| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Guest Access | Sign In via User Name/Password
|
|
|
|||||||
Guest Access | Sign In via User Name/Password |
|||||||||
Dr. Yusen is Assistant Professor of Medicine, Washington University School of Medicine.
Correspondence to: Roger D. Yusen, MD, Washington University School of Medicine, Campus Box 8052, 660 S. Euclid Ave, St. Louis, MO 63110; email: yusenr{at}msnotes.wustl.edu
Traditionally, pulmonary physicians rely on measures of lung function to diagnose, to assess disease severity, and to determine response to therapy in patients with COPD. The FEV1 has been used as the main outcome in many clinical studies. Survival has been the main end point in several clinical trials for COPD, but only a few interventions (eg, administration of supplemental oxygen to hypoxemic patients) have been demonstrated to improve survival. However, the bulk of therapy for COPD has been aimed at improving quality of life. Many clinical studies of patients with COPD have not used quality-of-life measures as outcomes.
Quality of life has been defined in many ways, such as "the gap between that which is desired in life and the extent to which this is achieved or achievable."1 The term health-related quality of life (HRQL) reflects the health- and disease-related aspects of quality of life. HRQL measurements quantify the impact of disease, treatments, and tests on daily life and well-being in a formal and standardized way.
As patients become symptomatic from COPD, the most common complaints are breathlessness, fatigue, sleep disturbances, irritability, and a sense of hopelessness. Dyspnea typically leads to inactivity, which leads to physical deconditioning, and a vicious cycle ensues, with devastating responses such as depression. Although a relationship between dyspnea and measures of lung function may exist,1 2 3 4 5 no single physiologic measurement (eg, FEV1) can adequately encompass the various disturbances that cause dyspnea in patients with COPD. Direct measurement of dyspnea and other areas of HRQL may provide better estimates of the impact of disease and treatment effects than measurement of physiologic variables.
FEV1 has been utilized as a surrogate marker of dyspnea and generic HRQL. However, pulmonary rehabilitation trials have demonstrated improvements in dyspnea without significant accompanying changes in parameters of lung function, including FEV1.6 In addition, use of surrogate markers as primary outcomes in treatment trials can be dangerous. Many technologies that succeeded in improving surrogate markers failed miserably for the patients. For example, the Coronary Arrhythmia Suppression Trial7 randomized patients with recent myocardial infarction to receive different anti-arrhythmic agents, including encainide and flecainide, to treat premature ventricular contractions (PVCs). The investigators hypothesized that PVC suppression would reduce the triggers responsible for initiating a sustained ventricular tachyarrhythmia and thus reduce the incidence of sudden death. Although the occurrence of low-grade arrhythmias did decrease dramatically, the study was terminated prematurely because patients who were given encainide or flecainide had greater mortality rates than those receiving placebo therapy. The surrogate markers were not tightly linked to the more important patient outcomes.
Once we decide to measure HRQL, what tools do we use? Researchers often classify HRQL instruments as disease-specific or generic. Preference-based HRQL measures are typically classified as a separate group.
Disease-specific measures focus on the symptoms of the specific disease, such as shortness of breath. Generic measures provide information about many aspects of patients’ lives. Compared with generic measures, disease-specific measures may be more sensitive, because a much higher proportion of their content is directly relevant to a specific disease (eg, emphysema). In addition, disease-specific measures are likely to be more responsive (eg, able to detect small but clinically important changes in health status) because they focus on the symptoms of the specific disease. Unlike generic measures, disease-specific measures are limited by their noncomprehensive approach and their inability to compare status across diseases. Examples of instruments specific to lung-disease include the St. George’s Respiratory Questionnaire, the Chronic Respiratory Questionnaire, the Oxygen Cost Diagram, the Baseline and Transitional Dyspnea Indexes, the Modified Medical Research Council Dyspnea Index, the Borg Scale, and the UCSD Shortness of Breath Questionnaire. Generic HRQL instruments include the SF- 36, the Quality of Well Being Questionnaire, and the Sickness Impact Profile.
