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The Proceedings of the American Thoracic Society 3:66-74 (2006)
© 2006 The American Thoracic Society

Pulmonary Rehabilitation

Nicholas S. Hill

Division of Pulmonary, Critical Care, and Sleep Medicine, Tufts–New England Medical Center, Boston, Massachusetts

Correspondence and requests for reprints should be addressed to Nicholas S. Hill, M.D., Division of Pulmonary, Critical Care, and Sleep Medicine, Tufts–New England Medical Center, 750 Washington Street #257, Boston, MA 02111. E-mail: nhill{at}tufts-nemc.org

ABSTRACT

Pulmonary rehabilitation programs use multidisciplinary teams to optimize physical and social functioning of patients with chronic respiratory impairment. These programs provide rehabilitation in inpatient, outpatient, or home settings, using at least three sessions weekly (one may be unsupervised) for at least 6 wk. The programs usually consist of exercise training, education, and psychosocial/behavioral components. Upper extremity exercises and instruction on breathing technique are included in most rehabilitation programs and reduce dyspnea, but the contribution of these to improved functional capacity remains unproven. Decreases in the sensation of dyspnea, increased functional exercise capacity, and enhanced quality of life of patients with chronic obstructive pulmonary disease (COPD) are established benefits of pulmonary rehabilitation. Evidence is lacking for the efficacy of rehabilitation for patients with non-COPD causes of pulmonary impairment, but many of these patients probably benefit. Despite the availability of strong evidence to support the efficacy of pulmonary rehabilitation programs in patients with severe COPD, third-party reimbursement policies have been inconsistent. Nonetheless, enrollment in a pulmonary rehabilitation program is encouraged for all appropriate candidates with chronic respiratory impairment, particularly for those with severe COPD.

Key Words: chronic obstructive pulmonary disease • rehabilitation exercise training

Pulmonary rehabilitation has been advocated for several decades as a way to provide comprehensive care and improve the functional status of patients with chronic respiratory diseases. However, convincing evidence in the form of randomized controlled trials to support the efficacy of this intervention has been available only for the past decade (1). In addition, many questions remain about pulmonary rehabilitation, including its effect on important outcomes like resource utilization or survival, responses of non–chronic obstructive pulmonary disease (non-COPD), optimal structure and essential components of a rehabilitation program, the best ways to assess outcomes, and reimbursement issues. According to the official statement of the American Thoracic Society, "pulmonary rehabilitation is a multidisciplinary program of care for patients with chronic respiratory impairment that is individually tailored and designed to optimize physical and social performance and autonomy" (2). This article describes the structure and essential components of a typical rehabilitation program, examines evidence supporting efficacy and probable mechanisms of action, and discusses reimbursement issues and questions for the future.

GOALS OF PULMONARY REHABILITATION

Patients who are candidates for pulmonary rehabilitation have respiratory impairment, defined as an underlying pathophysiologic defect that gives rise to a disability (i.e., some loss of function). This begets a handicap, which is the disadvantage caused by the disability, leading to a lower than desired level of functioning within the societal context. Thus, the goals of pulmonary rehabilitation are to (1) alleviate symptoms, (2) restore functional capabilities as much as possible, and (3) reduce handicap, thus enhancing overall quality of life.

These beg the question: Shouldn't all medical care for patients with chronic illnesses share these goals of a rehabilitation program? If so, then how does rehabilitation differ from optimal comprehensive care administered by any physician? The answer is that although all medical care of chronic illnesses should aim to optimize overall patient function and quality of life, pulmonary rehabilitation programs are structured to bring about specific enhancements by applying a multidisciplinary approach within the context of a focused program. The essential components include exercise training, education, other possible interventions, and outcomes assessment. To achieve the above goals, professionals from a variety of disciplines, as shown in Table 1, directly participate in pulmonary rehabilitation programs, or at least are readily available for consultation.


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  		TABLE 1. MULTIDISCIPLINARY TEAM PARTICIPATING ON A PULMONARY REHABILITATION TEAM

 
STRUCTURE OF A PULMONARY REHABILITATION PROGRAM

A physician, usually a pulmonologist, serves as medical director. This individual is responsible for overall medical direction of the program and should perform an initial assessment on all prospective patients to ascertain their appropriateness for the program, as well as to ensure that the medical regimen has been optimized. The physician can also identify comorbidities that might necessitate modifications in the patient's individualized program. A physician should be readily available to help with medical emergencies, or a plan should be in place for prompt action (i.e., calling 911) should a medical emergency arise. A physiatrist may also participate in the program, to assist with management of nonpulmonary handicaps.

