title: Association between Diurnal Variation of Ozone Concentration and Stroke Occurrence: 24-Hour Time Series Study.
abstract: OBJECTIVE
  Increasing ozone concentrations have been known to damage human health and ecosystems. Although ozone tends to display diurnal variation, most studies have reported only on the association between daily ozone concentrations and ischemic stroke occurrence on the same day, or with a 1-day lag. We investigated the effect of the diurnal variation of ozone on ischemic stroke occurrence during the same day.
  
  
  METHODS
  We included a consecutive series of 1,734 patients from January 1, 2008, to December 31, 2014, at a single tertiary hospital in Seoul, South Korea. We evaluated differences between temperature and pollutants at the time of stroke onset for each time interval and averaged those parameters across the 7-year study period.
  
  
  RESULTS
  During the interval from 13:00 to 16:59, we found a positive association between ischemic stroke occurrence and ozone concentration relative to other time periods. Upper median ozone levels from 13:00 to 16:59 were positively correlated with ischemic stroke (odds ratio, 1.550; 95% confidence intervals, 1.220 to 1.970; P = <0.001) when compared with lower median levels.
  
  
  CONCLUSIONS
  The results show diurnal patterns of ischemic stroke occurrence based on upper and lower median ozone levels for a 24-hour period, which extends understanding of the association between stroke occurrence and environmental influences.
authors.affiliation: Department of Neurosurgery, Hanyang University Guri Hospital, 153 Gyeongchun-ro, Guri 471-701, Gyonggi-do, Korea.
authors.forename: Myung-Hoon
authors.initials: MH
authors.lastname: Han
authors.affiliation: Department of Neurosurgery, Hanyang University Medical Center, 222-1, Wangsimni-ro, Seongdong-gu, Seoul, Korea.
authors.forename: Hyeong-Joong
authors.initials: HJ
authors.lastname: Yi
authors.affiliation: Department of Neurology, Hanyang University Medical Center, 222-1, Wangsimni-ro, Seongdong-gu, Seoul, Korea.
authors.forename: Young-Seo
authors.initials: YS
authors.lastname: Kim
authors.affiliation: Department of Neurosurgery, Hanyang University Medical Center, 222-1, Wangsimni-ro, Seongdong-gu, Seoul, Korea.
authors.forename: Yong
authors.initials: Y
authors.lastname: Ko
authors.affiliation: Department of Neurosurgery, Hanyang University Medical Center, 222-1, Wangsimni-ro, Seongdong-gu, Seoul, Korea.
authors.forename: Young-Soo
authors.initials: YS
authors.lastname: Kim
mesh_terms: D000368:Aged; D000393:Air Pollutants / Q000032:analysis; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D007511:Ischemia / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009585:Nitrogen Dioxide / Q000032:analysis; D016017:Odds Ratio; D010126:Ozone / Q000032:analysis*; D056910:Republic of Korea; D012189:Retrospective Studies; D020521:Stroke / Q000175:diagnosis* / Q000453:epidemiology* / Q000473:pathology; D013696:Temperature
chemical_list: D000393:Air Pollutants; D010126:Ozone; D009585:Nitrogen Dioxide