By Darbee, Joan C; Ohtake, Patricia J
INTRODUCTION
Breathlessness is a common complaint of individuals with respiratory disease. The sensation of difficult or uncomfortable breathing is probably the single most important determinant impacting day-to-day function of these patients. Dyspnea can lead to functional limitations and disability, including days lost from employment. The physiologic mechanisms resulting in dyspnea are poorly understood and thus quantification is difficult. Because of the multifactorial nature of dyspnea, it can be difficult to predict the level of breathlessness during activities of daily living using measures of respiratory disease. Therefore, the implementation of a specific measure for the determination of dyspnea is important. Specifically, the quantification of the relationship between dyspnea and physical exertion may be a very useful outcome measure to track the efficacy of interventions aimed at dyspnea reduction, improvements in functional ability, or both.
Objective quantification of disability related to dyspnea can be determined using several health status measures such as the St. George’s Respiratory Questionnaire1 and the Chronic Respiratory Disease Questionnaire.2 However, these questionnaires are complex to administer and score.1,2 The St. George’s Respiratory Questionnaire is a self-report health related quality of life tool that consists of 50 items divided into symptom (scored with a 4 or 5 point Likert scale), activity (scored with a true false format), and psychosocial impact (scored with a true/false format) categories. The questionnaire can be completed in approximately 15 minutes. The score is obtained by calculations involving the patient responses modified by empirically determined weights for each response. Category and total scores range from 100% (highest score-signifying profound impact of respiratory disease on health-related quality of life) to 0% (lowest score-signifying no impact of respiratory disease on health-related quality of life).1 The Chronic Respiratory Disease Questionnaire is also a disease-specific health-related quality of life measurement tool. An interviewer administers the 20- item questionnaire and patients respond using colored card responses. This questionnaire examines the domains of dyspnea, fatigue, emotional function, and mastery and requires approximately 20 minutes to administer. Scoring involves adding the scores together for each domain and dividing by the number of questions asked. The scores will range from 1 (most impact of respiratory disease) to 7 (least impact of respiratory disease).2 An alternative measure is the Medical Research Council (MRC) Dyspnea Scale. This measure is part of a larger measure, the MRC Respiratory Questionnaire,3 and was developed for use in epidemiologic studies to standardize the assessment of patients with occupational respiratory diseases.4
The MRC Dyspnea Scale is a simple, standardized, self- administered scale to quantify the effect of breathlessness on daily activities3 and therefore measures perceived respiratory disability. The original scale3 has been modified to include 55 or 6 categories (Table 1).6 Both the 5-point and the 6-point scales are commonly used, however, the 6-point scale seems to be more prevalent in recent investigations. The purpose of this article is to review the reliability and validity of the MCR Dyspnea Scale and thus determine the usefulness of this instrument to document the impact of dyspnea on a person’s physical functioning.
ADMINISTRATION
The MRC Dyspnea Scale is a questionnaire consisting of 5 or 6 statements about perceived breathlessness (Table 1). The difference between the two scales is that the MODERATE category of the 5-point scale is divided into MODERATE and MODERATELY SEVERE in the 6-point scale to distinguish the functional limitation between “walking slower than people of the same age on the level because of breath lessness” and “having to stop because of breath lessness when walking at own pace on the level.” This measure is a self- administered scale and is available in English. The patient reads the 5 or 6 statements and selects the grade that most closely describes the level of physical activity that precipitates their shortness of breath. The number associated with the selected statement is the score. The MRC Dyspnea Scale takes less than 5 minutes to complete and has been used successfully in patients age 6 to >80 years of age.7,8
Table 1. MRC Dyspnea Scales
PSYCHOMETRIC PROPERTIES
Reliability
To have acceptable reliability, the MRC Dyspnea Scale must provide consistent values with small errors of measurement and be able to differentiate between different clients. Specifically, the test must provide reasonable test-retest reliability and have high interrater reliability. Test-retest reliability, which demonstrates the stability of a patient’s response over time, has not been determined for this measure. Interrater reliability has been shown to be very good with a weighted kappa value (κ^sub w^) of 0.92.9
Validity
A measure is valid to the extent that a useful interpretation can be inferred from the measurement. In order to determine the overall validity of a measurement tool, it is necessary to examine several aspects of validity. Criterion validity is the extent to which the measure provides results that are consistent with a gold standard measurement. However, no gold standard exists for comparison for the MRC Dyspnea Scale therefore evaluation of the criterion validity of this measure is not applicable. However, it is possible to evaluate the MRC Dyspnea Scale utilizing concurrent validity as this validity evaluation is appropriately employed when there is no criterion or gold standard for comparison. Concurrent validity identifies the degree to which the result on the measure of interest agrees with the result of another measure assessing the same attribute when they are measured at the same time.10,11 Since the MRC Dyspnea Scale is intended to assess a person’s dyspnea during physical activity at a single point in time, the MRC Dyspnea score should demonstrate a moderately high correlation with results from other valid dyspnea measurement tools.