Physical, educational, and respiratory therapists are also essential to the program. The physical therapist prescribes a specific exercise regimen tailored to the individual patient's handicaps and goals, whereas the occupational therapist teaches conservation measures and assesses needs for prosthetic devices or wheelchairs. The respiratory therapist also helps to oversee the exercise program, and teaches breathing exercises, as well as proper use of aerosolized medications and oxygen. In some programs, nurses with special expertise in respiratory disorders help to oversee the exercise and educational components, particularly for inpatient programs. In others, an exercise physiologist prescribes and monitors the exercise program. A nutritionist should help patients formulate nutritional goals and educate on proper diet. A social worker assesses needs for home services, works with third-party payers to help patients obtain needed benefits, and may provide counseling. A psychologist may also be available to provide counseling as well as instruction in coping strategies and relaxation exercises. Professionals helping to run the rehabilitation program should meet on a regular basis to go over individual patient progress and discuss program modifications to help patients meet their goals. The specific professionals involved vary from program to program and no one blueprint applies to all. Programs can run successfully with a physician and one or two therapists (2), but individuals representing other disciplines should be available at least on a consultative basis.

SETTING FOR PULMONARY REHABILITATION

Pulmonary rehabilitation is administered in inpatient, outpatient, or home settings, or some combination of these. In the United States (but not in Europe), inpatient rehabilitation is usually reserved for patients who are too disabled to travel to and from an outpatient program and the focus of these programs is more often on optimizing medical or ventilator regimens than on the exercise components. In Europe, ambulatory patients may be admitted to an inpatient program to undergo intensive therapy and to avoid the inconvenience of daily travel. Possible indications for inpatient pulmonary rehabilitation in the United States are listed in Table 2.


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  		TABLE 2. INDICATIONS FOR INPATIENT AS OPPOSED TO OUTPATIENT PULMONARY REHABILITATION

 
Most studies on pulmonary rehabilitation have focused on the outpatient setting, sometimes with the expectation that patients will perform some of their exercises at home, and encouraging patients to continue exercise regimens at home after completion of the program. A number of studies have demonstrated improved endurance and/or quality of life after completion of home-based rehabilitation programs (4–8). A multicenter randomized controlled trial of home-based pulmonary rehabilitation is currently underway in Canada (9). One study found that a home-based program achieved more durable benefits than a hospital-based program (10), but direct comparisons between home-based and outpatient programs are lacking.

CANDIDATES FOR PULMONARY REHABILITATION

Candidates for pulmonary rehabilitation are patients with symptomatic impairment attributable to their respiratory condition (Table 3). Patients should be motivated, not have significant transportation problems, and be capable of understanding the purpose and educational content of the program. Though some randomized controlled trials suggest that even patients with mild impairment may benefit from rehabilitation, Medicare guidelines (see below) specify that only those with moderate to severe pulmonary function impairment or the need for chronic oxygen therapy will be reimbursed. Contraindications to participation include the lack of motivation, significant cognitive impairment, inability to attend the program consistently, unstable medical conditions that may pose risks, or the inability to participate in an exercise program because of a severe arthritic or other limiting condition. Although cigarette smoking is sometimes considered a contraindication, smokers and nonsmokers have similar responses to rehabilitation. Active smokers should be encouraged to quit, and participation in a smoking cessation program can be made a condition of their participation. A number of studies have examined predictors of a favorable response to rehabilitation. Zuwallach and coworkers (11) found that those with the lowest maximal oxygen uptakes at baseline had the largest proportionate improvements, whereas baseline pulmonary function was not predictive. Troosters and colleagues (12) found that patients with no ventilatory reserve and normal skeletal muscle strength (inspiratory muscles, handgrip, and quadriceps) were least likely to improve. Thus, the candidate most likely to benefit is a previously sedentary (and presumably deconditioned) patient with no more than moderately severe disease.


