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Nijmegen, the Netherlands
The authors are affiliated with the University Medical Center Nijmegan, the Netherlands.
Correspondence to: Tjard Schermer, University Medical Centre Nijmegen, PO Box 9101, Nijmegen, 6500 HB, the Netherlands
Too Relevant To Ignore, Too Conspicuous To Apply?
Clinical logic tells that loss of pulmonary function heralds decline in (respiratory) health status, and the study of Xie et al1 in this issue of CHEST (see page 2448) may help further explore this logic. Pulmonary function decline gains importance when its impact on the general population is taken into account. Our study in family medicine, the Detection, Intervention and Monitoring of COPD and Asthma (DIMCA) program, for example, detected in 1991 a persistently reduced lung function or increased bronchial hyperresponsiveness in 7.7% of the general population, whereas another 12.5% showed a rapid decline in lung function (> 80 mL/yr) in combination with signs of bronchial hyperresponsiveness.2 A further 19.4% showed mild objective signs of COPD or asthma. However, research failed to directly confirm intuition; in analyzing airflow limitation in conjunction to other patient characteristics, a poor correlation was found between FEV1 and respiratory signs and symptoms.3 In the early stage, respiratory symptoms and airflow limitation form more or less independent aspects of chronic obstructive respiratory disease, and this helps explain the underpresentation by patients and underdiagnosis by (family) physicians of asthma and COPD.4 With its resistance to interventions other than smoking cessation,5 decline in FEV1 appears to lose its central position in monitoring and managing COPD.
COPD is the end stage of a development over a long period of time, and this requires longitudinal research. So far, population studies56 have mainly focused on the rate of FEV1 decline in relation to mortality or smoking behavior, whereas several randomized controlled trials789 on inhaled corticosteroid treatment also related health status outcome to the progression of the disease. As yet, there are no studies on early presentation of symptoms and their prognostic value for the development of COPD in the long term. In the mean time, Xie et al1 present a longitudinal study demonstrating that the presence of airflow limitation predicted health-related quality of life 9 years later. Although the correlations found were weak, they pointed in the same direction in all domains. The findings of Xie et al1 are in agreement with previous studies that showed that impaired health and functional status are independently associated with the severity of airflow limitation in subjects with undiagnosed disease,8 as well as in patients with established COPD.10 In our DIMCA program,2 a representative sample of subjects with formerly undiagnosed disease recruited in family practice was screened for respiratory symptoms and airflow limitation. Although the long-term follow-up results from the DIMCA cohort have not been published yet, our preliminary analyses show that baseline lung function is indeed associated with future respiratory health status as measured with the Chronic Respiratory Questionnaire.11 After 5 years, the group of subjects who were initially at risk for chronic respiratory disease (who also had a lower mean baseline postbronchodilator FEV1) showed a mean Chronic Respiratory Questionnaire score that was 0.3 point lower than in the subjects who initially had good respiratory condition (5.95 ± 0.89 points vs 6.24 ± 0.56 points [± SD], p = 0.007). The DIMCA study also showed that impairment of quality of life due to dyspnea and fatigue and variability in lung function are better predictors of physician consultation than the mere presence of respiratory symptoms or a (gradually) reduced lung function.12
It seems that the impact on quality of life comes next to the impact on mortality (in the study of Xie et al,1 an important reason for loss to follow-up among those with initially low FEV1) and morbidity.13 In a recent article, Thomas and Levy14 state that "as COPD is an illness that has no cure, we must continue to strive for early detection and active management at all stages of the disease. The cycle of inactivity, social isolation, depression and de-conditioning so well described in COPD should be prevented." Xie et al1 conclude that the decrease of quality of life is largely mediated through the development of chronic respiratory symptoms. If symptoms do predict morbidity (and mortality) after all, early detection of COPD can be easily implemented in primary care practice by the use of office spirometry. Further research should point out whether early access to proactive care and thus to prophylactic vaccination, pharmacologic and nonpharmacologic treatment options, and early lifestyle interventions (including smoking cessation, improved diet, and increased exercise)49 prevents further deterioration of quality of life.
It remains an interesting question how many of the individuals in the study by Xie et al1 actually had COPD. On the group level, impairment of baseline pulmonary function had a negative impact on quality of life in future years. However, the correlation of FEV1 with quality of life was accompanied by a broad spread: where some suffer, others with the same degree of airflow limitation lead a relatively unimpaired life. This reduces the possibility to predict the individual course and consequently early detection of COPD.
And this brings us back at the heart of the matter. FEV1 has been regarded a method for early detection of COPD, thus creating the opportunity of early intervention. In fact, this was the underlying objective of the DIMCA program. With an observation spanning 10 years, it has now become obvious to us that a firm individual clinical diagnosis is necessary for the interpretation of (group) correlations and progression in early stage COPD. The way forward is expected to come from adding analysis of individual medical histories over time to the population studies, in order to fine-tune this information and build evidence-based case-finding: detection and monitoring of patients with airflow limitation in order to prevent further loss of quality of life.
References
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