The MRC Dyspnea Scale, when compared with other dyspnea evaluation measures, has been shown to have acceptable validity for use with individuals with respiratory disease (Table 2). The MRC Dyspnea Scale and the Oxygen Cost Diagram are one-dimensional measures that detect the threshold of activities that bring physical limitations caused by breathlessness whereas the Baseline Dyspnea Index and the St. George’s Respiratory Questionnaire present questions regarding the level of dyspnea that is provoked by performing activities of daily living.12 Score distributions of the MRC Dyspnea Scale, the Oxygen Cost Diagram, the Baseline Dyspnea Index, and the Activity subscale of the St. George’s Respiratory Questionnaire have been demonstrated to have approximately the same level of discriminatory power in accordance with a wide range of disease severity despite differences in the number of items, grading scales, and scoring.12 Evaluation of patients with a chief complaint of breath lessness [included 153 patients with COPD (n=91), interstitial lung disease (n=23), asthma (n=17), heart disease (n=9), obesity (n=6), and cystic fibrosis, chest wall abnormalities, or respiratory muscle weakness (n=7)] revealed that the MRC Dyspnea Scale scores correlated well with the scores on other dyspnea measurement tools including both the Oxygen Cost Diagram and the Baseline Dyspnea Index.9 For patients with COPD, the MRC Dyspnea Scale correlated well with the Oxygen Cost Diagram,13 the Baseline Dyspnea Index,13 and the total score on the St. George’s Respiratory Questionnaire.14 For patients with asthma, the MRC Dyspnea Scale correlated well with both the Baseline Dyspnea Questionnaire15-17 and the modified (0 – 10 scale) Borg scale.16
The MRC Dyspnea Scale scores demonstrate concurrent validity with measures of pulmonary function. Since many respiratory diseases result in dyspnea, it is plausible that the degree of respiratory impairment may result in breathlessness. Therefore, the relationship between the MRC Dyspnea Scale and measures of pulmonary function has been investigated (Table 3). In patients with a chief complaint of dyspnea as well as those with COPD, measurements of airflow obstruction and respiratory muscle strength demonstrate a fair negative correlation10 with the MRC Dyspnea Scale (Table 3) indicating that the lower the airflow and respiratory muscle strength, the greater the dyspnea score. For patients with asthma, measures of airflow obstruction (FEV^sub 1^) and the degree of hyperinflation (FRC, RV/TLC) have been found to have a fair negative correlation with the MRC Dyspnea Scale. However, unlike patients with COPD and dyspnea, respiratory muscle strength in patients with asthma did not correlate with the MRC Dyspnea Scale. For patients with restrictive lung disease, such as idiopathic pulmonary fibrosis, pulmonary function as well as gas exchange had fair to good negative correlation with the MRC Dyspnea Scale. Partial pressure of arterial carbon dioxide (PaCO^sub 2^) was also found to be \a strong predictor of dyspnea in this patient population suggesting that a reduction in PaCO^sub 2^ may be due to an increase in ventilation in an attempt for these patients to reduce their dyspnea.18 Additionally, the MRC Dyspnea score correlated very highly with the duration of the disease (r = 0.83).19 Finally, for patients with chronic lung infection and mucus production, as occurs with cystic fibrosis and bronchiectasis, a good to excellent correlation10 was observed between airflow obstruction and the MRC Dyspnea Scale.
