Detecting Asthma Flares Before They Start
Newer measures of asthma control
In this entry, I would like to discuss some exciting research on newer, non-invasive ways to assess asthma control in patients. While none of these techniques are being used in routine practice, their use is gaining momentum in the asthma research community and they may be integrated into routine care in the future.
Traditional versus newer approaches to assessing asthma control?
I want to be clear from the outset -- there is nothing wrong with so-called "traditional" means of assessing asthma control and using these means to help patients get better control over their asthma. They have served patients and asthma care providers for years, and for a good reason: they work. These traditional measures include peak expiratory flow (done at home or in the clinic), spirometry (breathing tests), and careful assessment of asthma symptoms by talking to patients. There are, however, key areas where these means fall short. Right now, we do a pretty good job of assessing if a patient's asthma is not well controlled. We do not have a good way, based on symptoms or breathing tests, of predicting whether someone's asthma is about to get worse. If we could detect, for example, very early changes in the function or state of a patient's breathing tubes before they start to have more wheeze or shortness of breath, we could change their treatment earlier to prevent an asthma flare.
Markers of inflammation of the breathing tubes in asthma
There are two tests I would like to discuss which have been looked at as markers of the asthmatic state of the breathing tubes which hold particular promise: exhaled nitric oxide and sputum eosinophils.
First, eosinophils are a particular type of white blood cell that is a major cell in the inflamed airways of asthmatics. Using non-invasive techniques, the sputum (phlegm) of asthmatics can be analyzed to look for the quantity of eosinophils. This "marker" has similarly been studied and found to correlate nicely with the degree of symptoms in asthmatics. There is optimism that this marker could be used to catch an asthma flare early, before patients feel very sick.
Second, researchers have found that when there is more asthmatic inflammation in the airways, the levels of the gas nitric oxide that is breathed out (exhaled) is increased. The technical term for this level is the "exhaled fraction of nitric oxide" (FENO). This is measured by a special analyzer into which a patient breathes for 1-2 minutes. Recent studies have found that using this measure is as good as traditional means (patient history, breathing tests, etc.) to direct treatment. There is hope in the research community that this measure, in the right patient populations, could become a marker of worsening inflammation in the airways (and later increases in symptoms) before it gets worse.
Neither FENO nor sputum eosinophils are the holy grail of asthma care (yet). FENO measurement requires expensive equipment and can be a finicky test and getting patients to bring up sputum from deep enough in the lungs for eosinophil analysis can be challenging. Some investigators are studying alternative sources of markers of disease control, such as saliva (spit). Saliva is easy to obtain (for patients and providers) and the technique of collection is easy to standardize. As the mouth is directly connected to the breathing tubes, this approach, though in its infancy, holds promise. As part of a National Institutes of Health-funded collaborative, I am currently exploring this approach.
As I have discussed in recent entries, we have come a long way in understanding the biology of asthma and applying new treatments. We now need to move towards a better understanding of the early "warning signs" that a patient's asthma is getting worse -- to "cut it off at the pass." Stay tuned...