Exercise and Chronic Obstructive Pulmonary Disease: Modest Fitness Gains Pay Big Dividends
Barry D. Mink, MD
Series Editor: Nicholas A. DiNubile, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 25 - NO. 11 - NOVEMBER 97
In Brief: Exercise cannot reverse the physiologic and structural deficits of chronic obstructive pulmonary disease, but it can reduce disability by improving endurance, breathing efficiency, and dyspnea tolerance, especially in severely impaired patients. An exercise prescription should begin with an assessment of cardiac risk and exercise capacity. Initial workloads should be light, increases gradual, and follow-up consistent. Patients need encouragement, and may also need supplemental oxygen and treatment with bronchodilators, mucolytics, and/or corticosteroids. Patients who follow an individualized program can often increase their work capacity 70% to 80% within 6 weeks.
An estimated 15 million to 25 million Americans suffer from chronic obstructive pulmonary disease (COPD), a term that includes emphysema and chronic bronchitis. The impact of COPD is major: Not only is it responsible for 200,000 deaths yearly, but in men over 40 it ranks second only to coronary heart disease as a cause of disability (1).
In patients who have COPD, disability is largely the result of progressive deconditioning. Initially, a patient's severely limited ventilatory capacity makes exertion unpleasant and leads to an increasingly sedentary lifestyle. Muscles of locomotion then decline, making exertion even more difficult. And so the downward deconditioning spiral continues (2).
Exercise has emerged as a primary modality for the reversal of deconditioning and for improving quality of life for healthy individuals as well as for those with various chronic medical conditions; such is the case in the management of COPD. Whereas mid-century physicians generally counseled their pulmonary patients to avoid physical exertion, virtually all pulmonary rehabilitation programs today give a central place to exercise training (3). The benefits of such training for patients, in both subjective and objective terms, have been well documented (4).
However, pulmonary patients are unique because their ability to exercise is compromised—in many cases severely and, in physiologic terms, irreversibly—by the permanent damage the disease has caused.
Are the Lungs Trainable?
Because of the destruction of the lung parenchyma in COPD, there is mismatching of inspired air and alveolar blood flow in some regions of the lung. The result is abnormal ventilation-perfusion ratios at these sites, with low ratios predominating. This in turn impairs gas exchange. As a result, a COPD patient's VO2 max may be severely compromised.
In most people, cardiac response or muscle endurance, not lung function, is the limiting factor in exercise capacity. The normal lung can move a tremendous volume of oxygen—more than enough to satisfy the demands of physical exertion. But the increased airway resistance and hyperinflation that characterize COPD dramatically raise a patient's metabolic cost of breathing. In pulmonary patients, up to 40% of total oxygen intake during low-level exercise is devoted to the respiratory muscles, compared to 10% to 15% in healthy persons (5).
In addition, the diseased lung is not "trainable" to the same extent as the muscles and cardiovascular system. In COPD patients, exercise does not appear to have a significant effect on lung function per se. In a review of 29 trials that included spirometry, only 2 showed improved FEV1 (2). Also, exercise does not reverse the physiologic or structural deterioration that characterizes COPD, nor does it affect survival. Although it has been suggested that ventilatory muscle endurance increases with exercise, the evidence is not definitive.
These limitations notwithstanding, there is abundant evidence that exercise training can effect important gains in exercise tolerance, even for patients whose ventilatory capacity is radically compromised by COPD. In a review of 32 studies, 31 showed increased exercise tolerance after a training program (2). In one controlled trial, for example, 119 patients with COPD were randomly assigned to either a rehabilitation regimen that included exercise training or an education program. After 8 weeks in the program, treadmill walking time nearly doubled in the exercise group (from 12.5 to 23.0 minutes), but remained virtually unchanged in the control group. The difference was still evident at follow-up 6 months later (6).
The most dramatic improvements are often seen in the most severely impaired patients. In one study, patients were allowed to exercise at their own level, three times a week for 9 weeks, in 2-hour sessions that included cycling, treadmill walking, and lifting weights. Cycling endurance increased from a mean of 129 to 726 watt-minutes, with the greatest percentage gains occurring in patients who had the lowest pretraining exercise capacity and FEV1 (7). Also, in a review of nine controlled studies that used timed walking tests, all but one of the studies found significant increases in distances walked. For example, one of the groups in the study had an 18% increase in distance in a 6-minute walking test, and another group showed a 22% increase in a 12-minute test (R. Casaburi, PhD, MD, unpublished data, February 1997).
Improvements associated with exercise training probably reflect both physiologic and psychological factors, and involve ventilation, oxygen consumption, and dyspnea.