Table 2. Concurrent Validity of the MRC Dyspnea Scale with Other Dyspnea Measurement Tools
MRC Dyspnea Scale scores demonstrate concurrent validity with measures of functional capacity. Because the MRC Dyspnea Scale measures the level of physical activity necessary to precipitate breathlessness, the degree of correlation of the MRC Dyspnea Scale with functional capacity has been examined. For patients with COPD, the MRC Dyspnea Scale was found to have a good correlation with functional capacity (maximal oxygen consumption; Table 4).12 Additionally, for patients with air flow limitation (COPD and asthma), MRC Dyspnea scores were found to correlate well with six minute walk distance (6MWD), indicating that dyspnea level identified with the MRC Dyspnea scale is a good correlate with distance walked in these patient populations.20-22 Interestingly, although the distance walked was correlated with the MRC Dyspnea score, the degree of oxygen desaturation was not.20 Thus, patients with COPD who indicated that they were severely disabled by breathlessness had the shortest 6MWD but did not necessarily have appreciable oxygen desaturation. However, in another study with patients with asthma, the MRC Dyspnea score did not correlate with 6MWD17 suggesting that more research is needed to determine the association between the MRC Dyspnea Scale and 6MWD for these patients.
Table 3. Concurrent Validity of the MRC Dyspnea Scale with Measures of Pulmonary Function
In patients with cystic fibrosis, the MRC Dyspnea score contributes significantly to the prediction of exercise capacity.7 Dyspnea during activities of daily living, as assessed by the MRC Dyspnea Scale, and the perceived dyspnea during an exercise test, assessed by the Borg scale at 50% of the maximal work rate, were related (Table 4)7 This correlation suggests that moderate exercise work loads might be comparable to the individual’s level of exertion during daily physical activities, and as such, dyspnea scores at moderate work loads might therefore be comparable to dyspnea scores during daily living.
The MRC Dyspnea score correlated strongly with the maximal work rate in individuals with bronchiectasis.23 The slope of the observed relationship indicated that the MRC Dyspnea score (0 – 4 scale) increased by 1 MRC unit for every 16% in the percentage of predicted maximal work rate [WRmax = 100.5 – (15.2 x MRC Dyspnea score)].23 This relationship indicates that it may be possible to use the MRC Dyspnea score to approximate exercise capacity when exercise testing is not available or is not indicated for this patient population.
MRC Dyspnea Scale scores demonstrate concurrent validity with measures of body mass index (BMI) and age. MRC Dyspnea scores are correlated with body mass index (BMI; kg/m^sup 2^) in patients with COPD and asthma. For patients with COPD, the correlation is -0.26 indicating that a lower BMI is associated with a higher MRC Dyspnea score.24 Specifically, in 2 groups of patients with COPD who had similar airways obstruction (FEV^sub 1^ = 46 13 vs. 49 13), the underweight patients had a higher MRC Dyspnea score as compared to normal weight patients (3.1 0.9 vs. 2.5+ 1.2; 0-5 scale).24 Conversely, for patients with asthma, the MRC Dyspnea Scale is positively correlated with BMI (r = 0.34).15 This correlation indicates that for patients with asthma, the heavier the patient, the higher the MRC Dyspnea score. For patients with asthma, age showed good, positive correlation with the MRC Dyspnea scores (r = 0.39 to 0.68), indicating that advancing age is associated with higher MRC Dyspnea scores.15-17 Information on the correlation of age with the MRC Dyspnea Scale is not available for other populations with respiratory disease.
