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Introduction
Air pollution is a well-established risk factor for adverse respiratory outcomes, including chronic lung diseases (Andersen et al. 2011; Karakatsani et al. 2003; Lindgren et al. 2009; Schikowski et al. 2005; Sunyer 2001), hospitalizations (Chen et al. 2005) and death (Dockery et al. 1993; Pope et al. 2002). Most recently, it has been estimated that for 2013 worldwide ambient particulate matter (PM) pollution accounts for nearly 170,000 deaths and nearly 4 million disability-adjusted life years (DALYs) due to chronic respiratory disease (Forouzanfar et al. 2015; IHME 2016).
A common sequela of chronic lung disease is the development of pulmonary hypertension and impairments to the heart, including right ventricular (RV) dysfunction (Freixa et al. 2013). The right ventricle pumps blood through the lungs to allow for its oxygenation. Then the oxygen-rich blood flows to the left ventricle for subsequent distribution to all tissues of the human body. Changes in RV structure and function can therefore result in many similar clinical sequelae of left ventricular (LV) changes, including dyspnea, exercise intolerance, lower-extremity edema, and (at advanced stages) severe heart failure (Voelkel et al. 2006). Although the left ventricle is vulnerable to increased pressures during ejection due to systemic hypertension or valvular disease, reduced blood supply, and hypoxia, the right ventricle may be similarly affected by changes in lung function [e.g., chronic obstructive pulmonary disorder (COPD)], LV function, and hypoxia (e.g., sleep disordered breathing). The RV has been thought to respond to this increased load through structural changes such as hypertrophy (i.e., thickening of the ventricle leading to increased mass), chamber dilation leading to greater end-diastolic volume, and lowered pumping efficiency (i.e., reduced ejection fraction) (Polak et al. 1983; Shah et al. 1986). Although these three manifestations of RV dysfunction are most likely in severe stages of lung disease, the right ventricle can also be affected early in lung disease (Hilde et al. 2013). RV dysfunction has public health importance because it has been linked to poor outcomes among persons with and without preexisting disease, such as COPD and cardiovascular disease (Burgess et al. 2002; France et al. 1988; Kawut et al. 2012).
Long-term exposures to air pollution are believed to affect the same biological mechanisms that lead to COPD and cardiovascular disease. There is evidence that...