Lung function decline in asthma

Abstract

Progressive decline in lung function in asthma has been well recognised but not fully explained. For example, in a Danish population study (the Copenhagen City Heart Study), three measurements of forced expiratory volume in one second (FEV1) were made over 15 yrs in 17,506 subjects, including 1,095 with asthma 1. Asthmatics showed a decline in FEV1 of 38 mL·yr−1 compared with 22 mL·yr−1 in normal individuals. However, accelerated decline is not invariable. Many asthmatics retain normal or close to normal lung function throughout life, showing reversibility from acute worsenings and return to previous function. Conversely, some patients develop “irreversible” asthma, as seen in population-based studies 2 and in specialist-treated patients whose obstruction persisted despite bronchodilators and oral corticosteroids 3. In the latter patients, lung function decreased with age, and with duration and severity of asthma. Progressive loss of function can be inexorable despite aggressive therapy, resulting in end-stage respiratory failure that occasionally justifies lung transplantation 4. Among 228 adults followed up after 21–33 yrs in a clinic in Groningen, the Netherlands, 16% had irreversible airway obstruction, which was defined as FEV1 <80% predicted with reversibility <9% pred 5. Irreversible disease was predicted by a lower FEV1, less reversibility and less (rather than greater, as one might have expected) airway hyperresponsiveness (AHR) at initial screening. Patients using regular treatment developed irreversible obstruction less frequently. Loss of lung function has serious consequences. In 89 asthmatics followed over 17 yrs in Perth, Australia, lower lung function, but not initial symptom severity, predicted mortality 6. The risk of death was higher with decreased FEV1 and increased FEV1 variability, age and treatment requirements. Both the Melbourne (Australia) 7 and Dunedin (New Zealand) 8 longitudinal studies of the natural history of asthma show that impaired lung function …