Table 4. Concurrent Validity of the MRC Dyspnea Scale with Measures of Functional Capacity
MRC Dyspnea Scale scores demonstrate concurrent validity with measures of health-related quality of life. The quality of life for individuals with respiratory disease has been shown to be lower than healthy individuals and has been attributed to a limitation in physical functioning.16,25 For individuals with mild to severe asthma, the MRC Dyspnea score correlated well with quality of life as determined by the Quality of Life in Asthma Questionnaire (r = 0.59).16 For patients with cystic fibrosis, limitation in function due to dyspnea was identified to be of greater importance to the quality of life than any other physiological parameter as evidenced by the strong correlation between the MRC Dyspnea scores and scores on the Sickness Impact Profile (overall: r = 0.75; physical: r = 0.64; psychosocial: r = 0.64).25 Thus interventions aimed at reducing dyspnea in this patient population are important and their efficacy can be monitored using the MRC Dyspnea Scale. For patients with idiopathic pulmonary fibrosis, the MRC Dyspnea score correlated well with measurements of health related quality of life (SF-36) subscales of physical functioning (r = -0.75), vitality (r = – 0.44), and social functioning (r = 0.46).26 Since breathlessness scales are usually easier and faster to administer than health- related quality of life tools, the MRC Dyspnea Scale may be a useful surrogate measure of health-related quality of life that is important to monitor in this patient population.
MRC Dyspnea Scale scores demonstrate longitudinal validity in response to therapeutic interventions. Longitudinal validity requires that the measure of interest demonstrate correlation with the results of change from a second measure.10 The MRC Dyspnea Scale has been shown to have longitudinal validity in investigations of the responses to pulmonary rehabilitation programs, lung volume reduction surgery (LVRS) procedures, and pharmacological interventions.
The responsiveness of the MRC Dyspnea Scale to changes in dyspnea following pulmonary rehabilitation has been studied. Pulmonary rehabilitation is known to provide reductions in dyspnea in patients with COPD.27 In patients with severe COPD (FEV^sub 1^
The MRC Dyspnea Scale has been used to quantify dyspnea in patients who are undergoing LVRS. In several studies of patients with severe COPD selected for LVRS, the MRC Dyspnea score decreased approximately 1 to 2 MRC units (Figure 1) within 1 month following the surgery and remained at this level for up to 24 months postoperatively.30-34 This reduction in MRC Dyspnea score was associated with clinically important improvements in average 6MWD (251 190 to 477 189 m) and airway obstruction (FEV^sub 1^; 960 369 to 1438 610 L).34
In patients who have had a pneumonectomy for management of unilateral lung destruction from pulmonary hypertension, the MRC Dyspnea score was found to decrease on average from 4.3 0.5 to 3.0 1.4 indicating that there was a clinically significant improvement in the level of dyspnea associated with physical activity following the pneumonectomy.35 The change in the MRC Dyspnea score was negatively correlated with the change in partial pressure of arterial oxygen (PaO^sub 2^)(r = -0.26), indicating that as PaO^sub 2^ increased, dyspnea decreased.35
Other studies have investigated the change in MRC Dyspnea score following the initiation of pharmacological treatment. In a study of patients with pulmonary hypertension due to chronic pulmonary thromboembolism, the MRC Dyspnea score decreased on average from 5.0 0 to 2.8 0.8 (0 – 5 scale) following administration for 6 weeks of the selective phosphodiesterase-5 inhibitor, sildenafil.36 The reduction in the MRC Dyspnea Score was correlated with an improvement in gas transfer (TL^sub CO^; r = -0.54).36 Other pharmacological trials have used the MRC Dyspnea Scale as an outcome measure. For individuals with COPD taking either theophylline or salbutamol for a 2-week period, there was a reduction in dyspnea with both medications with effect sizes of 0.313 and 0.350, respectively.37
Figure 1. Values are means ( SD) MRC Dyspnea scores observed following lung volume reduction surgery (LVRS). Measurements were made preoperatively and for up to 24 months postoperatively. There was an average reduction of 1 to 2 MRC units following LVRS in every study.
OBSERVED VALUES IN KNOWN POPULATIONS
The MRC Dyspnea Scale has shown good to excellent correlations with FEV^sub 1^ for patients with differing severity of both obstructive and restrictive lung disease (Table 2). Usual values are available for patient populations including COPD, asthma, cystic fibrosis, bronchiectasis, and idiopathic pulmonary fibrosis (Table 5). For all patient p\opulations, a reduction in FEV^sub 1^ is associated with an increase in the MRC Dyspnea score.