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  		TABLE 3. INDICATIONS AND CONTRAINDICATIONS TO PULMONARY REHABILITATION

 
INITIAL ASSESSMENT

The physician director performs a screening assessment to determine the suitability of prospective rehabilitation candidates. The physician takes a medical history and examines the patient, seeking underlying conditions that might alter or even preclude participation in a rehabilitation program. For example, patients at risk for coronary artery disease who have not yet undergone an adequate evaluation may be asked to complete an exercise stress test before being enrolled into the program. The physician should also ascertain that the patient is on an optimal medical regimen, including bronchodilators, antiinflammatory drugs, and oxygen supplementation as indicated.

ESSENTIAL COMPONENTS OF A PULMONARY REHABILITATION PROGRAM

Exercise Training
Virtually every pulmonary rehabilitation program includes exercise training as a centerpiece. In general, improvements in exercise performance can occur only if patients exercise on a regular basis. This is usually accomplished in a group setting using individually tailored exercise prescriptions supervised by therapists. Some programs offer one-to-one exercise supervision by a therapist, but the cost-effectiveness of this approach is dubious. Most programs offer a variety of exercise regimens aimed at improving strength and endurance. The frequency, intensity, and specificity of exercise sessions are considered the main determinants of the training effect.

Frequency.
For pragmatic reasons, most pulmonary rehabilitation programs hold sessions only two or three times weekly. Some evidence indicates that two sessions per week may be inadequate for a training effect (13), but most programs meeting only twice weekly instruct patients to exercise at home in between sessions. The frequency of exercise sessions to obtain an optimal training effect has not been established, but the regimen of twice-weekly supervised sessions with additional unsupervised sessions at home has been advocated by at least one consensus group (14).

Intensity.
Most studies indicate that there is a threshold for the training effect. If a level of intensity corresponding to 60 to 75% of the maximum oxygen uptake can be sustained for at least 20 to 30 min for a few days per week, an improvement in endurance is a virtual certainty (2), although concerns have been raised about patients' ability to adhere to a high-intensity regimen. Clark and colleagues (15) examined the efficacy of low-intensity isotonic exercises of the upper and lower extremities performed at home in a group of 40 patients with COPD. These authors demonstrated a dramatic improvement in treadmill walking time (Figure 1) and suggested that their program would be applicable in patients with COPD with a wide range of functional defects. Punzal and coworkers (16) used a high-intensity exercise program, exercising patients at approximately 85% of their maximal baseline treadmill walking speed, and also demonstrated significant endurance benefits. Vallet and coworkers (17) compared an individually tailored exercise regimen that targeted the heart rate at anaerobic threshold to a standard lower intensity regimen that targeted 50% of the maximal heart rate. The individually tailored regimen increased O2 pulse and reduced lactate accumulation compared with the standard regimen (Figure 2). However, many programs lack the facilities to monitor oxygen uptake and use symptom guidance instead (18). Patients exercise at a level that gives them moderate dyspnea (Borg 3) but at sustainable levels of exercise. Training at such levels has been shown to increase endurance at the end of a program (18).


Figure 1
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  		Figure 1. Total work performed on a treadmill (endurance walk test) is shown before and after exercise program in the training group (open circles) and in the control group (closed circles). The mean difference in the training group (before–after) was 6,372 J versus 430 J in the control group (p < 0.001 by Student's t test). Reproduced by permission from Reference 15.

 

Figure 2
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  		Figure 2. Effect of individualized training (open circles) and standard training (closed squares) regimens on lactate accumulation in seven patients with severe chronic obstructive pulmonary disease. Horizontal axis is percentage of pretraining maximal oxygen uptake. Individualized training decreases lactate accumulation at higher intensity exercise levels. *p < 0.05, **p < 0.01, ***p < 0.001 between groups. Reproduced by permission from Reference 17.

 
Specificity.
Training regimens are specific in that the type of exercise determines the nature of the gain. For example, walking endurance increases after training of the lower extremities but not upper extremities (19). Furthermore, endurance exercises improve endurance capabilities more than strength, whereas strength training (i.e., weightlifting) increases strength but not necessarily endurance (20) or other outcomes such as exercise capacity or health status (21). Therefore, most programs incorporate a variety of training regimens. Gradually increasing the duration and intensity of workouts on a track, treadmill, or cycle ergometer increases lower extremity endurance.

