As Minnesota school children, fairgoers and outdoor workers swelter in the heat, some medical researchers are trying to figure out ways to help more people survive heat waves, which can be deadly.
More than 700 people died in Chicago in 1995; a 2003 heat wave in France killed nearly 15,000. No one knows if Minnesota's current heat wave has killed anyone yet because the state doesn't require that data to be collected. But it's well known that heat-related hospitalizations rise during hot Minnesota summers. And elderly people account for most of those.
Dr. Michael Joyner, a Mayo Clinic physiologist and anesthesiologist who studies how people respond to heat by warming and cooling his subjects with a water-filled suit adapted from the U.S. space program, is trying to figure out if sensors in the body that drive breathing also detect temperature changes. And if so, he's trying to determine whether these sensors are faulty in people with heart failure, hypertension and diabetes - the three conditions that cause the most problems for people during periods of high heat.
"You could see how people might get into trouble -- they wouldn't sense that they were warm and some of the physiological adaptations to heating wouldn't occur and people wouldn't dissipate the heat, they'd store the heat," said Joyner. "Their core temperature would rise. And, if their core temperature rose enough, eventually they could get heat stroke."
Joyner's team is experimenting with certain medications to see if they can help some vulnerable people sense the heat better, or detect when their oxygen levels are low.
While researchers ponder these questions, public health experts are taking note of how weather changes could affect the health of Minnesotans in the future.
Overnight low temperatures in Minnesota have been rising faster than the maximum temperature, and that's a potential problem because heat-related conditions are cumulative, according to Katie Muehe of the Minnesota Climate and Health Program at the Minnesota Department of Health. In other words, the longer people experience high heat, the more likely they will develop health problems.
"The reason we're concerned about overnight low temperatures, and we really want to see those get low, is that it gives us a break; it gives our bodies a break, it gives buildings that don't have air conditioning a chance to release some of their heat," she said. "And when those stay high it makes it a lot hard to get any sort of break from the heat."
Winter temperatures are rising about twice as fast as annual average temperatures, she said. And temperature increases vary by geographic region, with the biggest increases appearing in the northern part of the state where people may not be as well adapted to the heat.
"The temperature has risen slightly over one degree in southern Minnesota to a little over two degrees Fahrenheit in the northern part of the state, and that is actually since the 1980s. So in the last 30 years we've seen an increase of one to two degrees Fahrenheit (in the) average yearly temperature."
Although people in big cities are traditionally thought to have a greater risk of hospitalizations from heat-related illness due to what's known as the "urban heat island effect," the Department of Health says state data suggest that is not necessarily the case in Minnesota. During the summers of 2001, 2005 and 2006, the rate of hospitalization for heat-related illness was higher in non-metro areas than in the metro.