For patients with COPD, those with a Global Initiative for Chronic Obstructive Lung Disease (GOLD) score of 2 (FEV^sub 1^/FVC
Predictive equations for MRC Dyspnea score (0 – 5 scale) based on FEV^sub 1^ have been developed for individuals with COPD:
Male (age 70 8) MRC score = 4.1 – 0.04 FEV^sub 1^ 6
Women (age 69 9) MRC Score = 4.6 – 0.04 FEV^sub 1^ 6
The average MRC Dyspnea score for a given FEV^sub 1^ for persons with cystic fibrosis and bronchiectasis is very similar to those observed for patients with COPD (Table 5). In contrast, the average MRC Dyspnea scores for individuals with asthma and idiopathic pulmonary fibrosis are approximately twice that observed for individuals with COPD and cystic fibrosis for the same FEV^sub 1^. This observation suggests that although there are good correlations between MRC Dyspnea score and FEV^sub 1^, the nature of the relationship varies depending on the respiratory disease.
In epidemiological studies of older populations, dyspnea predicts functional deterioration.38 In a recent investigation of community dwelling elderly individuals, the MRC Dyspnea Scale was used to quantify dyspnea related to physical functioning in the elderly (Table 5). In response to a postal survey, 55% of community- dwelling respondents (70 years or older) reported dyspnea on the MRC Dyspnea Scale, with 23% to 35% reporting moderate to severe levels.8,39 This reveals that 1 out of 3 people aged 70 or older who live in their homes experience dyspnea when walking on level ground with people their own age. Dyspnea symptoms were also associated with a hazard ratio for cardiovascular- or pulmonary-related death within 8 years of 1.4 (95% CI: 1.1-1.9) per point increase in the MRC Dyspnea score.8
CLINICAL APPLICATIONS
The MRC Dyspnea Scale is a reliable and valid measure of the level of physical activity that precipitates breathlessness. It is a simple, quick, self-administered tool. The MRC Dyspnea Scale has been used with individuals who have the following respiratory diseases: COPD, asthma, cystic fibrosis, bronchiectais, and idiopathic pulmonary fibrosis. It has been used successfully in patients age 6 to >80 years of age.7,8
Table 5. Average MRC Dyspnea Scores at Different Levels of FEV^sub 1^
This measure performs consistently with other dyspnea measurement tools such as the Oxygen Cost Diagram and the Baseline Dyspnea Index. The MRC Dyspnea Scale has demonstrated fair to excellent correlation with FEV^sub 1^ for all of the obstructive and restrictive respiratory diseases in which it has been studied. The MRC Dyspnea Scale has been shown to have longitudinal validity and thus is a useful measure to document responses to therapeutic interventions. With respect to measures of physical activity, the MRC Dyspnea Scale correlates well with functional measures such as the 6MWD. Thus as the MRC Dyspnea score changes, 6MWD is expected to change as well. Changes in MRC Dyspnea scores have been observed following successful pulmonary rehabilitation as well as surgical and medical interventions. Finally, quality of life has been shown to correlate well with the MRC Dyspnea Scale, indicating that dyspnea has a direct relationship with a person’s well-being.
The MRC Dyspnea Scale is an easy to use tool to document the impact of dyspnea on a person’s physical functioning. It has acceptable reliability and validity for use as a measurement tool and is also sensitive to change. As such, this outcome measure provides clinicians with the ability to quantify dyspnea in a meaningful way and to monitor the change in dyspnea in response to physical therapy interventions. It is recommended that the use of the MRC Dyspnea Scale be considered when evaluating an individual whose history indicates that they experience breathlessness during physical activities.
ACKNOWLEDGEMENTS
PJO is supported by a Research Grant from the American Lung Association.
REFERENCES
1. Jones PW, Quirk FH, Baveystock CM, Littlejohns P. A self- complete measure of health status for chronic airflow limitation. The St. George’s Respiratory Questionnaire. Am Rev Respir Dis. 1992;145:1321-1327.
2. Guyatt GH, Berman LB, Townsend M, Pugsley SO, Chambers LW. A measure of quality of life for clinical trials in chronic lung disease. Thorax. 1987;42:773-778.
3. Fletcher C. Standardised questionnaire on respiratory symptoms: a statement prepared and approved by the MRC Committee on the Aetiology of Chronic Bronchitis (MRC breathlessness score). Br Med J. 1960;2:1665.