Some patients with COPD become uncomfortably dyspneic while using the upper extremities for reaching or personal hygiene because this diverts shoulder girdle muscles that the patient is using to assist breathing. Upper extremity muscle training using unsupported weightlifting techniques (22), stretching of elastic bands (Ther-a-bands; Hygenic Corp., Akron, OH) or hand cranks (for endurance) can alleviate symptoms related to the use of the upper extremities. An arm-training program decreases the work effort, level of dyspnea, and dynamic hyperinflation associated with a given level of arm exercise (23).

Some programs also incorporate specific exercises aimed at improving respiratory muscle strength, such as inspiratory threshold training, a largely isometric exercise in which a device permits inspiratory flow only if a threshold negative pressure is reached, or inspiratory resistive training, in which patients inspire through a resistor. It is unclear whether one technique is superior to the other (24), perhaps partly because adherence to inspiratory threshold training has been a problem. In a meta-analysis, Lotters and colleagues (25) found a nonsignificant trend for improved exercise capacity after inspiratory muscle training (IMT) alone or as an adjunct to general exercise training. A subgroup analysis showed that patients with greater inspiratory muscle weakness at baseline had significantly more benefit than those with normal inspiratory muscle strength. They concluded that IMT is an important component of rehabilitation in patients with COPD with inspiratory muscle weakness, but failed to consider that this result could also be attributed to regression toward the mean.

More recently, Weiner and colleagues (26) demonstrated that resistance training of expiratory muscles might be useful as an adjunct to rehabilitation. Not only did patients with trained expiratory muscles have greater expiratory muscle strength and endurance than control subjects but they also had significantly greater 6-min walk distances. Another recent study found that hyperpnea training improved respiratory muscle endurance but did not translate into improved overall function (27). Given the lack of evidence for improvement in overall function attributable to strength or endurance training of the respiratory muscles, the place of respiratory muscle training in rehabilitation programs remains controversial (28).

Education
Pulmonary rehabilitation programs include an educational component usually provided during group teaching and discussion sessions, but sometimes to individuals (29). These group sessions are typically scheduled immediately before or after exercise sessions. Different topics are addressed, often on a weekly basis (Table 4). The effectiveness of the educational component has not been tested in controlled studies, and the importance of education as a component of a pulmonary rehabilitation program has not been established.


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  		TABLE 4. TOPICS OFTEN COVERED DURING GROUP EDUCATION SESSIONS

 
Psychosocial and Behavioral Component
Because of the psychologic and emotional stress patients experience as part of their chronic illness as well as the high rate of depression, most pulmonary rehabilitation programs incorporate psychosocial and behavioral interventions (30). Psychologists or social workers may administer these during educational sessions, teaching coping and stress reduction strategies as well as relaxation techniques (31). In a recent controlled trial, an occupational therapist taught controlled breathing and energy conservation techniques during specific activities such as bed making or table setting, and was able to show improved dyspnea and overall functional scores compared with didactic lectures (32). Sexual dysfunction may be addressed and sexual counseling offered. Patients with incapacitating stress, anxiety, or depression may warrant individual counseling or referral to a psychiatrist for medical therapy.

Other Interventions
Breathing techniques have traditionally been taught as part of pulmonary rehabilitation programs including pursed lip breathing and diaphragmatic breathing (33). Pursed lip breathing can improve oxygenation and relieve the sensation of dyspnea, although studies demonstrating that these gains translate into improved functional status or state of well-being are lacking. Beneficial effects of diaphragmatic breathing exercises have not been demonstrated (33).

Nutritional intervention is another important aspect of pulmonary rehabilitation, although most programs use nutritional consultants rather than include nutritionists as full-time members of the rehabilitation team. Patients with chronic respiratory conditions are frequently either over- or underweight, and a low body mass index correlates with a worse prognosis (34). Few studies have demonstrated that nutritional interventions improve outcomes, but one recently showed improvements in fat-free muscle mass, strength, and quality of life score in patients whose diets were supplemented with creatine (35).