Preference-based HRQL measures, which can simultaneously capture degree of impairment, degree of bother, and willingness to undergo risk to reduce bother, offer important means for measuring the health benefits of interventions (eg, lung volume reduction surgery). Unlike disease-specific and generic HRQL measures, preference measures typically include in their analyses and interpretation patients who have died. Preference data may be used to estimate utilities and to allow for the estimation of quality adjusted life years (QALYs), which take into consideration quantity as well as quality of life consequences of illnesses and their treatments. By determining QALYs, utilities help determine the cost-effectiveness or cost-utility of a procedure. Typical disease-specific or generic HRQL tools cannot measure cost-effectiveness. Examples of three standardized utility assessment instruments include the Quality of Well Being Questionnaire, the Health Utility Index, and the EuroQol.
Just as guidelines for performing spirometry have been published, guidelines for assessing HRQL are available. Valid, reliable, and responsive instruments exist for assessing disease-specific, generic, and preference-based HRQL. A battery of assessments offers the most flexibility.
Although COPD patients with the most severe airflow obstruction might be expected to have the most dyspnea, patients with comparable levels of FEV1 may have very different levels of dyspnea.4 Studies have shown inconsistent degrees of correlation between physiologic parameters (eg, FEV1) and measures of dyspnea, between the change in the FEV1 over time and the change in dyspnea over time, and between other physiologic or exercise parameters (eg, 6-min walk distance) and other measures of HRQL.1 2 3 4 5 6 In the September issue of CHEST, Leyenson et al8 described a lack of significant correlation between changes of measures of generic HRQL and changes of measures of lung function and exercise performance in a cohort of patients undergoing lung volume reduction surgery. Although the lack of statistically significant correlation may have been due to statistical method and sample size limitations, the study results are not surprising. The study illustrates that the lack of correlation may have been the result of unique information provided by the measures of HRQL.
In the lung volume reduction surgery program at Washington University (St. Louis, MO), similarly poor correlation has been demonstrated between baseline physiologic parameters and generic HRQL SF-36 scores in 200 patients with severe airflow obstruction due to emphysema. For example, Pearson correlation of the FEV1 and the SF-36 physical component summary scale (PCS) was extremely poor (r = 0.01), as was the correlation of the 6-min walk distance and the SF-36 PCS (r = 0.10). Although higher correlation was found between changes in lung function parameters and changes in PCS scores over time (comparing postoperative to preoperative scores), the changes in the PCS scores were clearly not explained solely by changes in a single physiologic parameter (correlation for the change in FEV1 and the change in the SF-36 PCS- [r = 0.39; p < 0.001]; correlation for the change in the 6-min walk distance and the change in the SF-36 PCS [r = 0.53; p < 0.001]).
One message is clear. For patients with symptomatic COPD, measures of HRQL provide information above and beyond that provided by measures of lung function or exercise performance. Thus, HRQL assessment should be an integral part of the conduct and interpretation of clinical studies.
References
This article has been cited by other articles:
|
|
 |
|
  H. Somand and T. L Remington Tiotropium: A Bronchodilator for Chronic Obstructive Pulmonary Disease Ann. Pharmacother., September 1, 2005; 39(9): 1467 - 1475. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K Dheda, A Crawford, G Hagan, and C M Roberts Implementation of British Thoracic Society guidelines for acute exacerbation of chronic obstructive pulmonary disease: impact on quality of life Postgrad. Med. J., March 1, 2004; 80(941): 169 - 171. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. D. Yusen, S. S. Lefrak, D. S. Gierada, G. E. Davis, B. F. Meyers, G. A. Patterson, and J. D. Cooper A Prospective Evaluation of Lung Volume Reduction Surgery in 200 Consecutive Patients Chest, April 1, 2003; 123(4): 1026 - 1037. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Govindaraj and R. D. Yusen Defining Dyspnea Chest, February 1, 2002; 121(2): 662 - 669. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