4. Samet JM. A historical and epidemiologic perspective on respiratory symptoms questionnaires. Am J Epidemiol. 1978;108:435- 446.
5. American Thoracic Society. Surveillance of respiratory hazards in the occupational setting. Am Rev Respir Dis. 1982;126:952-956.
6. Eltayara L, Becklake MR, Volta CA, Milic-Emili J. Relationship between chronic dyspnea and expiratory flow limitation in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 1996;154(6 Pt 1):1 726-1734.
7. de Jong W, van der Schans CP, Mannes GP, van Aalderen WM, Grevink RG, Koeter GH. Relationship between dyspnoea, pulmonary function and exercise capacity in patients with cystic fibrosis. Respir Med. 1997;91:41-46.
8. Huijnen B, van der Horst F, van Amelsvoort L, et al. Dyspnea in elderly family practice patients. Occurrence, severity, quality of life and mortality over an 8-year period. Fam Pract. Aug 22, 2005.
9. Mahler DA, Wells CK. Evaluation of clinical methods for rating dyspnea. Chest. 1988;93:580-586.
10. Portney LG, Watkins MP. Foundations of Clinical Research: Applications to Practice. 2nd ed. Upper Saddle River, NJ: Prentice Hall Health; 2000.
11. Rothstein JM, Echternach JL. Primer on Measurement: An Introductory Guide to Measurement Issues. Alexandria, Va: APTA; 1993.
12. Hajiro T, Nishimura K, Tsukino M, Ikeda A, Koyama H, Izumi T. Analysis of clinical methods used to evaluate dyspnea in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 1998;158:1185-1189.
13. Mahler DA, Rosiello RA, Harver A, Lentine T, McGovern JF, Daubenspeck JA. Comparison of clinical dyspnea ratings and psychophysical measurements of respiratory sensation in obstructive airway disease. Am Rev Respir Dis. 1987;135:1229-1233.
14. Hajiro T, Nishimura K, Tsukino M, Ikeda A, Oga T. Stages of disease severity and factors that affect the health status of patients with chronic obstructive pulmonary disease. Respir Med. 2000;94:841-846.
15. Filippelli M, Pacini F, Romagnoli I, et al. Airway obstruction and chronic exertional dyspnoea in patients with persistent bronchial asthma. Respir Med. 2000;94:694-701.
16. Martinez-Moragon E, Perpina M, Belloch A, de Diego A, Martinez-Frances M. Determinants of dyspnea in patients with different grades of stable asthma. J Asthma. 2003;40:375-382.
17. Grazzini M, Scano G, Foglio K, et al. Relevance of dyspnoea and respiratory function measurements in monitoring of asthma: a factor analysis. Respir Med. 2001;95:246-250.
18. Papiris SA, Daniil ZD, Malagari K, et al. The Medical Research Council dyspnea scale in the estimation of disease severity in idiopathic pulmonary fibrosis. Respir Med. 2005;99:755-761.
19. Tzanakis N, Samiou M, Lambiri I, Antoniou K, Siafakas N, Bouros D. Evaluation of health-related quality-of-life and dyspnea scales in patients with idiopathic pulmonary fibrosis. Correlation with pulmonary function tests. Eur J Intern Med. 2005;16:105-112.
20. Mak VH, Bugler JR, Roberts CM, Spiro SG. Effect of arterial oxygen desaturation on six minute walk distance, perceived effort, and perceived breathlessness in patients with airflow limitation. Thorax. 1993;48:33-38.
21. Marin JM, Carrizo SJ, Gascon M, Sanchez A, Gallego B, Celli BR. Inspiratory capacity, dynamic hyperinflation, breathlessness, and exercise performance during the 6-minute-walk test in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2001;163:1395-1399.
22. Wegner RE, Jorres RA, Kirsten DK, Magnussen H. Factor analysis of exercise capacity, dyspnoea ratings and lung function in patients with severe COPD. Eur Respir J. 1994;7:725-729.
23. Koulouris NG, Retsou S, Kosmas E, et al. Tidal expiratory flow limitation, dyspnoea and exercise capacity in patients with bilateral bronchiectasis. Eur Respir J. 2003;21:743-748.
