In-car particles and cardiovascular health: an air conditioning-based intervention study

Air pollution exposure in active versus passive travel modes across five continents: A Bayesian random-effects meta-analysis

Epidemiological studies on health effects of air pollution usually estimate exposure at the residential address. However, ignoring daily mobility patterns may lead to biased exposure estimates, as documented in previous exposure studies. To improve the reliable integration of exposure related to mobility patterns into epidemiological studies, we conducted a systematic review of studies across all continents that measured air pollution concentrations in various modes of transport using portable sensors. To compare personal exposure across different transport modes, specifically active versus motorized modes, we estimated pairwise exposure ratios using a Bayesian random-effects meta-analysis. Overall, we included measurements of six air pollutants (black carbon (BC), carbon monoxide (CO), nitrogen dioxide (NO2), particulate matter (PM10, PM2.5) and ultrafine particles (UFP)) for seven modes of transport (i.e., walking, cycling, bus, car, motorcycle, overground, underground) from 52 published studies. Compared to active modes, users of motorized modes were consistently the most exposed to gaseous pollutants (CO and NO2). Cycling and walking were the most exposed to UFP compared to other modes. Active vs passive mode contrasts were mostly inconsistent for other particle metrics. Compared to active modes, bus users were consistently more exposed to PM10 and PM2.5, while car users, on average, were less exposed than pedestrians. Rail modes experienced both some lower exposures (compared to cyclists for PM10 and pedestrians for UFP) and higher exposures (compared to cyclist for PM2.5 and BC). Ratios calculated for motorcycles should be considered carefully due to the small number of studies, mostly conducted in Asia. Computing exposure ratios overcomes the heterogeneity in pollutant levels that may exist between continents and countries. However, formulating ratios on a global scale remains challenging owing to the disparities in available data between countries.

Randomized Cross-Over Study of In-Vehicle Cabin Air Filtration, Air Pollution Exposure, and Acute Changes to Heart Rate Variability, Saliva Cortisol, and Cognitive Function

To determine how traffic-related air pollution (TRAP) exposures affect commuter health, and whether cabin air filtration (CAF) can mitigate exposures, we conducted a cross-over study of 48 adults exposed to TRAP during two commutes with and without CAF. Measurements included particulate air pollutants (PM_2.5, black carbon [BC], ultrafine particles [UFPs]), volatile organic compounds, and nitrogen dioxide. We measured participants' heart rate variability (HRV), saliva cortisol, and cognitive function. On average, CAF reduced concentrations of UFPs by 26,232 (95%CI: 11,734, 40,730) n/cm³, PM_2.5 by 6 (95%CI: 5, 8) μg/m³, and BC by 1348 (95%CI: 1042, 1654) ng/m³, or 28, 30, and 32%, respectively. Each IQR increase in PM_2.5 was associated with a 28% (95%CI: 2, 60) increase in high-frequency power HRV at the end of the commute and a 22% (95%CI: 7, 39) increase 45 min afterward. IQR increases in UFPs were associated with increased saliva cortisol in women during the commute (18% [95%CI: 0, 40]). IQR increases in UFPs were associated with strong switching costs (19% [95%CI: 2, 39]), indicating a reduced capacity for multitasking, and PM_2.5 was associated with increased reaction latency, indicating slower responses (5% [95%CI: 1, 10]). CAF can reduce particulate exposures by almost a third.

The pathophysiological and molecular mechanisms of atmospheric PM2.5 affecting cardiovascular health: A review

BACKGROUND

Exposure to ambient fine particulate matter (PM2.5, with aerodynamic diameter less than 2.5 µm) is a leading environmental risk factor for global cardiovascular health concern.

OBJECTIVE

To provide a roadmap for those new to this field, we reviewed the new insights into the pathophysiological and cellular/molecular mechanisms of PM2.5 responsible for cardiovascular health.

