Myocardial infarction and cardiac regulation in relation to vibration exposure

Sammanfattning: The purpose of this thesis was to assess the possible risk of myocardial infarction in work entailing exposure to vibration, and to study whether there is any relation between short-term exposure to vibration and cardiac regulation.Epidemiological methods were applied to investigate a possible association between occupational exposure to vibration and myocardial infarction. Two study populations were used; one case-control study (n=475) and one cohort of iron-ore miners in Kiruna and Malmberget, Sweden (n=13621). In the former, the cases were first-time myocardial infarction patients and the controls were selected to match for sex, age and hospital catchment area. Job-exposure matrixes for vibration were established for both the case-control study and the cohort study.In order to study acute effects on cardiac regulation, an experimental study was conducted on healthy subjects (n=20) who were exposed to hand-arm vibration exclusively and in combination with exposure to noise. The effect on the autonomic balance was measured by heart rate-variability.In the case-control study, an increased risk of contracting myocardial infarction was found among occupations entailing vibration exposure. The results from the cohort show an increased risk of myocardial infarction mortality compared to a reference population. The increment was higher for those younger than 60 years. Relative risks for myocardial infarction mortality increased with increasing exposure to vibration in the group at working-age and the increased risk remained after adjusting for exposure to dust. In the experimental study, exposure to hand-arm vibration was found to acutely affect the autonomic nervous system as the total heart-rate variability decreased during exposure to hand-arm vibration.To conclude: work entailing exposure to vibration is a risk factor for myocardial infarction, increased myocardial infarction mortality attributed to exposure to vibration seems to be mainly observed at working-age, and exposure to hand-arm vibration acutely decreases heart-rate variability and thus affects heart-rate regulation.