Outcome Assessment
Pulmonary rehabilitation programs monitor outcomes partly as indicators of performance and to ensure quality, but also because many third-party payers now require such assessments to qualify for reimbursement. Outcome measures usually include a functional assessment. Many programs use the 6-min walk test or the 10-m shuttle test (36, 37). Both are widely applied tests of functional endurance that are of prognostic value. The shuttle walk test is an incremental test, but both it and the 6-min walk test are effort-dependent and subject to nonrespiratory limitations such as weakness, pain, or arthritis. Some programs perform maximal cardiopulmonary exercise tests that test maximal capacity rather than endurance. These tests are usually combined with a dyspnea assessment as a rough gauge of effort, such as the Borg score or rating on a visual analog scale.

Many programs also use dyspnea scales such as the Baseline and Transitional Dyspnea indices that assess dyspnea as related to function, effort, and task (38). In addition, most programs use questionnaires to assess overall quality of life (or health status). The Short Form-36 is a commonly used proprietary instrument that tests overall health status. Disease-specific questionnaires such as the St. George's Respiratory Questionnaire (SGRQ) (39) or the Chronic Respiratory Disease Questionnaire (CRQ) (40) are also commonly used. Both are validated questionnaires in patients with COPD, and some evidence suggests that the CRQ is a bit more sensitive than the SGRQ in detecting improvements (41). A composite index has recently been described that combines body mass index (B), severity of airway obstruction (O), dyspnea index (D), and exercise capacity (E) (BODE index) and correlates with prognosis of patients with COPD (34). This has registered improvement after completion of a pulmonary rehabilitation program and was associated with improved outcomes (42). Whether this composite index adds to the value of traditional single-outcome indices remains to be determined.

EVIDENCE FOR THE EFFICACY OF PULMONARY REHABILITATION

Patients with COPD
Numerous randomized controlled trials have established the efficacy of pulmonary rehabilitation for COPD (3, 4, 43–48) (see Table 5). One of the most comprehensive is that by Ries and coworkers (49) on 119 patients randomized to receive education plus exercise training or education alone. In this study, tests of both maximal and endurance exercise showed significant benefits that persisted for 1 yr. Dyspnea and self-efficacy were also improved, but lung function and quality of well-being did not change. There were trends for improved survival (67 vs. 56% after up to 6 yr of follow-up) and reduced hospital days per patient per year (–2.3 vs. +1.3 d/patient/yr), but these did not reach statistical significance.


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  		TABLE 5. SIGNIFICANT BENEFITS OF PULMONARY REHABILITATION

 
More recently, a Cochrane meta-analysis assessed the efficacy of pulmonary rehabilitation for COPD (50), but the Ries study was excluded because it had an educational intervention in its control group, not just conventional therapy. The Cochrane analysis examined results of 23 randomized controlled trials, concluding that rehabilitation of patients with COPD significantly (both statistically and clinically) improves dyspnea and disease-specific quality of life, including scales of fatigue and mastery. Functional exercise capacity as assessed by the 6-min walk distance also increased significantly, an average of 49 m, which is at the margin of the estimated minimal clinically significant difference of 54 m (51). The greatest benefit was apparent in patients with severe as opposed to mild to moderate COPD; benefit was maintained for at least 6 mo; and supervised programs tended to offer greater benefit than unsupervised programs. Although the Cochrane analysis found no overall reduction in the need for hospitalization after rehabilitation, some individual studies have found significant reductions in hospital days per year (52) as well as annual health care use and direct costs (53). A recent study also found reductions in patients with COPD with anxiety and depression after pulmonary rehabilitation compared with matched control subjects (54). A follow-up meta-analysis focusing just on patients with mild–moderate COPD concluded that exercise can improve conditioning in these patients, but that studies are lacking to support the idea that rehabilitation favorably influences dyspnea, quality of life, or disease progression in the mild–moderate subgroup (55).

An important limitation inherent to all of the controlled studies is the inability to blind patients or investigators to treatment group, leaving the results open to bias. Nonetheless, the authors of the Cochrane review concluded that no additional trials are needed comparing pulmonary rehabilitation with conventional therapy in patients with COPD. However, they opined that additional study is needed to determine what components of a rehabilitation program are essential, the ideal program length, the best combination of intensity, frequency and specific exercises for the training program, the value of breathing exercises, and how best to maintain benefits.

