Cardiovascular risk factors (e.g CCSVI symptoms) and atmospheric pressure.
Interesting paper - 'Periods of low atmospheric pressure are associated with high abdominal aortic aneurysm rupture rates in Northern Ireland.'
D. W. Harkin, M. O'Donnell, J. Butler, P. H. Blair, J. M. Hood, and A. A. B. Barros D'Sa Ulster Med J. 2005 September; 74(2): 113–121 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2475387/