Summer is a humid time of year in many places around the United States. Humid weather not only makes you sweaty and sticky, but also can make it hard to breathe for some asthma patients.
People with asthma can have difficulty breathing in humid weather because hot and humid air may trigger nerves that are sensitive to rises in temperature.
Fortunately, ipratropium (sold as Atrovent) can increase airflow to the lungs of asthma patients.
Research has shown that cold air can tighten the airways of people with asthma. However, little is known about the effects of hot air on asthma patients.
"We know that breathing cold, dry air induces airway constriction in asthmatics," says Don Hayes, MD, of the Lung and Heart-Lung Transplant Program at Nationwide Children's Hospital.
"But the effects that temperature increases have on airway function in these patients are generally overlooked. We know very little about the mechanisms that cause symptoms when asthmatic patients are exposed to hot, humid air," he says.
So Dr. Hayes and colleagues set up a study to measure the effects of breathing humid air in people with asthma.
The study compared six patients with mild asthma to six healthy people. The participants breathed through a device that carried air at different levels of temperature and humidity.
When the asthma patients breathed the hot and humid air, their airways immediately constricted. In contrast, hot and humid air had very little or no effect on the airways of the healthy participants.
In addition, asthma patients experienced consistent coughing after breathing the hot and humid air.
When the asthma patients inhaled ipratropium before breathing humid air, their airways did not constrict.
It is still unclear what drives these responses, explains Dr. Hayes. However, results of another study from the same research team show that specific nerves in the airway - called C-fiber nerves - are activated when the temperature in the chest rises to about 102 degrees Fahrenheit.
According to Dr. Hayes, the lungs' defense system can respond in a number of ways when C-fiber nerves are stimulated.
"This study is a good example of how we can translate findings from a research laboratory into a better understanding and more in-depth knowledge about how to prevent and treat diseases in patients," explains Lu-Yuan Lee, MD, of the University of Kentucky and the scientist in whose lab the C-fiber findings were made.
The results of these studies show that air temperature and humidity play an important role in asthma, says Dr. Hayes. This research eventually could lead to new drug targets in the treatment of asthma, he adds.
Dr. Hayes concludes that more research is needed to gain a better understanding of how hot, humid air affects the bodies of asthma patients.
Considering the small size of the current study (12 participants), larger studies are particularly needed.
This research received support from the National Institutes of Health, the US Army Medical Research & Materiel Command (USAMRMC) Telemedicine & Advanced Technology Research Center (TATRC), the University of Kentucky Clinical Research Development & Operations Center, and the Kentucky Pediatric Research Institute.
The results appear in the American Journal of Respiratory and Critical Care Medicine.