University of Michigan scientists, headed up by Dr. Robert Brook, discovered that breathing in bad air can increase blood pressure and cause unhealthy changes in blood vessels. These changes can last hours or even days.
Participants in the study were exposed to the same amount of particulates and ozone that would be found near local highways in two cities, Ann Arbor, Michigan and Toronto, Canada. Compared to those who inhaled filtered air, breathers of polluted air showed higher blood-pressure readings shortly after exposure. In addition, their blood vessels were impaired as long as 24 hours later. This type of prolonged high blood pressure is a risk factor for both stroke and heart disease.
Although it was previously known that fine particles in the air were associated with higher rates of heart disease and stroke, it was not known how the damage was done or what components of pollution were the most damaging.
The study's findings, however, suggest that particulates are worse than ozone and that two processes are likely occurring as unhealthy air is inhaled: Firstly, the central nervous system experiences changes as particulate matter is breathed in, causing the body to switch to a fight-or-fight mode. This raises blood pressure and heart rate.
Secondly, even after the pollution is less concentrated and blood pressure returns to normal, the particles which can lodge deep within the lungs induce inflammation. This inflammation can stiffen blood vessels and lead to longer-term damage to the flexibility of the blood vessels. These weakened blood vessels also cause an increased risk of heart disease or stroke.
The good news is for most healthy urban residents, the blood pressure changes aren't dangerous. However, Brook points out, ‘It's plausible that if someone has underlying hypertension or coronary disease, then these changes in blood pressure and blood-vessel function might be exaggerated and might even trigger a heart attack. The levels at which we encounter these particles today is still dangerous to people who are unhealthy and at high risk.’
Still, the air in average North American cities contains about 14 micrograms of particles per cubic meter of air. This is much better than a decade ago because of clean-air laws. Levels deemed dangerous by the Environmental Protection Agency are between 151 and 200 micrograms. Cities like Los Angeles, Detroit, and Pittsburgh reach dangerous levels on many days.
Many people who live in polluted cities or who live near highways find relief from purifying the air in their homes with an air purifier. This is especially important for young children and individuals with respiratory problems like allergies and asthma.