Several recent studies have shed light on some of these questions. A study in the United Kingdom found that early rehabilitation (within 10 d) after a hospitalization for a COPD exacerbation improved exercise capacity and health status at the 3-mo time point compared with standard care (56). A Danish group using hour-long exercise sessions twice weekly for 8 wk found no significant improvement in 6-min walk distance or health-related quality of life, and speculated that two sessions weekly might be too few to produce a training effect (13). However, there was a high dropout rate and adherence with the exercise program was not specified. Clearly, there must be a minimum threshold of exercise frequency if a training effect is to be achieved, and two sessions/wk may be close to that threshold, but exercise duration (each session as well as the duration of the program) as well as exercise intensity must also be factored in. With regard to the optimal duration of a pulmonary rehabilitation program, Green and colleagues (57) found that 7 wk of rehabilitation was better than 4 wk. Another recent study found that 6-min walk distance of patients with severe COPD increased between 12 and 24 wk of pulmonary rehabilitation and recommended that supervised programs extend for at least 24 wk to optimize benefits, but this study was uncontrolled (58). For pragmatic reasons, including the reimbursement policies of insurers, however, most programs last between 6 and 12 wk.

Non-COPD Disorders
Most evidence and all of the randomized controlled trials pertain to the efficacy of pulmonary rehabilitation for patients with COPD. However, rehabilitation is still of potential benefit for patients with many non-COPD disorders (Table 6). As long as patients have enough reserve to perform some exercise, it is likely that they can obtain a training effect. Furthermore, education about their disease may enhance coping abilities as well as adherence to their medical regimen.


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  		TABLE 6. NON–CHRONIC OBSTRUCTIVE PULMONARY DISEASE CHRONIC RESPIRATORY CONDITIONS THAT MAY BENEFIT FROM A PULMONARY REHABILITATION PROGRAM

 
Because patients with non-COPD disorders may have unique requirements, the pulmonary rehabilitation program needs to be individually tailored for them. For example, patients with asthma may not have as much exercise impairment as most patients with COPD, but for them, education about the proper use of medication, especially during emergencies, as well as environmental controls deserves more emphasis. Patients with asthma enrolled in a swim training program increased their 12-min walk distance after 10 wk of training, with a decrease in the occurrence of exercise-induced bronchospasm (59). Patients with certain neuromuscular diseases, such as post-polio syndrome, may benefit from comprehensive rehabilitation (60), demonstrating increased strength and endurance of affected muscles (61). However, muscle strengthening or conditioning exercises are unlikely to be helpful in patients with advanced progressive neuromuscular diseases, such as muscular dystrophies (62). Such patients may still benefit from flexibility exercises to minimize contractures or programs to optimize their use of ventilator assistance regimens. Patients with lung cancer require different kinds of education and may be recovering from the effects of radiation or chemotherapy (63). They may also have pain management problems that demand special attention. Those with interstitial fibrosis may experience profound exercise-induced oxygen desaturations that pose challenges for the delivery of high-flow oxygen during exercise, and patients with cystic fibrosis may need coaching on secretion removal or special precautions if they are harboring highly resistant organisms, such as Burkholderia cepacia. Small, uncontrolled series of patients with cystic fibrosis indicate that they respond favorably to exercise programs (64, 65). Patients with bronchiectasis also respond to exercise training, but without added benefit from IMT (66). With the advent of new and more effective therapies for pulmonary arterial hypertension, the initiation of an exercise program to coincide with the initiation of new medical therapy may enhance functional improvement in such patients. Pulmonary rehabilitation has also been used pre- and postoperatively for lung resection, lung transplantation (67), and lung volume reduction surgeries, and was included as standard therapy in both the surgery and control arms in the National Emphysema Therapy Trial, which evaluated the efficacy of lung volume reduction surgery (68).

MAINTENANCE OF BENEFIT

Some studies have monitored patients for up to 2 yr (47, 49). Ries and colleagues (49) found that improvements in functional exercise capacity are sustained for at least 12 mo. Troosters and coworkers (69) later demonstrated that improvements in the 6-min walk test and quality of life exceeded minimal clinically significant differences for 18 mo. Ideally, patients are to apply what they have learned in the rehabilitation phase of the program, undergoing a lifestyle change that includes regular exercise. Unfortunately, many if not most patients fail to adhere to this ideal, and programmatic benefits are eventually lost. Some programs encourage patients to return to the rehabilitation center two or three times weekly after completion of the formal program so that the exercise program can be maintained. They offer continued but less intense supervision and usually charge a small fee because such maintenance programs are not covered by insurance.

