Multivariate analysis of meteorological factors and evaluation of circadian rhythm: their relation to the occurrence of acute myocardial infarction]

We statistically analysed the occurrence of acute myocardial infarction (AMI) in relation to meteorology and circadian rhythm. The study subjects included 581 patients with AMI in Asahikawa observed for the last 10 years, and 177 in Yamagata observed for the past three years. Monthly fluctuations of AMI occurrence were not statistically significant. The expected frequency of AMI estimated by grading meteorological factors every 5 degrees C from maximum to minimum temperatures did not correlate with the real frequency. A relatively cold period was defined as a term during which mean atmospheric temperature was below 0 degrees C in Asahikawa and below 3 degrees C in Yamagata Canonical discriminatory analyses were made of 10 meterological factors between days with and without AMI occurrences during a 10-year term in Asahikawa; and between days with and without outdoor occurrences. To compare regional difference, the same analysis was performed during a three-year cold period in Yamagata. Correlations among the three analyses were negligible (0.03%, 1.53% and 0.97%, respectively); thus, the days on which AMI occurred could not be identified with the 10 meteorological factors. Circadian rhythm of two cycles/day was recognized concerning the time of occurrence by power spectral analysis in 562 patients in Asahikawa, in whom the time of onset of AMI was recorded. It was concluded that there are no external meteorological risk factors for the occurrence of AMI. However, the intrinsic biological rhythm supposedly participates in triggering the occurrence of AMI as an intrinsic transient risk factor.