A team from Rice University and the Houston Fire Department EMS has found a direct correlation between out-of-hospital cardiac arrests (OHCA) and levels of air pollution and ozone. The research, based on a massive data set unique to Houston, was published this month in the American Heart Association journal Circulation.
Given that the American Lung Association has ranked Houston eighth in the United States for high-ozone days, Rice statisticians Katherine Ensor and Loren Raun, and David Persse, Houston Fire Department EMS physician director, set out to see if there is a link between ambient ozone levels and cardiac arrest. Ensor is a professor and chair of Rice’s Department of Statistics, and Raun is a research professor in Rice’s Department of Statistics.
The authors analyzed eight years’ worth of data drawn from Houston’s extensive network of air-quality monitors and more than 11,000 concurrent OHCA logged by Houston Emergency Medical Services (EMS). They found a positive correlation between OHCAs and exposure to both fine particulate matter (airborne particles smaller than 2.5 micrograms) and ozone.
The researchers found that a daily average increase in particulate matter of 6 micrograms per day over two days raised the risk of OHCA by 4.6%, with particular impact on those with pre-existing (and not necessarily cardiac-related) health conditions. Increases in ozone level were similar, but on a shorter timescale: Each increase of 20 parts per billion over one to three hours also increased OHCA risk, with a peak of 4.4%. Peak-time risks from both pollutants rose as high as 4.6%. Relative risks were higher for men, African-Americans and people over 65.
For the study, OHCA events were defined as cases where EMS personnel performed chest compressions. The patients died in more than 90% of the cases, which occurred more during the hot summer months (55% of total cases).
The researchers also looked at the effects of nitrogen dioxide, sulfur dioxide and carbon monoxide levels, none of which were found to impact the occurrence of OHCA.
The work is expected to help Houston EMS fine-tune its deployment of personnel and equipment and provide early warnings to health officials and the public when weather and/or incidents warrant an alert for high ozone levels in specific areas, Ensor said.
Katherine B. Ensor; Loren H. Raun; David Persse (2013) A Case-Crossover Analysis of Out-of-Hospital Cardiac Arrest and Air Pollution. Circulation. doi: 10.1161/CIRCULATIONAHA.113.000027