Given that the American Lung Association has ranked Houston eighth in the United States for high-ozone days, statisticians Katherine Ensor and Loren Raunthe set out to see if there is a link between ambient ozone levels and cardiac arrest.
For the new study, the authors analyzed eight years’ worth of data drawn from Houston’s extensive network of air-quality monitors and more than 11,000 concurrent out-of-hospital cardiac arrests (OHCA) logged by Houston Emergency Medical Services (EMS).
They found a positive correlation between cardiac arrests 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 percent, 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 percent. Peak-time risks from both pollutants rose as high as 4.6 percent. 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. Ensor and Raun noted the patients died in more than 90 percent of the cases, which occurred more during the hot summer months (55 percent 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.
Co-author David Persse, Houston Fire Department EMS physician director and a public-health authority for the city, said it’s long been thought by EMS workers that certain types of air pollution, including ozone, have significant negative effects on cardiac and respiratory health. “But this mathematically and scientifically validates what we know,” he said.
Houston is already acting upon the results.
“The city has targeted educational resources to at-risk communities, where they’re now doing intensive bystander CPR training,” Raun said. Early intervention is seen as critical, as the chance of survival for a person suffering cardiac arrest drops 10 percent for every minute he or she is left unattended. She said statistics show one life is saved for every 26 to 36 people who receive cardiopulmonary resuscitation from a bystander.
Houston’s effort is part of a range of interventions to mitigate the consequences of poor air quality days, though none are substitutes for the primary strategy of improving air quality, according to the city’s Health and Human Services Department.
