Recognition and validation of COPD phenotypes has an important role to play in the selection of evidence-based targeted therapy in the future management of COPD, but regardless of the diagnostic terms, patients with COPD should be assessed and treated according to their individual treatable characteristics. COPD is now widely recognized as a complex heterogeneous syndrome with pulmonary and extrapulmonary features. The aim of this article is to discuss the challenges of accurately diagnosing and assessing COPD, to present the evidence for the importance of defining COPD phenotypes, and to provide guidance on how these phenotypes could be assessed.
An accurate diagnosis guides the physician to identify the most appropriate management strategy. Prior to diagnosis, many patients with COPD may not recognize their symptoms as being due to a disease, since breathlessness may be attributed to aging, and cough and sputum production may be considered a consequence of smoking. An accurate diagnosis may help patients accept that they have COPD and to take action to change their lifestyle and help manage their symptoms.
Spirometry is mandatory to confirm the presence of persistent airflow limitation, a defining, but not a pathognomonic characteristic of COPD. In an effort to improve the management of patients with COPD and encourage a more comprehensive assessment of patients, the GOLD guidelines were revised recently to include COPD categories based on a combined score for symptoms, degree of airflow limitation, risk of exacerbation, and presence of comorbidities Table 1.
One of the functional consequences of the pathological changes that occur in COPD is over-inflation of the lungs. IC decreases linearly with increasing airflow limitation 8 and is sufficiently sensitive to signal airway obstruction even in mild disease when FEV 1 is largely unaffected. During exercise, the central drive to breathe continues to increase, but the ability of the respiratory muscles to respond to this drive progressively diminishes because of the effects of dynamic lung hyperinflation critical reduction in IRV. It follows that a much greater respiratory effort is required to generate the same tidal volume as at rest, thereby leading to intolerable shortness of breath.
Increasing IC with bronchodilators is associated with reduced dyspnea ratings and improved exercise tolerance.
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Figure 1 Comparison of pulmonary dynamics in health and COPD showing tidal pressure-volume curves during rest filled area and exercise open area. The clinical importance of dynamic lung hyperinflation in COPD. This test is simple to perform, correlates well with peak oxygen uptake, and is a good index of functional disability.
It relates to daily activities and has predictive value in relation to health status and survival, but not hospitalizations for COPD exacerbations. Another method of measuring the functional impact of COPD is to use cardiopulmonary exercise testing. This requires more equipment than other field tests, and provides a measure of the integrated function of the respiratory, cardiocirculatory, peripheral muscle, and neurosensory systems under stress.
It accurately quantifies abnormalities in pulmonary gas exchange, ventilatory demand, and dynamic respiratory mechanics and their sensory consequences. Furthermore, peak oxygen uptake measured during incremental exercise tests has prognostic value in relation to survival in COPD.
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Thoracic computed tomography CT scanning can be used to quantify the extent, type, distribution, and progression of emphysema; 16 , 17 however, measurement of airway dimensions using CT scanning has been more problematic. The goal of COPD phenotyping is to be able to classify patients into distinct subgroups according to prognosis and response to therapy in order to better select the appropriate therapy that can optimize clinically meaningful outcomes for patients. Prospective validation of COPD phenotypes against clinical outcomes or response to treatment is essential in defining a phenotype.
Alpha-1 antitrypsin deficiency is a genetic condition that predisposes patients to COPD and liver disease, and has been identified as a specific phenotype that may respond positively to augmentation therapy. This phenotype appears to respond well to lung volume reduction surgery, which improves survival. Therapies that reduce the frequency of exacerbations are available and they also improve quality of life in this phenotype.
Several other potential phenotypes have been proposed, but are not yet fully validated against clinical outcomes. These include a phenotype of mild airway obstruction but disproportionately severe dyspnea; these patients may be detectable using tests for exercise performance and radiographic imaging. Compared with patients without chronic bronchitis, patients with this phenotype are more likely to be younger, male, Caucasian, have a greater extent of dyspnea, higher frequency of exacerbations, greater airway obstruction, and increased airway wall thickening, detectable both clinically and radiologically.
There are reports of a subgroup of COPD patients with chronic bacterial airway colonization who are at increased risk for frequent exacerbations, have higher levels of both airway and systemic inflammation, and are at increased risk of cardiovascular complications compared with those without chronic bacterial airway colonization. Some phenotypes describe COPD co-existing with other conditions. Patients with COPD may develop pulmonary hypertension, which is usually mild, but a specific phenotype with severe pulmonary hypertension disproportionate to the underlying COPD has been proposed.
