Transient but not sustained blood pressure increments by occupational noise. An ambulatory blood pressure measurement study

Objective Studies on the effects of chronic exposure to industrial noise on clinic blood pressure (BP) at rest have yielded inconsistent results. The aim of this study was to evaluate the effect of occupational noise exposure on ambulatory blood pressure (ABP) in normotensive subjects. Methods We studied 476 normotensive workers, aged 20-50 years (systolic blood pressure (SBP) <140, diastolic blood pressure (DBP) <90), at a metallurgical factory; 238 were exposed to high levels of noise (> 85 dB), while 238 were not exposed (<80 dB). Clinical evaluation included measurements of casual BP (by standard mercury sphygmomanometer, Korotkoff sound phase I and V) and heart rate (HR) (by pulse palpation), body height and weight. All subjects underwent a 24 h non-invasive ABP monitoring (by SpaceLabs 90207 recorder; SpaceLabs, Redmond, Washington, USA) twice within 14 days: one during a normal working day and one during a non-working day. Measurements were performed every 15 min. Computed analysis of individual recordings provided average SBP, DBP and HR values for 24 h, daytime working hours (0800-1700 h), daytime non-working hours (1700-2300 h) and night-time (2300-0800 h). Results No significant difference in clinic SBP, DBP and HR was observed between exposed and non-exposed subjects. Results obtained by ABP monitoring showed in the exposed workers: (a) a higher SBP (by a mean of 6 mmHg, P <0.0001 versus controls) and DBP (by a mean of 3 mmHg, P <0.0001) during the time of exposure and the following 2 or 3 h, whereas no difference between the two groups was found during the non-working day; (b) an increase in HR, which was present not only during the time of exposure to noise (+3.7 beats-per-minute (bpm), P <0.0001 versus controls), but also during the non-working hours (+2.8 bpm, P <0.001) and during the day-time hours of the non-working day (+2.8 bpm, P <0.003); (c) a significant increase in BP variability throughout the working day. Conclusions These findings suggest that in normotensive subjects below the age of 50 years, chronic exposure to occupational noise is associated with a transient increase in BP, which is not reflected in a sustained BP elevation. The possible role of repeated BP and HR fluctuations due to frequent and prolonged exposure to noise in accounting for the higher prevalence of hypertension reported in noise-exposed workers above age 50 years, requires longitudinal studies to be clarified.