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 blo od pressure (SBP)< 140, diastolic blood pressure (DBP) < 90), at a metallur gical factory; 238 were exposed to high levels of noise (> 85 dB), while 23 8 were not exposed (< 80 dB). Clinical evaluation included measurements of casual Up (by standard mercury sphygmomanometer, Korotkoff sound phase I an d V) and heart rate (HR) (by pulse palpation), body height and weight. All subjects underwent a 24 h noninvasive ABP monitoring (by SpaceLabs 90207 re corder; SpaceLabs, Redmond, Washington, USA) twice within 14 days: one duri ng a normal working day and one during a non-working day. Measurements were performed every 15 min. Computed analysis of individual recordings provide d average SEP, DBP and HR values for 24 h, daytime working hours (0800-1700 h), daytime nonworking hours (1700-2300 h) and night-time (2300-0800 h). Results No significant difference in clinic SEP, DBP and HR was observed be tween exposed and non-exposed subjects. Results obtained by ABP monitoring showed in the exposed workers: (a) a higher SEP (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 beat s-per-minute (bpm), P< 0.0001 versus controls), but also during the nonwork ing hours (+2.8 bpm, P < 0.001) and during the daytime hours of the non-wor king day (+2.8 bpm, P < 0.003); (c) a significant increase in BP variabilit y 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 elevat ion. The possible role of repeated BP and HR fluctuations due to frequent a nd prolonged exposure to noise in accounting for the higher prevalence of h ypertension reported in noise-exposed workers above age 50 years, requires longitudinal studies to be clarified.