MAIN FINDINGS

PM2.5 is able to disrupt multiple physiological barriers integrity and translocate into the systemic circulation and get access to a range of secondary target organs. An ever-growing body of epidemiological and controlled exposure studies has evidenced a causal relationship between PM2.5 exposure and cardiovascular morbidity and mortality. A variety of cellular and molecular biology mechanisms responsible for the detrimental cardiovascular outcomes attributable to PM2.5 exposure have been described, including metabolic activation, oxidative stress, genotoxicity, inflammation, dysregulation of Ca2+ signaling, disturbance of autophagy, and induction of apoptosis, by which PM2.5 exposure impacts the functions and fates of multiple target cells in cardiovascular system or related organs and further alters a series of pathophysiological processes, such as cardiac autonomic nervous system imbalance, increasing blood pressure, metabolic disorder, accelerated atherosclerosis and plaque vulnerability, platelet aggregation and thrombosis, and disruption in cardiac structure and function, ultimately leading to cardiovascular events and death. Therein, oxidative stress and inflammation were suggested to play pivotal roles in those pathophysiological processes.

CONCLUSION

Those biology mechanisms have deepen insights into the etiology, course, prevention and treatment of this public health concern, although the underlying mechanisms have not yet been entirely clarified.

Protecting Cardiovascular Health From Wildfire Smoke

Wildfire smoke is a rapidly growing threat to global cardiovascular health. We review the literature linking wildfire smoke exposures to cardiovascular effects. We find substantial evidence that short-term exposures are associated with key cardiovascular outcomes, including mortality, hospitalization, and acute coronary syndrome. Wildfire smoke exposures will continue to increase over the majority of Earth's surface. For example, the United States alone has experienced a 5-fold increase in annual area burned since 1972, with 82 million individuals estimated to be exposed to wildfire smoke by midcentury. The associated rise in excess morbidity and mortality constitutes a growing global public health crisis. Fortunately, the effect of wildfire smoke on cardiovascular health is modifiable at the individual and population levels through specific interventions. Health systems therefore have an opportunity to help safeguard patients from smoke exposures. We provide a roadmap of evidence-based interventions to reduce risk and protect cardiovascular health. Key interventions include preparing health systems for smoke events; identifying and educating vulnerable patients; reducing outdoor activities; creating cleaner air environments; using air filtration devices and personal respirators; and aggressive management of chronic diseases and traditional risk factors. Further research is needed to test the efficacy of interventions on reducing cardiovascular outcomes.

Personal exposure to PM2.5 in five commuting modes under hazy and non-hazy conditions

Effective reducing exposure to fine particulate matter (PM_2.5) during commuting can help lower the risk of adverse health effects therefrom; however, few studies have examined the influence of different background levels of air pollution-particularly in China where PM_2.5 concentrations are high globally. In this study, personal sampling was conducted to measure individual exposure during five different modes of commuting (bus, metro, car, bicycle and walking) in Shanghai, China. A total of 125 measurements were conducted for five days under haze and non-haze conditions, following which the corresponding doses of PM_2.5 inhaled were estimated. The mean concentrations (±standard deviation, SD, 1-min averaging) of background PM_2.5 were 155.9 (±98.7) μg/m³ during haze and 36.3 (±17.6) μg/m³ under the non-haze conditions. Under both conditions, active commuters were exposed to higher PM_2.5 concentrations than those using motorized commuting modes (Wilcoxon test, p < 0.01). Moreover, driving with closed windows and air conditioning effectively reduces the PM_2.5 concentrations in cars by 35 %-57 %. Cyclists inhaled the highest doses (539.8 ± 313.2 and 134.8 ± 71.3 μg/h under haze and non-haze conditions, respectively), whereas car drivers inhaled the lowest doses (28.8 ± 21.2 and 3.7 ± 2.6 μg/h under haze and non-haze conditions, respectively). Individual exposure to PM_2.5 during commuting varied with the modes; the discrepancy between the latter depended largely on the ambient concentration. Our findings provided evidence that traffic-related air pollution contributed to daily pollutant exposure and highlighted the importance of taking personal protective measures while commuting, particularly during haze.

Clean Air, Smart Cities, Healthy Hearts: Action on Air Pollution for Cardiovascular Health

More than twenty percent of all cardiovascular disease (CVD) deaths are caused by air pollution — more than three million deaths every year — and these numbers will continue to rise unless the global community takes action. Nine out of ten people worldwide breathe polluted air, which disproportionately affects those living in low-resource settings. The World Heart Federation (WHF) is committed to reducing the impact of air pollution on people’s health and has made this a priority area of its global advocacy efforts. In pursuit of this goal, WHF has formed an Air Pollution Expert Group to inform action on air pollution for CVD health and recommend changes to public health policy. This policy paper lays out the health impacts of air pollution, examines its position on the global policy agenda, demonstrates its relevance to the cardiovascular community, and proposes actionable policy measures to mitigate this deadly risk factor to health. The paper considers the important roles to be played by the Members of WHF, including scientific societies and the physicians that constitute them, heart health foundations, and patient advocacy groups. The paper concludes with a detailed table of recommendations for the various sub-target groups at the global, national, local, and patient level.