Ventilation. As with other patients, training for COPD patients has been shown to reduce ventilation at comparable oxygen consumption levels (although only to a third the extent of that seen in normal subjects) (8). Such reductions occur even at very low training levels, perhaps reflecting improved breathing efficiency or diminished anxiety (9).
Similarly, some studies have shown large reductions in ventilation—in some cases as great as one quarter—in response to identical tasks before and after exercise training programs. These reductions are more likely to be the result of a learning effect, in which the metabolic demand of an exercise task declines as the task is practiced and better performance strategies are developed, rather than indicating a true aerobic training effect (2).
Maximal oxygen consumption. Evidence of increases in VO2 max with exercise are inconsistent. A review of 18 studies found that this variable improved in 10 of the studies. But the significance of such findings is unclear; the increases might be the result of greater motivation and effort rather than evidence of true physiologic changes (2).
The best marker of an authentic aerobic training effect is blood lactate, which accumulates at higher levels of exertion and at a slower rate with a patient's increased cardiorespiratory fitness. In a study of 19 patients who had moderate COPD (8), increased levels of blood lactate were noted during exercise, even at low levels of exertion, prior to an exercise training program. The program consisted of exercising on a stationary cycle: Half of the group trained for 45 minutes per day, 5 days a week for 8 weeks at an intensity above the anaerobic threshold; the others trained at a rate below the threshold but for a longer period.
In tests performed after the 8-week training period, the increase in blood lactate was found to be delayed and reduced in both groups, but with a significantly greater effect in the high-intensity-exercise group. Among those patients, ventilation and blood lactate levels declined proportionally, heart rate at a given level of exertion declined, and endurance nearly doubled. All these findings suggest the development of a true aerobic training response.
Dyspnea. Perhaps the single most important benefit of exercise training in COPD is its effect on dyspnea. Shortness of breath plagues almost all pulmonary patients, and the fear of dyspnea often inhibits exertion and severely compromises the ability to perform such day-to-day activities as shopping or housecleaning.
There is ample evidence that an exercise program can delay the appearance of dyspnea to higher levels of exertion. In one study (10), 20 patients were randomly assigned to either a control group or a group following a schedule of light, biweekly exercise. The exercise group showed declines in dyspnea at a given treadmill workload. In another study (9), patients whose protocol included upper- and lower-body exercise to tolerance achieved significant reductions in dyspnea with incremental exercise.
While some of these improvements may reflect physiologic changes such as a higher anaerobic threshold, a significant proportion are no doubt psychological. Dyspnea is a subjective experience, and exercise appears to effect a kind of desensitization. With appropriate counseling, patients learn to tolerate breathlessness and fear it less, and thus become capable of greater activity. No other intervention—medication and supplemental oxygen included—is able to produce this desensitization.
Any Exercise Helps
Trials of exercise for COPD patients have used a wide variety of protocols. Cycling, walking, treadmill exercise, and stair climbing have all yielded comparable gains. The question of exercise intensity is an open one. Structured, high-intensity programs that monitor physiologic and metabolic parameters have been shown to yield aerobic training effects. But less structured, less demanding protocols that allow the patient's tolerance to determine the level of exertion can also produce significant improvements in exercise tolerance and reductions in minute ventilation and dyspnea, even when the disease is quite severe (11).
While most studies have focused on endurance exercise, strength training may also be beneficial. Muscle fatigue is a common problem for COPD patients, and a third of COPD patients cite it as the limiting factor to their exercise capacity (12). In one trial (13), a program of arm- and leg-strengthening exercises yielded improvements in strength, cycling endurance, and respiratory symptoms.
In sum, exercise of any type is clearly beneficial for patients who have COPD, although it is difficult to say exactly why it helps. It may not lengthen life expectancy, but it does improve its quality; it clearly yields measurable physical and psychological benefits that no other modality can offer.
The Exercise Prescription
For all the reasons described above, an exercise program of some sort (table 1) should be a central feature of treatment for virtually all pulmonary patients, including those who are severely disabled (see the Patient Adviser, "Your Exercise Treatment for Lung Disease"). It must be kept in mind, however, that many of these individuals are extremely limited in the amount of exercise they can do. The kinds of improvements you might expect in cardiac patients, for example, are probably not to be expected. But even small advances in physical capacity can be rewarding for patient and physician alike. The most dramatic improvements are typically seen in those who are most deconditioned.
Patient evaluation. COPD patients who have significant disease severity should begin with a supervised rehabilitation program. The first step for any COPD patient beginning an exercise program is a careful evaluation to assess cardiac risk and exercise capacity. Many of these patients also have some cardiac impairment, and exercise levels that will not cause arrhythmias or hypoxia should be determined.
