The development of persistent childhood asthma – characterised by having trouble breathing on an almost daily basis – is not well understood. In most cases, childhood asthma resolves with time, but as many as 20% of children with asthma will go on to have potentially severe symptoms in adulthood. In the largest and longest US analysis of persistent asthmatics to date, investigators at Brigham and Women's Hospital (BWH) found a link between persistent childhood asthma and chronic obstructive pulmonary disease (COPD) in early adulthood.
The study found that early lung function predicts lung growth later in life, regardless of asthma treatment and smoking exposure.
"This work tells us that persistent childhood asthma can develop into COPD, something that up until now has not been well described," said Dr Scott T Weiss, one of the paper's senior authors and co-director of the systems genetics and genomics section of the BWH Channing Division of Network Medicine. "Children who had low lung function at the start of the trial followed a series of predicted growth patterns: most had reduced lung growth with time and a significant number would go on to meet the criteria for COPD."
The study followed 684 participants in the Childhood Asthma Management Programme (CAMP) from ages 5-12 until they were at least 23 years old. Each participant reported once a year to one of eight research centres around the US and Canada to complete lung function measurements like spirometry, a test that records how much air a participant can breathe out in one second.
With these annual recordings, the researchers were able to characterise the patterns of growth in asthmatics’ lung function. By the end of the study, 11% met the criteria for COPD, a progressive disease that makes breathing difficult. In addition to low lung function at the start of the study, being male also predicted worse outcomes, but this is likely a consequence of higher asthma prevalence in boys. By early adulthood, 75% of the children with persistent asthma displayed an early decline in lung function and/or reduced lung growth. Treatment did not change these patterns.
"It is astonishing," said co-senior author Dr Robert C Strunk, professor of paediatrics at Washington University School of Medicine. "For people barely into adulthood to already have COPD is terrible. As the COPD evolves, they are likely to have health problems that will make it difficult to participate in normal day-to-day responsibilities such as holding a job."
"With this understanding, physicians need to identify at-risk children earlier and counsel them about potential preventative measures. Since asthma itself is a risk factor for developing COPD, these patients should be advised against risk related environmental exposures, like smoking, that could intensify their symptoms and increase their COPD risk," said Weiss. "It is important that we recognise this link between persistent childhood asthma and COPD as a potential problem and focus on prevention efforts."
Background: Tracking longitudinal measurements of growth and decline in lung function in patients with persistent childhood asthma may reveal links between asthma and subsequent chronic airflow obstruction.
Methods: We classified children with asthma according to four characteristic patterns of lung-function growth and decline on the basis of graphs showing forced expiratory volume in 1 second (FEV1), representing spirometric measurements performed from childhood into adulthood. Risk factors associated with abnormal patterns were also examined. To define normal values, we used FEV1 values from participants in the National Health and Nutrition Examination Survey who did not have asthma.
Results: Of the 684 study participants, 170 (25%) had a normal pattern of lung-function growth without early decline, and 514 (75%) had abnormal patterns: 176 (26%) had reduced growth and an early decline, 160 (23%) had reduced growth only, and 178 (26%) had normal growth and an early decline. Lower baseline values for FEV1, smaller bronchodilator response, airway hyper-responsiveness at baseline, and male sex were associated with reduced growth (P Conclusions: Childhood impairment of lung function and male sex were the most significant predictors of abnormal longitudinal patterns of lung-function growth and decline. Children with persistent asthma and reduced growth of lung function are at increased risk for fixed airflow obstruction and possibly COPD in early adulthood.