major Canadian cities. Identical surveys and methodology were used to collect this data: random sample telephone selection within the identified telephone exchanges, computer-assisted telephone interviews, overselection of children and weekends in the 24-h recall diary and the same interviewers. Very similar response rates were obtained: 63% (NHAPS) and 64.5% (CHAPS). Results of comparisons by age within major activity and location groups suggest activity and location patterns are very similar (most differences being less than 1% or 14 min in a 24-h day) with the exception of seasonal differences. Canadians spend less time outdoors in winter and less time indoors in summer than their U.S. counterparts. When exposure assessments use time of year or outdoor/indoor exposure gradients, these differences may result in significant differences in exposure assessments. Otherwise, the 24-h time activity patterns of North Americans are remarkably similar and use of the combined data set for some exposure assessments may be feasible.

Association between ambient carbon monoxide levels and hospitalizations for congestive heart failure in the elderly in 10 Canadian cities

We examined the role that ambient air pollution plays in exacerbating cardiac disease by relating daily fluctuations in admissions to 134 hospitals for congestive heart failure in the elderly to daily variations in ambient concentrations of carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone, and the coefficient of haze in Canadas 10 largest cities for the 11‐year period 1981–1991 inclusive. We adjusted the hospitalization time series for seasonal, subseasonal, and weekly cycles and for hospital usage patterns. The logarithm of the daily high‐hour ambient carbon monoxide concentration recorded on the day of admission displayed the strongest and most consistent association with hospitalization rates among the pollutants, after stratifying the time series by month of year and adjusting simultaneously for temperature, dew point, and the other ambient air pollutants. The relative risk for a change from 1 ppm to 3 ppm, the 25th and 75th percentiles of the exposure distribution, was 1.065 (95% confidence interval = 1.028–1.104). The regression coefficients of the other air pollutants were much more sensitive to simultaneous adjustment for either multiple pollutant or weather model specifications.

The Association between Ambient Carbon Monoxide Levels and Daily Mortality in Toronto, Canada

The role of ambient levels of carbon monoxide (CO) in the exacerbation of heart problems in individuals with both cardiac and other diseases was examined by comparing daily variations in CO levels and daily fluctuations in nonaccidental mortality in metropolitan Toronto for the 15-year period 1980-1994. After adjusting the mortality time series for day-of-the-week effects, nonparametic smoothed functions of day of study and weather variables, statistically significant positive associations were observed between daily fluctuations in mortality and ambient levels of carbon monoxide, nitrogen dioxide, sulfur dioxide, coefficient of haze, total suspended particulate matter, sulfates, and estimated PM2.5 and PM10. However, the effects of this complex mixture of air pollutants could be almost completely explained by the levels of CO and total suspended particulates (TSP). Of the 40 daily nonaccidental deaths in metropolitan Toronto, 4.7% (95% confidence interval of 3.4%-6.1%) could be attributable to CO while TSP contributed an additional 1.0% (95% confidence interval of 0.2-1.9%), based on changes in CO and TSP equivalent to their average concentrations. Statistically significant positive associations were observed between CO and mortality in all seasons, age, and disease groupings examined. Carbon monoxide should be considered as a potential public health risk to urban populations at current ambient exposure levels.

Associations between short-term changes in nitrogen dioxide and mortality in Canadian cities.

The association between daily variations in ambient concentrations of nitrogen dioxide (NO2) and mortality was examined in 12 of Canadas largest cities, using a 19-yr time-series analysis (from 1981-1999). The authors employed parametric statistical methods that are not subject to the recently discovered convergence and error estimation problems of generalized additive models. An increase in the 3-d moving average of NO2 concentrations equivalent to the population-weighted study mean of 22.4 ppb was associated with a 2.25% (t = 4.45) increase in the daily nonaccidental mortality rate and was insensitive to adjustment for ozone, sulfur dioxide, carbon monoxide, coefficient of haze, size-fractionated particulate mass, and the sulfate ion measured on an every-6th-day sampling schedule. The 3-d moving average of NO2 was sensitive to adjustment for fine particulate matter measured daily during the 1998-2000 time period.

The effects of ambient ozone on lung function in children: a reanalysis of six summer camp studies.

Studies of children attending summer camps often have observed relationships between daily outdoor ozone (O3) concentrations and decreased lung function that are qualitatively similar to results seen in human chamber studies. The former studies, focusing on the pulmonary effects of O3 and associated pollutants on children under natural conditions of exposure, are potentially of great importance to understanding the public health impact of ambient O3. However, a thorough assessment of the results of these studies has been hampered by differences in the analysis and reporting of data across the various studies. We obtained data sets from six summer camp studies carried out by three separate investigative groups, including two New Jersey studies performed by New York University, two studies in Ontario carried out by Health and Welfare Canada, and two studies in southern California. The data consisted of sequential, daily measurements of forced expiratory volume in 1 sec (FEV1), peak expiratory flow rate (PEFR), and 1-hr O3 concentration in the hour preceding lung function measurements for each child. We analyzed the relationships between lung function and O3 using linear regression models that fit subject-specific intercepts and a single, pooled O3 slope. These models were fit for each of the six studies separately and for all studies combined. All of the study-specific slopes of FEV1 on O3 were negative (i.e., increased O3 associated with decreased FEV1); five of six were statistically significant. Analysis of the combined six-study data set yielded a slope of -0.50 ml FEV1/ppb O3 (p<0.0001). Addition of time-trend variables to the combined-data analysis diminished, but did not eliminate, the FEV1-O3 relationship. Study-specific slopes for PEFR on O3 were more variable. Combined over studies, no significant relationship was observed between PEFR and O3. However, this negative finding appeared to be partially confounded by time trends in PEFR. The results of this reanalysis provide strong evidence that children exposed to O3 under natural conditions experience decreases in FEV1 of the kind demonstrated in laboratory studies, and raise concern that other acute respiratory effects observed in those studies (e.g., pulmonary inflammation) may also occur in young people exposed to ambient O3.