Characterising professional drivers' exposure to traffic-related air pollution: Evidence for reduction strategies from in-vehicle personal exposure monitoring

Professional drivers working in congested urban areas are required to work near harmful traffic related pollutants for extended periods, representing a significant, but understudied occupational risk. This study collected personal black carbon (BC) exposures for 141 drivers across seven sectors in London. The aim of the study was to assess the magnitude and the primary determinants of their exposure, leading to the formulation of targeted exposure reduction strategies for the occupation. Each participant's personal BC exposures were continuously measured using real-time monitors for 96 h, incorporating four shifts per participant. 'At work' BC exposures (3.1 ± 3.5 µg/m³) were 2.6 times higher compared to when 'not at work' (1.2 ± 0.7 µg/m³). Workers spent 19% of their time 'at work driving', however this activity contributed 36% of total BC exposure, highlighting the disproportionate effect driving had on their daily exposure. Taxi drivers experienced the highest BC exposures due to the time they spent working in congested central London, while emergency services had the lowest. Spikes in exposure were observed while driving and were at times greater than 100 µg/m³. The most significant determinants of drivers' exposures were driving in tunnels, congestion, location, day of week and time of shift. Driving with closed windows significantly reduced exposures and is a simple behaviour change drivers could implement. Our results highlight strategies by which employers and local policy makers can reduce professional drivers' exposure to traffic-related air pollution.

Personal-Level Protective Actions Against Particulate Matter Air Pollution Exposure: A Scientific Statement From the American Heart Association

Since the publication of the last American Heart Association scientific statement on air pollution and cardiovascular disease in 2010, unequivocal evidence of the causal role of fine particulate matter air pollution (PM2.5, or particulate matter ≤2.5 μm in diameter) in cardiovascular disease has emerged. There is a compelling case to provide the public with practical personalized approaches to reduce the health effects of PM2.5. Such interventions would be applicable not only to individuals in heavily polluted countries, high-risk or susceptible individuals living in cleaner environments, and microenvironments with higher pollution exposures, but also to those traveling to locations with high levels of PM2.5. The overarching motivation for this document is to summarize the current evidence supporting personal-level strategies to prevent the adverse cardiovascular effects of PM2.5, guide the use of the most proven/viable approaches, obviate the use of ineffective measures, and avoid unwarranted interventions. The significance of this statement relates not only to the global importance of PM2.5, but also to its focus on the most tested interventions and viable approaches directed at particulate matter air pollution. The writing group sought to provide expert consensus opinions on personal-level measures recognizing the current uncertainty and limited evidence base for many interventions. In doing so, the writing group acknowledges that its intent is to assist other agencies charged with protecting public health, without minimizing the personal choice considerations of an individual who may decide to use these interventions in the face of ongoing air pollution exposure.

Individual- and Household-Level Interventions to Reduce Air Pollution Exposures and Health Risks: a Review of the Recent Literature

PURPOSE OF REVIEW

We reviewed recent peer-reviewed literature on three categories of individual- and household-level interventions against air pollution: air purifiers, facemasks, and behavior change.

RECENT FINDINGS

High-efficiency particulate air/arresting (HEPA) filter air purifier use over days to weeks can substantially reduce fine particulate matter (PM2.5) concentrations indoors and improve subclinical cardiopulmonary health. Modeling studies suggest that the population-level benefits of HEPA filter air purification would often exceed costs. Well-fitting N95 and equivalent respirators can reduce PM2.5 exposure, with several randomized crossover studies also reporting improvements in subclinical cardiovascular health. The health benefits of other types of face coverings have not been tested and their effectiveness in reducing exposure is highly variable, depends largely on fit, and is unrelated to cost. Behavior modifications may reduce exposure, but there has been little research on health impacts. There is now substantial evidence that HEPA filter air purifiers reduce indoor PM2.5 concentrations and improve subclinical health indicators. As a result, their use is being recommended by a growing number of government and public health organizations. Several studies have also reported subclinical cardiovascular health benefits from well-fitting respirators, while evidence of health benefits from other types of facemasks and behavior changes remains very limited. In situations when emissions cannot be controlled at the source, such as during forest fires, individual- or household-level interventions may be the primary option. In most cases, however, such interventions should be supplemental to emission reduction efforts that benefit entire communities.

