Int. J. Environ. Res. Public Health 2010, 7 Abbreviations SBP = systolic blood pressure DBP = diastolic blood pressure mm HG = millimeters of mercury dB(A) = sound pressure using decibel A filter 1. Introduction 3458 Many children throughout the world, but especially those in developing countries, are chronically exposed to high levels of community noise [1]. Chronic noise exposure among youth usually comes from transportation (i.e., road traffic, airplanes, trains), music, and other people [2]. Stress theory has been applied to help explain a variety of ill effects attributed to chronic noise exposure [1,3,4], including dysregulation of blood pressure [4-6]. In the present study, we examine how chronic noise exposure relates to children’s resting blood pressure and the regulation of blood pressure responses to acute stressors. To the extent that chronic noise exposure in children is associated with higher than average levels of blood pressure at rest and during stressors, it could be a risk factor for cardiovascular and coronary heart disease. For example, elevated resting and stress-reactive blood pressure in children has been positively correlated with elevated resting blood pressure in later years [7-9]. To the extent that chronic noise exposure has the opposite effect of diminishing children’s level of arousal in response to acute stressors, it could undermine adaptive behavioral coping responses and other biological processes relevant to health and disease processes [10]. There have been a number of studies on the link between chronic noise exposure and resting blood pressure in children (for reviews, see [1,2]). Some investigators have found higher resting diastolic blood pressure (DBP) and/or systolic blood pressure (SBP) among children exposed to high versus relatively low levels of chronic noise from automobile traffic, airplanes, or trains [3,4,11-14]. In contrast, other investigators have found gender-specific relations [15], nil relations [16], and negative relations between chronic noise exposure due to airplane or traffic noise and resting blood pressure in children [17]. Additional research will further advance our understanding of the parameters under which chronic noise may be a risk factor for elevated resting blood pressure in children. We know practically nothing about the relation between chronic noise exposure and blood pressure reactivity during acute stress exposures in children. A novel contribution of the present study is that it examines how chronic noise stress exposure in children relates to their blood pressure reactivity when they are exposed to a stressor that matches the one they are exposed to chronically (an acute noise stressor) versus one that is more novel (an acute mental arithmetic challenge). Prior research has shown that animals repeatedly exposed to a stressor will exhibit a diminished response (habituation) when they encounter a similar acute stressor and an exaggerated response (sensitization) when they encounter a novel acute stressor [18]. Whether humans exposed to chronic stressors develop this dual response pattern of habituation and sensitization in blood pressure responses to similar versus novel acute stressors, respectively, has yet to be established. Habituation to noise may be adaptive to the extent that it reduces levels of sustained arousal—and associated risks of such arousal—among individuals chronically noise exposed. However, a pattern of