Ambient carbon monoxide may influence heart rate variability in subjects with coronary artery disease.

Days of high ambient carbon dioxide (CO) have been associated with increased hospital admissions for cardiac disease. This study was conducted to determine if daily concentrations of CO and fine particulates (PM2.5) are associated with daily changes in heart rate variability.Each of 36 adults with coronary artery disease had personal exposure to PM2.5 and CO measured along with heart rate variability for one 24-hour period each week for up to 10 weeks.Among those not taking beta-receptor blockers, there was a positive association between the standard deviation of the R-to-R intervals and CO (P = 0.02). No effect was found for PM2.5.Urban exposure to CO may exert a biologic effect on the heart, which may be modified by medications.