Scientists have taken a huge step toward understanding chronic bronchitis and developing a diagnostic test for this lung condition.

Despite a multitude of tests to assess lung function, including chest X-rays and pulmonary function tests, there is currently no single test for chronic bronchitis, nor is there a solid understanding of the biological pathways causing the buildup of phlegm that characterizes the disease.

'Until now, we have had little knowledge of what causes the airway mucus accumulation that plagues chronic bronchitis patients, and the only way we have to diagnose chronic bronchitis is based on what the patient tells us," said Richard Boucher, M.D., co-author of a paper recently published in the New England Journal of Medicine.

"Frankly, it's a little embarrassing," said Boucher, the director of the UNC Marsico Lung Institute at the University of North Carolina at Chapel Hill. "Chronic bronchitis is a very common reason why people see their doctor, and we have had no real understanding how it develops or how to diagnose it. This study is a breakthrough in our understanding of this serious condition that affects millions of people in the United States."

Roughly 10 million people in the United States are diagnosed with chronic bronchitis each year, according to the American Lung Association. Chronic bronchitis is a type of chronic obstructive pulmonary diseases (COPD), which is the third-leading cause of death in the nation.

Chronic bronchitis is a condition characterized by inflamed bronchial tubes that produce excessive amounts of mucus. Specifically, chronic bronchitis is a muco-obstructive lung disease in that mucus obstructs airway lumens.

Mucin is a type of protein that makes mucus thick. One biophysical model suggests that mucin is a key variable that controls mucus transport in healthy people but stops the transport of mucus in those with chronic bronchitis. This model suggests that a high mucin concentration produces the sputum and disease progression associated with chronic bronchitis.

However, the physiological process behind the accumulation of mucus in the lungs of those with chronic bronchitis and the progression of the disease remains somewhat of a mystery.

The results of the study suggest that an inability to hydrate airway surfaces normally increases mucin concentrations and subsequent mucus accumulation in the lung. In time, the process results in increased phlegm production and chronic airway infections that characterize chronic bronchitis.

In the study, the scientists describe how the concentration of mucins is abnormally high in those with chronic bronchitis. They also note an association between high mucin concentration and disease severity.

The researchers enrolled 917 participants from the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) into the study. To characterize the COPD status of the participants, the scientists administered questionnaires, chest tomography and spirometry, and they examined induced sputum samples. The researchers used size-exclusion chromatography and refractometry to measure total mucin concentrations in the sputum samples.

They found that the mean total mucin concentrations were higher in current or former smokers with severe COPD than in the control group who never smoked. Mucin concentrations were also higher in participants who experienced two or more respiratory exacerbations per year than in those with no exacerbations.

These findings may become the first objective marker of chronic bronchitis and may someday lead to the development of diagnostic and prognostic tools for the disease. The results of the research also raise the possibility that drugs could someday reduce mucin concentrations to relieve symptoms of chronic bronchitis and prevent progression of the disease.

"As a next step, we plan to look for ways to translate our findings into a practical test that could find its way into your doctor's office, not just for chronic bronchitis but also for other muco-obstructive diseases of the lung, such as bronchiectasis and asthma," said research leader Mehmet Kesimer, Ph.D.