Mapping the Brain's Response to Breathlessness
In a unique study, HSPH researchers and colleagues from the Imperial College School of Medicine in London have identified the area of the brain that is activated during shortness of breath. The findings could eventually aid the recognition and management of conditions such as asthma in which dyspnea, or breathlessness, is a hallmark. The study was published in the July 14 issue of NeuroReport.
The
circled areas indicate the part of the brain that was activated when subjects
experienced dyspnea during the study.
"This kind of basic science underlies the understanding one needs to use breathlessness as a tool of diagnosis," said Robert Banzett, associate professor in the Department of Environmental Health and lead author of the study.
In the experiment, healthy men were placed on ventilators, and their ability to take deep breaths was controlled. As their breathing was regulated, their brains were imaged using a PET camera. The images were then compared to scans taken prior to the experiment to see which areas, if any, were turned on when the body perceived it was not getting enough air.
Banzett and another of the study's authors were two of the research subjects. "I always try to participate in my experiments when it is possible," said Banzett. "You are sometimes making subjects very uncomfortable. There's hardly anything worse than feeling that you are not getting enough air."
The researchers found that a small part of the brain called the insula was activated when the study subjects could not breathe deeply. The insula is buried underneath the surface of the brain and therefore is not easy to study. It is part of the limbic system, which is involved in emotion, memory, and behavior.
Hunger, thirst, nausea, and nasty tastes and odors also activate the insula.
The researchers found interesting parallels between dyspnea and pain. Both activate the same part of the brain and are common symptoms of underlying diseases. Banzett cited a recent study of 1,500 people who were hospitalized for serious illnesses that identified a large group of patients who both suffered from pain and had trouble breathing. Yet pain is researched much more broadly than dyspnea.
"Everybody experiences pain in their daily lives," said Banzett. "People also experience shortness of breath, but they can almost always stop it. You may get short of breath after running up stairs, but you can stop it by slowing down. It's when you have a disease that prevents you from easily resuming normal breathing that dyspnea becomes a problem."
Part of the challenge of treating dyspnea is that there is no common language with which to analyze the condition.
"Two people can look at a napkin and have a common basis on which to talk about its color, but only you can feel your dyspnea," said Banzett. "That's why developing the language is hard. It makes measuring the sensation a challenge."
To help build a language, Banzett is part of a team that is applying methods used by psychophysicists in pain studies. Psychophysicists study the relationship between psychology and physiology and have developed a standard vocabulary describing people's responses to discomfort. Now, Banzett and his colleagues have revised the tools to study dyspnea, systematically interviewing study subjects about the words that best describe the feeling and intensity of breathlessness.
In the NeuroReport study, patients were asked to rate the sensations they felt using descriptions such as "starved for air" and the feeling one gets after holding one's breath for a long time.
"I am interested in this mechanism because it is important and clinically related," said Banzett. "I hope my information will help people who want to treat dyspnea."
