Daily noise duration influences cardiovascular responses

In this study, third in a series on non-auditory health effects of noise, we provide data on the previously developed proposition that exposure to intense noise is linked with altered blood pressure regulation through the establishment of a long-term dose----response relationship between the two variables. We also sought to determine the effect of interposed rest sessions on the course of heart rate (HR) and blood pressure (BP) during 97 days of exposure to tape-recorded industrial noise. The stimulus, delivered to 2 female adult macaque monkeys (M. fascicularis) fitted with indwelling cannulas, consisted of pile-driver impacts and other construction noises presented either in 4-hr (Leq24 = 86.6 db) or 8-hr (Leq24 = 89.6 db) daily sessions. When compared to their pre-exposure responses, mean arterial pressure (MAP) for the Ss rose 8.2% during 4-hr and 16.5% during 8-hr exposure sessions, i.e., close to a doubling effect for a doubling of total energy. When compared with control monkeys (N:10) used in earlier studies, however, MAP rose in the present Ss only 44% for the same doubling of energy. In general, HR and BP displayed quite different tendencies during the per-exposure rest sessions and the post-exposure period: HR tended to return to baseline levels upon noise termination whereas MAP, once elevated, tended to remain significantly elevated. Applicability of the "law" of Initial Values was demonstrated for noise-induced BP increases, in the sense that the percentage of change in BP produced by 8-hr exposure sessions in the 2 present Ss was 16.5%, or somewhat less than that previously observed in exposed monkeys with lower baseline levels (i.e., 30.5%), even though absolute levels of per-exposure MAP were similar (i.e., 99 vs 100 mmHg) for the two sets of exposed monkeys.