Whether formal maintenance programs after completion of the rehabilitation program extend or enhance initial benefits has not been established. Ries and colleagues (70) tested a maintenance program consisting of weekly phone calls and monthly reinforcement sessions. Functional exercise capacity and overall health status were better sustained by maintenance than conventional management for 12 mo, but the advantage disappeared by 24 mo. In another study, once-weekly training sessions after a 3-mo intensive rehabilitation period failed to sustain the benefits achieved, but 2 to 3 h of exercise weekly during the maintenance period prevented some of the deterioration (71). Distractive stimuli during exercise sessions (music via earphones) have been found to improve maintenance of the beneficial effects of a rehabilitation program (72).

MECHANISM OF BENEFIT

For years, physiologists have pointed to the mechanical disadvantages and propensity to fatigue of the respiratory muscles in patients with COPD and have speculated that therapies aimed at increasing the strength and endurance of inspiratory muscles would improve overall function (73). Numerous studies demonstrate that specific muscle training can enhance strength and/or endurance of the inspiratory muscles in patients with COPD, but these specific improvements have not been shown to contribute to enhancements in overall functional or health status. Moreover, the improvements in dyspnea scores, functional exercise capacity, and health status that accrue from participation in a pulmonary rehabilitation program do not correlate with improvements in pulmonary function.

Alternative possible mechanisms for the benefits of rehabilitation include improved cardiovascular conditioning and efficiency as demonstrated by increased VO2max, lower heart rate for a given VO2 and lower VO2 for a given work load (74), and strengthening and conditioning of weakened peripheral muscles (75). Saey and colleagues (76) recently demonstrated that mechanisms of exercise limitation differ between patients with COPD: some (fatiguers) had evidence of quadriceps muscle fatigue and had no improvement after inhalation of ipratropium, whereas others (nonfatiguers) had no evidence of quadriceps fatigue but rather had ventilatory limitation and responded to ipratropium by increasing exercise endurance. Mador and coworkers (77) have shown that quadriceps muscles of patients with COPD are more resistant to fatigue after completion of a rehabilitation program. Optimization of and improved adherence to the medical regimen, weight loss, and smoking cessation, and better treatment of comorbidities, such as cardiovascular disease or obstructive sleep apnea, are other possible but unsubstantiated mechanisms of benefit. The increased attention from professionals as well as the educational component in rehabilitation programs may also be important in improving overall health status, but this has not been established. Thus, although conditioning of peripheral (i.e., quadriceps) muscle appears to be an important mechanism of rehabilitation benefit in many patients with COPD, identification of a single mechanism that applies to all patients seems unlikely; rather, multiple factors appear to play a role in limiting patient function and a multipronged approach is most likely to be successful in effecting improvement, with specific reversible factors varying from one individual patient to another.

USE OF OXYGEN SUPPLEMENTATION IN PULMONARY REHABILITATION

Oxygen supplementation has long been considered routine in pulmonary rehabilitation to maintain O2 saturation of more than 88%, on the basis of studies showing that O2 supplementation used in this fashion improves exercise performance. Recently, Emtner and colleagues (78) demonstrated that even patients with COPD who do not desaturate during exercise still have significant gains with O2 supplementation, including greater exercise endurance (30% prolongation) and improved health quality. The mechanism of this benefit is unclear, and this finding must be confirmed before routine adoption can be recommended. Heliox, the mixture of oxygen (up to 40%) and helium, reduces gas density compared with air and lowers resistance to airflow in regions of turbulence. It can reduce air trapping and enhance exercise tolerance in patients with COPD and could serve as an additional way to augment the training effect (79).

NONINVASIVE VENTILATION AS AN ADJUNCT TO REHABILITATION

The use of long-term use of noninvasive positive-pressure ventilation to improve functional and health status of patients with severe, stable COPD has long been controversial. A recent randomized study from Italy (80) has demonstrated that noninvasive ventilation used for 2 yr in patients with severe COPD and chronic CO2 retention prevented the deterioration in daytime gas exchange and health status that was observed among control subjects, and tended to reduce hospital days per patient per year. Noninvasive positive-pressure techniques can also be used during exercise training to permit the attainment of a higher level of intensity during training, potentially augmenting the training effect (81, 82). Continuous positive airway pressure, pressure support (83), and proportional assist ventilation (84) all augment the level of exercise intensity attainable, with the greatest effect attributable to proportional assist ventilation. However, no study has yet demonstrated that this greater exercise intensity actually translates into improved functional exercise capacity, and one study suggests otherwise (85).