A subgroup of patients with COPD has been identified as non-smokers who may have developed COPD following exposure to dust and fumes not related to smoking. These individuals are at greater risk for pneumonia but have no additional risk for cardiovascular comorbidities or all-cause mortality compared with non-smokers without airway obstruction.
Although the overlap of symptoms between asthma and COPD has been recognized for many years, its characterization as a separate phenotype has recently attracted much interest due to the publication of a consensus statement by Global Initiative for Asthma GINA and GOLD on the diagnosis, assessment, and treatment of this condition. In many patients, asthma and COPD have typical clinical features that usually make the two diseases distinguishable. The clinical features of COPD are reduced lung function, with limited reversibility, emphysema, and sometimes cor pulmonale and hypoxemia.
Patients usually have a smoking history of many pack-years. Although guidelines 2 , 49 define both asthma and COPD as inflammatory disorders of the respiratory system, distinct inflammatory patterns exist, driven by different chemical mediators. A key histopathological difference is the destruction of alveolar walls in COPD that leads to emphysema. Figure 2 Sputum inflammatory mediators in patients with asthma and COPD having phenotypes for A eosinophilic airway inflammation and B non-eosinophilic airway inflammation. Notes: Reproduced with permission from S.
Karger AG, Basel, Switzerland. Profiling of sputum inflammatory mediators in asthma and chronic obstructive pulmonary disease. While smoking is a key driver of lung function decline in COPD, 27 allergens are the main protagonists in asthma; however, smoking also accelerates lung function decline in asthma. Several COPD phenotypes based on predominant symptoms have been described in this article and specific interventions are available to improve patient outcomes.
[Full text] Diagnosis, assessment, and phenotyping of COPD: beyond FEV1 | COPD
Thus, a range of treatable traits may occur in an individual COPD patient. Asthma and COPD are both inflammatory lung disorders that result in airflow limitation. In particular, tackling a diagnosis that differentiates asthma from COPD is sometimes challenging because they share many clinical and pathological similarities Table 2. While a smaller proportion of patients with asthma are smokers or ex-smokers than among patients with COPD, smoking has negative consequences for both diseases in relation to morbidity, mortality, disease control, and response to medication.
Patients with ACOS tend to be older than those with asthma, they have a significant smoking history, present with asthmatic features to their COPD, and have persistent airflow limitation. COPD is a complex heterogeneous disease where assessment and management have traditionally been based on the severity of airflow limitation measured as FEV 1. However, it is now recognized that FEV 1 does not describe the complexity of the disease and that other factors need to be measured to fully assess this condition. More recently, the GOLD strategy document has proposed a combined assessment using three variables: symptoms, airflow limitation, and exacerbations.
In addition, it has been proposed that in the future more variables should be added to the assessment that reflect the three domains of disease severity, activity, and impact Figure 4.
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Figure 4 Proposal for a COPD assessment control panel of variables that relate to three domains of the disease — severity, activity, and impact. Agusti A, MacNee W. Volume 68 7 , pages — Thus, regardless of the diagnostic labeling, which may change over time, the authors of this review believe that patients with COPD should be assessed beyond FEV 1 and treated according to their individual clinical characteristics.
Medical writing support for this review was funded by Almirall S. DEO has previously received speaker fees from Almirall. The authors report no other conflicts of interest in this work. Chronic obstructive pulmonary disease phenotypes: the future of COPD. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease [updated ]. Accessed March 30, COPD management: role of symptom assessment in routine clinical practice. COPD patients perspectives at the time of diagnosis: a qualitative study.
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Lancet Respir Med. Using pulmonary imaging to move chronic obstructive pulmonary disease beyond FEV 1. Airway imaging in disease: gimmick or useful tool? J Appl Physiol Changes in forced expiratory volume in 1 second over time in COPD. N Engl J Med. Chronic obstructive pulmonary disease exacerbations in the COPDGene study: associated radiologic phenotypes.
Computed tomographic emphysema distribution: relationship to clinical features in a cohort of smokers. Airway dimensions in COPD: relationships with clinical variables. Respir Med. A randomized trial comparing lung-volume-reduction surgery with medical therapy for severe emphysema. The final sections outline the non-pulmonary effects of COPD and their management.