Ozone Pollution Levels Linked To Cardiac Arrest

Rice University researchers in Houston, Texas have uncovered a correlation between cardiac arrest and ozone pollution.

Ozone is found naturally in small concentrations in the stratosphere, a layer of Earth’s upper atmosphere. Stratospheric ozone is referred to as “good” ozone because it protects the Earth’s surface from dangerous ultraviolet light.

Ozone can also be found in the troposphere, the lowest layer of the atmosphere. Tropospheric ozone is man-made, a result of air pollution, and is termed “bad” ozone or smog. This ozone is composed of automobile exhaust, industrial emissions, nitrogen oxide gases, and volatile organic compounds, all by-products of burning gasoline and coal.

The nitrogen oxide gases and volatile compounds combine chemically with oxygen to form ozone during warm, sunny conditions.

High levels of ozone are usually formed in the heat of the afternoon and dissipate during the cooler evening temperatures.

Cardiac arrest is the cessation of normal blood circulation due to the heart failing to contract effectively. Cardiac arrest and heart attacks differ in how the blood flow to the heart muscle is impaired. Cardiac arrest is caused when the heart’s electrical system malfunctions, causing a dysrhythmia.

Arrested blood circulation prevents delivery of oxygen to the rest of the body. Lack of oxygen to the brain causes loss of consciousness. If left untreated for more than a few minutes, cardiac arrest can result in a neurological impairment and death. Survival and brain health requires immediate medical attention.

According to the American Heart Association, nearly 360,000 cardiac arrests are addressed by emergency medical services annually in the United States.

The Houston-based research, published in the American Heart Association journal Circulation, cited the potential need to increase CPR training in at-risk communities.

The treatment for cardiac arrest is cardiopulmonary resuscitation (CPR) to reestablish circulatory support, followed by defibrillation if available. Defibrillation is a common treatment for life-threatening cardiac dysrhythmias and consists of delivering a therapeutic dose of electrical energy to the heart. This is achieved with a device called a defibrillator. The shock depolarizes a critical mass of the heart muscle, terminating the dysrhythmia, and allowing the normal rhythm to return.

The American Lung Association ranks Houston eighth in the United States for high-ozone days; therefore, the Rice researchers set out to see if there was a link between their frequently high ambient ozone levels and cardiac arrest.

Statisticians involved in the Rice University research, Katherine Ensor and Loren Raun, revealed their findings at the American Association for the Advancement of Science (AAAS) conference in Boston, Massachusetts.

Eight years’ worth of data was analyzed, drawn from both the Houston’s network of air-quality monitors and more than 11,600 cardiac arrests (OHCA) logged by Houston Emergency Medical Services (EMS) from 2004 to 2011. Only OHCA events requiring chest compressions were used in the study.

Patients died in more than 90 percent of the cases reviewed. These deaths occurred more during the hot summer months, making up 55 percent of total cases.

Each year, an average of 1,400 people in Houston have a cardiac arrest outside the hospital, and about 1,260 deaths occur. If the research findings are valid, they suggest that about 45 of these deaths are related to increases in ozone levels

Researchers found a relationship between logged OHCAs and exposure to both fine particulate matter (airborne particles smaller than 2.5 micrograms) and ozone. The risk of cardiac arrest increased by 4.6 percent with an emergent density of particulate matter of 6 mcg, especially in individuals with pre-existing health conditions.

When examining the increases of ozone effects, a similar trend was found. OHCA risk peaked at 4.4 percent with each increase of 20 parts-per billion (ppb) of ozone over one to three hours, especially for men, African-Americans, and people over 65.

[Image via Wikicommons]