24. Sahebjami H, Sathianpitayakul E. Influence of body weight on the severity of dyspnea in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2000;161(3 Pt 1):886-890.
25. de Jong W, Kaptein AA, van der Schans CP, et al. Quality of life in patients with cystic fibrosis. Pediatr Pulmonol. 1997;23:95- 100.
26. Baddini Martinez JA, Martinez TY, Lovetro Galhardo FP, de Castro Pereira CA. Dyspnea scales as a measure of health-related quality of life in patients with idiopathic pulmonary fibrosis. Med Sci Monit. 2002;8: CR405-410.
27. Lacasse Y, Brosseau L, Milne S, et al. Pulmonary rehabilitation for chronic obstructive pulmonary disease. Cochrane Database Syst Rev. 2002:CD003793.
28. de Torres JP, Pinto-Plata V, Ingenito E, et al. Power of outcome measurements to detect clinically significant changes in pulmonary rehabilitation of patients with COPD. Chest. 2002;121:1092- 1098.
29. Lorenzi CM, Cilione C, Rizzard\i R, et al. Occupational therapy and pulmonary rehabilitation of disabled COPD patients. Respiration. 2004;71:246-251.
30. Stammberger U, Thurnheer R, Bloch KE, et al. Thoracoscopic bilateral lung volume reduction for diffuse pulmonary emphysema. Eur J Cardiothorac Surg. 1997;11:1005-1010.
31. Venuta F, de Giacomo T, Rendina EA, et al. Bronchoscopic lung- volume reduction with one-way valves in patients with heterogenous emphysema. Ann Thorac Surg. 2005;79:411-416; discussion 416-417.
32. Harnacher J, Buchi S, Georgescu CL, et al. Improved quality of life after lung volume reduction surgery. Eur Respir J. 2002;19:54-60.
33. Snell GI, Solin P, Chin W, et al. Lung volume reduction surgery for emphysema. Med J Aust. 1997;167:529-532.
34. Demertzis S, Wilkens H, Lindenmeir M, Graeter T, Schafers HJ. Lung volume reduction surgery for severe emphysema. J Cardiovasc Surg (Torino). 1998;39:843-847.
35. Tanaka H, Matsumura A, Okumura M, Iuchi K. Pneumonectomy for unilateral destroyed lung with pulmonary hypertension due to systemic blood flow through broncho-pulmonary shunts. Eur J Cardiothorac Surg. 2005;28:389-393.
36. Sheth A, Park J, Ong Y, Ho T, Madden B. Early haemodynamic benefit of sildenafil in patients with coexisting chronic thromboembolic pulmonary hypertension and left ventricular dysfunction. Vascular Pharmacology. 2004;42:41-45.
37. Guyatt GH, Townsend M, Keller J, Singer J, Nogradi S. Measuring functional status in chronic lung disease: conclusions from a randomized control trial. Respir Med. 1989;83:293-297.
38. Vestbo J, Knudsen KM, Rasmussen FV. Should we continue using questionnaires on breathlessness in epidemiologic surveys? Am Rev Respir Dis. 1988;137:1114-1118.
39. Ho SF, O’Mahony MS, Steward JA, Breay P, Buchalter M, Burr ML. Dyspnoea and quality of life in older people at home. Age Ageing. 2001;30:155-159.
40. Goetghebeur D, Sarni D, Grossi Y, et al. Tidal expiratory flow limitation and chronic dyspnoea in patients with cystic fibrosis. Eur Respir J. 2002;19:492-498.
Joan C. Darbee, PT, PhD;1 Patricia J. Ohtake, PT, PhD2
1 Assistant Professor, University of Kentucky, College of Health Sciences, Division of Physical Therapy, Lexington, KY
2 Associate Professor, Department of Rehabilitation Science, University at Buffalo, Buffalo, NY
Address correspondence to: Patricia J. Ohtake, PT, PhD, Department of Rehabilitation Science, 515 Kimball Tower, University at Buffalo, Buffalo, NY 14214 ([email protected]).
Copyright Cardiopulmonary Physical Therapy Journal Mar 2006
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