An appropriate form of testing is to use a treadmill or stationary cycle following the Naughton protocol, for example, that starts at a very low workload and is increased extremely slowly. A pulse oximeter should be used to monitor desaturation.
Training modes. The stationary cycle is an extremely useful mode for training programs with these patients. Many COPD patients are unsteady on their feet and feel more secure sitting down, and the exercise intensity can be controlled accurately. Other aerobic exercises such as bicycling, treadmill exercise, walking, or stair climbing are also acceptable. For patients who cannot tolerate much leg activity, the arm ergometer is a reasonable substitute.
Exercise rate and progression. Ideally, patients should aim to exercise at 60% to 80% of their maximum heart rate for 20 to 30 minutes, 3 days a week. But this goal may not be achievable for months, if at all. The patient's capacity should be your guide: If at first he or she can only exercise for 5 minutes—or even as little as 2 minutes—build on that.
Patients should progress slowly; even small increments can make a significant difference in the quality of their lives. In fact, over a 6-week period, most patients can achieve a 70% to 80% increase over their initial work capacity.
Many patients can graduate to an independent exercise program after 6 weeks of structured rehabilitation, but some will require a longer period in the supervised program, and some may always need some supervision.
Pulmonary patients generally require more active encouragement and reassurance than others. Anxiety and discomfort associated with shortness of breath are likely to be a problem, particularly in the beginning, and in the first few sessions, patients may need a substantial amount of education and patience to allay their fears.
Exercise and Other Treatments
Forms of treatment other than exercise are necessary for the majority of COPD patients. Most patients who have significant COPD require oxygen supplementation. Many also need regular treatment with bronchodilators (adrenergic agonists and/or aminophylline derivatives) for reversible airway obstruction. Some patients may require mucolytics to thin obstructing mucus. And corticosteroids (inhaled or oral) are often employed to reduce inflammation.
Exercise therapy is thoroughly compatible with these modalities; in fact, it may yield useful information that will make them more effective, safe, and appropriate. Many patients, for example, will need supplementary oxygen while they exercise. Exercise testing provides a good opportunity to monitor saturation and determine the amount of oxygen that is truly necessary.
By the same token, many COPD patients are accustomed to using bronchodilators to cope with shortness of breath, and it may be difficult to determine the extent to which a patient's need is psychological rather than physiologic. Monitored exercise that accurately reveals lung function during exercise activity can show whether these agents are actually needed, make it possible to titrate dosage to saturation, and provide a safe context for alleviating any unnecessary dependence.
Monitoring during exercise also allows the physician to determine if beta-agonist inhalers or aminophylline derivatives are causing side effects such as cardiac arrhythmias.
In addition to a preprogram evaluation, the supervised phase of the exercise program, and periodic postprogram follow-ups, other important aspects of COPD rehabilitation are psychological and nutritional counseling.
Prescribing an exercise regimen for COPD patients is likely to take more time and energy than working with others, such as cardiac patients: With COPD patients, the initial assessment must be meticulous, and an uncommon amount of reassurance and encouragement is likely to be an indispensable part of the rehabilitation process.
Increases in exercise endurance and the capacity for everyday activity are often very slow and, if measured by conventional standards, unimpressive—but the impact of seemingly small strides can make a big difference in quality of life for these patients. Anyone who works with COPD patients is familiar with the fear in the eyes of a person with severe emphysema who becomes dyspneic just getting out of a chair. When one sees, several months later, that the patient is able to ride a stationary cycle for 15 minutes, three times a week, it is like winning the Super Bowl.
This article was prepared by contributing editor Carl Sherman
Dr Mink practices medicine in Aspen, Colorado. He is a board certified internist and a fellow of both the American College of Physicians and the American College of Sports Medicine. He was medical officer and US team physician at the 1980 Lake Placid and 1994 Lillehammer winter Olympics, and has been a team physician for the US biathlon team since 1979. Dr DiNubile is an orthopedic surgeon in private practice in Havertown, Pennsylvania, specializing in sports medicine and arthroscopy. He is the director of Sports Medicine and Wellness at the Crozer-Keystone Healthplex in Springfield, Pennsylvania; a clinical assistant professor in the department of orthopedic surgery at the University of Pennsylvania in Philadelphia; and a member of the editorial board of the Physician and Sportsmedicine. Address correspondence to Barry D. Mink, MD, 100 E Main St, #201, Aspen, CO 81611; e-mail correspondence to [email protected].
Copyright (C) 1997. The McGraw-Hill Companies. All Rights Reserved