Residential exposure to volatile organic compounds and asthma.

We critically analysed the literature concerning exposure to volatile organic compounds and asthma. Observational studies have consistently found a relation between volatile organic compounds and indicators of asthma, such as symptoms, peak flows, and objectively measured bronchial reactivity. In contrast, interventional studies have generally failed to find a relation between exposure to residential levels of formaldehyde and other volatile organic compounds and asthma. One hypothesis to explain the discrepancy in findings between interventional and observational studies is that the effect size is small requiring relatively large numbers of study subjects, common in observational studies but often not feasible in interventional studies. Another hypothesis is that longer duration of exposure is important, a common circumstance in observational studies where the home environment is the exposure setting. In contrast, duration of exposure in interventional studies is usually of minutes‐to‐hours in a chamber. Finally, the observed association in observational studies could be confounded by a factor which is a determinant of asthma and is also associated with exposure to volatile organic compounds.

Respiratory health effects associated with ambient sulfates and ozone in two rural Canadian communities

A cross-sectional epidemiological study investigating the respiratory health of children in two Canadian communities was conducted in 1983-1984 in Tillsonburg, Ontario, located in a region of moderately elevated concentrations of transported air pollutants, and in Portage la Prairie, Manitoba, situated in a low pollution area. There were no significant local sources of industrial emissions in either community. Seven hundred and thirty-five children aged 7-12 were studied in the first town and 895 in the second. Respiratory health was assessed by the measurement of the forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV1.0) of each child, and by evaluation of the childs respiratory symptoms and illnesses using a parent-completed questionnaire. Sulfur dioxide (SO2), sulfate, and particulate nitrate levels were significantly higher in Tillsonburg than in Portage la Prairie (P less than 0.05), but nitrogen dioxide (NO2) and inhalable particles (PM10) differed little between the communities. Historical data in the vicinity of Tillsonburg indicated that average annual levels of sulfates, total nitrates, and ozone (O3) did not vary markedly in the 9-year period preceding the study. The results show that Tillsonburg children had statistically significant (P less than 0.001) lower levels of 2% for FVC and 1.7% for FEV1.0 as compared with children in Portage la Prairie. These differences could not be explained by parental smoking or education, the use of gas cooking or wood heating fuels, pollution levels on the day of testing, or differences in age, sex, height, or weight. The differences persisted when children with cough with phlegm, asthma, wheeze, inhalant allergies, or hospitalization before age 2 for a chest illness were excluded from analysis. With the exception of inhalant allergies, which occurred more frequently in Tillsonburg children, the prevalence of chronic respiratory symptoms and illnesses was similar in the two communities.

Addressing the Linkage between Exposure to Pesticides and Human Health Effects—Research Trends and Priorities for Research

In recent years, there has been escalating concern over the possible association between exposure to pesticides and adverse human health effects by a number of non-governmental organizations, professional and public interest groups. Recognizing the need to document the scientific basis of these concerns as a foundation for initiating a research theme devoted to linkages between exposures to pesticides and human health effects, the Canadian Institutes of Health Research (CIHR) requested a summary of recent research trends that address these linkages. Experts across Canada in the field of pesticide regulation and research were invited to participate in the review. The review summarizes the limitations of past and current studies related to pesticides and human health effects research and makes suggestions for future research priorities and proposed study designs that will improve the assessment of pesticide exposure, the associated health risks, and improved methodology for regulatory decision making.

Measuring Progress in the Management of Ambient Air Quality: The Case for Population Health

Although progress has been made in the last few decades at reducing ambient concentrations of air pollutants, scientific evidence suggests that there remains a risk to human health from exposure to these pollutants at current levels in Canada. Much of the motivation for air pollution reduction efforts is to protect population health. This article presents a method of monitoring changes in air pollution-related health outcomes over time in conjunction with temporal changes in ambient pollution concentrations. The progress measure is a function of temporal changes in location-specific ambient concentrations and the potentially time-dependent association between those concentrations and daily deaths. The progress measure can be determined for a single location or at a national level. The measure can also be extended to include several pollutants. The progress measure is illustrated with an example of how changes in nitrogen dioxide levels in 12 Canadian cities from 1981 to 1999 have translated into changes in the percent of nonaccidental mortality burden attributable to this pollutant over time.