In-vehicle carbon dioxide and adverse effects: An air filtration-based intervention study

Drowsiness is considered a potential risk for traffic accidents. Exposure to high carbon dioxide (CO₂) levels in vehicles may result in unpleasant feeling, fatigue, drowsiness or lethargy among drivers and passengers. However, little is known about whether reducing CO₂ levels in vehicles by air filtration can relieve adverse effects among human subjects during driving. We recruited a panel of 84 healthy participants to drive a vehicle equipped with a CO₂ filtration system for 1 h on a coastal road in a Northern Taiwan rural area. The operation modes of the CO₂ filtration system, including fresh air from open windows without a CO₂ filtration system (Control-mode), fresh air from an air conditioning (AC) system with closed windows and a false CO₂ filtration system in operation (Off-mode) or a true CO₂ filtration system in operation (On-mode), were examined. The repeated measurements of heart rate (HR), blood pressure (BP), CO₂, total volatile organic compounds (TVOCs), particulate matter ≤2.5 μm in aerodynamic diameter (PM_2.5) and a simple question about drowsiness were obtained for each participant in three different modes. We found that decreased HR, systolic BP (SBP) and diastolic BP (DBP) and increased drowsiness were associated with increased levels of in-vehicle CO₂. The effects of in-vehicle CO₂ on adverse effects were highest in the Off-mode during driving. In the On-mode, the participants showed slight decreases in HR, SBP and DBP and slight increases in drowsiness. We concluded that the utilization of a CO₂ filtration system can reduce in-vehicle CO₂ levels and modify the effect of in-vehicle CO₂ on HR, BP and drowsiness among human subjects during driving.

A Clean Air Plan for Sydney: An Overview of the Special Issue on Air Quality in New South Wales

This paper presents a summary of the key findings of the special issue of Atmosphere on Air Quality in New South Wales and discusses the implications of the work for policy makers and individuals. This special edition presents new air quality research in Australia undertaken by (or in association with) the Clean Air and Urban Landscapes hub, which is funded by the National Environmental Science Program on behalf of the Australian Government’s Department of the Environment and Energy. Air pollution in Australian cities is generally low, with typical concentrations of key pollutants at much lower levels than experienced in comparable cities in many other parts of the world. Australian cities do experience occasional exceedances in ozone and PM2.5 (above air pollution guidelines), as well as extreme pollution events, often as a result of bushfires, dust storms, or heatwaves. Even in the absence of extreme events, natural emissions play a significant role in influencing the Australian urban environment, due to the remoteness from large regional anthropogenic emission sources. By studying air quality in Australia, we can gain a greater understanding of the underlying atmospheric chemistry and health risks in less polluted atmospheric environments, and the health benefits of continued reduction in air pollution. These conditions may be representative of future air quality scenarios for parts of the Northern Hemisphere, as legislation and cleaner technologies reduce anthropogenic air pollution in European, American, and Asian cities. However, in many instances, current legislation regarding emissions in Australia is significantly more lax than in other developed countries, making Australia vulnerable to worsening air pollution in association with future population growth. The need to avoid complacency is highlighted by recent epidemiological research, reporting associations between air pollution and adverse health outcomes even at air pollutant concentrations that are lower than Australia’s national air quality standards. Improving air quality is expected to improve health outcomes at any pollution level, with specific benefits projected for reductions in long-term exposure to average PM2.5 concentrations.

Indoor Air Pollution in Cars: An Update on Novel Insights

From a global viewpoint, a lot of time is spent within the indoor air compartment of vehicles. A German study on mobility has revealed that, on average, people spend 45 minutes per day inside vehicles. In recent years the number of cars has increased to around 43 million vehicles in private households. This means that more than one car can be used in every household. The ratio has been growing, especially in eastern Germany and rural areas. "Overall and especially outside the cities, the car remains by far number one mode of transport, especially in terms of mileage". Therefore, numerous international studies have addressed different aspects of indoor air hygiene, in the past years. In this paper, meaningful original studies on car indoor air pollution, related to VOCs, COx, PMs, microbials, BFRs, OPFRs, cigarettes, electronic smoking devices, high molecular weight plasticizer, and NOx are summarized in the form of a review. This present review aimed to summarize recently published studies in this important field of environmental medicine and points to the need for further studies with special recommendations for optimizing the interior air hygiene.