Another way to use noninvasive ventilation as an adjunct to rehabilitation is to rest respiratory muscles between exercise periods. Garrod and coworkers (86) used this approach in a controlled trial of patients with severe, stable COPD undergoing rehabilitation. They found that the noninvasive positive-pressure ventilation–treated group improved its performance on the shuttle walk test (Figure 3) and had an improved quality of life (CRQ), even though the average patient used noninvasive positive-pressure ventilation for only 2 h daily. However, because this study was not blinded, the possibility of bias could not be entirely excluded.


Figure 3
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  		Figure 3. Changes in shuttle walk test (SWT) in noninvasive ventilation plus exercise (NPPV + ET) and exercise therapy (ET) groups at each assessment. p = 0.009 difference between the groups in final 4 wk of training (A3 and A4); p = 0.01 difference between the groups over 12-wk period (A1 and A4). Open circles represent the ET group; closed circles represent the NPPV + ET group. A1: baseline assessment; A2: prerehabilitation assessment (4 wk); A3: midrehabilitation assessment (8 wk); A4: postrehabilitation assessment (12 wk). Reproduced by permission from Reference 86.

 
Although some of the above studies are promising, noninvasive ventilation is not yet a standard component of pulmonary rehabilitation and should remain an investigational technique pending further study.

REIMBURSEMENT ISSUES

Third-party payers have long been ambivalent about reimbursing for pulmonary rehabilitation. Reimbursement policies have varied from time to time, payer to payer, and region to region. Although the Center for Medicaid and Medicare Services has created codes for pulmonary rehabilitation, there is no national policy on reimbursement, and regional Medicare providers often deny payment.

Pending a national policy, most providers of pulmonary rehabilitation rely on collections for physical therapy and billable tests. Several physical therapy codes can be used and are often reimbursed as long as patients meet certain criteria. These include an International Classification of Diseases–9 diagnosis of emphysema, COPD, or chronic bronchitis, and having a reduced FEV1 (ranging from 50 to 65% of predicted depending on the state) or meeting the criteria for oxygen therapy. In addition, patients must have ceased smoking for at least 3 mo.

These guidelines are not based on scientific evidence but must be met nonetheless. Many managed-care plans pattern their reimbursement policies after Medicare guidelines, but others may be willing to pay global rates. Plans that use case managers for patients with chronic illnesses are often willing to negotiate on an individual patient basis.

CONCLUSIONS

Pulmonary rehabilitation decreases the sensation of dyspnea, increases functional exercise capacity, and improves the quality of life of patients with severe COPD and probably in those with other chronic non-COPD causes of pulmonary impairment. Multidisciplinary programs provide rehabilitation in inpatient, outpatient, or home settings using at least three sessions weekly (one may be unsupervised) over at least 6 wk. The programs usually consist of exercise training, education, and psychosocial/behavioral components, but lower extremity conditioning is the only component with established benefit. Upper extremity exercises and instruction on breathing technique are included in most rehabilitation programs, but the contribution of these to improved functional exercise capacity remains unproven. The value of IMT is likewise unclear and such training is not considered a routine component of rehabilitation.

Despite the availability of strong evidence to support the efficacy of pulmonary rehabilitation programs in patients with severe COPD, third-party reimbursement policies have been inconsistent, and there is currently no national policy. Despite this impediment, enrollment in a pulmonary rehabilitation program is encouraged for all appropriate candidates with chronic respiratory impairment, particularly for those with severe COPD. Investigators are encouraged to accumulate evidence to fill current knowledge gaps, including the establishment of what mechanisms and components of pulmonary rehabilitation are essential to success, what specific exercise prescriptions bring about the largest benefit, how best to sustain benefits over the long-term, and what non-COPD causes of respiratory impairment respond favorably to rehabilitation.

FOOTNOTES

Conflict of Interest Statement: N.S.H. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

(Received in original form November 23, 2005; accepted in final form December 5, 2005)

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