Cardiac reactivity to traffic noise during sleep in man

Abstract A relation between stimulus characteristics of traffic noise and cardiac response mechanisms during sleep was studied in 12 subjects, living along a highway with a high traffic density. Two experimental conditions were created inside the bedroom with (1) a normal sound level and (2) a reduced sound level. The indoor sound levels were reduced by means of acoustical double glazing of the windows facing the motorway with high traffic density. Ten nights were recorded per subject in each condition. Evoked Cardiac Responses (ECR) were observed due to peaks in the indoor recorded sound level signal in both conditions. The lowering of the sound level by sound insulation did not reduce the magnitude or the absolute level of the cardiac responses to the peaks in the traffic noise. This may be related to the fact that the sound insulation decreased the mean sound level, but not the number of sound peaks, thus indicating that the double glazing sound insulation was not optimal. Cardiac acceleration due to traffic noise stimuli did not decrease with time over the ten nights with high sound level. A relation was found between the magnitude of the ECR and the slope and the duration of the peaks in the sound level signal of the traffic noise as recorded in the bedroom. Our results provide evidence that “cardiac arousal” in response to traffic noise persists even during sleep. The cardiac reactivity was sensitive to changes in stimulus characteristics. Thus traffic noise can disturb sleep even without waking the subjects.