Lack of effect of nitrogen dioxide exposure on heart rate variability in patients with stable coronary heart disease and impaired left ventricular systolic function

Objectives Epidemiological studies of air pollution on cardiovascular health show associations of cardiac mortality and admissions with exposure to nitrogen dioxide (NO₂) at low concentrations. These associations could be causal or NO₂ could be acting as a surrogate measure for another air pollutant, most likely ultrafine particles. No studies of cardiac susceptibility to acute exposure to NO₂ have been undertaken.

Methods Randomised controlled exposures to NO₂ (400 ppb for 1 h) and air in subjects with coronary heart disease and impaired left ventricular systolic function not taking β adrenoceptor blocking drugs.

Results There were no significant changes in heart rate, blood pressure, leucocyte coping capacity or any heart rate variability measure following NO₂ exposure compared with air.

Conclusion These findings suggest that NO₂ does not affect heart rate variability at these concentrations (which are high for urban background levels) and in the absence of other pollutants. While a synergistic effect has not been ruled out, these data lend support to the idea that the epidemiological data associating cardiac outcomes with NO₂ are more likely due to an associated pollutant rather than NO₂ itself.