Cardiovascular benefits of short-term indoor air filtration intervention in elderly living in Beijing: An extended analysis of BIAPSY study

BACKGROUND

Adverse cardiovascular effects associated with air pollution exposure have been widely demonstrated. However, inconsistent cardiovascular responses were observed from reducing indoor air pollution exposure. We aimed to assess whether short-term air filtration intervention could benefit cardiovascular health in elderly living in high pollution area.

METHODS

A randomized crossover intervention study of short-term indoor air filtration intervention on cardiovascular health was conducted among 35 non-smoking elderly participants living in Beijing in the winter of 2013, as part of Beijing Indoor Air Purifier StudY (BIAPSY). Portable air filtration units were randomly allocated to active filtration for 2 weeks and sham filtration for 2 weeks in the households. Twelve-hour daytime ambulatory heart rate variability (HRV) and blood pressure (ABP) were measured during active and sham filtration. Concurrently, real-time indoor and outdoor particulate matter with diameter less than 2.5 µm (PM_2.5) and indoor black carbon (BC) concentrations were measured. We applied generalized additive mixed models to evaluate the associations of 1- to 10-h moving average (MA) exposures of indoor PM_2.5 and BC with HRV and ABP indices, and to explore whether these associations could be modified by air filtration.

RESULTS

We observed decreases of 34.8% in indoor PM_2.5 and 35.3% in indoor BC concentrations during active filtration. Indoor PM_2.5 and BC exposures were significantly associated with reduced HRV and increased ABP indices, and greater changes were observed during sham filtration. In specific, each 10 μg/m³ increase in indoor PM_2.5 at MA8-h was associated with a significant reduction of 1.34% (95% CI: -2.42, -0.26) in SDNN during sham filtration, compared with a non-significant reduction of 0.81% (95% CI: -6.00, 4.68) during active filtration (P_inter< 0.001). Each 1 μg/m³ increase in indoor BC at MA8-h was associated with a significant increase of 2.41% (95% CI: 0.38, 4.47) in SBP during sham filtration, compared with a non-significant increase of -1.09% (95% CI: -4.06, 1.96) during active filtration (P_inter = 0.135). Nonlinear inverse exposure-response relationships of indoor air pollution exposures with predicted HRV and ABP indices also confirmed some cardiovascular benefits of short-term air filtration intervention.

CONCLUSIONS

Our results suggested that short-term indoor air filtration intervention can be of some cardiovascular benefits in elderly living with high pollution episodes.

Indoor PM2.5 exposure affects skin aging manifestation in a Chinese population

Traffic-related air pollution is known to be associated with skin aging manifestations. We previously found that the use of fossil fuels was associated with skin aging, but no direct link between indoor air pollutants and skin aging manifestations has ever been shown. Here we directly measured the indoor PM_2.5 exposure in 30 households in Taizhou, China. Based on the directly measured PM_2.5 exposure and questionnaire data of indoor pollution sources, we built a regression model to predict the PM_2.5 exposure in larger datasets including an initial examination group (N = 874) and a second examination group (N = 1003). We then estimated the association between the PM_2.5 exposure and skin aging manifestations by linear regression. In the initial examination group, we showed that the indoor PM_2.5 exposure levels were positively associated with skin aging manifestation, including score of pigment spots on forehead (12.5% more spots per increase of IQR, P-value 0.0371), and wrinkle on upper lip (7.7% more wrinkle on upper lip per increase of IQR, P-value 0.0218). The results were replicated in the second examination group as well as in the pooled dataset. Our study provided evidence that the indoor PM_2.5 exposure is associated with skin aging manifestation in a Chinese population.

Understanding Air Pollution and Cardiovascular Diseases: Is It Preventable?

Fine particulate matter (<2.5 µm, PM_2.5) air pollution is a leading risk factor for morbidity and mortality worldwide. The largest portion of adverse health effects is from cardiovascular diseases. In North America, PM_2.5 concentrations have shown a steady decline over the past several decades; however, the opposite trend has occurred throughout much of the developing world whereby daily concentrations commonly reach extraordinarily high levels. While air quality regulations can reduce air pollution at a societal level, what individuals can do to reduce their personal exposures remains an active field of investigation. Here, we review the emerging evidence that several interventions (e.g., air filters) and/or behavioral changes can lower PM pollution exposure and as such, may be capable of mitigating the ensuing adverse cardiovascular health consequences. Air pollution remains a worldwide epidemic and a multi-tiered prevention strategy is required in order to optimally protect global public health.

What can individuals do to reduce personal health risks from air pollution?

In many areas of the world, concentrations of ambient air pollutants exceed levels associated with increased risk of acute and chronic health problems. While effective policies to reduce emissions at their sources are clearly preferable, some evidence supports the effectiveness of individual actions to reduce exposure and health risks. Personal exposure to ambient air pollution can be reduced on high air pollution days by staying indoors, reducing outdoor air infiltration to indoors, cleaning indoor air with air filters, and limiting physical exertion, especially outdoors and near air pollution sources. Limited evidence suggests that the use of respirators may be effective in some circumstances. Awareness of air pollution levels is facilitated by a growing number of public air quality alert systems. Avoiding exposure to air pollutants is especially important for susceptible individuals with chronic cardiovascular or pulmonary disease, children, and the elderly. Research on mechanisms underlying the adverse health effects of air pollution have suggested potential pharmaceutical or chemopreventive interventions, such as antioxidant or antithrombotic agents, but in the absence of data on health outcomes, no sound recommendations can be made for primary prevention. Health care providers and their patients should carefully consider individual circumstances related to outdoor and indoor air pollutant exposure levels and susceptibility to those air pollutants when deciding on a course of action to reduce personal exposure and health risks from ambient air pollutants. Careful consideration is especially warranted when interventions may have unintended negative consequences, such as when efforts to avoid exposure to air pollutants lead to reduced physical activity or when there is evidence that dietary supplements, such as antioxidants, have potential adverse health effects. These potential complications of partially effective personal interventions to reduce exposure or risk highlight the primary importance of reducing emissions of air pollutants at their sources.

Exposure to traffic-related air pollution during physical activity and acute changes in blood pressure, autonomic and micro-vascular function in women: a cross-over study

Background

Traffic-related air pollution may contribute to cardiovascular morbidity. In urban areas, exposures during physical activity are of interest owing to increased breathing rates and close proximity to vehicle emissions.

Methods

We conducted a cross-over study among 53 healthy non-smoking women in Montreal, Canada during the summer of 2013. Women were exposed to traffic pollutants for 2-hours on three separate occasions during cycling on high and low-traffic routes as well as indoors. Personal air pollution exposures (PM_2.5, ultrafine particles (UFP), black carbon, NO₂, and O₃) were evaluated along each route and linear mixed-effects models with random subject intercepts were used to estimate the impact of air pollutants on acute changes in blood pressure, heart rate variability, and micro-vascular function in the hours immediately following exposure. Single and multi-pollutant models were examined and potential effect modification by mean regional air pollution concentrations (PM_2.5, NO₂, and O₃) was explored for the 24-hour and 5-day periods preceding exposure.

Results

In total, 143 exposure routes were completed. Each interquartile increase (10,850/cm³) in UFP exposure was associated with a 4.91% (95% CI: -9.31, -0.512) decrease in reactive hyperemia index (a measure of micro-vascular function) and each 24 ppb increase in O₃ exposure corresponded to a 2.49% (95% CI: 0.141, 4.84) increase in systolic blood pressure and a 3.26% (95% CI: 0.0117, 6.51) increase in diastolic blood pressure 3-hours after exposure. Personal exposure to PM_2.5 was associated with decreases in HRV measures reflecting parasympathetic modulation of the heart and regional PM_2.5 concentrations modified these relationships (p < 0.05). In particular, stronger inverse associations were observed when regional PM_2.5 was higher on the days prior to the study period. Regional PM_2.5 also modified the impact of personal O₃ on the standard deviation of normal to normal intervals (SDNN) (p < 0.05): a significant inverse relationship was observed when regional PM_2.5 was low prior to study periods and a significant positive relationship was observed when regional PM_2.5 was high.

Conclusion

Exposure to traffic pollution may contribute to acute changes in blood pressure, autonomic and micro-vascular function in women. Regional air pollution concentrations may modify the impact of these exposures on autonomic function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-014-0070-4) contains supplementary material, which is available to authorized users.